SharePoint 2010 - is it possible to populate a dataform web part with REST?

I have a custom page in SharePoint 2010 that is using a DataFormWebPart to display data from a very large list (almost 5000 items). I have a query defined in XSL in the DataFormWebPart that is querying data from the list. When I increase the size of the list to over 5000 items, I get an error saying that I'm exceeding the list view threshold.

I'm using a simple CAML query to filter the data from the list. My query should never return even close to 5000 items. I've got indexing turned on for the columns that I'm filtering on in the query. I'm not sure what else to try at this point, except to possibly try a different data source.

Is it possible to replace the SPDataSource call to the list with a REST call?

edit: Here's the CAML query

<Query><Where><Contains><FieldRef Name='Location' /><Value Type='Lookup'>{$Location}</Value></Contains></Where></Query>

Solution

Alright, here's what I've discovered.

Filtering against the text value of a lookup column does not work in a CAML query vs a list that has surpassed the list view threshold.

It appears that indexing a lookup column only indexes the lookup IDs of the column values, not the lookup values themselves.

You can, however, filter against the lookup ID of the lookup column in your CAML query.

Example: Filtering on Timbuku

For example, let's say you want to query for any items with their Location lookup column set to "Timbuktu".

You might use this query:

<Where>
    <Eq>
        <FieldRef Name=\"Location\" />
        <Value Type=\"Lookup\">Timbuktu</Value>
    </Eq>
</Where>

That query will work up until the list reaches the list view threshold of 5000, at which point it will fail, even if the Location column is indexed.

To work around this, you can find Timbuktu's corresponding item in the foreign list and determine its ID. Let's say it's 42. You can then use the ID number in the query like so:

<Where>
    <Eq>
        <FieldRef Name=\"Location\" LookupId=\"true\" />
        <Value Type=\"Lookup\">42</Value>
    </Eq>
</Where>

Note the addition of the LookupId=\"true\" in the FieldRef element.

That will work even after the list view threshold is surpassed.

What this means for you

Overall, it's not good news for your web part.

You would need to first query the locations lookup list for any items corresponding to the desired value, then use the IDs of those items to filter your actual data.

This actually isn't too tough to do programmatically, either with REST or the JavaScript Object Model, but it means you'll likely need to scrap the existing XSLT web part.