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The Criteria API is a predefined API used to define queries for entities. It is the alternative way of defining a JPQL query. These queries are type-safe, and portable and easy to modify by changing the syntax. Similar to JPQL it follows abstract schema (easy to edit schema) and embedded objects. The metadata API is mingled with criteria API to model persistent entity for criteria queries.

The major advantage of the criteria API is that errors can be detected earlier during compile time. String based JPQL queries and JPA criteria based queries are same in performance and efficiency.

History of criteria API

The criteria API is included into all versions of JPA therefore each step of criteria API is notified in the specifications of JPA.

• In JPA 2.0, the criteria query API, standardization of queries are developed.
• In JPA 2.1, Criteria update and delete (bulk update and delete) are included.

Criteria Query Structure

The Criteria API and the JPQL are closely related and are allowed to design using similar operators in their queries. It follows javax.persistence.criteria package to design a query. The query structure means the syntax criteria query.

The following simple criteria query returns all instances of the entity class in the data source.

The query demonstrates the basic steps to create a criteria.

• EntityManager instance is used to create a CriteriaBuilder object.
• CriteriaQuery instance is used to create a query object. This query object’s attributes will be modified with the details of the query.
• CriteriaQuery.from method is called to set the query root.
• CriteriaQuery.select is called to set the result list type.
• TypedQuery<T> instance is used to prepare a query for execution and specifying the type of the query result.
• getResultList method on the TypedQuery<T> object to execute a query. This query returns a collection of entities, the result is stored in a List.

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Example of criteria API

Let us consider the example of employee database. Let us assume the jpadb.employee table contains following records:

Create a JPA Project in the eclipse IDE named JPA_Eclipselink_Criteria. All the modules of this project are shown as follows:

Creating Entities

Create a package named com.tutorialspoint.eclipselink.entity under ‘src’ package.

Create a class named Employee.java under given package. The class Employee entity is shown as follows:

Persistence.xml

Persistence.xml file is required to configure the database and the registration of entity classes.

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Persistence.xml will be created by the eclipse IDE while cresting a JPA Project. The configuration details are user specification. The persistence.xml file is shown as follows:

Service classes

This module contains the service classes, which implements the Criteria query part using the MetaData API initialization. Create a package named ‘com.tutorialspoint.eclipselink.service’. The class named CriteriaAPI.java is created under given package. The DAO class is shown as follows:

After compilation and execution of the above program you will get output in the console panel of Eclipse IDE as follows: