title: Why does the `FetchMode` query property remove fields from the parent data source?
body: <p>When opening the query <code>SalesTableListPage</code> from the AOT, you can choose the field <code>MatchingAgreement</code> (shown as "Agreement Header record ID (Record-ID)") in the field lookup. The same is not possible for query <code>SalesUpdate</code>, field <code>MatchingAgreement</code> and several others (which seem to be related to relation fields where the relation is built with a RecId) are not shown in the lookup. </p>
  
  <p>After some research I found out that the reason seems to be the <code>FetchMode</code> property on the joined <code>SalesLine</code> data source. If it is 1:n, the fields are not shown in the lookup. If it is 1:1, the fields are shown in the lookup.</p>
  
  <p>I have not tested this with other tables, but I suspect the same behavior. I also have only tested this with AX 2012 R2 and R3, but I suspect the same behavior in other 2012 versions.</p>
  
  <p>Why does the <code>FetchMode</code> of a joined data source remove some fields from the parent data source in the query dialog?</p>