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# sql/types_api.py
# Copyright (C) 2005-2021 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php
"""Base types API.
"""
from . import operators
from .base import SchemaEventTarget
from .traversals import NO_CACHE
from .visitors import Traversible
from .visitors import TraversibleType
from .. import exc
from .. import util
# these are back-assigned by sqltypes.
BOOLEANTYPE = None
INTEGERTYPE = None
NULLTYPE = None
STRINGTYPE = None
MATCHTYPE = None
INDEXABLE = None
TABLEVALUE = None
_resolve_value_to_type = None
class TypeEngine(Traversible):
"""The ultimate base class for all SQL datatypes.
Common subclasses of :class:`.TypeEngine` include
:class:`.String`, :class:`.Integer`, and :class:`.Boolean`.
For an overview of the SQLAlchemy typing system, see
:ref:`types_toplevel`.
.. seealso::
:ref:`types_toplevel`
"""
_sqla_type = True
_isnull = False
_is_tuple_type = False
_is_table_value = False
_is_array = False
_is_type_decorator = False
class Comparator(operators.ColumnOperators):
"""Base class for custom comparison operations defined at the
type level. See :attr:`.TypeEngine.comparator_factory`.
"""
__slots__ = "expr", "type"
default_comparator = None
def __clause_element__(self):
return self.expr
def __init__(self, expr):
self.expr = expr
self.type = expr.type
@util.preload_module("sqlalchemy.sql.default_comparator")
def operate(self, op, *other, **kwargs):
default_comparator = util.preloaded.sql_default_comparator
o = default_comparator.operator_lookup[op.__name__]
return o[0](self.expr, op, *(other + o[1:]), **kwargs)
@util.preload_module("sqlalchemy.sql.default_comparator")
def reverse_operate(self, op, other, **kwargs):
default_comparator = util.preloaded.sql_default_comparator
o = default_comparator.operator_lookup[op.__name__]
return o[0](self.expr, op, other, reverse=True, *o[1:], **kwargs)
def _adapt_expression(self, op, other_comparator):
"""evaluate the return type of <self> <op> <othertype>,
and apply any adaptations to the given operator.
This method determines the type of a resulting binary expression
given two source types and an operator. For example, two
:class:`_schema.Column` objects, both of the type
:class:`.Integer`, will
produce a :class:`.BinaryExpression` that also has the type
:class:`.Integer` when compared via the addition (``+``) operator.
However, using the addition operator with an :class:`.Integer`
and a :class:`.Date` object will produce a :class:`.Date`, assuming
"days delta" behavior by the database (in reality, most databases
other than PostgreSQL don't accept this particular operation).
The method returns a tuple of the form <operator>, <type>.
The resulting operator and type will be those applied to the
resulting :class:`.BinaryExpression` as the final operator and the
right-hand side of the expression.
Note that only a subset of operators make usage of
:meth:`._adapt_expression`,
including math operators and user-defined operators, but not
boolean comparison or special SQL keywords like MATCH or BETWEEN.
"""
return op, self.type
def __reduce__(self):
return _reconstitute_comparator, (self.expr,)
hashable = True
"""Flag, if False, means values from this type aren't hashable.
Used by the ORM when uniquing result lists.
"""
comparator_factory = Comparator
"""A :class:`.TypeEngine.Comparator` class which will apply
to operations performed by owning :class:`_expression.ColumnElement`
objects.
The :attr:`.comparator_factory` attribute is a hook consulted by
the core expression system when column and SQL expression operations
are performed. When a :class:`.TypeEngine.Comparator` class is
associated with this attribute, it allows custom re-definition of
all existing operators, as well as definition of new operators.
Existing operators include those provided by Python operator overloading
such as :meth:`.operators.ColumnOperators.__add__` and
:meth:`.operators.ColumnOperators.__eq__`,
those provided as standard
attributes of :class:`.operators.ColumnOperators` such as
:meth:`.operators.ColumnOperators.like`
and :meth:`.operators.ColumnOperators.in_`.
Rudimentary usage of this hook is allowed through simple subclassing
of existing types, or alternatively by using :class:`.TypeDecorator`.
See the documentation section :ref:`types_operators` for examples.
"""
sort_key_function = None
"""A sorting function that can be passed as the key to sorted.
The default value of ``None`` indicates that the values stored by
this type are self-sorting.
.. versionadded:: 1.3.8
"""
should_evaluate_none = False
"""If True, the Python constant ``None`` is considered to be handled
explicitly by this type.
The ORM uses this flag to indicate that a positive value of ``None``
is passed to the column in an INSERT statement, rather than omitting
the column from the INSERT statement which has the effect of firing
off column-level defaults. It also allows types which have special
behavior for Python None, such as a JSON type, to indicate that
they'd like to handle the None value explicitly.
To set this flag on an existing type, use the
:meth:`.TypeEngine.evaluates_none` method.
.. seealso::
:meth:`.TypeEngine.evaluates_none`
.. versionadded:: 1.1
"""
def evaluates_none(self):
"""Return a copy of this type which has the :attr:`.should_evaluate_none`
flag set to True.
E.g.::
Table(
'some_table', metadata,
Column(
String(50).evaluates_none(),
nullable=True,
server_default='no value')
)
The ORM uses this flag to indicate that a positive value of ``None``
is passed to the column in an INSERT statement, rather than omitting
the column from the INSERT statement which has the effect of firing
off column-level defaults. It also allows for types which have
special behavior associated with the Python None value to indicate
that the value doesn't necessarily translate into SQL NULL; a
prime example of this is a JSON type which may wish to persist the
JSON value ``'null'``.
