Hibernate joining two table and fetch all records?

Question

I have two entity class Category and Events.I need to join both the tables and fetch all records which matching the given condition

Answer 1

Hibernate is about mapping objects and the relations, however you are mapping simple id fields.

In your Events class you have the followingL

@Entity
@Table(name = "events")
public class Events implements Serializable { 

    @Column(name = "category_i")
    private Integer categoryI;

}

However it should be a Category instead of an Integer.

@Entity
@Table(name = "events")
public class Events implements Serializable { 

    @ManyToOne
    @Column(name = "category_i")
    private Category category;

}

Then in your Category you should add the mappedBy field to the @ManyToOne on the events field and remove the @JoinColumn.

@Entity
@Table(name = "category")
public class Category implements Serializable {

    @OneToMany(mappedBy="category")
    private Events events;
}

The same applies to the parentCategoryId of the Category class.

Now that you have your mapping corrected you should be able to write the query as you wanted to.

Answer 2

This query should do the job:

from Category as c
inner join c.events as e
where c.parentCategoryId = 1

Plus you seem to have a typo (missing "d" at the end) here:

@JoinColumn(name="category_i"))

Answer 3

You need to think in terms of Java objects when using ORM tools.

From your question I think the query that you're trying to write will look something like:

public List<Category> getCategoryList(int id) {
    List<Category> groupList;
    Session session = sessionFactory.getCurrentSession();
    Query query = session.createQuery("select c from Category c join fetch c.events where c.parentCategory.categoryId = 1");
    //query.setParameter("id", id);
    groupList = query.list();
    return groupList;
}

One of the benefits of using an ORM is that it works out the full join query for you.

For this to work you need to update your class model as follows:

import java.io.Serializable;
import java.util.Date;
import javax.persistence.*;

@Entity
@Table(name = "events")
public class Event implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "event_id")
    private int eventId;

    @Column(name = "event_name")
    private String eventName;

    @Column(name = "event_description")
    private String eventDescription;

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

    @Column(name = "is_trending_event")
    private Integer isTrendingEvent;

    @Column(name = "image_url")
    private String imageUrl;

    private Integer status;

    @Column(name = "created_date")
    @Temporal(javax.persistence.TemporalType.DATE)
    private Date createdDate;

    @Column(name = "last_updated_date")
    @Temporal(javax.persistence.TemporalType.DATE)
    private Date lastUpdatedDate;

    ...

}

and

import java.io.Serializable;
import java.util.Date;
import javax.persistence.*;

@Entity
@Table(name = "category")
public class Category implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "category_id")
    private int categoryId;

    @Column(name = "category_name")
    private String categoryName;

    @ManyToOne
    @JoinColumn(name="parent_category_id")
    private Category parentCategory;

    @Column(name = "created_date")
    @Temporal(javax.persistence.TemporalType.DATE)
    private Date createdDate;

    @Column(name = "last_updated_date")
    @Temporal(javax.persistence.TemporalType.DATE)
    private Date lastUpdatedDate;

    @OneToMany(mappedBy="category")
    private List<Event> events;

    ...

}

Answer 4

Ty this below code

public List<Object[]> getCategoryList(int id) throws SQLException, ClassNotFoundException, IOException {


        Session session = sessionFactory.getCurrentSession();
        return session.createCriteria(Catagory.class)
        .setFetchMode("events", FetchMode.JOIN)
        .add(Restrictions.eq("parentCatagoryId", 1))
        .list();

}

Hope this stuff works.