Creating Queries Using the Java Persistence Query Language (original) (raw)
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3. Getting Started with Web Applications
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Part V Contexts and Dependency Injection for the Java EE Platform
28. Introduction to Contexts and Dependency Injection for the Java EE Platform
29. Running the Basic Contexts and Dependency Injection Examples
30. Contexts and Dependency Injection for the Java EE Platform: Advanced Topics
31. Running the Advanced Contexts and Dependency Injection Examples
32. Introduction to the Java Persistence API
33. Running the Persistence Examples
34. The Java Persistence Query Language
Simplified Query Language Syntax
Queries That Navigate to Related Entities
A Simple Query with Relationships
Navigating to Single-Valued Relationship Fields
Traversing Relationships with an Input Parameter
Traversing Multiple Relationships
Navigating According to Related Fields
Queries with Other Conditional Expressions
BNF Grammar of the Java Persistence Query Language
Collection Member Declarations
Operators and Their Precedence
Empty Collection Comparison Expressions
35. Using the Criteria API to Create Queries
36. Creating and Using String-Based Criteria Queries
37. Controlling Concurrent Access to Entity Data with Locking
38. Using a Second-Level Cache with Java Persistence API Applications
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The EntityManager.createQuery and EntityManager.createNamedQuery methods are used to query the datastore by using Java Persistence query language queries.
The createQuery method is used to create dynamic queries, which are queries 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, or queries that are defined in metadata by 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 queryelement 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:
@PersistenceContext public EntityManager em; ... customers = em.createNamedQuery("findAllCustomersWithName") .setParameter("custName", "Smith") .getResultList();
Named Parameters in Queries
Named parameters are query parameters that are prefixed with a colon (:). Named parameters in a query are bound to an argument by the following method:
javax.persistence.Query.setParameter(String name, Object value)
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 use positional parameters instead of named parameters in queries. 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.
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