In all cases, the actual NULL SQL value can be always be
persisted in any column by using
the :obj:`_expression.null` SQL construct in an INSERT statement
or associated with an ORM-mapped attribute.
.. note::
The "evaluates none" flag does **not** apply to a value
of ``None`` passed to :paramref:`_schema.Column.default` or
:paramref:`_schema.Column.server_default`; in these cases,
``None``
still means "no default".
.. versionadded:: 1.1
.. seealso::
:ref:`session_forcing_null` - in the ORM documentation
:paramref:`.postgresql.JSON.none_as_null` - PostgreSQL JSON
interaction with this flag.
:attr:`.TypeEngine.should_evaluate_none` - class-level flag
"""
typ = self.copy()
typ.should_evaluate_none = True
return typ
def copy(self, **kw):
return self.adapt(self.__class__)
def compare_against_backend(self, dialect, conn_type):
"""Compare this type against the given backend type.
This function is currently not implemented for SQLAlchemy
types, and for all built in types will return ``None``. However,
it can be implemented by a user-defined type
where it can be consumed by schema comparison tools such as
Alembic autogenerate.
A future release of SQLAlchemy will potentially implement this method
for builtin types as well.
The function should return True if this type is equivalent to the
given type; the type is typically reflected from the database
so should be database specific. The dialect in use is also
passed. It can also return False to assert that the type is
not equivalent.
:param dialect: a :class:`.Dialect` that is involved in the comparison.
:param conn_type: the type object reflected from the backend.
.. versionadded:: 1.0.3
"""
return None
def copy_value(self, value):
return value
def literal_processor(self, dialect):
"""Return a conversion function for processing literal values that are
to be rendered directly without using binds.
This function is used when the compiler makes use of the
"literal_binds" flag, typically used in DDL generation as well
as in certain scenarios where backends don't accept bound parameters.
.. versionadded:: 0.9.0
"""
return None
def bind_processor(self, dialect):
"""Return a conversion function for processing bind values.
Returns a callable which will receive a bind parameter value
as the sole positional argument and will return a value to
send to the DB-API.
If processing is not necessary, the method should return ``None``.
:param dialect: Dialect instance in use.
"""
return None
def result_processor(self, dialect, coltype):
"""Return a conversion function for processing result row values.
Returns a callable which will receive a result row column
value as the sole positional argument and will return a value
to return to the user.
If processing is not necessary, the method should return ``None``.
:param dialect: Dialect instance in use.
:param coltype: DBAPI coltype argument received in cursor.description.
"""
return None
def column_expression(self, colexpr):
"""Given a SELECT column expression, return a wrapping SQL expression.
This is typically a SQL function that wraps a column expression
as rendered in the columns clause of a SELECT statement.
It is used for special data types that require
columns to be wrapped in some special database function in order
to coerce the value before being sent back to the application.
It is the SQL analogue of the :meth:`.TypeEngine.result_processor`
method.
The method is evaluated at statement compile time, as opposed
to statement construction time.
.. seealso::
:ref:`types_sql_value_processing`
"""
return None
@util.memoized_property
def _has_column_expression(self):
"""memoized boolean, check if column_expression is implemented.
Allows the method to be skipped for the vast majority of expression
types that don't use this feature.
"""
return (
self.__class__.column_expression.__code__
is not TypeEngine.column_expression.__code__
)
def bind_expression(self, bindvalue):
"""Given a bind value (i.e. a :class:`.BindParameter` instance),
return a SQL expression in its place.
This is typically a SQL function that wraps the existing bound
parameter within the statement. It is used for special data types
that require literals being wrapped in some special database function
in order to coerce an application-level value into a database-specific
format. It is the SQL analogue of the
:meth:`.TypeEngine.bind_processor` method.
The method is evaluated at statement compile time, as opposed
to statement construction time.
Note that this method, when implemented, should always return
the exact same structure, without any conditional logic, as it
may be used in an executemany() call against an arbitrary number
of bound parameter sets.
.. seealso::
:ref:`types_sql_value_processing`
"""
return None
@util.memoized_property
def _has_bind_expression(self):
"""memoized boolean, check if bind_expression is implemented.
Allows the method to be skipped for the vast majority of expression
types that don't use this feature.
"""
return util.method_is_overridden(self, TypeEngine.bind_expression)
@staticmethod
def _to_instance(cls_or_self):
return to_instance(cls_or_self)
def compare_values(self, x, y):
"""Compare two values for equality."""
return x == y
def get_dbapi_type(self, dbapi):
"""Return the corresponding type object from the underlying DB-API, if
any.
This can be useful for calling ``setinputsizes()``, for example.
"""
return None
@property
def python_type(self):
"""Return the Python type object expected to be returned
by instances of this type, if known.
Basically, for those types which enforce a return type,
or are known across the board to do such for all common
DBAPIs (like ``int`` for example), will return that type.
If a return type is not defined, raises
``NotImplementedError``.
Note that any type also accommodates NULL in SQL which
means you can also get back ``None`` from any type
in practice.
"""
raise NotImplementedError()
def with_variant(self, type_, dialect_name):
r"""Produce a new type object that will utilize the given
type when applied to the dialect of the given name.
e.g.::
from sqlalchemy.types import String
from sqlalchemy.dialects import mysql
s = String()
s = s.with_variant(mysql.VARCHAR(collation='foo'), 'mysql')
The construction of :meth:`.TypeEngine.with_variant` is always
from the "fallback" type to that which is dialect specific.
The returned type is an instance of :class:`.Variant`, which
itself provides a :meth:`.Variant.with_variant`
that can be called repeatedly.
