SQLAlchemy 0.8 Documentation
Runtime Inspection API¶
The inspection module provides the inspect() function, which delivers runtime information about a wide variety of SQLAlchemy objects, both within the Core as well as the ORM.
The inspect() function is the entry point to SQLAlchemy’s public API for viewing the configuration and construction of in-memory objects. Depending on the type of object passed to inspect(), the return value will either be a related object which provides a known interface, or in many cases it will return the object itself.
The rationale for inspect() is twofold. One is that it replaces the need to be aware of a large variety of “information getting” functions in SQLAlchemy, such as Inspector.from_engine(), orm.attributes.instance_state(), orm.class_mapper(), and others. The other is that the return value of inspect() is guaranteed to obey a documented API, thus allowing third party tools which build on top of SQLAlchemy configurations to be constructed in a forwards-compatible way.
New in version 0.8: The inspect() system is introduced as of version 0.8.
- sqlalchemy.inspection.inspect(subject, raiseerr=True)¶
Produce an inspection object for the given target.
The returned value in some cases may be the same object as the one given, such as if a orm.Mapper object is passed. In other cases, it will be an instance of the registered inspection type for the given object, such as if a engine.Engine is passed, an engine.Inspector object is returned.
- subject – the subject to be inspected.
- raiseerr – When True, if the given subject does not correspond to a known SQLAlchemy inspected type, sqlalchemy.exc.NoInspectionAvailable is raised. If False, None is returned.
Available Inspection Targets¶
Below is a listing of many of the most common inspection targets.
- Connectable (i.e. Engine, Connection) - returns an Inspector object.
- ClauseElement - all SQL expression components, including Table, Column, serve as their own inspection objects, meaning any of these objects passed to inspect() return themselves.
- object - an object given will be checked by the ORM for a mapping - if so, an InstanceState is returned representing the mapped state of the object. The InstanceState also provides access to per attribute state via the AttributeState interface as well as the per-flush “history” of any attribute via the History object.
- type (i.e. a class) - a class given will be checked by the ORM for a mapping - if so, a Mapper for that class is returned.
- mapped attribute - passing a mapped attribute to inspect(), such as inspect(MyClass.some_attribute), returns a QueryableAttribute object, which is the descriptor associated with a mapped class. This descriptor refers to a MapperProperty, which is usually an instance of ColumnProperty or RelationshipProperty, via its QueryableAttribute.property attribute.
- AliasedClass - returns an AliasedInsp object.