Hibernate what is a projection

In the 2nd example, on 3rd and 4th line i have noticed a mistake. Kindly change it SivaTeja sir. We cannot create objects to an interface. Pls explain what the projections class return then and how?

Please explain what the projections class return then and how? Please consider disabling your ad blocker for Java4s. November 22, at AM. April 18, at AM.

Nagul Saida says:. October 22, at AM. Rahul says:. May 9, at AM. The org. Criteria interface allows you to build up a criteria query object. You can create criteria with the help of one of the overloaded createCriteria methods from Hibernate Session interface. You need to pass to the createCriteria method the persistent object class.

After the Criteria object will be able to return the persistence object class entities after you execute a criteria query.

In the new version of Hibernate 5 all createCriteria methods are marked as deprecated. So, if you are working on a new project you have to use:. After, we need to call the getCriteriaBuilder method and create an instance of CriteriaBuilder. It is possible to use aggregate functions with CriteriaBuilder max , min , count , avg , countDistinct , etc. Here we will count a number of selected rows from User table. IN the our case it will be the number of all users:. The package org.

It is the way to show in the object-oriented representation a query result set of a Criteria query. There are built-in projections in the Projections factory class. This interface might be implemented to define custom projections. Hibernate Projection is used to get the particular columns from the database table. The Projection class produces projection objects. This class contains just static methods and they return the projection interface object.

Projection usually is used for the Criteria query object. The Projections class contains some in-built functions like sum, max, min, rowCount, etc, therefore you can perform the aggregation operations in Hibernate.

You can add a projection object to the criteria object by calling the criteria. If we want to read more than 1 column employeeName, salary with projections, we should have to use ProjectinList class. We should prepare all projections and bind all projections into a single ProjectionList like below. On the above example, we will get the salary, departmentId and employeeName from the employee table. Since those are multiple projections, first we need to add all projections to ProjectionList object and then add ProjectionList object to criteria object.

Can we apply pagination on Projection queries.. Previous Next.