Execute a Create Table Query through the JPA Entit

问题:

I need to create a new Table in a Database I access through a JPA EntityManager. Do JPA NativeQueries support Queries other than "Select" or "Update"? Or is there another state-of-the-art way to execute a complex SQL query in a JPA Context?

回答1:

The jpa "native queries" can only be used for DML statements (Data Manipulation Language). To issue any DDL, such as a create table, you'll need to get the underlying connection from the EntityManager.

How to extract the connection from the EM will depend on which JPA implementation you're using, but will definitely include invoking EntityManager.getDelegate().

Alternatively (and I think it's a better approach), inject the DataSource or a JDBCTemplate if you're using spring to the object that tries to create the table, and use that class to create the table.

回答2:

JPA (at least Hibernate) can let you execute DDL statements directly using createNativeQuery() and executeUpdate() as follows:

EntityManager em = ...;
em.createNativeQuery("CREATE TABLE FOO (FOO_ID NUMBER)").executeUpdate();
em.createNativeQuery("DROP TABLE FOO").executeUpdate();

It's not ideal, but you can do it.