One way would be to create a DataType based on ListItem, in the Developer tab. Add the manufacturers to this DataType, and then add this DataType to your Product DocumentType, call it 'manufacturer' say.

You could then search for the Product nodes that have the value of manufacturer set to the manufacturer that you are interested in, $filterCriteria, like this:

<xsl:variable name="selectedNodes" select="$currentPage//node [@nodeTypeAlias='NewsItem'][string(data [@alias='umbracoNaviHide']) != '1'][contains(data[@alias='categorisation'],$filterCriteria)]"/>

"contains" was used in this example as "categorisation" was a checkbox field. But you could change [contains(data[@alias='categorisation'],$filterCriteria)] to [string(data [@alias='manufacturer']) != 'ford']

Richard

Hmm I think I have done what you suggested.

I created a new  Data type "manufacturer picker" set it to Ultimate Picker and set the node to the root of the manufactures in the hierachy.

Within the product doc type I have included this new data type control.This works just fine.

However I am a bit confused with the syntax to pull in the Manufacturer logo  ("manufLogo") which is a upload control with the "Manufacturers" doc type.

I need to match the Manufacturer Name  called "bodyTitle" from the  "Manufacturers" heirarchy to the selected product field "manufacturer" in the products heirarchy, then get the manufLogo path to insert into a img src 

Where do I setup the filterCriteria?

I suspect the XSLT needs to traverse the tree until it gets to  manufacturers  and then find a match with the sub nodes that have a matching BodyTitle.

It seems a little backward to be matching varchars when a numeric would be much faster...or is that not really a consideration? 

What value is being stored in the product doc type with the Ultimate Picker field, that has the manufacturer picker. If you do the following, what output do you get? With the old schema (what version of Umbraco/schema are you using?):

Manu: <xsl:copy-of select="./data[@alias='manufacturer']"/><br/>

new schema:

Manu: <xsl:copy-of select="./manufacturer"/><br/>

Richard

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