CODEWITHSUNDEEP
hibernate
mangoCar
mangoCar

Reputation: 665

HQL for referencing join column in self join

Hi I just need a HQL query to reference join column in self join.when i am trying to access join column it is throwing an exception unable to resolve category_id.Thanks in advance.

package com.rst;

 import java.util.HashSet;
 import java.util.Set;

 import javax.persistence.CascadeType;
 import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.Id;
 import javax.persistence.JoinColumn;
 import javax.persistence.ManyToOne;
 import javax.persistence.OneToMany;
 import javax.persistence.Table;

 import org.hibernate.annotations.GenericGenerator;
 import org.hibernate.annotations.Parameter;

 @Entity
 @Table
 public class SubCategory {
@Id
@GeneratedValue(generator="Category_Sequence_StyleGenerator")


private int subCategory_id;

private String category_name;

@ManyToOne(cascade = {CascadeType.ALL})
@JoinColumn(name = "category_id")
private SubCategory category;

@OneToMany(mappedBy = "category")
private Set<SubCategory> set = new HashSet<SubCategory>();

public SubCategory() {
    super();
    // TODO Auto-generated constructor stub
}

public SubCategory(String category_name) {
    super();
    this.category_name = category_name;
}

public String getCategory_name() {
    return category_name;
}

public void setCategory_name(String category_name) {
    this.category_name = category_name;
}

public SubCategory getCategory() {
    return category;
}

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

public Set<SubCategory> getSet() {
    return set;
}

public void setSet(Set<SubCategory> set) {
    this.set = set;
}

}

This is my Manager class where i am trying to get all the sub categories of a category by referencing join column(in my case "category_id").

package com.rst;

 import java.util.List;

 import org.hibernate.Query;
 import org.hibernate.Session;
 import org.hibernate.SessionFactory;

 public class CategoryManager {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    SessionFactory sessionFactory;
    try {
        sessionFactory = Util.getSessionFactory();
    }
    catch(Throwable th){
        System.out.println("some error"+th);
        throw new ExceptionInInitializerError();
    }

    Session session = sessionFactory.openSession();

    Query q = session.createQuery(
              "select s.category_name from SubCategory s where s.category_id = 17");
    List<String> lst = q.list();
    for(String str:lst){
        System.out.println(str);
    }
}

}

Upvotes: 0

Views: 2631

Answers (1)

JB Nizet
JB Nizet

Reputation: 691695

HQL works on entities, their persistent fields, and their associations. Never on table and column names. So your HQL is invalid: there is no persistent field named category_id in the entity SubCategory.

What you want is

 select s.category_name from SubCategory s where s.category.id = 17

Note that you're not respecting the Java naming conventions, which also increases your confusion between table columns and entity fields. The category_name field should be renamed to categoryName, or simply name. The query would thus become

select s.name from SubCategory s where s.category.id = 17

Upvotes: 2

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