More descriptive error message for "Indexed order_by can only be performed on a TABLE or TABLE_SLICE"

[danielcompton]

I was running

r.db('local_ip').table('todos').filter({list: "home"}).orderBy({index: 'title'})

and got the error:

RqlRuntimeError: Indexed order_by can only be performed on a TABLE or TABLE_SLICE in:
r.db("local_ip").table("todos").filter({list: "home"}).orderBy({index: "title"})
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This was a confusing error to me, as I thought I was operating on a TABLE. After doing some search I understand the issue with secondary indexing and why this doesn't work. I think it would be helpful for users if the error message explained what type the indexed order_by was trying to operate on if it wasn't a TABLE, and maybe link to more docs about this.

[mlucy]

Thanks for opening an issue. I think you're right that we can probably make the error message clearer.

[sanchopanca]

I agree, very confusing message. Link to documentation in error message would be helpful.