:param type\_: a :class:`.TypeEngine` that will be selected
as a variant from the originating type, when a dialect
of the given name is in use.
:param dialect_name: base name of the dialect which uses
this type. (i.e. ``'postgresql'``, ``'mysql'``, etc.)
"""
return Variant(self, {dialect_name: to_instance(type_)})
@util.memoized_property
def _type_affinity(self):
"""Return a rudimental 'affinity' value expressing the general class
of type."""
typ = None
for t in self.__class__.__mro__:
if t in (TypeEngine, UserDefinedType):
return typ
elif issubclass(t, (TypeEngine, UserDefinedType)):
typ = t
else:
return self.__class__
@util.memoized_property
def _generic_type_affinity(self):
best_camelcase = None
best_uppercase = None
if not isinstance(self, (TypeEngine, UserDefinedType)):
return self.__class__
for t in self.__class__.__mro__:
if (
t.__module__
in (
"sqlalchemy.sql.sqltypes",
"sqlalchemy.sql.type_api",
)
and issubclass(t, TypeEngine)
and t is not TypeEngine
and t.__name__[0] != "_"
):
if t.__name__.isupper() and not best_uppercase:
best_uppercase = t
elif not t.__name__.isupper() and not best_camelcase:
best_camelcase = t
return best_camelcase or best_uppercase or NULLTYPE.__class__
def as_generic(self, allow_nulltype=False):
"""
Return an instance of the generic type corresponding to this type
using heuristic rule. The method may be overridden if this
heuristic rule is not sufficient.
>>> from sqlalchemy.dialects.mysql import INTEGER
>>> INTEGER(display_width=4).as_generic()
Integer()
>>> from sqlalchemy.dialects.mysql import NVARCHAR
>>> NVARCHAR(length=100).as_generic()
Unicode(length=100)
.. versionadded:: 1.4.0b2
.. seealso::
:ref:`metadata_reflection_dbagnostic_types` - describes the
use of :meth:`_types.TypeEngine.as_generic` in conjunction with
the :meth:`_sql.DDLEvents.column_reflect` event, which is its
intended use.
"""
if (
not allow_nulltype
and self._generic_type_affinity == NULLTYPE.__class__
):
raise NotImplementedError(
"Default TypeEngine.as_generic() "
"heuristic method was unsuccessful for {}. A custom "
"as_generic() method must be implemented for this "
"type class.".format(
self.__class__.__module__ + "." + self.__class__.__name__
)
)
return util.constructor_copy(self, self._generic_type_affinity)
def dialect_impl(self, dialect):
"""Return a dialect-specific implementation for this
:class:`.TypeEngine`.
"""
try:
return dialect._type_memos[self]["impl"]
except KeyError:
return self._dialect_info(dialect)["impl"]
def _unwrapped_dialect_impl(self, dialect):
"""Return the 'unwrapped' dialect impl for this type.
For a type that applies wrapping logic (e.g. TypeDecorator), give
us the real, actual dialect-level type that is used.
This is used by TypeDecorator itself as well at least one case where
dialects need to check that a particular specific dialect-level
type is in use, within the :meth:`.DefaultDialect.set_input_sizes`
method.
"""
return self.dialect_impl(dialect)
def _cached_literal_processor(self, dialect):
"""Return a dialect-specific literal processor for this type."""
try:
return dialect._type_memos[self]["literal"]
except KeyError:
pass
# avoid KeyError context coming into literal_processor() function
# raises
d = self._dialect_info(dialect)
d["literal"] = lp = d["impl"].literal_processor(dialect)
return lp
def _cached_bind_processor(self, dialect):
"""Return a dialect-specific bind processor for this type."""
try:
return dialect._type_memos[self]["bind"]
except KeyError:
pass
# avoid KeyError context coming into bind_processor() function
# raises
d = self._dialect_info(dialect)
d["bind"] = bp = d["impl"].bind_processor(dialect)
return bp
def _cached_result_processor(self, dialect, coltype):
"""Return a dialect-specific result processor for this type."""
try:
return dialect._type_memos[self][coltype]
except KeyError:
pass
# avoid KeyError context coming into result_processor() function
# raises
d = self._dialect_info(dialect)
# key assumption: DBAPI type codes are
# constants. Else this dictionary would
# grow unbounded.
d[coltype] = rp = d["impl"].result_processor(dialect, coltype)
return rp
def _cached_custom_processor(self, dialect, key, fn):
try:
return dialect._type_memos[self][key]
except KeyError:
pass
# avoid KeyError context coming into fn() function
# raises
d = self._dialect_info(dialect)
impl = d["impl"]
d[key] = result = fn(impl)
return result
def _dialect_info(self, dialect):
"""Return a dialect-specific registry which
caches a dialect-specific implementation, bind processing
function, and one or more result processing functions."""
if self in dialect._type_memos:
return dialect._type_memos[self]
else:
impl = self._gen_dialect_impl(dialect)
if impl is self:
impl = self.adapt(type(self))
# this can't be self, else we create a cycle
assert impl is not self
dialect._type_memos[self] = d = {"impl": impl}
return d
def _gen_dialect_impl(self, dialect):
return dialect.type_descriptor(self)
@util.memoized_property
def _static_cache_key(self):
names = util.get_cls_kwargs(self.__class__)
return (self.__class__,) + tuple(
(
k,
self.__dict__[k]._static_cache_key
if isinstance(self.__dict__[k], TypeEngine)
else self.__dict__[k],
)
for k in names
if k in self.__dict__ and not k.startswith("_")
)
def adapt(self, cls, **kw):
"""Produce an "adapted" form of this type, given an "impl" class
to work with.
