Creating Queries

The EntityManager.createQuery and EntityManager.createNamedQuery methods are used to query the datastore using Java Persistence query language queries. See Chapter 27, The Java Persistence Query Language for more information on the query language.

The createQuery method is used to create dynamic queries, queries that are defined directly within an application’s business logic.

public List findWithName(String name) {
return em.createQuery(
    "SELECT c FROM Customer c WHERE c.name LIKE :custName")
    .setParameter("custName", name)
    .setMaxResults(10)
    .getResultList();
}

The createNamedQuery method is used to create static queries, queries that are defined in metadata using the javax.persistence.NamedQuery annotation. The name element of @NamedQuery specifies the name of the query that will be used with the createNamedQuery method. The query element of @NamedQuery is the query.

@NamedQuery(
    name="findAllCustomersWithName",
    query="SELECT c FROM Customer c WHERE c.name LIKE :custName"
)

Here’s an example of createNamedQuery, which uses the @NamedQuery defined above.

@PersistenceContext
public EntityManager em;
...
customers = em.createNamedQuery("findAllCustomersWithName")
    .setParameter("custName", "Smith")
    .getResultList();

Named Parameters in Queries

Named parameters are parameters in a query that are prefixed with a colon (:). Named parameters in a query are bound to an argument by the javax.persistence.Query.setParameter(String name, Object value) method. In the following example, the name argument to the findWithName business method is bound to the :custName named parameter in the query by calling Query.setParameter.

public List findWithName(String name) {
    return em.createQuery(
        "SELECT c FROM Customer c WHERE c.name LIKE :custName")
        .setParameter("custName", name)
        .getResultList();
}

Named parameters are case-sensitive, and may be used by both dynamic and static queries.

Positional Parameters in Queries

You may alternately use positional parameters in queries, instead of named parameters. Positional parameters are prefixed with a question mark (?) followed the numeric position of the parameter in the query. The Query.setParameter(integer position, Object value) method is used to set the parameter values.

In the following example, the findWithName business method is rewritten to use input parameters:

public List findWithName(String name) {
    return em.createQuery(
        “SELECT c FROM Customer c WHERE c.name LIKE ?1”)
        .setParameter(1, name)
        .getResultList();
}

Input parameters are numbered starting from 1. Input parameters are case-sensitive, and may be used by both dynamic and static queries.