sqlalchemy.ext.associationproxy.AssociationProxy

class documentation

class AssociationProxy(interfaces.InspectionAttrInfo):

A descriptor that presents a read/write view of an object attribute.

Method	`__init__`	Construct a new `.AssociationProxy`.
Method	`for_class`	Return the internal state local to a specific mapped class.
Class Variable	`is_attribute`	True if this object is a Python :term:`descriptor`.
Instance Variable	`info`	Info dictionary associated with the object, allowing user-defined data to be associated with this `.InspectionAttr`.
Method	`__delete__`	Undocumented
Method	`__get__`	Undocumented
Method	`__repr__`	Undocumented
Method	`__set__`	Undocumented
Method	`_as_instance`	Undocumented
Method	`_calc_owner`	Undocumented
Method	`_default_getset`	Undocumented
Instance Variable	`cascade_scalar_deletes`	Undocumented
Instance Variable	`creator`	Undocumented
Instance Variable	`getset_factory`	Undocumented
Instance Variable	`key`	Undocumented
Instance Variable	`proxy_bulk_set`	Undocumented
Instance Variable	`proxy_factory`	Undocumented
Instance Variable	`target_collection`	Undocumented
Instance Variable	`value_attr`	Undocumented

Inherited from InspectionAttr (via InspectionAttrInfo):

Class Variable	`__slots__`	Undocumented
Class Variable	`_is_internal_proxy`	True if this object is an internal proxy object.
Class Variable	`is_aliased_class`	True if this object is an instance of `.AliasedClass`.
Class Variable	`is_bundle`	True if this object is an instance of `.Bundle`.
Class Variable	`is_clause_element`	True if this object is an instance of `_expression.ClauseElement`.
Class Variable	`is_instance`	True if this object is an instance of `.InstanceState`.
Class Variable	`is_mapper`	True if this object is an instance of `_orm.Mapper`.
Class Variable	`is_property`	True if this object is an instance of `.MapperProperty`.
Class Variable	`is_selectable`	Return True if this object is an instance of `_expression.Selectable`.

def __init__(self, target_collection, attr, creator=None, getset_factory=None, proxy_factory=None, proxy_bulk_set=None, info=None, cascade_scalar_deletes=False):

Construct a new .AssociationProxy.

The .association_proxy function is provided as the usual entrypoint here, though .AssociationProxy can be instantiated and/or subclassed directly.

Parameters
target_collection	Name of the collection we'll proxy to, usually created with `_orm.relationship`.
attr	Attribute on the collected instances we'll proxy for. For example, given a target collection of [obj1, obj2], a list created by this proxy property would look like [getattr(obj1, attr), getattr(obj2, attr)]
creator	Optional. When new items are added to this proxied collection, new instances of the class collected by the target collection will be created. For list and set collections, the target class constructor will be called with the 'value' for the new instance. For dict types, two arguments are passed: key and value. If you want to construct instances differently, supply a 'creator' function that takes arguments as above and returns instances.
getset_factory	Optional. Proxied attribute access is automatically handled by routines that get and set values based on the `attr` argument for this proxy. If you would like to customize this behavior, you may supply a `getset_factory` callable that produces a tuple of `getter` and `setter` functions. The factory is called with two arguments, the abstract type of the underlying collection and this proxy instance.
proxy_factory	Optional. The type of collection to emulate is determined by sniffing the target collection. If your collection type can't be determined by duck typing or you'd like to use a different collection implementation, you may supply a factory function to produce those collections. Only applicable to non-scalar relationships.
proxy_bulk_set	Optional, use with proxy_factory. See the _set() method for details.
info	optional, will be assigned to `.AssociationProxy.info` if present. New in version 1.0.9.
cascade_scalar_deletes	when True, indicates that setting the proxied value to `None`, or deleting it via `del`, should also remove the source object. Only applies to scalar attributes. Normally, removing the proxied target will not remove the proxy source, as this object may have other state that is still to be kept. New in version 1.3. See Also :ref:`cascade_scalar_deletes` - complete usage example

def for_class(self, class_, obj=None):

Return the internal state local to a specific mapped class.

E.g., given a class User:

class User(Base):
    # ...

    keywords = association_proxy('kws', 'keyword')

If we access this .AssociationProxy from _orm.Mapper.all_orm_descriptors, and we want to view the target class for this proxy as mapped by User:

inspect(User).all_orm_descriptors["keywords"].for_class(User).target_class

This returns an instance of .AssociationProxyInstance that is specific to the User class. The .AssociationProxy object remains agnostic of its parent class.

New in version 1.3: - .AssociationProxy no longer stores any state specific to a particular parent class; the state is now stored in per-class .AssociationProxyInstance objects.

Parameters
class_	the class that we are returning state for.
obj	optional, an instance of the class that is required if the attribute refers to a polymorphic target, e.g. where we have to look at the type of the actual destination object to get the complete path.

is_attribute: bool =

overrides sqlalchemy.orm.base.InspectionAttr.is_attribute

True if this object is a Python :term:`descriptor`.

This can refer to one of many types. Usually a .QueryableAttribute which handles attributes events on behalf of a .MapperProperty. But can also be an extension type such as .AssociationProxy or .hybrid_property. The .InspectionAttr.extension_type will refer to a constant identifying the specific subtype.