我会利用日本财团开展一个项目,而且在大多数情况下,都希望获得实体,但有一些案例(报告是其中之一,但还有其他一些)我不想或需要获得实体,而是希望选择价值观。 JPA是否支持这一点? 如果是的话,使用它是否有意义,或者在这些情况下使用直线的亚行是否有意义?
Q1: Yes, it does.
它提出了所谓的cal问题,例如:
select u.name from User u
而不是
select u from User u
Q2: When it comes to sense of using it: Such queries have sense - you just simply need a single property not the whole object. But if you plan to make all your queries only fetching separate values, then the question why? seems valid. The whole idea of O/R mappers is to allow you operate on objects, not (related) tables and ids. So fetching ids using JPA usually doesn t make sense. Once you have objects mapped to database, it should be easier for you to operate on the data.
SQLResultsetMappingWithAlias at java2s.com,似乎就你所期待的情况提供了一个实例。
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