Using repeater to show content from same category as parent page

For something like this I set a category on the parent in a separate field (not the normal category setup) and then set the repeater's category with a macro. For instance, /Page-A I add a text field called PageCategory and set the control to a single category selector. Then in the repeater on /Page-A I set the category with macro {%PageCategory%}.

Seems sometimes redundant but it works well and doesn't require a complex WHERE statement.

You can use where clause for the query and use the LIMIT attribute to limit the no of results without specifying in the query.

I also do something similar as Brenden. I will tie PageCategory to my page type and use it as a filter for where clause and use LIMIT to restrict results.

You have a document of type A with categories from parent and you want to show document of type B with matching categories. You can use repeater with a custom query, create a query something like:

select DocumentName, DocumentURLPath, CategoryID, * from View_Type_B_Joined vw join cms_documentCategory dc on vw.DocumentID =  dc.documentid
where ##WHERE##  and published = 1

And then in WHERE property of web part you put macro CategoryID in ({% String.Join(",",CurrentDocument.Parent.Categories.IDs)) |(identity)GlobalAdministrator%}) It is much faster, no DB call. Make sure your check 'Search on each page load' property

Keep in mind using a specific page type's view AND published = 1 in your WHERE clause will not work in version 9 and newer as the specific views for page types were removed and so was the published flag.