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Wednesday, 9 July 2014

Annotation ManyToMany

By Shambhu Kumar  |  02:53 No comments

Annotation ManyToMany

Target: Fields (including property get methods)
Defines a many-valued association with many-to-many multiplicity.
Every many-to-many association has two sides, the owning side and the non-owning, or inverse, side. The join table is specified on the owning side. If the association is bidirectional, either side may be designated as the owning side. If the relationship is bidirectional, the non-owning side must use the mappedBy element of the ManyToMany annotation to specify the relationship field or property of the owning side.
The join table for the relationship, if not defaulted, is specified on the owning side.
The ManyToMany annotation may be used within an embeddable class contained within an entity class to specify a relationship to a collection of entities. If the relationship is bidirectional and the entity containing the embeddable class is the owner of the relationship, the non-owning side must use the mappedBy element of the ManyToMany annotation to specify the relationship field or property of the embeddable class. The dot (".") notation syntax must be used in the mappedByelement to indicate the relationship attribute within the embedded attribute. The value of each identifier used with the dot notation is the name of the respective embedded field or property.

Example 1:

    // In Customer class:
     @ManyToMany
    @JoinTable(name="CUST_PHONES")
    public Set<PhoneNumber> getPhones() { return phones; }
 
    // In PhoneNumber class:
     @ManyToMany(mappedBy="phones")
    public Set<Customer> getCustomers() { return customers; }

Example 2:

    // In Customer class:
     @ManyToMany(targetEntity=com.acme.PhoneNumber.class)
    public Set getPhones() { return phones; }
 
    // In PhoneNumber class:
     @ManyToMany(targetEntity=com.acme.Customer.class, mappedBy="phones")
    public Set getCustomers() { return customers; }

Example 3:

    // In Customer class:
 
    @ManyToMany
    @JoinTable(name="CUST_PHONE",
        joinColumns=
            @JoinColumn(name="CUST_ID", referencedColumnName="ID"),
        inverseJoinColumns=
            @JoinColumn(name="PHONE_ID", referencedColumnName="ID")
        )
    public Set<PhoneNumber> getPhones() { return phones; }
 
    // In PhoneNumberClass:
 
    @ManyToMany(mappedBy="phones")
    public Set<Customer> getCustomers() { return customers; }

Annotation ManyToMany
Target: Fields (including  property get methods)
Defines a many-valued association with many-to-many multiplicity.
Every many-to-many association has two sides, the owning side and the non-owning, or inverse, side. The join table is specified on the owning side. If the association is bidirectional, either side may be designated as the owning side. If the relationship is bidirectional, the non-owning side must use the mappedBy element of the ManyToMany annotation to specify the relationship field or property of the owning side.
The join table for the relationship, if not defaulted, is specified on the owning side.
The ManyToMany annotation may be used within an embeddable class contained within an entity class to specify a relationship to a collection of entities. If the relationship is bidirectional and the entity containing the embeddable class is the owner of the relationship, the non-owning side must use the mappedBy element of the ManyToMany annotation to specify the relationship field or property of the embeddable class. The dot (".") notation syntax must be used in the mappedBy element to indicate the relationship attribute within the embedded attribute. The value of each identifier used with the dot notation is the name of the respective embedded field or property.
Example 1
UserList.java
@ManyToMany
@JoinTable(name = "userroles")
private Set<Roles> roleSet = new HashSet<Roles>();
Roles.java
@ManyToMany(mappedBy = "roleSet")
private Set<UserList> userLists = new HashSet<UserList>();




  
Example 2
UserList.java

@ManyToMany(targetEntity = Roles.class)
@JoinTable(name = "userroles")
private Set<Roles> roleSet = new HashSet<Roles>();
Roles.java

@ManyToMany(mappedBy = "roleSet", targetEntity = UserList.class)
private Set<UserList> userLists = new HashSet<UserList>();



Example 3
UserList.java
@ManyToMany(targetEntity = Roles.class, fetch = FetchType.LAZY)
@JoinTable(name = "userroles",
        joinColumns = @JoinColumn(name = "UserID",
                                  referencedColumnName = "UserID"),
        inverseJoinColumns = @JoinColumn(name = "RoleID",
                                        referencedColumnName = "RoleID"))


       private Set<Roles> roleSet = new HashSet<Roles>();









Author: Shambhu Kumar

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