JPQL Create new Object In Select Statement – avoid or embrace?

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Don’t avoid it, the SELECT NEW is there because there are perfectly valid use cases for it as reminded in the §10.2.7.2. JPQL Constructor Expressions in the SELECT Clause of the EJB 3.0 JPA Specification:

A constructor may be used in the
SELECT list to return one or more Java
instances. The specified class is not
required to be an entity or to be
mapped to the database. The
constructor name must be fully
qualified.

If an entity class name is specified
in the SELECT NEW clause, the
resulting entity instances are in the
new state.

SELECT NEW com.acme.example.CustomerDetails(c.id, c.status, o.count)
FROM Customer c JOIN c.orders o
WHERE o.count > 100

In short, use the SELECT NEW when you don’t want to retrieve a full entity or a full graph of objects in a type safe way (as opposed to an Object[]). Whether you map the result of a query in an entity class or a non mapped class will depend on your select. A typical example would be a list screen (where you might not want all the details).

In other words, don’t use it everywhere but don’t forbid its use (few things are only black or white).

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