mapreduce - How to do a cross join / cartesian product in RavenDB? -

i have web application uses ravendb on backend , allows user keep track of inventory. 3 entities in domain are:

public class location {     string id     string name  }  public class itemtype {     string id     string name }  public class item {     string id     denormalizedref<location> location     denormalizedref<itemtype> itemtype } 

on web app, there page user see summary breakdown of inventory have @ various locations. specifically, shows location name, item type name, , count of items.

the first approach took map/reduce index on inventoryitems:

this.map = inventoryitems =>     inventoryitem in inventoryitems     select new     {         locationname = inventoryitem.location.name,         itemtypename = inventoryitem.itemtype.name,         count = 1     });  this.reduce = indexentries =>     indexentry in indexentries     group indexentry new     {         indexentry.locationname,         indexentry.itemtypename,     } g     select new     {         g.key.locationname,         g.key.itemtypename,         count = g.sum(entry => entry.count),     }; 

that working fine displays rows location/itemtype pairs have non-zero count of items. need have show all locations , each location, item types don't have items associated them.

i've tried few different approaches no success far. thought turn above multi-map/reduce index , add map give me cartesian product of locations , itemtypes count of 0. feed reduce , have record every location/itemtype pair.

this.addmap<object>(docs =>     itemtype in docs.whereentityis<itemtype>("itemtypes")     location in docs.whereentityis<location>("locations")     select new     {         locationname = location.name,         itemtypename = itemtype.name,         count = 0     }); 

this isn't working though i'm thinking ravendb doesn't kind of mapping. there way cross join / cartesian product ravendb? alternatively, other way accomplish i'm trying do?

edit: clarify, locations, itemtypes, , items documents in system user of app creates. without items in system, if user enters 3 locations "london", "paris", , "berlin" along 2 itemtypes "desktop" , "laptop", expected result when @ inventory summary, see table so:

| location | item type | count | |----------|-----------|-------| | london   | desktop   | 0     | | london   | laptop    | 0     | | paris    | desktop   | 0     | | paris    | laptop    | 0     | | berlin   | desktop   | 0     | | berlin   | laptop    | 0     | 

here how can empty locations well:

addmap<inventoryitem>(inventoryitems =>     inventoryitem in inventoryitems     select new     {         locationname = inventoryitem.location.name,         items = new[]{             {                 itemtypename = inventoryitem.itemtype.name,                 count = 1}             }     }); )  this.addmap<location>(locations=>     location in locations     select new     {         locationname = location.name,         items = new object[0]     });   this.reduce = results =>      result in results     group result result.locationname g     select new     {         locationname = g.key,         items = item in g.selectmany(x=>x.items)                 group item item.itemtypename gi                 select new                 {                     itemtypename = gi.key,                     count = gi.sum(x=>x.count)                 }      };