Merging and retrieving children using Hibernate

I have a model that looks like this:

A -- Many-toMany --> B -- Many-toMany --> C

Both A and B have the CascadeType of All and FetchType of Lazy.

When I make the following call:

A mergedA = (A) session.merge(a);

The mergedA has the collection of B objects resolved. B however does not have its collection of C objects resolved.

If I make the following call:

B mergedB = (B) session.merge(b);

The mergedB has the collection of C objects resolved.

If both A and B have the C开发者_运维百科ascadeType of All, why does the collections of C objects not get resolved for the collection of Bs when I call session.merge(a);?

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Its because, it does it for the single step deep in the object graph and C is at the second step. Thus, it did just for the immediate one.

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I think its because cascade has to do with transitive persistence, and nothing to do with lazy vs non lazy.

Transitive persistence as a concept applies to logical operations that you want to 'transit' from parents to children. So its all about "you deleted a parent, and should that cascade down to children?" -- its about the semantics you want in your object relationships.

lazy vs non lazy is a persistence implementation detail. So its all about "do I as a persistence layer load this thing now?" -- its about how to optimize the persistence layer.

As a note, Im wondering if this is a correct application of merge. Merge is for reattaching a detached object to the session when an object with the same id is already in the session. Im a bit surprised that it is loading the children at all.