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I am working in a project which uses JPA ORM and framework provides two kinds of method to create queries.

  • entityManager.createQuery(query1);
  • entityManager.createNativeQuery(query2);

I understand the kinds of query string is to be passed to use them, but I don't know exactly why do we need to create native query? Probably we don't want to use ORM capabilities there?

Vardan Gupta
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3 Answers3

15

You do not need to create a native query unless you want to. JPQL eventually is translated into SQL by the framework but the framework lets you call the native query also. Why would want to do that:

  • Low level access, which means that you can optimize and handle the mapping by yourself; with SQL you actually access the database table while with JPQL you access the entity objects;
  • Maybe you do not want to learn JPQL if you already know SQL
  • You already have the queries written in SQL, and do not have resources/time to port them to JPQL
Random42
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createQuery uses JPAs own query language, you select from Class names instead of table names. This is not SQL, it is just similar, and is later transformed to real SQL. Mapping to java classes will be done automatically and actual class instances will be returned as result.

createNativeQuery uses real SQL, and will not be able to use JPA features. This method is used in general if you need to do something really odd that is not supported by JPA. A list of Object[] will be returned, and mapping to java objects will have to be done manually. In other words, its just like working with a DB before JPA came to, just slightly more convenient since connection handling is done automatically.

Rasmus Franke
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I have used it for optimization purposes. Using Native queries means that the ORM mapping is not in place, and instead of JPQL, you use the DB's native syntax. So, as @RasmusFranke also pointed out, if you need something that is not supported by JPA (like when you want to use DB vendor specific extensions, which is conceptually a bad idea, since JPA is all about being DB agnostic, but happens nevertheless. I know...)

The other effect of this is that by using native queries, only the supplied query is run. No eager fetching of other entities, or other unwanted stuff. This way, if you deal with huge amounts of objects, you can save some heap space.

ppeterka
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