This method is used internally to associate generic
types with "implementation" types that are specific to a particular
dialect.
"""
return util.constructor_copy(self, cls, **kw)
def coerce_compared_value(self, op, value):
"""Suggest a type for a 'coerced' Python value in an expression.
Given an operator and value, gives the type a chance
to return a type which the value should be coerced into.
The default behavior here is conservative; if the right-hand
side is already coerced into a SQL type based on its
Python type, it is usually left alone.
End-user functionality extension here should generally be via
:class:`.TypeDecorator`, which provides more liberal behavior in that
it defaults to coercing the other side of the expression into this
type, thus applying special Python conversions above and beyond those
needed by the DBAPI to both ides. It also provides the public method
:meth:`.TypeDecorator.coerce_compared_value` which is intended for
end-user customization of this behavior.
"""
_coerced_type = _resolve_value_to_type(value)
if (
_coerced_type is NULLTYPE
or _coerced_type._type_affinity is self._type_affinity
):
return self
else:
return _coerced_type
def _compare_type_affinity(self, other):
return self._type_affinity is other._type_affinity
def compile(self, dialect=None):
"""Produce a string-compiled form of this :class:`.TypeEngine`.
When called with no arguments, uses a "default" dialect
to produce a string result.
:param dialect: a :class:`.Dialect` instance.
"""
# arg, return value is inconsistent with
# ClauseElement.compile()....this is a mistake.
if not dialect:
dialect = self._default_dialect()
return dialect.type_compiler.process(self)
@util.preload_module("sqlalchemy.engine.default")
def _default_dialect(self):
default = util.preloaded.engine_default
return default.StrCompileDialect()
def __str__(self):
if util.py2k:
return unicode(self.compile()).encode( # noqa
"ascii", "backslashreplace"
) # noqa
else:
return str(self.compile())
def __repr__(self):
return util.generic_repr(self)
class VisitableCheckKWArg(util.EnsureKWArgType, TraversibleType):
pass
class UserDefinedType(util.with_metaclass(VisitableCheckKWArg, TypeEngine)):
"""Base for user defined types.
This should be the base of new types. Note that
for most cases, :class:`.TypeDecorator` is probably
more appropriate::
import sqlalchemy.types as types
class MyType(types.UserDefinedType):
def __init__(self, precision = 8):
self.precision = precision
def get_col_spec(self, **kw):
return "MYTYPE(%s)" % self.precision
def bind_processor(self, dialect):
def process(value):
return value
return process
def result_processor(self, dialect, coltype):
def process(value):
return value
return process
Once the type is made, it's immediately usable::
table = Table('foo', meta,
Column('id', Integer, primary_key=True),
Column('data', MyType(16))
)
The ``get_col_spec()`` method will in most cases receive a keyword
argument ``type_expression`` which refers to the owning expression
of the type as being compiled, such as a :class:`_schema.Column` or
:func:`.cast` construct. This keyword is only sent if the method
accepts keyword arguments (e.g. ``**kw``) in its argument signature;
introspection is used to check for this in order to support legacy
forms of this function.
.. versionadded:: 1.0.0 the owning expression is passed to
the ``get_col_spec()`` method via the keyword argument
``type_expression``, if it receives ``**kw`` in its signature.
"""
__visit_name__ = "user_defined"
ensure_kwarg = "get_col_spec"
def coerce_compared_value(self, op, value):
"""Suggest a type for a 'coerced' Python value in an expression.
Default behavior for :class:`.UserDefinedType` is the
same as that of :class:`.TypeDecorator`; by default it returns
``self``, assuming the compared value should be coerced into
the same type as this one. See
:meth:`.TypeDecorator.coerce_compared_value` for more detail.
"""
return self
class Emulated(object):
"""Mixin for base types that emulate the behavior of a DB-native type.
An :class:`.Emulated` type will use an available database type
in conjunction with Python-side routines and/or database constraints
in order to approximate the behavior of a database type that is provided
natively by some backends. When a native-providing backend is in
use, the native version of the type is used. This native version
should include the :class:`.NativeForEmulated` mixin to allow it to be
distinguished from :class:`.Emulated`.
Current examples of :class:`.Emulated` are: :class:`.Interval`,
:class:`.Enum`, :class:`.Boolean`.
.. versionadded:: 1.2.0b3
"""
def adapt_to_emulated(self, impltype, **kw):
"""Given an impl class, adapt this type to the impl assuming "emulated".
The impl should also be an "emulated" version of this type,
most likely the same class as this type itself.
e.g.: sqltypes.Enum adapts to the Enum class.
"""
return super(Emulated, self).adapt(impltype, **kw)
def adapt(self, impltype, **kw):
if hasattr(impltype, "adapt_emulated_to_native"):
if self.native:
# native support requested, dialect gave us a native
# implementor, pass control over to it
return impltype.adapt_emulated_to_native(self, **kw)
else:
# non-native support, let the native implementor
# decide also, at the moment this is just to help debugging
# as only the default logic is implemented.
return impltype.adapt_native_to_emulated(self, **kw)
else:
if issubclass(impltype, self.__class__):
return self.adapt_to_emulated(impltype, **kw)
else:
return super(Emulated, self).adapt(impltype, **kw)
class NativeForEmulated(object):
"""Indicates DB-native types supported by an :class:`.Emulated` type.
.. versionadded:: 1.2.0b3
"""
@classmethod
def adapt_native_to_emulated(cls, impl, **kw):
"""Given an impl, adapt this type's class to the impl assuming
"emulated".
