TinyTds::Error: No column name was specified for column 2 of ‘__rnt’

This is an obscure error that I encountered today and about which I found very little information.  In my particular case (see my previous post regarding the Spider Database UI), I encountered this problem as soon as I added a feature by which selected records of the current user table could be used to qualify the records shown for the parent and children relationships.

What this means is that, previously, I was simply showing all records of the parent and child relationships, which was being loaded in the index function of the table viewer controller:

@parent_dataset = load_fk_tables(@parent_tables)
@child_dataset = load_fk_tables(@child_tables)

Now however, I was qualifying the parent and child tables based on the (optional) selected records of the selected user table:

@parent_dataset = load_fk_tables(@parent_tables, self.parent_qualifiers)
@child_dataset = load_fk_tables(@child_tables, self.child_qualifiers)

The error in the subject line of this post began occurring at this point.  Interestingly, as soon as I forced the record to load through any means, such as:

records = DynamicTable.where(where).paginate(page: page, per_page: items_per_page)


d = records[0]


records.each do |record| q=5 end

The problem went away.    I am actually completely at a loss to explain why lazy-loading is the issue — digging into the will_paginate and active_record source code, I didn’t find anything that would particularly lead me to understanding the issue.  However, I do know that forcing the load solved the problem.  Possible explanations:

  1. This may simply have to do with having more than one set of tables set up for lazy loading.  I notice this problem occurs only when I have multiple tables in the “lazy load” state being referenced by the view.
  2. This may be related to some interaction with will_paginate, as it seems that the offending query deals with selecting rows within a page range and also involves hidden fields (like ‘__rn’) that will_paginate adds to the query.
  3. It also has something to do with TinyTds.  There are some interesting posts about this error and TinyTds, but they’re not related, as far as I can tell because there are no un-aliased fields.  None-the-less, because TinyTDS is emitting the error, it is clearly suspect somewhere in the process.

Regarding number 3, here’s the query it’s trying to execute:

SELECT TOP (7) [__rnt].* FROM ( SELECT ROW_NUMBER() OVER (ORDER BY [Person].[StateProvince].[StateProvinceID] ASC) AS [__rn], [Person].[BusinessEntityAddress].* FROM [Person].[StateProvince] ) AS [__rnt] WHERE [__rnt].[__rn] > (0) ORDER BY [__rnt].[__rn] ASC'

You will note that __rnt is definitely not defined!  So somewhere in the lazy load process, __rnt gets lost.

Hopefully this post will provide a clue to others that encounter this bizarre problem.







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