incorrectly joining 2 entities in spring data jpa - spring

Question

#Entity
#Table(name = "product_table")
public class Product {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "Product_id" , nullable = false, unique= true , length = 5)
private int ProductId;
#Column(name = "Product_Name" ,nullable = false , length = 50)
private String ProductName;
#Column(name = "Description" ,nullable = false , length = 200)
private String Description;
#Column(name ="Price" , nullable = false, unique= true , length = 5)
private Double Price;
#Column(name = "Discount" , nullable = false, unique= true , length = 5)
private Double Discount;
#Column(name ="Delivery_Charges" , nullable = false, unique= true , length = 5)
private Double DeliveryCharges;
#Column(name = "Avg_Rating",nullable = false, unique= true , length = 5)
private int AvgRating;
#Column(name = "Seller_Name",nullable = false, unique= true , length = 15)
private String SellerName;
#OneToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "Product_id", insertable = false, updatable = false)
#Fetch(FetchMode.JOIN)
private Cart Cart;
#OneToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "ProductId", insertable = false, updatable = false)
#Fetch(FetchMode.JOIN)
private WishList WishList;
public String getSellerName() {
return SellerName;
}
public void setSellerName(String sellerName) {
SellerName = sellerName;
}
public int getProductId() {
return ProductId;
}
public void setProductId(int productId) {
ProductId = productId;
}
public String getProductName() {
return ProductName;
}
public void setProductName(String productName) {
ProductName = productName;
}
public String getDescription() {
return Description;
}
public void setDescription(String description) {
Description = description;
}
public Double getPrice() {
return Price;
}
public void setPrice(Double price) {
Price = price;
}
public Double getDiscount() {
return Discount;
}
public void setDiscount(Double discount) {
Discount = discount;
}
public Double getDeliveryCharges() {
return DeliveryCharges;
}
public void setDeliveryCharges(Double deliveryCharges) {
DeliveryCharges = deliveryCharges;
}
public int getAvgRating() {
return AvgRating;
}
public void setAvgRating(int avgRating) {
AvgRating = avgRating;
}
}
#Entity
#Table(name = "Cart_table")
public class Cart {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "Cart_Id" , nullable = false, unique = true, length = 5)
private int CartId;
#Column(name = "Product_Name" , nullable = false, length = 50)
private String ProductName;
#Column(name = "Seller_Name" , nullable = false,length = 15)
private String SellerName;
#Column(name = "Quantity" , nullable = false)
private int Quantity;
#Column(name = "Cart_Offer_Price" , unique = true)
private Double CartOfferPrice;
#Column(name = "Product_id" , nullable = false, unique = true, length = 5)
private int ProductId;
public int getProductId() {
return ProductId;
}
public void setProductId(int productId) {
ProductId = productId;
}
#OneToOne(targetEntity = Product.class, mappedBy = "Cart", orphanRemoval = false, fetch = FetchType.LAZY)
private Product product;
#OneToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "Cart_Id", insertable = false, updatable = false)
#Fetch(FetchMode.JOIN)
private OrdersCartMapping OrdersCartMapping;
public int getCartId() {
return CartId;
}
public void setCartId(int cartId) {
CartId = cartId;
}
public String getProductName() {
return ProductName;
}
public void setProductName(String productName) {
ProductName = productName;
}
public String getSellerName() {
return SellerName;
}
public void setSellerName(String sellerName) {
SellerName = sellerName;
}
public int getQuantity() {
return Quantity;
}
public void setQuantity(int quantity) {
Quantity = quantity;
}
public Double getCartOfferPrice() {
return CartOfferPrice;
}
public void setCartOfferPrice(Double cartOfferPrice) {
CartOfferPrice = cartOfferPrice;
}
}
#Repository
public interface CartRepository extends JpaRepository<Cart , Integer> {
#Query("SELECT new com.megamartonline.dto.CartProductDto(c.ProductName,c.CartOfferPrice,c.Quantity , p.Price ,p.Discount,p.DeliveryCharges,c.CartId ) "
+ "FROM Cart c INNER JOIN c.product p")
List<CartProductDto> fetchProductCartDataInnerJoin();
}
Here i m trying to join Product with Cart using Product_id column but when i test my repository method it is incorrectly joining as below
select
cart0_.product_name as col_0_0_,
cart0_.cart_offer_price as col_1_0_,
cart0_.quantity as col_2_0_,
product1_.price as col_3_0_,
product1_.discount as col_4_0_,
product1_.delivery_charges as col_5_0_
from
cart_table cart0_
inner join
product_table product1_
on cart0_.cart_id=product1_.product_id
please help , what i am doing wrong here.
Here i m trying to join 2 Product with Cart using Product_id column but when i test my repository method it is incorrectly joining.

Answer 1

In Product, instead of productId, you have to declare the join to JPA in the entity this way:
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "Product_id")
private Product Product;
Hibernate now knows how to handle the join.
You can't use both an ID column and a JoinColumn; it won't know which one to use, so you should remove productId.
I suggest a #ManyToOne because the #OneToOne join you are using seems strange for a cart. Usually a cart has multiple (many) products.

Answer 2

You can easily change the fetch type from lazy to eager