JPA本机查询返回具有多个表的字段的实体

Question

I have a query in JPA NativeSql, where I do "unions" of tables and joins. I made an entity with all the query fields which are from multiple tables. So I can not do "@Column" "@ table" as usual with JPA.

How could I set the given values ​​of the query to my entity?

Answer 1

You can map the columns returned by your native SQL query to your entity by using @SqlResultSetMapping .

Example :

Query q = em.createNativeQuery(
    "SELECT o.id AS order_id, " +
        "o.quantity AS order_quantity, " +
        "o.item AS order_item, " +
        "i.name AS item_name, " +
    "FROM Order o, Item i " +
    "WHERE (order_quantity > 25) AND (order_item = i.id)",
    "OrderResults");

@SqlResultSetMapping(name="OrderResults", 
    entities={ 
        @EntityResult(entityClass=com.acme.Order.class, fields={
            @FieldResult(name="id", column="order_id"),
            @FieldResult(name="quantity", column="order_quantity"), 
            @FieldResult(name="item", column="order_item")
        })
    },
    columns={
        @ColumnResult(name="item_name")}
)

More examples can be found here .

Answer 2

您可以使用重载的EntityManager＃createNativeQuery（sql，resultClass）方法。

Answer 3

IMHO using DAOs with JPA isn't a good idea. But have a look at the Criteria API . You can construct such queries like the one you described with the CriteriaBuilder .

Answer 4

JPA native SQL is same as generic SQL . You can do union operation same as SQL query do. But, if you want to do it with JPQL , than you need to use EclipseLink , becasue JPQL of JPA does not support of Union operation.

Answer 5

Why not put the NATIVE SQL into a view? Then just create an entity mapped to the view like any normal entity would be mapped to table. The only difference being you cannot insert, update or delete entities based off of the view.