There's a table with a "FK" column whose values might point back to either TableA or TableB, something like this:
CREATE TABLE TableC (
"id" bigint GENERATED BY DEFAULT AS IDENTITY,
"linked_entity_id" integer,
"linked_entity_type" varchar(15),
...other columns
PRIMARY KEY ("id")
);
I'm struggling with representing this in JPA. I'd like to have both TableA and TableB entities in JPA to have a List. Is there a way to do this?
This is my attempt, having TableC entity modeled like this:
@Entity
public class TableC {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private Long linkedEntityId;
@Enumerated(EnumType.STRING)
private LinkedEntityType linkedEntityType;
@ManyToOne
@JoinColumn(name = "linked_entity_id", referencedColumnName = "id", insertable=false, updateable=false)
private TableA tableA;
@ManyToOne
@JoinColumn(name = "linked_entity_id", referencedColumnName = "id", insertable=false, updateable=false)
private TableB tableB;
}
But, what happens when the TableC has a row whose id in the linked_entity_id column belongs to TableA id not to TableB? I think an exception would be thrown.
PS: TableA and TableB do not have anything in common.
CodePudding user response：
You must use the @Where annotation:
@ManyToOne
@Where(clause = "linked_entity_type = 'TableA'")
@JoinColumn(name = "linked_entity_id", referencedColumnName = "id", insertable=false, updateable=false)
private TableA tableA;
@ManyToOne
@Where(clause = "linked_entity_type = 'TableB'")
@JoinColumn(name = "linked_entity_id", referencedColumnName = "id", insertable=false, updateable=false)
private TableB tableB;