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#330 - Polished README on JPA 2.1 examples for manual result set mappings.

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Oliver Gierke
2018-05-09 16:47:23 +02:00
parent 6a0f692e71
commit 7a31deb2d6
1 changed files with 15 additions and 15 deletions
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jpa/jpa21/README.md
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@@ -55,35 +55,35 @@ Calling `UserRepository.plus1BackedByOtherNamedStoredProcedure(…)` will execut
## Support for custom SqlResultSetMapping with ConstructorResult ## Support for custom SqlResultSetMapping with ConstructorResult
Sometimes, e.g. for analytics, it is handy to be able to return a different entity result type from a Repository query method than the base Repository entity type or an interface based projection. Sometimes, e.g. for analytics, it is handy to be able to return a different entity result type from a Repository query method than the base Repository entity type or an interface based projection.
In those cases one can leverage JPAs `SqlResultSetMapping` feature to map the columns of the result of a query to different fields. In those cases one can leverage JPAs `SqlResultSetMapping` feature to map the columns of the result of a query to different fields.
JPA 2.1 introduced the new `SqlResultSetMapping` type `ConstructorResult` which allows to map columns of a result set row to a constructor invocation JPA 2.1 introduced the new `SqlResultSetMapping` type `ConstructorResult` which allows to map columns of a result set row to a constructor invocation
which can be nicely used in combination with Value Objects. which can be nicely used in combination with Value Objects.
This example shows how to define a custom `SqlResultSetMapping` for the result of an analytical native query that reports the usage summary for a set of Subscriptions. This example shows how to define a custom `SqlResultSetMapping` for the result of an analytical native query that reports the usage summary for a set of Subscriptions.
`SqlResultSetMapping` definition on the Subscription entity class: `SqlResultSetMapping` definition on the `Subscription` entity class:
```java ```java
@Entity @Entity
@NoArgsConstructor @NoArgsConstructor
@SqlResultSetMapping( @SqlResultSetMapping(
name="subscriptionSummary", name = "subscriptionSummary",
classes = @ConstructorResult( classes = @ConstructorResult(
targetClass = SubscriptionSummary.class, targetClass = SubscriptionSummary.class,
columns={ columns = {
@ColumnResult(name="productName", type=String.class), @ColumnResult(name = "productName", type = String.class),
@ColumnResult(name="subscriptions", type=long.class) @ColumnResult(name = "subscriptions", type = long.class)
})) }))
@NamedNativeQuery( @NamedNativeQuery(
name="Subscription.findAllSubscriptionSummaries", name = "Subscription.findAllSubscriptionSummaries",
query="select product_name as productName, count(user_id) as subscriptions from subscription group by product_name order by productName", query = "select product_name as productName, count(user_id) as subscriptions from subscription group by product_name order by productName",
resultSetMapping = "subscriptionSummary" resultSetMapping = "subscriptionSummary"
) )
@Data @Data
public class Subscription { public class Subscription {
... …
} }
``` ```
@@ -92,9 +92,8 @@ public class Subscription {
@Value @Value
public class SubscriptionSummary { public class SubscriptionSummary {
private final String product; String product;
Long usageCount;
private final Long usageCount;
} }
``` ```
@@ -102,6 +101,7 @@ The `SubscriptionRepository` declares the custom query method `findAllSubscripti
```java ```java
interface SubscriptionRepository extends CrudRepository<Subscription,Long> { interface SubscriptionRepository extends CrudRepository<Subscription,Long> {
List<SubscriptionSummary> findAllSubscriptionSummaries(); @Query(nativeQuery = true)
List<SubscriptionSummary> findAllSubscriptionSummaries();
} }
``` ```