🐻JPA/Hibernate

Common Linking Use Cases

Many to Many

ACCOUNT 1..* to POSITION 1..* via a mapping Table ACCOUNT_POSITION

// Account class

@ManyToMany(cascade = Cascade.ALL, fetch FetchType.EAGER)
@LazyCollection(LazyCollection.FALSE)
@Fetch(FetchMode.SUBSELECT)
@JoinTable(inverseJoinColumns = @JoinColumn(name = "POSITION_ID"))
private List<Position> positions;

One to One

POSITION to POSITION_EXTENSION without mapping table. POSITION_EXTENSION holds the ID referring to POSITION. POSITION_EXTENSION entries are only created if necessary.

// PositionExtension class
@OneToOne(cascade = CascadeType.ALL)
@JoinColumn(name = "POSITION_ID")
private Position position;

// Position class (reverse mapping)
// mappedBy refers to class variable
@OneToOne(mappedBy = "position", cascade = CascadeType.ALL)
private PositionExtension positionsExtension;

Troubleshooting

• Check if one or more persistence.xml exist that need to contain the new entities

• Do the entities have an empty default constructor for JPA? e.g. Position(){}