Folders first in paged results using CamlQuery and ListItemCollectionPosition

I'm implementing paging using CamlQuery and ListItemCollection, sorting results by the name field. I would like folders to come first, as they do in UI, e.g. "folder A2, folder B2, file A1, file B1", but instead I get "file A1, folder A2, file B1, folder B2".

What is the best way to accomplish such sorting and paging? Note that for paging I have to specify the value of the sorting field which will be the first record of the page – I've considered adding two sorting fields into CAML, but I'm not sure whether I can use two fields in ListItemCollectionPosition.PagingInfo.

The code I'm currently using is like this:

var queryText = @"
   <View> 
       <Query> 
           <OrderBy Override='TRUE'> 
               <FieldRef Name='FileLeafRef' Ascending='True' />
           </OrderBy> 
       </Query> 
           ...
       <RowLimit> 
           10
       </RowLimit> 
   </View>";
var camlQuery = new CamlQuery();
camlQuery.ViewXml = queryText;
camlQuery.ListItemCollectionPosition = new ListItemCollectionPosition
    {
        PagingInfo = "Paged=TRUE&p_ID=1002&p_FileLeafRef=A1"
    };
var items = list.GetItems(camlQuery);

Solution

For getting results sorted by object type you could utilize FSObjType property, for example the following CAML expressions tells server to return folder items first and then file items:

<OrderBy Override='TRUE'> 
     <FieldRef Name='FSObjType' Ascending='False' />
</OrderBy>

Regarding ListItemCollectionPosition.PagingInfo property, the following expression tells to return items that come after the item with ID specified via p_ID parameter and sorted by object type:

var camlQuery = new CamlQuery();
camlQuery.ListItemCollectionPosition = new ListItemCollectionPosition
{
   PagingInfo = "Paged=TRUE&p_FSObjType=1&p_ID=200"
};

Example

The following example returns 200 items:

with with ID starting from 100
and sorted by object type (folder items comes first)

Code:

var itemsCount = 200;
var startItemId = 100;

var queryText = @"
<View> 
   <Query> 
       <OrderBy Override='TRUE'> 
           <FieldRef Name='FSObjType' Ascending='False' />
       </OrderBy> 
   </Query> 
   <RowLimit> 
       {0}
   </RowLimit> 
</View>";

 var camlQuery = new CamlQuery
 {
       ViewXml = string.Format(queryText, itemsCount),
       ListItemCollectionPosition = new ListItemCollectionPosition
       {
           PagingInfo = $"Paged=TRUE&p_FSObjType=1&p_ID={startItemId - 1}"
       }
 };
 var items = list.GetItems(camlQuery);
 ctx.Load(items);
 ctx.ExecuteQuery();

Update

The example of PagingInfo expression for items to be sorted by type first and then by name:

Paged=TRUE&p_FSObjType=1&p_FileLeafRef=B2&p_ID=100