Hibernate createNativeQuery returns duplicate rows - sql

Question

I have 2 database tables Customer and Items with 1 -> many relation. To fetch data from database i am using the following query.
select customer.id, customer.name, items.itemName, items.itemPrice from testdb.customer INNER JOIN items ON items.customer_Id = customer.id
I have an entity class Customers
#Entity
public class Customer{
#Id
private int id;
#Column
private String name;
#Column
private String itemName;
#Column
private int itemPrice;
public Customer() {}
//Getter and setter are here
.......
}
in Service class i have the following code.
#GET #Path("/getCustomerInfo")
#Produces(MediaType.APPLICATION_JSON)
public List getCustomerInfo() {
CustomerDao dao = new CustomerDao();
return dao.getBuildingsCustomerInfo();
}
in my DAO class i have the following code
public List<Customer> getCustomerInfo(){
Session session = SessionUtil.getSession();
String queryString = "the above mentioned query";
List<Customer> customerInfo = session.createNativeQuery(queryString, Customer.class) ;
session.close();
return customerInfo;
}
I am getting the following JSON response from the service
[id:1, name:"Alfred", itemName:"jeans", itemprice:10],[id:1, name:"Alfred", itemName:"jeans", itemprice:10],[id:2, name:"James", itemName:"watch", itemPrice:20 ],[id:2, name:"James", itemName:"watch", itemPrice:20 ], [id:2, name:"James", itemName:"watch", itemPrice:20 ]
The number of results are 5 which is correct But 2nd result is a copy of 1st, 4th and 5th are copies of 3rd. In 2nd, 4th and 5th results the itemName and the itemPrice should be different.
if I use createSQLQuery(queryString); instead of createNativeQuery(queryString, Customer.class); I am getting the correct result but without entity attribut names.
[1, "Alfred", "jeans", 10],[1, "Alfred", "shirt", 15],[2, "James", "watch", 20], [2, "James", "coffee", 25], [2, "James", "drinks", 30]
I have seen number of articles but could not find the solution. I have to use createNativeQuery() not createSQLQuery() because I need to map the entity class attributes. Please let me know if i am doing something wrong.

Answer 1

Your data structure is wrong on the Java side and not corresponding to the database relation. In the relation you describe you need to have a list of items:
#Entity
public class Customer implements Serializable {
// ... the fields you have so far
// assuming the parent field on the other side is called customer
// you may also want to set the cascade and orphanRemoval properties of the annotation
#OneToMany(mappedBy = "customer")
#JsonManagedReference // assuming you're using Jackson databind JSON
private List<Item> items;
}
And on the Item side:
#Entity
public class Item implements Serializable {
#Id
private int id;
#JsonBackReference
#ManyToOne
#JoinColumn(name = "customer_Id")
private Customer customer;
}
Then if you really the JSON data strucutred that way, you need a third Entity class to use as a ResultSetMapping.
#Entity
#SqlResultSetMapping(
name = "CustomerItem",
entities = #EntityResult(entityClass = CustomerItem.class)
)
#NamedNativeQueries({
#NamedNativeQuery(
name = "CustomerItem.getAll",
resultSetMapping = "CustomerItem"
query = "select customer.id as cid, items.id as iid, customer.name,"
+ " items.itemName, items.itemPrice from testdb.customer INNER JOIN"
+ " items ON items.customer_Id = customer.id"
)
})
public class CustomerItem implements Serializable {
#Id
private int cid;
#Id
private int iid;
#Column
private String name;
#Column
private String itemName;
#Column
private int itemPrice;
... getters and setters
}
Then you can use the native query in named variant, which should offer some slight optimizations.
List<CustomerItem> lst = em.createNamedQuery("CustomerItem.getAll", CustomerItem.class)
.getResultList();
The use of #SqlResultSetMapping is so that the returned entities are not monitored for changes, but you can still use the defined entity for the result. I believe that by JPA specification it should also work without it, but in Hibernate it doesn't. Could be a bug, or a planned, but not implemented feature, or I could just be misinterpreting the JPA usage, but this workaround does work with Hibernate 5+.

Answer 2

Not sure about the exact reason behind duplicates but SELECT DISTINCT will solve your issue as it will take only distinct records.
Refer using-distinct-in-jpa

Answer 3

I solve this issue by using #SqlResultSetMapping