Hibernate Many to Many without third table

Question

I have two tables (Users and UserRole)

create table Users (
    UserId serial not null,
    UserName varchar(100) not null,
    UserType varchar(15) not null,
    Constraint PK_Users primary key (UserId)
)
;

CREATE TABLE UserRole
(
   RoleId serial not null, 
   RoleType varchar(20) not null, 
   AccessTo varchar(100) not null,  
   CONSTRAINT PK_UserRoleId PRIMARY KEY (RoleId)
) 
;

insert into Users (default,'Raj','Admin');
insert into Users (default,'Kumar','Internal');
insert into Users (default,'Ramesh','Internal');
insert into Users (default,'Muthu','External');
insert into Users (default,'Sundar','External');

insert into UserRole (default, 'Admin','/**');
insert into UserRole (default, 'Internal','/parking/*');
insert into UserRole (default, 'Internal','/vehciles/*');
insert into UserRole (default, 'External','/Upload/*');
insert into UserRole (default, 'External','/ViewParkings/*');

// The following join syntax doesn't work

@ManyToMany(fetch = FetchType.EAGER)
@JoinTable(name = "UserRole",
JoinColumns(
{
    JoinColumn(updatable=false,insertable=false, name="UserType"
             , referencedColumnName="RoleType"),

}
private Set<UserRole> userRoles = new HashSet<userRoles>();

I am trying to establish connection between two tables without using third table (link table). Is it possible when I use hibernate?

score 4 · Accepted Answer · answered Feb 10 '16 at 05:27

It doesn't work like that for a many to many relationship you must have a join table with the keys from the other two tables. hibernate annotaion is just a mapping for the existing ERD

here is the documentation

Open Declaration javax.persistence.ManyToMany

@Target(value={METHOD, FIELD}) @Retention(value=RUNTIME)

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:

// 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; }

Since: Java Persistence 1.0

Hibernate Many to Many without third table

1 Answers1

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