emcreateNamedQueryUserfindByEmail

em.createNamedQuery is a method of the Java Persistence API (JPA) EntityManager that creates a query from a predefined named query by its name. Named queries are defined on entity classes or in mapping files and consist of a unique name and a query string written in JPQL. The JPA provider may validate and optimize these queries at deployment time, contributing to consistency and potential performance benefits.

Named queries are typically defined using annotations such as @NamedQuery on an entity class or in an orm.xml file. For example, a named query might be defined as name="Customer.findAll" with the corresponding JPQL query "SELECT c FROM Customer c". The queries can return either a general Query or a typed result query, depending on which overload of createNamedQuery is used.

Usage commonly involves obtaining an EntityManager, invoking createNamedQuery with the query name, and optionally specifying the result type. For instance, TypedQuery<Customer> q = em.createNamedQuery("Customer.findAll", Customer.class); Then you can execute q.getResultList() or q.getSingleResult(). If the named query contains parameters, these are set with q.setParameter("paramName", value) before execution.

Benefits of using named queries include centralized query definitions, potential early validation, and reuse across different parts of an application. Limitations include the need to maintain the named query name consistency and the fact that named queries are best for static queries rather than highly dynamic ones. em.createNamedQuery complements dynamic queries created via em.createQuery or the Criteria API.