Question

When trying to save an ID from my parent class into a child class, I keep getting the error
“ERROR – Field ‘parent_id’ doesn’t have a default value”

I have tried all types of mappings. I am using annotations.

Any help on this would be appreciated

Parent:

      @Id
      @Column(name="id")
      @GeneratedValue(strategy=GenerationType.AUTO)
      private long id;
      @Column(name="description")
      private String description;
      @OneToMany
      @Cascade(value= {org.hibernate.annotations.CascadeType.SAVE_UPDATE, org.hibernate.annotations.CascadeType.DELETE})
      @JoinColumn(name="parent_id")
      private List<Child> children;

Child:

  @Id
  @Column(name="id")
  @GeneratedValue(strategy=GenerationType.AUTO)
  private long id;
  @Column(name="description")
  private String description;

Thanks.

Answer 1

You must have something wrong somewhere else because those mappings will work the way they are. They could be better, but they’ll work. Specifically, all the @Column annotations are redundant and unnecessary, and as non sequitor noted, you should use the cascade property of JPA’s @OneToMany instead of Hibernate’s @Cascade. I’ve created a runnable example with the cleaned-up version of what you posted. If you have git and maven, you can run it with:

git clone git://github.com/zzantozz/testbed tmp
cd tmp
mvn -q compile exec:java \
    -Dexec.mainClass=rds.hibernate.UnidirectionalManyToOneJoinColumn \
    -pl hibernate-unidirectional-one-to-many-with-join-column

It creates a parent with two children, saves them, and then loads them and prints out the graph. The output is:

Creating parent with two children
Loading saved parent
Parent{description='parent', children=[Child{description='child 2'}, Child{description='child 1'}]}