Thoroughly understand the inverse (2)-zz in hibernate

In most cases, "inverse = false" is rarely used, but I still want to study it carefully (so that I can better understand "inverse = true "). Pai_^ Why is "inverse = false" rarely used "? The reason is very simple as mentioned earlier, that is, the two-way relationship will not be optimized. Let's look at a parent-child example: Relationship ing in the parent
{Set name = children lazy = true inverse = false}
{Key column = parent_id /}
{One-to-learn class = test. Child /}
Link ing in {/set} son
{Role-to-one name = parent column = parent_id not-null = true/} code: parent P = new parent ();
Child C = new child ();
P. getchildren (). Add (C );
C. setparent (p); Session. Save (P );
Session. Save (C );
Session. Flush (); Result: hibernate: insert into parent (ID) values (?)
Hibernate: insert into child (parent_id, ID) values (?, ?)
Hibernate: Update Child set parent_id =? Where id =? Here we should understand why "inverse = true" will optimize the SQL statement! In addition, we also mentioned that "inverse = false" is used to maintain the relationship, which is maintained by the father. Suppose I drop flush () between SAVE (P) and save (c). What is the result? In fact, we cannot do this! Because my father is responsible for maintaining the relationship, if I add flush () between them, then the association update will not be available (my father needs a persistent son to trigger the association update). Next let's take a look at the update: parent P = (parent) session. load (parent. class, parentid );
Parent P2 = (parent) Session. Load (parent. Class, parentid2 );

C = (child) Session. Find (
"From child as child where child. Parent =? ",
P, hibernate. Entity (parent. Class). Get (0); p. getchildren (). Remove (C );
P2.getchildren (). Add (C );
C. setparent (P2); Result: hibernate: Select parent0 _. ID as ID from parent parent0 _ Where parent0 _. ID =? // Get parent 1
Hibernate: Select parent0 _. ID as ID from parent parent0 _ Where parent0 _. ID =? // Get parent 2
Hibernate: Select child0 _. ID as ID, child0 _. parent_id as parent_id from child child0 _ Where (child0 _. parent_id =? )
// Get first child for parent 1 hibernate: Select child0 _. ID as ID __, child0 _. ID as ID, child0 _. parent_id as parent_id from child child0 _ Where child0 _. parent_id =?
Hibernate: Select child0 _. ID as ID __, child0 _. ID as ID, child0 _. parent_id as parent_id from child child0 _ Where child0 _. parent_id =? Hibernate: Update Child set parent_id =? Where id =? // Child. setparent
Hibernate: Update Child set parent_id = NULL where parent_id =? // Remove
Hibernate: Update Child set parent_id =? Where id =? // The add result indicates that when "inverse = false" is set, the relationship is maintained by the father and son. This efficiency is much lower than the "inverse = true" I mentioned earlier. The relationship was maintained by my father. I changed the code again: parent P = (parent) Session. Load (parent. Class, parentid );
Parent P2 = (parent) Session. Load (parent. Class, parentid2 );

C = (child) Session. Find (
"From child as child where child. Parent =? ",
P, hibernate. entity (parent. class )). get (0); p2.getchildren (). add (c); Result: hibernate: Select parent0 _. ID as ID from parent parent0 _ Where parent0 _. id =? // Get parent 1
Hibernate: Select parent0 _. ID as ID from parent parent0 _ Where parent0 _. ID =? // Get parent 2
Hibernate: Select child0 _. ID as ID, child0 _. parent_id as parent_id from child child0 _ Where (child0 _. parent_id =? )
// Get first child for parent 1 hibernate: Select child0 _. ID as ID __, child0 _. ID as ID, child0 _. parent_id as parent_id from child child0 _ Where child0 _. parent_id =?
Hibernate: Select child0 _. ID as ID __, child0 _. ID as ID, child0 _. parent_id as parent_id from child child0 _ Where child0 _. parent_id =? Hibernate: Update Child set parent_id =? Where id =? // Add is correct at first glance, but the children statuses of Father P and P2 are inconsistent! Conclusion: "inverse = true" can be used to optimize the code. We recommend that you use "inverse = true" when establishing a bidirectional relationship "!