Describe the loading behavior of a StrategizedProperty object.
The LoaderStrategy interacts with the querying process in three ways:
Describe a modification to an OperationContext or Query.
Manage the relationship of a Mapper to a single class attribute, as well as that attribute as it appears on individual instances of the class, including attribute instrumentation, attribute access, loading behavior, and dependency calculations.
Return a compare operation for the columns represented by this MapperProperty to the given value, which may be a column value or an instance.
Called when the mapper receives a row.
instance is the parent instance corresponding to the row.
Return a WHERE clause suitable for this MapperProperty corresponding to the given key/value pair, where the key is a column or object property name, and value is a value to be matched. This is only picked up by PropertyLoaders.
This is called by a Query's join_by method to formulate a set of key/value pairs into a WHERE criterion that spans multiple tables if needed.
Called after all mappers are compiled to assemble relationships between mappers, establish instrumented class attributes.
Return True if this MapperProperty's mapper is the primary mapper for its class.
This flag is used to indicate that the MapperProperty can define attribute instrumentation for the class at the class level (as opposed to the individual instance level).
Merge the attribute represented by this MapperProperty from source to destination object
Called by the Mapper in response to the UnitOfWork calling the Mapper's register_dependencies operation. Should register with the UnitOfWork all inter-mapper dependencies as well as dependency processors (see UOW docs for more details).
Serve as a context during a query construction or instance loading operation.
Accept MapperOption objects which may modify its state before proceeding.
A MapperOption that is applied to a property off the mapper or one of its child mappers, identified by a dot-separated key.
A MapperOption that affects which LoaderStrategy will be used for an operation by a StrategizedProperty.
A MapperProperty which uses selectable strategies to affect loading behavior.
There is a single default strategy selected, and alternate strategies can be selected at selection time through the usage of StrategizedOption objects.