"""
impltype = impl.__class__
return impl.adapt(impltype, **kw)
@classmethod
def adapt_emulated_to_native(cls, impl, **kw):
"""Given an impl, adapt this type's class to the impl assuming "native".
The impl will be an :class:`.Emulated` class but not a
:class:`.NativeForEmulated`.
e.g.: postgresql.ENUM produces a type given an Enum instance.
"""
return cls(**kw)
class TypeDecorator(SchemaEventTarget, TypeEngine):
"""Allows the creation of types which add additional functionality
to an existing type.
This method is preferred to direct subclassing of SQLAlchemy's
built-in types as it ensures that all required functionality of
the underlying type is kept in place.
Typical usage::
import sqlalchemy.types as types
class MyType(types.TypeDecorator):
'''Prefixes Unicode values with "PREFIX:" on the way in and
strips it off on the way out.
'''
impl = types.Unicode
cache_ok = True
def process_bind_param(self, value, dialect):
return "PREFIX:" + value
def process_result_value(self, value, dialect):
return value[7:]
def copy(self, **kw):
return MyType(self.impl.length)
The class-level ``impl`` attribute is required, and can reference any
:class:`.TypeEngine` class. Alternatively, the :meth:`load_dialect_impl`
method can be used to provide different type classes based on the dialect
given; in this case, the ``impl`` variable can reference
``TypeEngine`` as a placeholder.
The :attr:`.TypeDecorator.cache_ok` class-level flag indicates if this
custom :class:`.TypeDecorator` is safe to be used as part of a cache key.
This flag defaults to ``None`` which will initially generate a warning
when the SQL compiler attempts to generate a cache key for a statement
that uses this type. If the :class:`.TypeDecorator` is not guaranteed
to produce the same bind/result behavior and SQL generation
every time, this flag should be set to ``False``; otherwise if the
class produces the same behavior each time, it may be set to ``True``.
See :attr:`.TypeDecorator.cache_ok` for further notes on how this works.
Types that receive a Python type that isn't similar to the ultimate type
used may want to define the :meth:`TypeDecorator.coerce_compared_value`
method. This is used to give the expression system a hint when coercing
Python objects into bind parameters within expressions. Consider this
expression::
mytable.c.somecol + datetime.date(2009, 5, 15)
Above, if "somecol" is an ``Integer`` variant, it makes sense that
we're doing date arithmetic, where above is usually interpreted
by databases as adding a number of days to the given date.
The expression system does the right thing by not attempting to
coerce the "date()" value into an integer-oriented bind parameter.
However, in the case of ``TypeDecorator``, we are usually changing an
incoming Python type to something new - ``TypeDecorator`` by default will
"coerce" the non-typed side to be the same type as itself. Such as below,
we define an "epoch" type that stores a date value as an integer::
class MyEpochType(types.TypeDecorator):
impl = types.Integer
epoch = datetime.date(1970, 1, 1)
def process_bind_param(self, value, dialect):
return (value - self.epoch).days
def process_result_value(self, value, dialect):
return self.epoch + timedelta(days=value)
Our expression of ``somecol + date`` with the above type will coerce the
"date" on the right side to also be treated as ``MyEpochType``.
This behavior can be overridden via the
:meth:`~TypeDecorator.coerce_compared_value` method, which returns a type
that should be used for the value of the expression. Below we set it such
that an integer value will be treated as an ``Integer``, and any other
value is assumed to be a date and will be treated as a ``MyEpochType``::
def coerce_compared_value(self, op, value):
if isinstance(value, int):
return Integer()
else:
return self
.. warning::
Note that the **behavior of coerce_compared_value is not inherited
by default from that of the base type**.
If the :class:`.TypeDecorator` is augmenting a
type that requires special logic for certain types of operators,
this method **must** be overridden. A key example is when decorating
the :class:`_postgresql.JSON` and :class:`_postgresql.JSONB` types;
the default rules of :meth:`.TypeEngine.coerce_compared_value` should
be used in order to deal with operators like index operations::
class MyJsonType(TypeDecorator):
impl = postgresql.JSON
cache_ok = True
def coerce_compared_value(self, op, value):
return self.impl.coerce_compared_value(op, value)
Without the above step, index operations such as ``mycol['foo']``
will cause the index value ``'foo'`` to be JSON encoded.
"""
__visit_name__ = "type_decorator"
_is_type_decorator = True
def __init__(self, *args, **kwargs):
"""Construct a :class:`.TypeDecorator`.
Arguments sent here are passed to the constructor
of the class assigned to the ``impl`` class level attribute,
assuming the ``impl`` is a callable, and the resulting
object is assigned to the ``self.impl`` instance attribute
(thus overriding the class attribute of the same name).
If the class level ``impl`` is not a callable (the unusual case),
it will be assigned to the same instance attribute 'as-is',
ignoring those arguments passed to the constructor.
Subclasses can override this to customize the generation
of ``self.impl`` entirely.
"""
if not hasattr(self.__class__, "impl"):
raise AssertionError(
"TypeDecorator implementations "
"require a class-level variable "
"'impl' which refers to the class of "
"type being decorated"
)
self.impl = to_instance(self.__class__.impl, *args, **kwargs)
coerce_to_is_types = (util.NoneType,)
"""Specify those Python types which should be coerced at the expression
level to "IS <constant>" when compared using ``==`` (and same for
``IS NOT`` in conjunction with ``!=``).
For most SQLAlchemy types, this includes ``NoneType``, as well as
``bool``.
:class:`.TypeDecorator` modifies this list to only include ``NoneType``,
as typedecorator implementations that deal with boolean types are common.
