How to obtain User Field Properties in Lookup List via Rest Api

Question

I have a List (Topics) which has a MultiLookupField to a List named (Speakers)

Speakers has a User Field (UserName).

What I'm trying to do is to read some of the User Fields Properties. Which works when I'm querying the List with the User Field directly:

_api/web/getbytitle('Speaker')/items(1)?$select=UserName/Id&$expand=UserName

However I'm not able to get the User Field through the Topics list:

These are my desperate attempts which are all not working:

_api/web/lists/getbytitle('Topics')/items(1)?$select=Speakers/ID,Speakers/UserName&$expand=Speakers

_api/web/lists/getbytitle('Topics')/items(1)?$select=Speakers/ID,Speakers/UserNameId&$expand=Speakers

_api/web/lists/getbytitle('Topics')/items(1)?$select=Speakers/ID,Speakers/UserName/Id&$expand=Speakers,Speakers/UserName/Id

Edit:

I'm also facing the same behaviour when I'm trying to select Boolean or Choice Fields in the Lookup List.

Providing a little Image which should show my situation:

so for clarification my Topics List has a MultiLookup Column Speakers which is bound to the List Speakers. The List Speakers has some other fields and a User Field.

And I'm trying to expand some of the User's Field Properties through Rest.

Answer 1

Isn't possible expand lookup via Rest Api. Only for user(column default) and field with atribute Deferred.

But have solution for this:

loop items and get all items and selecting only the SpeakersID

_api/Web/Lists/GetByTitle('Topics')/items?$select=SpeakersId

will return as show image below:

but isn't suficient for get user info:

Update(2):

then you will use 2 rest api for your case.

_api/Web/Lists/GetByTitle('Topics')/items?$select=SpeakersId;
_api/Web/Lists/GetByTitle('Speakers')/items(n)?$select=UserName/Id,UserName/Title&$expand=UserName;

logic generic.

url="..../_api/Web/Lists/GetByTitle('Topics')/items?$select=SpeakersId";
call ajax....(sucess:getItems,...)
function getItems(data){
  var items = data.d.results; // array of items
  var item;
  for(var i =0;i<items.length;i++){
    item = items[i];
    speakers = item.SpeakersId.results;
    for(var j =0;j<speakers.length;j++){
      var LookupID_Speaker = speakers[j];
      var url = "_api/Web/Lists/GetByTitle('Speakers')/items("+LookupID_Speaker +")?$select=UserName/Id,UserName/Title&$expand=UserName";
      // set ajax async to false;
      call ajax....(sucess:getProperties,...)
    }
  }
}

function getProperties(data){
  var UserID = data.UserNameId;
  var UserTitle = data.Title;

  // do you code here.

}

Answer 2

The REST API doesn't seem to want to fetch the UserName field, try Name instead and you should get the value that's actually in UserName even though my User Information List has a field called Name with a different value in it.

I find Id works when proper cased, but not upper (so no ID)

Try this query:

_api/web/lists/getbytitle('Topics')/items(1)?
    $select=Speakers/Id,Speakers/Name&$expand=Speakers

This works with the standard "User Information List" fields for Users. It may not work the same on a customized list holding user information.