Add an uninitialized instance of an entity class, as a placeholder to ensure object identity. Must be called before postHydrate(). Create a "temporary" entry for a newly instantiated entity. The entity is uninitialized, but we need the mapping from id to instance in order to guarantee uniqueness.

Perform the second step of 2-phase load. Fully initialize the entity instance. After processing a JDBC result set, we "resolve" all the associations between the entities which were instantiated and had their state "hydrated" into an array

Register the "hydrated" state of an entity instance, after the first step of 2-phase loading. Add the "hydrated state" (an array) of an uninitialized entity to the session. We don't try to resolve any associations yet, because there might be other entities waiting to be read from the JDBC result set we are currently processing