A database 'FOREIGN KEY' constraint is not detected by default
--------------------------------------------------------------
Key: OPENJPA-1936
URL: https://issues.apache.org/jira/browse/OPENJPA-1936
Project: OpenJPA
Issue Type: Improvement
Affects Versions: 2.0.1
Reporter: Heath Thomann
Assignee: Heath Thomann
Priority: Minor
Take the following SQL to create two tables in a database:
CREATE TABLE PARENT (
"ID" INT NOT NULL,
PRIMARY KEY ("ID")
)
CREATE TABLE CHILD (
"ID" INT NOT NULL,
"PARENT_ID" INT,
PRIMARY KEY ("ID"),
FOREIGN KEY ("PARENT_ID") REFERENCES "PARENT" ("ID")
)
Take the following two entities:
public class Parent implements Serializable {
@Id
private int id;
@OneToMany(mappedBy = "parent", cascade = CascadeType.ALL, fetch =
FetchType.EAGER, orphanRemoval = true)
private Collection<Child> childs;
.........
public class Child implements Serializable {
@Id
private int id;
@ManyToOne
private Parent parent;
.........
If a scenario is executed in which an existing Parent is removed, an existing
Child(s) associated with the Parent will also be removed given the definition
of the @OneToMany relationship. However, when OpenJPA executes the SQL to
remove the Parent and Child, the SQL to remove the Parent will be executed
first. Given the 'FOREIGN KEY' constraint on the Child table, a database will
throw some kind of 'constraint violation' exception when a Parent is removed
before its Child (if it were not for the 'FOREIGN KEY' constraint on the Child
table, the SQL order would be fine). In this case, OpenJPA should execute the
SQL to remove the Child first, then the Parent. However, by default, OpenJPA
knows nothing about the 'FOREIGN KEY' constraint on the Child table and OpenJPA
never assumes that there are database constraints for relationships. As a
result, OpenJPA does not take them into account when executing SQL. To tell
OpenJPA that there are database level constraints, and thus to effect the order
of the SQL in this case, a user can perform one of the following options:
1) Use the @ForeignKey annotation
(org.apache.openjpa.persistence.jdbc.ForeignKey) in entities (on the ToOne
fields).
2) Have OpenJPA read in the table definitions from the database by adding the
following property:
<property name="openjpa.jdbc.SchemaFactory" value="native(ForeignKeys=true)"/>
While either of these two options will properly handle the above scenario, it
can be argued that OpenJPA should detect the 'FOREIGN KEY' constraint, and not
require a user to add an annotation to their code or set a property. This JIRA
will be used to investigate possible solutions to change the way the
constraints are detected.
Thanks,
Heath
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