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JPA - @OneToMany Examples

JPA JAVA EE 

@Entity
public class EntityA {
    @Id
    @GeneratedValue
    private int myIdA;
    @OneToMany
    private List<EntityB> entityBList;
    .............
}

@Entity
public class EntityB {
    @Id
    @GeneratedValue
    private int myIdB;
    private String str;
    .............
}
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@Entity
public class EntityA {
    @Id
    @GeneratedValue
    private int myIdA;
    private String strA;
    @OneToMany
    @JoinColumn(name = "MY_FK_COL")
    private List<EntityB> entityBList;
    .............
}

@Entity
public class EntityB {
    @Id
    @GeneratedValue
    private int myIdB;
    private String strB;
    .............
}
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Bidirectional one-to-many example:

@Entity
public class EntityA {
    @Id
    @GeneratedValue
    private int myIdA;
    private String strA;
    @OneToMany(mappedBy = "refEntityA")
    private List<EntityB> entityBList;
    .............
}

@Entity
public class EntityB {
    @Id
    @GeneratedValue
    private int myIdB;
    private String strB;
    @ManyToOne
    private EntityA refEntityA;
    .............
}
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@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    @OneToMany
    private Map<Date, Task> tasks;
    .............
}

@Entity
public class Task {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    private String description;
    .............
}
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@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    @OneToMany
    @JoinTable(name = "ASSIGNED_TASKS",
            joinColumns = {@JoinColumn(name = "EMPLOYEE_FK")},
            inverseJoinColumns = {@JoinColumn(name = "TASK_FK")})
    @MapKeyColumn(name = "TASK_DATE")
    private Map<Date, Task> tasks;
    .............
}

@Entity
public class Task {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    private String description;
    .............
}
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Foreign key mapping strategy: 

@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    @OneToMany
    @JoinColumn(name = "EMPLOYEE_FK")
    @MapKeyColumn(name = "TASK_DATE", nullable = true)
    private Map<Date, Task> tasks;
    .............
}

@Entity
public class Task {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    private String description;
    .............
}
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Bidirectional @OneToMany on Map values: 

@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    @OneToMany(mappedBy = "taskEmployee", cascade = CascadeType.ALL)
    @MapKeyColumn(name = "TASK_DATE", nullable = true)
    private Map<Date, Task> tasks;
    .............
}

@Entity
public class Task {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    private String description;
    @ManyToOne
    @JoinColumn(name = "EMP_FK")
    private Employee taskEmployee;
    .............
}
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@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    @ElementCollection
    @OneToMany
    private Map<AssignInfo, Task> taskMap;
    .............
}

@Entity
public class AssignInfo {
    @Id
    @GeneratedValue
    private long id;
    private Date startDate;
    private Date endDate;
    .............
}

@Entity
public class Task {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    private String description;
    .............
}
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See Also