Custom :class:`.TypeDecorator` classes can override this attribute to
return an empty tuple, in which case no values will be coerced to
constants.
"""
cache_ok = None
"""Indicate if statements using this :class:`.TypeDecorator` are "safe to
cache".
The default value ``None`` will emit a warning and then not allow caching
of a statement which includes this type. Set to ``False`` to disable
statements using this type from being cached at all without a warning.
When set to ``True``, the object's class and selected elements from its
state will be used as part of the cache key, e.g.::
class MyType(TypeDecorator):
impl = String
cache_ok = True
def __init__(self, choices):
self.choices = tuple(choices)
self.internal_only = True
The cache key for the above type would be equivalent to::
(<class '__main__.MyType'>, ('choices', ('a', 'b', 'c')))
The caching scheme will extract attributes from the type that correspond
to the names of parameters in the ``__init__()`` method. Above, the
"choices" attribute becomes part of the cache key but "internal_only"
does not, because there is no parameter named "internal_only".
The requirements for cacheable elements is that they are hashable
and also that they indicate the same SQL rendered for expressions using
this type every time for a given cache value.
.. versionadded:: 1.4.14 - added the ``cache_ok`` flag to allow
some configurability of caching for :class:`.TypeDecorator` classes.
.. seealso::
:ref:`sql_caching`
"""
class Comparator(TypeEngine.Comparator):
"""A :class:`.TypeEngine.Comparator` that is specific to
:class:`.TypeDecorator`.
User-defined :class:`.TypeDecorator` classes should not typically
need to modify this.
"""
__slots__ = ()
def operate(self, op, *other, **kwargs):
kwargs["_python_is_types"] = self.expr.type.coerce_to_is_types
return super(TypeDecorator.Comparator, self).operate(
op, *other, **kwargs
)
def reverse_operate(self, op, other, **kwargs):
kwargs["_python_is_types"] = self.expr.type.coerce_to_is_types
return super(TypeDecorator.Comparator, self).reverse_operate(
op, other, **kwargs
)
@property
def comparator_factory(self):
if TypeDecorator.Comparator in self.impl.comparator_factory.__mro__:
return self.impl.comparator_factory
else:
return type(
"TDComparator",
(TypeDecorator.Comparator, self.impl.comparator_factory),
{},
)
@property
def _static_cache_key(self):
if self.cache_ok is None:
util.warn(
"TypeDecorator %r will not produce a cache key because "
"the ``cache_ok`` flag is not set to True. "
"Set this flag to True if this type object's "
"state is safe to use in a cache key, or False to "
"disable this warning." % self
)
elif self.cache_ok is True:
return super(TypeDecorator, self)._static_cache_key
return NO_CACHE
def _gen_dialect_impl(self, dialect):
"""
#todo
"""
adapted = dialect.type_descriptor(self)
if adapted is not self:
return adapted
# otherwise adapt the impl type, link
# to a copy of this TypeDecorator and return
# that.
typedesc = self.load_dialect_impl(dialect).dialect_impl(dialect)
tt = self.copy()
if not isinstance(tt, self.__class__):
raise AssertionError(
"Type object %s does not properly "
"implement the copy() method, it must "
"return an object of type %s" % (self, self.__class__)
)
tt.impl = typedesc
return tt
@property
def _type_affinity(self):
"""
#todo
"""
return self.impl._type_affinity
def _set_parent(self, column, outer=False, **kw):
"""Support SchemaEventTarget"""
super(TypeDecorator, self)._set_parent(column)
if not outer and isinstance(self.impl, SchemaEventTarget):
self.impl._set_parent(column, outer=False, **kw)
def _set_parent_with_dispatch(self, parent):
"""Support SchemaEventTarget"""
super(TypeDecorator, self)._set_parent_with_dispatch(
parent, outer=True
)
if isinstance(self.impl, SchemaEventTarget):
self.impl._set_parent_with_dispatch(parent)
def type_engine(self, dialect):
"""Return a dialect-specific :class:`.TypeEngine` instance
for this :class:`.TypeDecorator`.
In most cases this returns a dialect-adapted form of
the :class:`.TypeEngine` type represented by ``self.impl``.
Makes usage of :meth:`dialect_impl`.
Behavior can be customized here by overriding
:meth:`load_dialect_impl`.
"""
adapted = dialect.type_descriptor(self)
if not isinstance(adapted, type(self)):
return adapted
else:
return self.load_dialect_impl(dialect)
def load_dialect_impl(self, dialect):
"""Return a :class:`.TypeEngine` object corresponding to a dialect.
This is an end-user override hook that can be used to provide
differing types depending on the given dialect. It is used
by the :class:`.TypeDecorator` implementation of :meth:`type_engine`
to help determine what type should ultimately be returned
for a given :class:`.TypeDecorator`.
By default returns ``self.impl``.
"""
return self.impl
def _unwrapped_dialect_impl(self, dialect):
"""Return the 'unwrapped' dialect impl for this type.
This is used by the :meth:`.DefaultDialect.set_input_sizes`
method.
"""
# some dialects have a lookup for a TypeDecorator subclass directly.
# postgresql.INTERVAL being the main example
typ = self.dialect_impl(dialect)
# if we are still a type decorator, load the per-dialect switch
# (such as what Variant uses), then get the dialect impl for that.
if isinstance(typ, self.__class__):
return typ.load_dialect_impl(dialect).dialect_impl(dialect)
else:
return typ
def __getattr__(self, key):
"""Proxy all other undefined accessors to the underlying
implementation."""
return getattr(self.impl, key)
def process_literal_param(self, value, dialect):
"""Receive a literal parameter value to be rendered inline within
a statement.
