Custom Query for fetching data from multiple tables in spring Data Jpa

Question

Entities are following

Product Table

@Entity
public class Product implements Serializable {
/*@Id
@GeneratedValue(strategy = Generation         


        

Answer 1

Your query is not a valid HQL query, which hiberate understands. You can use a native SQL query, but the use case mentioned can be easily achieved with HQL. Before that, lets use the proper annotations mappings for ManytoMany association:

@Entity
@Table(name = "order_detail")
public class OrderDetail {

     @Id
     @GeneratedValue(strategy = GenerationType.AUTO)
     private Integer id;


     @ManyToOne
     @JoinColumn(name="purchased_By")
     private user PurchasedBy;


     @ManyToMany
     @JoinTable(
       name="order_detail_productlist",
       joinColumns=@JoinColumn(name="order_detail_id", referencedColumnName="id"),
       inverseJoinColumns=@JoinColumn(name="productlist_id", referencedColumnName="id"))
      private Set<Product> productlist = new HashSet<Product>();

Product:

@Entity
@Table(name ="product")
public class Product implements Serializable {

      @Id
      @GeneratedValue(strategy = GenerationType.AUTO)
      private Integer id;

      @NotNull(message = "Product name must not be null")
      @NotEmpty
      @Column(name = "name", nullable = false)
      private String name;


      @ManyToOne
      @JoinColumn(name="category_id")
      private Category category;

      @ManyToMany(mappedBy = "productlist")
      private List<OrderDetail> orderDetail =new ArrayList<OrderDetail>();

And query :

public final static String product_ordered ="Select p from Product p Join p.orderDetail od Where od.id = :id";

@Query(product_ordered)
public List<Product> findById(@Param("id") int id);

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Answer 2

The way you are doing is not possible because you are assigning the result set to List<Product> but the query has some joins, it mean that the result of query is not a Product entity.

You can try to do a Native query. For example:

@PersistenceContext
private EntityManager entityManager;

public List<Object[]> customQuery(int id) {
    Query nativeQuery = entityManager.createNativeQuery(product_ordered).setParameter("id",id);
    return nativeQuery.getResultList();
}