JPA already defines a mechanism for defining queries, with the @javax.persistence.NamedQuery and @javax.persistence.NamedQueries annotations. In theory these can be annotated on any class, but by convention they go on the class being returned.

For example, we might want to search for Customers by their id, or by their surname (family name):

@NamedQueries({
    @NamedQuery(name="findCustomerById", query="from Customer where id=:id"),
    @NamedQuery(name="findCustomersBySurname", query="from Customer where surname=:surname"),
})
@Entity
@DiscriminatorValue("CUS")
public class Customer {

    ...
    @Id
    public Integer getId() { ... }

    ...
    @Basic
    public String getFamilyName() { ... }

    ...
}

These named queries are then referenced in the repository implementations, covered next (Section 5.3, “Repository Implementation”).