Hibernate CriteriaBuilder

Overview

This project demonstrates the use of the CriteriaBuilder interface in Hibernate, which is part of the javax.persistence.criteria package. The CriteriaBuilder was introduced to overcome the drawbacks of the Criteria API. It allows us to create different types of criteria to perform specific operations without hardcoding queries as strings.

Key Components

CriteriaBuilder

• Purpose: Acts as a builder to generate objects for different types of criteria.
• Usage: Create an instance using the getCriteriaBuilder() method from the session object.
• Functionality: Helps construct queries using inbuilt methods, but does not execute them.

Criteria Types

1. CriteriaQuery

   • Purpose: Used for data retrieval from the database.
   • Creation: Use createQuery() method from CriteriaBuilder.
   • Methods:
     • from(): Fetches all records from the respective table and stores them in a root element.
   • Execution: Use the Query interface to execute the constructed query.

   // Example of CriteriaQuery
   Session session = sessionFactory.openSession();
   CriteriaBuilder cb = session.getCriteriaBuilder();
   CriteriaQuery<Employee> cq = cb.createQuery(Employee.class);
   Root<Employee> root = cq.from(Employee.class);
   cq.select(root);
   Query<Employee> query = session.createQuery(cq);
   List<Employee> employees = query.getResultList();

2. CriteriaUpdate

   • Purpose: Used for updating data in the database.
   • Creation: Use createCriteriaUpdate() method from CriteriaBuilder.
   • Methods:
     • from(): Fetches all records from the respective table and stores them in a root element.
     • set(): Sets the values for columns to be updated.
   • Execution: Use the Query interface to execute the constructed query using executeUpdate() method.

   // Example of CriteriaUpdate
   Session session = sessionFactory.openSession();
   CriteriaBuilder cb = session.getCriteriaBuilder();
   CriteriaUpdate<Employee> cu = cb.createCriteriaUpdate(Employee.class);
   Root<Employee> root = cu.from(Employee.class);
   cu.set("salary", 50000);
   cu.where(cb.equal(root.get("id"), 1));
   Query query = session.createQuery(cu);
   int rowsUpdated = query.executeUpdate();

3. CriteriaDelete

   • Purpose: Used for deleting data from the database.
   • Creation: Use createCriteriaDelete() method from CriteriaBuilder.
   • Methods:
     • from(): Fetches all records from the respective table and stores them in a root element.
   • Execution: Use the Query interface to execute the constructed query using executeUpdate() method.

   // Example of CriteriaDelete
   Session session = sessionFactory.openSession();
   CriteriaBuilder cb = session.getCriteriaBuilder();
   CriteriaDelete<Employee> cd = cb.createCriteriaDelete(Employee.class);
   Root<Employee> root = cd.from(Employee.class);
   cd.where(cb.equal(root.get("id"), 1));
   Query query = session.createQuery(cd);
   int rowsDeleted = query.executeUpdate();

Notes

CriteriaBuilder

• It is an interface present in javax.persistence.criteria package.
• It was introduced to overcome the drawbacks of Criteria API.
• Using CriteriaBuilder we can create different types of criteria to perform specific operations.
• CriteriaBuilder acts as a builder responsible for generating objects for different types of criteria.
• We can create an object of CriteriaBuilder by invoking the getCriteriaBuilder() method using the session object.
• Using CriteriaBuilder, we don't need to hardcode the query as a string; instead, we use inbuilt methods to construct the query.
• It is only used to construct the query and not responsible for executing it.
• To execute the query, we need to create an instance of the Query interface.

CriteriaQuery

• It is an interface present in javax.persistence.criteria package.
• It is used specifically for data retrieval from the database.
• We can create an object of CriteriaQuery by invoking the createQuery() method using the CriteriaBuilder object.
• The createQuery() method accepts the entity class name as the parameter to construct the query.
• It has a method called from() which accepts the entity class name as the parameter to fetch all records from the respective table and store them inside a root element.
• The user is provided with several methods to represent the where clause and various other expressions needed for the query.
• To execute the query after it is constructed, we need to use the Query interface.

CriteriaUpdate

• It is an interface present in javax.persistence.criteria package.
• It is used specifically for updating data in the database.
• We can create an object of CriteriaUpdate by invoking the createCriteriaUpdate() method using the CriteriaBuilder object.
• The createCriteriaUpdate() method accepts the entity class name as the parameter to construct the query.
• It has a method called from() which accepts the entity class name as the parameter to fetch all records from the respective table and store them inside a root element.
• We use the set method from CriteriaUpdate to set the values for columns to be updated.
• The user is provided with several methods to represent the where clause and various other expressions needed for the query.
• To execute the query after it is constructed, we need to use the Query interface and the executeUpdate() method.

CriteriaDelete

• It is an interface present in javax.persistence.criteria package.
• It is used specifically for deleting data from the database.
• We can create an object of CriteriaDelete by invoking the createCriteriaDelete() method using the CriteriaBuilder object.
• The createCriteriaDelete() method accepts the entity class name as the parameter to construct the query.
• It has a method called from() which accepts the entity class name as the parameter to fetch all records from the respective table and store them inside a root element.
• The user is provided with several methods to represent the where clause and various other expressions needed for the query.
• To execute the query after it is constructed, we need to use the Query interface and the executeUpdate() method.