title: How to use entiy queryBuilder in connection queryBuilder?
body: <p>I have two entities: tableUnion, tags.
  I created two queryBuilders for them.
  How to use it in connection query builder?
  I want to keep them remain separate functions.</p>
  <pre><code>    const entityManager = getManager();
      const connection = getConnection();
  
      const tableUn = this.tableUnion.createQueryBuilder('tu')
          .select('id')
          .addSelect('description', 'name');
  
      const tableTg = this.tags.createQueryBuilder('tg')
          .select(['id', 'name']);
  
      return await connection
          .createQueryBuilder()
          .select('*')
          .from(
              tableUn =&gt; tableUn,
              'tu'
          )
          .addFrom(
              tableTg =&gt; tableTg,
              'tg'
          ).getRawMany();
  </code></pre>