Package ejava.examples.orm.map

Class OneManyMapTest

java.lang.Object

ejava.examples.orm.rel.DemoBase

ejava.examples.orm.map.OneManyMapTest

public class OneManyMapTest
extends DemoBase

This class demonstrates a One-to-Many relationship represented as a map in the parent. There are two types of parents and children represented in these tests:

OneManyInverseParent to/from OneManyOwningChild - in this case, the foreign key to the parent is supplied in the child table. The child owns the relationship and the parent has a inverse reference back to the child represented as a Map. OneManyOwningParent to OneManyChild - in this case, the parent owns the relationship and the child class knows nothing of the relationship. The parent forms a link table to host the 1:1 foreign key to the child and a 1:N relationship to the parent. The child object is referenced by the parent through a Map.

The other cases are meaningless to demonstrate because they would either involve the parent not knowing about the child (thus no Map), or neither parent or child knowing about one another (totally senseless for this example).

Field Summary

Fields inherited from class ejava.examples.orm.rel.DemoBase

em, emf, logBase, logger

Constructor Summary

Constructors

Constructor	Description
OneManyMapTest()

Method Summary

Modifier and Type	Method	Description
protected void	cleanup()	This method will cleanup the database of our OneToMany entities.
protected void	postcleanup()
protected void	precleanup()
void	testOneToManyInverseParentMap()	This method tests the case where the child owns the relationship and the parent is the inverse side.
void	testOneToManyOwningParentMap()	This method tests the case where the parent owns the relationship.

Methods inherited from class ejava.examples.orm.rel.DemoBase

setUpBase, setUpDownShared, tearDownBase, tearDownBaseClass

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

OneManyMapTest

public OneManyMapTest()

Method Detail

precleanup

protected void precleanup()
                   throws Exception

Overrides:

precleanup in class DemoBase

Throws:

Exception

postcleanup

protected void postcleanup()
                    throws Exception

Overrides:

postcleanup in class DemoBase

Throws:

Exception

cleanup

protected void cleanup()
                throws Exception

This method will cleanup the database of our OneToMany entities. We start with the owning entities, since they own the foreign keys or the link/join tables with the foreign keys. Once the associations have been deleted, all inverse and oblivious entities can be safely removed.

Throws:

Exception

testOneToManyInverseParentMap

public void testOneToManyInverseParentMap()

This method tests the case where the child owns the relationship and the parent is the inverse side. If we model the Java form of the relationship without defining a @MapKey, then the following schema gets created,

    create table ORMMAP_ONEMANY_INVPARENT (
        name varchar(255) not null,
        primary key (name)
    );

    create table ORMMAP_ONEMANY_OWNCHILD (
        name varchar(255) not null,
        oneInverseParent_name varchar(255),
        mapkey varchar(255),
        primary key (name)
    );
         

But runtime reports

     null index column for collection: 
     ejava.examples.orm.map.annotated.OneManyInverseParent.ownedByChildren
     

When @MapKey(name="name") is added to the parent definition...

testOneToManyOwningParentMap

public void testOneToManyOwningParentMap()

This method tests the case where the parent owns the relationship. Since children in a one-to-many relationship are required by JPA to own the relationship, we can only test this with children that know nothing of the parent. In this case, there is only an owning side. If we model the Java form of the relationship without defining a @MapKey, then the following schema gets created (note that in this class, the name property has been mapped to the @Column(name="ID") within each Entity class).

    create table ORMMAP_ONEMANY_CHILD (
        ID varchar(255) not null,
        primary key (ID)
    );

    create table ORMMAP_ONEMANY_OWNPARENT (
        ID varchar(255) not null,
        primary key (ID)
    );

    create table ORMMAP_ONEMANY_OWNPARENT_ORMMAP_ONEMANY_CHILD (
        ORMMAP_ONEMANY_OWNPARENT_ID varchar(255) not null,
        ownedChildren_ID varchar(255) not null,
        mapkey varchar(255),
        primary key (ORMMAP_ONEMANY_OWNPARENT_ID, mapkey)
    );
     

At runtime, we get the following data in the link table.

ORMMAP_ONEMANY_OWNPARENT_ID OWNEDCHILDREN_ID MAPKEY
--------------------------- ---------------- ------
fred                        chip             chip
fred                        ernie            ernie
     

When @MapKey(name="name") is added to the parent definition...