Hibernate（使用Spring）多对多查询

Question

I have user and a userRole table with a many-to-many relationship. I have the following Hibernate mapping:

<hibernate-mapping>
<class name="domain.User" schema="dbo" table="Users">
<id name="userId" type="int">
  <column name="UserId"/>
  <generator class="native"/>
</id>
<property name="username" type="string">
  <column name="Username" not-null="true"/>
</property>
<property name="password" type="string">
  <column name="Password" not-null="true"/>
</property>
<set cascade="all" inverse="true" name="userRole" table="UserRoleRelationships">
  <key>
    <column name="UserId"/>
  </key>
  <many-to-many class="domain.UserRole" column="RoleId" />
</set>
</class>
</hibernate-mapping>

and:

<hibernate-mapping>
<class name="domain.UserRole" schema="dbo" table="UserRoles">
<id name="roleId" type="int">
  <column name="RoleId"/>
  <generator class="native"/>
</id>
<property name="role" type="string">
  <column name="Role" not-null="true"/>
</property>
</class>
</hibernate-mapping>

My beans look like:

public class User {

private Integer userId;
private String username;
private String password;
private Set<UserRole> userRole;

// getters and setters
}

public class UserRole {

private Integer roleId;
private String role;
private User user;

// getters and setters
}

The query for selecting a user by its username looks like:

public List<User> getWithUsername(String username){
    return getHibernateTemplate().find("from User as u "
            + "inner join fetch u.userRole "
            + "where u.username = '" + username + "'" );
}

The problem is that when I try to print this out with the following loop(s):

for (User u : list){
            System.out.println(u.getUsername());

            for (UserRole ur : u.getUserRole()){
                System.out.println(ur.getRole());
            }  
        }

It prints it double up:

Username: jorgen
User role: User
User role: Admin
Username: jorgen
User role: User
User role: Admin

What am I doing wrong? Please help:)

Answer 1

You're not doing anything wrong. Hibernate just does this, and it's related to the way it builds queries. If you would do the same thing in SQL, you'd also have two rows.

There are two general ways of solving this:

• You can use the DistinctRootEntityProjection but as far as I know, that only works with criteria
• You can filter out the duplicates yourself (I suggest you encapsulate that logic in the class calling your hibernate). The easiest way is to just throw your items in a set and get them out again.

Answer 2

I found a solution doing it with criteria:

public List<User> getWithUsername(String username){

    Criteria criteria = getSession().createCriteria(IWUser.class)
    .add(Restrictions.like("username", username))
    .setFetchMode("userRole", FetchMode.EAGER)
    .setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);

    return criteria.list();

}