This method is used when the compiler renders a
literal value without using binds, typically within DDL
such as in the "server default" of a column or an expression
within a CHECK constraint.
The returned string will be rendered into the output string.
.. versionadded:: 0.9.0
"""
raise NotImplementedError()
def process_bind_param(self, value, dialect):
"""Receive a bound parameter value to be converted.
Subclasses override this method to return the
value that should be passed along to the underlying
:class:`.TypeEngine` object, and from there to the
DBAPI ``execute()`` method.
The operation could be anything desired to perform custom
behavior, such as transforming or serializing data.
This could also be used as a hook for validating logic.
This operation should be designed with the reverse operation
in mind, which would be the process_result_value method of
this class.
:param value: Data to operate upon, of any type expected by
this method in the subclass. Can be ``None``.
:param dialect: the :class:`.Dialect` in use.
"""
raise NotImplementedError()
def process_result_value(self, value, dialect):
"""Receive a result-row column value to be converted.
Subclasses should implement this method to operate on data
fetched from the database.
Subclasses override this method to return the
value that should be passed back to the application,
given a value that is already processed by
the underlying :class:`.TypeEngine` object, originally
from the DBAPI cursor method ``fetchone()`` or similar.
The operation could be anything desired to perform custom
behavior, such as transforming or serializing data.
This could also be used as a hook for validating logic.
:param value: Data to operate upon, of any type expected by
this method in the subclass. Can be ``None``.
:param dialect: the :class:`.Dialect` in use.
This operation should be designed to be reversible by
the "process_bind_param" method of this class.
"""
raise NotImplementedError()
@util.memoized_property
def _has_bind_processor(self):
"""memoized boolean, check if process_bind_param is implemented.
Allows the base process_bind_param to raise
NotImplementedError without needing to test an expensive
exception throw.
"""
return util.method_is_overridden(
self, TypeDecorator.process_bind_param
)
@util.memoized_property
def _has_literal_processor(self):
"""memoized boolean, check if process_literal_param is implemented."""
return util.method_is_overridden(
self, TypeDecorator.process_literal_param
)
def literal_processor(self, dialect):
"""Provide a literal processing function for the given
:class:`.Dialect`.
Subclasses here will typically override
:meth:`.TypeDecorator.process_literal_param` instead of this method
directly.
By default, this method makes use of
:meth:`.TypeDecorator.process_bind_param` if that method is
implemented, where :meth:`.TypeDecorator.process_literal_param` is
not. The rationale here is that :class:`.TypeDecorator` typically
deals with Python conversions of data that are above the layer of
database presentation. With the value converted by
:meth:`.TypeDecorator.process_bind_param`, the underlying type will
then handle whether it needs to be presented to the DBAPI as a bound
parameter or to the database as an inline SQL value.
.. versionadded:: 0.9.0
"""
if self._has_literal_processor:
process_param = self.process_literal_param
elif self._has_bind_processor:
# the bind processor should normally be OK
# for TypeDecorator since it isn't doing DB-level
# handling, the handling here won't be different for bound vs.
# literals.
process_param = self.process_bind_param
else:
process_param = None
if process_param:
impl_processor = self.impl.literal_processor(dialect)
if impl_processor:
def process(value):
return impl_processor(process_param(value, dialect))
else:
def process(value):
return process_param(value, dialect)
return process
else:
return self.impl.literal_processor(dialect)
def bind_processor(self, dialect):
"""Provide a bound value processing function for the
given :class:`.Dialect`.
This is the method that fulfills the :class:`.TypeEngine`
contract for bound value conversion. :class:`.TypeDecorator`
will wrap a user-defined implementation of
:meth:`process_bind_param` here.
User-defined code can override this method directly,
though its likely best to use :meth:`process_bind_param` so that
the processing provided by ``self.impl`` is maintained.
:param dialect: Dialect instance in use.
This method is the reverse counterpart to the
:meth:`result_processor` method of this class.
"""
if self._has_bind_processor:
process_param = self.process_bind_param
impl_processor = self.impl.bind_processor(dialect)
if impl_processor:
def process(value):
return impl_processor(process_param(value, dialect))
else:
def process(value):
return process_param(value, dialect)
return process
else:
return self.impl.bind_processor(dialect)
@util.memoized_property
def _has_result_processor(self):
"""memoized boolean, check if process_result_value is implemented.
Allows the base process_result_value to raise
NotImplementedError without needing to test an expensive
exception throw.
"""
return util.method_is_overridden(
self, TypeDecorator.process_result_value
)
def result_processor(self, dialect, coltype):
"""Provide a result value processing function for the given
:class:`.Dialect`.
This is the method that fulfills the :class:`.TypeEngine`
contract for result value conversion. :class:`.TypeDecorator`
will wrap a user-defined implementation of
:meth:`process_result_value` here.
User-defined code can override this method directly,
though its likely best to use :meth:`process_result_value` so that
the processing provided by ``self.impl`` is maintained.
:param dialect: Dialect instance in use.
:param coltype: A SQLAlchemy data type
This method is the reverse counterpart to the
:meth:`bind_processor` method of this class.
"""
if self._has_result_processor:
process_value = self.process_result_value
impl_processor = self.impl.result_processor(dialect, coltype)
if impl_processor:
def process(value):
return process_value(impl_processor(value), dialect)
else:
def process(value):
return process_value(value, dialect)
return process
else:
return self.impl.result_processor(dialect, coltype)
@util.memoized_property
def _has_bind_expression(self):
return (
util.method_is_overridden(self, TypeDecorator.bind_expression)
or self.impl._has_bind_expression
)
def bind_expression(self, bindparam):
return self.impl.bind_expression(bindparam)
@util.memoized_property
def _has_column_expression(self):
"""memoized boolean, check if column_expression is implemented.
