Annotation Interface ConstructorResult

@Target(METHOD)
@Retention(RUNTIME)
@Repeatable(ConstructorResult.ConstructorResults.class)
public @interface ConstructorResult

Used in conjunction with the SqlResultSetMapping or NamedNativeQuery annotation to map the SELECT clause of a SQL query to the constructor of an arbitrary Java class.

When processing a result set, the provider instantiates the target class by calling a matching constructor of the class, passing as arguments the values of the specified columns() of the result set. Columns must be explicitly listed by columns() in the same order as their corresponding parameters occur in the argument list of the constructor.

The target class need not be a managed type. Any instance of an entity class returned as a constructor result will be in either the new or detached state, depending on whether a primary key was assigned to the constructed object.

Consider the following SQL query:

Query customerDetails =
        em.createNativeQuery(
            """
               SELECT c.id, c.name,
                      COUNT(o) as order_count,
                      AVG(o.price) AS avg_price
               FROM Customer c
               JOIN Orders o ON o.cid = c.id
               GROUP BY c.id, c.name
            """,
            ResultMappings_.CUSTOMER_DETAILS
        );

The result set mapping might be defined as follows:

 @SqlResultSetMapping(
     name = "CustomerDetails",
     classes = @ConstructorResult(
         targetClass = CustomerDetails.class,
         columns = {
             @ColumnResult(name = "id"),
             @ColumnResult(name = "name"),
             @ColumnResult(name = "order_count"),
             @ColumnResult(name = "avg_price",
                           type = Double.class)
         }
     )
)
interface ResultMappings {}

At runtime, a ConstructorResult annotation is represented by an instance of ConstructorMapping in the ResultSetMapping returned by EntityManagerFactory.getResultSetMappings(Class).

This annotation may be placed directly on a method annotated NativeQuery.

@NativeQuery("SELECT pub_id, count(*) AS book_count FROM books GROUP BY pub_id")
@ConstructorResult(
    targetClass = PublisherBookCount.class,
    columns = {@ColumnResult("pub_id"),
               @ColumnResult("book_count")}
)
List<PublisherBookCount> publisherBookCounts(String pattern);

Since:

2.1

See Also:

• SqlResultSetMapping
• NamedNativeQuery
• ColumnResult
• ConstructorMapping

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static @interface	ConstructorResult.ConstructorResults

Required Element Summary

Required Elements

Modifier and Type	Required Element	Description
Class<?>	targetClass	(Required) The class whose constructor is to be invoked.

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element	Description
ColumnResult[]	columns	(Optional) The mapping of columns in the SELECT list to arguments of a constructor of the specified Java target class, in order.
EntityResult[]	entities	(Optional) The mapping of columns in the SELECT list to entity results which are then assigned to parameters of a constructor of the specified Java target class, in order.

Element Details

targetClass

Class<?> targetClass

(Required) The class whose constructor is to be invoked. This may be any Java class with a constructor matching the specified columns.

columns

ColumnResult[] columns

(Optional) The mapping of columns in the SELECT list to arguments of a constructor of the specified Java target class, in order.

Constructor parameters mapping directly to column results must occur before parameters mapping to entities.

Default:

{}

entities

EntityResult[] entities

(Optional) The mapping of columns in the SELECT list to entity results which are then assigned to parameters of a constructor of the specified Java target class, in order.

Constructor parameters mapping to entity results must occur after parameters mapping to columns.

Since:

4.0

Default:

{}