如何在休眠实体中初始化复杂类型

Question

A member of my class is of Type Byte. As you know its initial value would be NULL . But I want it to be 0 if no one calls constructor by default. So would the way I do it be the right way? Because in my database this value is not allowed to be NULL . So I need to give it a value which by default should be 0 .

@Entity
@Table(name = "Holiday")
public class Holiday {

   @Column(columnDefinition = "Bit(2)")
   private Byte approved = (byte) 0;

   public Holiday() {
   }

   public Holiday( Byte approved) {
      super();
      this.approved = approved;
   }

PS: Of course this class has many more members and also another constructor. But for demo I removed all the other members.

Answer 1

Try to add nullable = false :

    @Entity
    @Table(name = "Holiday")
    public class Holiday {

        @Column(columnDefinition = "Bit(2)", nullable = false)
        private Byte approved = (byte) 0;

        public Holiday() {
        }

        public Holiday( Byte approved) {
            super();
            this.approved = approved;
        }

Or add in columnDefinition NOT NULL DEFAULT 0

 @Column(columnDefinition = "Bit(2) NOT NULL DEFAULT 0")

Answer 2

So would the way I do it be the right way?

Yes, it's right way. You can see a lot of similar examples in the hibernate documentation (especially for collections). I would suggest you to put this initialization in the default constructor and, if you have other constructors, call this constructor from them.

@Entity
@Table(name = "Holiday")
public class Holiday {

   @Column(columnDefinition = "Bit(2)")
   private Byte approved;

   public Holiday() {
      this.approved = 0;
      // other default initialization
   }

   public Holiday(Byte approved) {
      this();
      this.approved = approved;
   }
   // ...
}

Answer 3

Since you already use columnDefinition , you can define the default value there:

columnDefinition = "Bit(2) NOT NULL DEFAULT 0" . This will set the constraint on the database level while rejecting NULL values.

If you would rather do it on the application level you can set it on the field instead, that's perfectly fine for default values.