When connecting caravel to hive server, throws error when loading a table
<pre><code>2016-07-06 19:39:09,153:ERROR:root:Compiler &lt;sqlalchemy.sql.compiler.GenericTypeCompiler object at 0x10c75d150&gt; can't render element of type &lt;class 'impala.sqlalchemy.STRING'&gt;
Traceback (most recent call last):
  File "/Users/user_name/.virtualenvs/caravel27/lib/python2.7/site-packages/caravel/models.py", line 771, in fetch_metadata
    datatype = "{}".format(col.type).upper()
  File "/Users/user_name/.virtualenvs/caravel27/lib/python2.7/site-packages/sqlalchemy/sql/type_api.py", line 481, in __str__
    return unicode(self.compile()).\
  File "/Users/user_name/.virtualenvs/caravel27/lib/python2.7/site-packages/sqlalchemy/sql/type_api.py", line 468, in compile
    return dialect.type_compiler.process(self)
  File "/Users/user_name/.virtualenvs/caravel27/lib/python2.7/site-packages/sqlalchemy/sql/compiler.py", line 261, in process
    return type_._compiler_dispatch(self, **kw)
  File "/Users/user_name/.virtualenvs/caravel27/lib/python2.7/site-packages/sqlalchemy/sql/visitors.py", line 79, in _compiler_dispatch
    raise exc.UnsupportedCompilationError(visitor, cls)
</code></pre>

<p>Similar issue has been reported <a href="https://github.com/cloudera/impyla/issues/71" rel="nofollow">here</a>.</p>

<p>However I do not know how to pass <code>bind=engine</code> in case of using <code>sqlalchemy</code> via <code>caravel</code></p>

<p>This is how you can replicate the error :</p>

<p>Install then run caravel using <code>caravel runserver -d</code>. Then add a hive2 database to caravel. To do this you need impyla. After installation use this as the sqlAlchemyURL <code>impala://somehostname.compute.amazonaws.com:10000/database_name?auth_mechanism=‌​PLAIN</code>. The test connection should return <code>Seems OK</code>. Caravel should also able to discover all the tables in database_name. However, when I add a table, caravel identifies all the columns as UNKNOWN type. Then look at the logs posted by caravel and the above mentioned error should be logged. </p>