Add @invariant decorator to explicitly configure invariants #425
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This commit introduces two fields in every entity to track their lineage: root and owner. The owner is the immediate parent of an entity. This is the entity (or aggregate) that has the association field. The root is the aggregate root. This is the first step to being able to satisfy invariants across an aggregate's clustes of entities.
Add @invariant decorator, and configure aggregate and element classes to parse through methods and record them for later use.
When an aggregate or entity object is initialized, or its attribute value is changed, this commit ensures that all `clean()` methods (which in turn run all invariant validations) are run across the aggregate. This commit also adds `atomic_change` context manager for scenarios where multiple aggregates in an aggregate need to be changed before it becomes valid again.
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Invariants are usually buried deep in business logic, making them more complex to maintain over time and difficult to document. This PR introduces the
@invariantdecorator to configure invariants in an aggregate cluster explicitly.All methods marked
@invariantare invoked once an aggregate/entity object is initialized and triggered when anattribute is updated across the board. Explicit invariants ensure that the entire aggregate cluster remains valid at all times.
Two additional changes are present in this PR:
atomic_change, has been introduced, which temporarily turns off validations and runs them on the exit of the context manager.