Spring data JPA Specifications - Find all data using a key to join 3 tables

Question

I have a problem to get paginated data, I have 3 tables named Machine, Category, Role.

Machine have many-to-one relationship with Category
Category have one-to-Many relationship with Roles (one category may linked with multiple roles)

ROLE ENTITY

    @Table(name = "role")
    public class UserRole {


        private Long roleId;

        private String roleName;

        //getter and setters

private Set<CategoryRoleMapping> categoryRoleMappings = new HashSet<CategoryRoleMapping>(0);


@OneToMany(fetch = FetchType.LAZY, mappedBy = "category")
    public Set<CategoryRoleMapping> getCategoryRoleMappings() {
        return categoryRoleMappings;
    }

    public void setCategoryRoleMappings(Set<CategoryRoleMapping> categoryRoleMappings) {
        this.categoryRoleMappings = categoryRoleMappings;
    }
    }

ROLE CATEGORY MAPPING

@Table(name = "category_role_mapping")
public class CategoryRoleMapping implements Serializable {


    private static final long serialVersionUID = 1L;

    private Long crMappingId;
    private UserRole userRole;
    private Category category;

@Id
    @GeneratedValue(strategy = IDENTITY)

    @Column(name = "CR_MAPPING_ID", unique = true, nullable = false)
    public Long getCrMappingId() {
        return crMappingId;
    }

    public void setCrMappingId(Long crMappingId) {
        this.crMappingId = crMappingId;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "ROLE_ID", nullable = false)
    public UserRole getUserRole() {
        return userRole;
    }

    public void setUserRole(UserRole userRole) {
        this.userRole = userRole;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "CATEGORY_ID", nullable = false)
    public Category getCategory() {
        return category;
    }

    public void setCategory(Category category) {
        this.category = category;
    }
}

CATEGORY ENTITY

@Table(name = "category")
public class Category implements java.io.Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    @JsonView(DataTablesOutput.View.class)
    private Long categoryId;
    @JsonView(DataTablesOutput.View.class)
    private String categoryName;

private Set<CategoryRoleMapping> categoryRoleMappings = new HashSet<CategoryRoleMapping>(0);

//getter and setters

@OneToMany(fetch = FetchType.LAZY, mappedBy = "category")
    public Set<CategoryRoleMapping> getCategoryRoleMappings() {
        return categoryRoleMappings;
    }

    public void setCategoryRoleMappings(Set<CategoryRoleMapping> categoryRoleMappings) {
        this.categoryRoleMappings = categoryRoleMappings;
    }

}

role table and category table linked via category_role_mapping entity.

MACHINE ENTITY

@Table(name = "machine")
public class Machine implements java.io.Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private Long machineId;
    private String machineName;

    private Category category;

    //getter and setters

@ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "CATEGORY_ID", unique = true, nullable = false)
    public Category getCategory() {
        return this.category;
    }

    public void setCategory(Category category) {
        this.category = category;
    }
}

I need to select all records from machine based on role id. I am using spring jpa data specifications... Please Provide some possible suggestions.

Answer 1

You can go with something like this

List<Machine> machine = entityManager.createQuery(
    "select m " +
    "from Machine m " +
    "inner join fetch m.category c " +
    "inner join fetch c.categoryRoleMappings crm " +
    "inner join fetch crm.userRole ur " +
    "where ur.id = :roleId", Machine.class)
.setParameter("roleId", roleId)

Spring data: use this query in your machine repository interface (maybe you need some changes in query variable)

 @Query(value = "select m from Machine m inner join fetch m.category c inner join fetch c.categoryRoleMappings crm inner join fetch crm.userRole ur where ur.id= :roleId")
List<Machine> machine = findByRoleId(@Param("roleId") long roleId));