违反外键约束JPA

Question

Edit: This code actually works correctly. The problem was un-related and was due to a conflicting Entity which was creating a foreign key constraint and stopping me from inserting into the DataFile table.

I'm having some real trouble with some JPA mappings for a simple @OneToMany mapping.

I'm using EclipseLink and DerbyDB.

@Entity( name = "study2" )
@Access( AccessType.FIELD )
public class Study2 extends EntityBaseItem {

private List<DataFile> datafiles = new ArrayList<DataFile>();

public Study2() { }

@OneToMany( cascade = CascadeType.ALL, orphanRemoval = true )
@JoinColumn( name="STUDY_ID", referencedColumnName = "ID" )
@Access( AccessType.PROPERTY )
public List<DataFile> getDatafiles() {
    return this.datafiles;
}

public void setDatafiles( List<DataFile> dfList ) {
    this.datafiles = dfList;
}

DataFile.java

@Entity( name = "DataFile" )
public class DataFile extends EntityBaseItem<DataFile> {
    private String filename;
    private long filesize;
    private String fileStatus;
    private String fileType;
    private String fileSubType;

    public DataFile() { }
}

This is my EntityBaseItem.java where the @Id resides:

@MappedSuperclass
public abstract class EntityBaseItem {

    @Id
    @GeneratedValue( strategy = GenerationType.TABLE )  
    protected Integer id;

    protected EntityBaseItem() {}

    public Integer getId() {
        return id;
    }

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

    @Override  
    public int hashCode() {  
        int hash = 0;  
        hash += ( this.getId() != null ? this.getId().hashCode() : 0);  

        return hash;  
    }  

    @Override  
    public boolean equals(Object object) {  
        if (this == object)  
            return true;  
        if (object == null)  
            return false;  
        if (getClass() != object.getClass())  
            return false;  

        EntityBaseItem other = (EntityBaseItem)object;  

        if (this.getId() != other.getId() && (this.getId() == null || !this.id.equals(other.id))){  
            return false;  
        }

        return true;  
    }
}

The problem is that when I create a Study2 object with some DataFile objects and try to persist it to my DB then I get the error

UPDATE on table 'DATAFILE' caused a violation of foreign key constraint 'DATAFILE_STUDY_ID' for key

If I change the annotation on getDataFiles() and remove the @JoinColumn ( see below ) then the mapping works, however it creates a join table and I'd really rather just have a join column in the DataFile table:

@OneToMany( cascade = CascadeType.ALL, orphanRemoval = true )
@Access( AccessType.PROPERTY )
public List<DataFile> getDatafiles() {
    return this.datafiles;
}

I guess it's down to having my @Id in EntityBaseItem as when I removed that and added @Id in the Study2 class then it worked as expected, however there must be some way to keep @Id in the EntityBaseItem and still use a @JoinColumn ? I've not had any issues elsewhere in my code, and I have various other mappings which are not as simple as this one.

I know what the error means, however I don't know why it's happening. To me I'd expect my code to work and cascade the DataFiles automatically with a new id for each.

Here is the code that actually causes the error to be thrown:

Study2 testStudy = new Study2();
// set some datafiles etc.

EntityManager em = getEM(); // gives me EntityManager
em.getTransaction().begin();
em.persist( testStudy );
em.getTransaction().commit();

I'd simplified it down to that for testing, throws error on .commit() and then it rolls back the commit.

Answer 1

Change your mappings

public class Study2(){

@OneToMany( cascade = CascadeType.ALL, orphanRemoval = true,mappedBy="study2")
@Access( AccessType.PROPERTY )
public List<DataFile> getDatafiles() {
    return this.datafiles;
}
}

Here we say that DataFile is mappedBy "study2" in DataFile class and Study2 has JoinColumn. And the Study2 is inverse side of relationship and will not update the relationship when it gets updated.

Add one field Study2 in DataFile, I have given mapping on field.You can change that

   @ManyToOne
   @JoinColumn(name="STUDY_ID", referencedColumnName = "ID")
   private Study2 study2;

It states that many DataFile are present in one Study2 class