Allows the method to be skipped for the vast majority of expression
types that don't use this feature.
"""
return (
util.method_is_overridden(self, TypeDecorator.column_expression)
or self.impl._has_column_expression
)
def column_expression(self, column):
return self.impl.column_expression(column)
def coerce_compared_value(self, op, value):
"""Suggest a type for a 'coerced' Python value in an expression.
By default, returns self. This method is called by
the expression system when an object using this type is
on the left or right side of an expression against a plain Python
object which does not yet have a SQLAlchemy type assigned::
expr = table.c.somecolumn + 35
Where above, if ``somecolumn`` uses this type, this method will
be called with the value ``operator.add``
and ``35``. The return value is whatever SQLAlchemy type should
be used for ``35`` for this particular operation.
"""
return self
def copy(self, **kw):
"""Produce a copy of this :class:`.TypeDecorator` instance.
This is a shallow copy and is provided to fulfill part of
the :class:`.TypeEngine` contract. It usually does not
need to be overridden unless the user-defined :class:`.TypeDecorator`
has local state that should be deep-copied.
"""
instance = self.__class__.__new__(self.__class__)
instance.__dict__.update(self.__dict__)
return instance
def get_dbapi_type(self, dbapi):
"""Return the DBAPI type object represented by this
:class:`.TypeDecorator`.
By default this calls upon :meth:`.TypeEngine.get_dbapi_type` of the
underlying "impl".
"""
return self.impl.get_dbapi_type(dbapi)
def compare_values(self, x, y):
"""Given two values, compare them for equality.
By default this calls upon :meth:`.TypeEngine.compare_values`
of the underlying "impl", which in turn usually
uses the Python equals operator ``==``.
This function is used by the ORM to compare
an original-loaded value with an intercepted
"changed" value, to determine if a net change
has occurred.
"""
return self.impl.compare_values(x, y)
@property
def sort_key_function(self):
return self.impl.sort_key_function
def __repr__(self):
return util.generic_repr(self, to_inspect=self.impl)
class Variant(TypeDecorator):
"""A wrapping type that selects among a variety of
implementations based on dialect in use.
The :class:`.Variant` type is typically constructed
using the :meth:`.TypeEngine.with_variant` method.
.. seealso:: :meth:`.TypeEngine.with_variant` for an example of use.
"""
cache_ok = True
def __init__(self, base, mapping):
"""Construct a new :class:`.Variant`.
:param base: the base 'fallback' type
:param mapping: dictionary of string dialect names to
:class:`.TypeEngine` instances.
"""
self.impl = base
self.mapping = mapping
@util.memoized_property
def _static_cache_key(self):
# TODO: needs tests in test/sql/test_compare.py
return (self.__class__,) + (
self.impl._static_cache_key,
tuple(
(key, self.mapping[key]._static_cache_key)
for key in sorted(self.mapping)
),
)
def coerce_compared_value(self, operator, value):
result = self.impl.coerce_compared_value(operator, value)
if result is self.impl:
return self
else:
return result
def load_dialect_impl(self, dialect):
if dialect.name in self.mapping:
return self.mapping[dialect.name]
else:
return self.impl
def _set_parent(self, column, outer=False, **kw):
"""Support SchemaEventTarget"""
if isinstance(self.impl, SchemaEventTarget):
self.impl._set_parent(column, **kw)
for impl in self.mapping.values():
if isinstance(impl, SchemaEventTarget):
impl._set_parent(column, **kw)
def _set_parent_with_dispatch(self, parent):
"""Support SchemaEventTarget"""
if isinstance(self.impl, SchemaEventTarget):
self.impl._set_parent_with_dispatch(parent)
for impl in self.mapping.values():
if isinstance(impl, SchemaEventTarget):
impl._set_parent_with_dispatch(parent)
def with_variant(self, type_, dialect_name):
r"""Return a new :class:`.Variant` which adds the given
type + dialect name to the mapping, in addition to the
mapping present in this :class:`.Variant`.
:param type\_: a :class:`.TypeEngine` that will be selected
as a variant from the originating type, when a dialect
of the given name is in use.
:param dialect_name: base name of the dialect which uses
this type. (i.e. ``'postgresql'``, ``'mysql'``, etc.)
"""
if dialect_name in self.mapping:
raise exc.ArgumentError(
"Dialect '%s' is already present in "
"the mapping for this Variant" % dialect_name
)
mapping = self.mapping.copy()
mapping[dialect_name] = type_
return Variant(self.impl, mapping)
@property
def comparator_factory(self):
"""express comparison behavior in terms of the base type"""
return self.impl.comparator_factory
def _reconstitute_comparator(expression):
return expression.comparator
def to_instance(typeobj, *arg, **kw):
if typeobj is None:
return NULLTYPE
if callable(typeobj):
return typeobj(*arg, **kw)
else:
return typeobj
def adapt_type(typeobj, colspecs):
if isinstance(typeobj, type):
typeobj = typeobj()
for t in typeobj.__class__.__mro__[0:-1]:
try:
impltype = colspecs[t]
break
except KeyError:
pass
else:
# couldn't adapt - so just return the type itself
# (it may be a user-defined type)
return typeobj
# if we adapted the given generic type to a database-specific type,
# but it turns out the originally given "generic" type
# is actually a subclass of our resulting type, then we were already
# given a more specific type than that required; so use that.
if issubclass(typeobj.__class__, impltype):
return typeobj
return typeobj.adapt(impltype)
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