JPA Criteria API是否支持实体类型表达式？JPQL已有对应示例

Absolutely! The JPA Criteria API fully supports entity type expressions, just like the JPQL snippet you provided (SELECT e FROM Employee e WHERE TYPE(e) IN (Exempt, Contractor)). Here's how to replicate that logic using the Criteria API:

Step-by-Step Implementation #

Let’s assume Employee is your base entity class, with Exempt and Contractor as its subclasses (works with any JPA inheritance strategy like SINGLE_TABLE, JOINED, or TABLE_PER_CLASS):

1. Set up your CriteriaBuilder and CriteriaQuery:

   CriteriaBuilder cb = entityManager.getCriteriaBuilder();
   CriteriaQuery<Employee> query = cb.createQuery(Employee.class);
   Root<Employee> employeeRoot = query.from(Employee.class);
   

2. Build the type filter condition:
   Use cb.type(employeeRoot) to get an expression representing the entity's runtime type, then chain in() to match multiple subclass types:

   query.select(employeeRoot)
        .where(cb.in(cb.type(employeeRoot))
            .value(Exempt.class)
            .value(Contractor.class));
   

3. Execute the query:

   List<Employee> filteredEmployees = entityManager.createQuery(query).getResultList();
   

Bonus: Matching a Single Subclass Type #

If you only need to filter for one specific subclass, you can use cb.equal() instead of in():

query.where(cb.equal(cb.type(employeeRoot), Contractor.class));

This feature is incredibly useful when working with inherited entity hierarchies, letting you precisely target specific subclasses without messy manual filters.

内容的提问来源于stack exchange，提问作者eastwater