Red Hat Summit Red Hat SummitSupportKonsoleEntwicklerDemo startenKontakt

Dieser Inhalt ist in der von Ihnen ausgewählten Sprache nicht verfügbar.

22.2. Bidirectional one-to-many

Suppose we start with a simple <one-to-many> association from Parent to Child. 
<set name="children">
    <key column="parent_id"/>
    <one-to-many class="Child"/>
</set>
Copy to Clipboard Toggle word wrap
If we were to execute the following code: 
Parent p = .....;
Child c = new Child();
p.getChildren().add(c);
session.save(c);
session.flush();
Copy to Clipboard Toggle word wrap
Hibernate would issue two SQL statements:
  • an INSERT to create the record for c
  • an UPDATE to create the link from p to c
This is not only inefficient, but also violates any NOT NULL constraint on the parent_id column. You can fix the nullability constraint violation by specifying not-null="true" in the collection mapping: 
<set name="children">
    <key column="parent_id" not-null="true"/>
    <one-to-many class="Child"/>
</set>
Copy to Clipboard Toggle word wrap
However, this is not the recommended solution.
The underlying cause of this behavior is that the link (the foreign key parent_id) from p to c is not considered part of the state of the Child object and is therefore not created in the INSERT. The solution is to make the link part of the Child mapping. 
<many-to-one name="parent" column="parent_id" not-null="true"/>
Copy to Clipboard Toggle word wrap
You also need to add the parent property to the Child class.
Now that the Child entity is managing the state of the link, we tell the collection not to update the link. We use the inverse attribute to do this: 
<set name="children" inverse="true">
    <key column="parent_id"/>
    <one-to-many class="Child"/>
</set>
Copy to Clipboard Toggle word wrap
The following code would be used to add a new Child: 
Parent p = (Parent) session.load(Parent.class, pid);
Child c = new Child();
c.setParent(p);
p.getChildren().add(c);
session.save(c);
session.flush();
Copy to Clipboard Toggle word wrap
Only one SQL INSERT would now be issued.
You could also create an addChild() method of Parent. 
public void addChild(Child c) {
    c.setParent(this);
    children.add(c);
}
Copy to Clipboard Toggle word wrap
The code to add a Child looks like this: 
Parent p = (Parent) session.load(Parent.class, pid);
Child c = new Child();
p.addChild(c);
session.save(c);
session.flush();
Copy to Clipboard Toggle word wrap
Nach oben
Red Hat logoGithubredditYoutubeTwitter

Lernen

Testen, kaufen und verkaufen

Communitys

Über Red Hat Dokumentation

Wir helfen Red Hat Benutzern, mit unseren Produkten und Diensten innovativ zu sein und ihre Ziele zu erreichen – mit Inhalten, denen sie vertrauen können. Entdecken Sie unsere neuesten Updates.

Mehr Inklusion in Open Source

Red Hat hat sich verpflichtet, problematische Sprache in unserem Code, unserer Dokumentation und unseren Web-Eigenschaften zu ersetzen. Weitere Einzelheiten finden Sie in Red Hat Blog.

Über Red Hat

Wir liefern gehärtete Lösungen, die es Unternehmen leichter machen, plattform- und umgebungsübergreifend zu arbeiten, vom zentralen Rechenzentrum bis zum Netzwerkrand.

Theme

© 2025 Red Hat