In JPA, is there a DB agnostic way to check if a table exists?

Question

I'm wondering if there's a db agnostic way to check if a certain table exists in JPA (specifically, eclipse link). Right now the way we do it is with a native query like this:

select count(*) from table_name where 1=2

If this throws an exception, we know the table doesn't exist. And, as far as I know, this will work on most SQL databases. The thing I don't is it's a hacky query and it throws a SQL exception when the table doesn't exist. I'd prefer to be able to do a query that returns a true / false instead of a no error / error . But the only way I know how to do that is to query data dictionaries, and that won't be database agnostic.

In JPA, is there a DB agnostic way to check if a table exists?

Answer 1

I'll raise Joe Rinehart's comment to answer level. Using DatabaseMetaData.getTables() helped me query a table's existence in a mostly agnostic way without raising errors. A couple of comments.

1. getTables may have issues, for example with Teradata as pointed out by Durandal .
2. The resulting table names case is database dependent. For example, PostgreSQL converts to lower case by default whereas H2 converts to upper case by default.

A more agnostic method is to define a count method in a repository, such as the following (where Todo class is a JPA entity).

@org.springframework.stereotype.Repository
public interface TodoRepository extends Repository<Todo, Long> {
    Long count();
}

The above is agnostic but will throw errors which must be caught, as shown below.

private long countTodos() {
    try {
        return todoRepository.count();
    } catch (Exception e) {
        getLogger().info("Count error: {}", e.getMessage());
    }
    return 0;
}

Errors will also show up in the log when no table is present.

2016-08-04 12:02:11.190  INFO 5788 --- [           main] o.h.h.i.QueryTranslatorFactoryInitiator  : HHH000397: Using ASTQueryTranslatorFactory
2016-08-04 12:02:11.296  WARN 5788 --- [           main] o.h.engine.jdbc.spi.SqlExceptionHelper   : SQL Error: 42102, SQLState: 42S02
2016-08-04 12:02:11.296 ERROR 5788 --- [           main] o.h.engine.jdbc.spi.SqlExceptionHelper   : Table "TodosTable_name" not found; SQL statement:
select count(*) as col_0_0_ from "TodosTable_name" todo0_ [42102-192]
2016-08-04 12:02:11.303  INFO 5788 --- [           main] c.s.e.SpringJpaDemoApplicationTests      : Count error: could not prepare statement; SQL [select count(*) as col_0_0_ from "TodosTable_name" todo0_]; nested exception is org.hibernate.exception.SQLGrammarException: could not prepare statement