@GeneratedValue(strategy = GenerationType.AUTO) not working as thought

问题

I'm trying to persist an object to a database. Keep getting 'Column ID cannot accept null value error'. My object looks like this:

    @Entity
public class TestTable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id = 0;

    @Column(nullable=false, length=256)
    private String data = "";

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getData() {
        return data;
    }

    public void setData(String data) {
        this.data = data;
    }

}

My persist function:

public static synchronized boolean persistObject(Object obj){
        boolean success = true;
        EntityManager em = null;
        EntityTransaction tx = null;
        try{
            em = getEmf().createEntityManager();
            tx = em.getTransaction();
            tx.begin();
            em.persist(obj);
            tx.commit();

        } catch (Exception e){
            success = false;
        } finally{
            try{
                em.close();
            } catch(Exception e){
                //nothing
            }
        }
        return success;
    }

回答1:

You may use GenerationType.TABLE. That way, jpa uses a sequence table for id assigment and you may never need to generate sequence or auto-increment values or triggers that lowers portability.

Also note that in java int type is initiated with 0 default, so you may get rid of that also.

回答2:

In my case it was about bad dialect:

hibernate.dialect=org.hibernate.dialect.H2Dialect

instead of:

hibernate.dialect=org.hibernate.dialect.PostgreSQL9Dialect

when I switched to the production database. Hibernate tried to use strategy prepared for different db engine.

回答3:

I had a problem with a similar manifestation to yours. I eventually discovered that the configuration of my database connection was wrong: I was connecting to an old database that had an incorrect schema. The new schema declared the primary-key column as

"ID" BIGINT NOT NULL GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1)

so the database itself automatically generated the primary key whereas the old schema declared it as

"ID" INTEGER NOT NULL

Hibernate executed the correct code for the new schema, which failed on the old schema because the old schema demanded the SQL INSERT provide a value for the ID column.

回答4:

Hibernate fails in silent and mysterious ways when the ID column is an Int. Try changing it to Long in the code and an unsigned 64-bit integer in the database. That fixed the issue for me.

回答5:

Or try with @GeneratedValue(strategy = GenerationType.AUTO) instead of @GeneratedValue(strategy = GenerationType.SEQUENCE).

来源：https://stackoverflow.com/questions/5129552/generatedvaluestrategy-generationtype-auto-not-working-as-thought

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hibernate

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