Can a @ManyToOne JPA relation be null?

Question

I have a table that has foreign key of another table (many to one relationship) but i want it to be nullable.

Something like this:

public class SubType() {

    @Id
    @GeneratedValue(generator = "system-uuid")
    @GenericGenerator(name = "system-uuid", strategy = "uuid")
    private String id;

}

public class TopUp {

    @Column(nullable = true)
    @ManyToOne(optional = false, fetch = FetchType.LAZY)
    private SubType subType;

}

But @Column(nullable = true) throws the NullPointerException and says subtype can not be null. Is there any way to get the ManyToOne accept null?

Answer 1

The @ManyToOne associations are optional by default, so you don't need to set anything if you want them to be nullable.

However, because you set the optional=false attribute, you made it mandatory.

So instead of:

@ManyToOne(optional = false, fetch = FetchType.LAZY)

Set it like this:

@ManyToOne(fetch = FetchType.LAZY)

The optional is true by default.

On the other hand, the @Column(nullable=true) is to instruct the DDL generation tool to include a NULL SQL column type constraint.