The NHibernate Query by Criteria API lets you build a query by manipulating criteria objects at runtime. This approach lets you specify constraints dynamically without direct string manipulations, but it doesn’t lose much of the flexibility or power of HQL.

What is projection in criteria?

Projection can be applied to the Criteria query. Projection is an Object-Oriented Representation of a query result set. If we want to read more than one property from the database, then we have to add Projection objects to ProjectionList, and then we need to set ProjectionList object to Criteria.

What is DetachedCriteria in NHibernate?

The DetachedCriteria class lets you create a query outside the scope of a session, and then later execute it using some arbitrary ISession. A DetachedCriteria may also be used to express a sub-query.

What is QueryOver?

The ICriteria API is NHibernate’s implementation of Query Object. Note: QueryOver is intended to remove the references to ‘magic strings’ from the ICriteria API while maintaining it’s opaqueness. It is not a LINQ provider; NHibernate has a built-in Linq provider for this.

How projection is used in JPA?

To use this class as a projection with plain JPA, you need to use a constructor expression in your query. It describes a call of the constructor. It starts with the keyword new, followed by the DTO class’s fully-qualified class name and a list of constructor parameters.

What is NHibernate in C#?

NHibernate is a mature, open source object-relational mapper for the . NET framework. It’s actively developed, fully featured and used in thousands of successful projects. Easily map regular C# or VB.NET object models designed in Visual Studio.

What are projections in JPA?

JPA and Hibernate support 3 groups of projections:

• Entities are the easiest and most common projection.
• Scalar projections are returned as Object[]s or instances of the Tuple interface.
• DTO projections provide similar performance as scalar value projections but are much easier to use.

How to group by in NHibernate iprojection?

The class NHibernate.Expression.Projections is a factory for IProjection instances. We apply a projection to a query by calling SetProjection () . There is no explicit “group by” necessary in a criteria query. Certain projection types are defined to be grouping projections , which also appear in the SQL group by clause.

What is NHibernate criteria query?

NHibernate features an intuitive, extensible criteria query API. 16.1. Creating an ICriteria instance The interface NHibernate.ICriteria represents a query against a particular persistent class. The ISession is a factory for ICriteria instances. 16.2. Narrowing the result set

What is a projection in NHibernate?

I don’t know about NHibernate, but in general, a projection is a transformation of a set into another set. In SQL, it is expressed as a SELECT. Share Improve this answer Follow answered Jan 20 ’11 at 12:27

What is projectionlist in hibernate projection?

Projection is an Object-Oriented Representation of a query result set. Hibernate Projection is used to read a partial entity from the database. If we want to read more than one property from the database, then we have to add Projection objects to ProjectionList, and then we need to set ProjectionList object to Criteria.