REST + SharePoint Online: Update Single User Lookup Field to null

Question

I'm using Javascript to update my fields in a SharePoint list via Rest requests.

I have several columns in my list representing different people (some multiple people columns, some single).

When updating a multiple-user type column, I have no problem passing back an array of the ID's I want in the array to update. If I want to remove all of the people, I simply post an empty array in the column and the field is essentially null.

This works well with an option list with multiple users:

//Note, this is inside a function that gives me the "ThisPhase", "ControlToUpdate" and "ThisColumn" objects.
var UsersSelected = [];  //this is the array we save back to sharepoint for the current column we're editing.
var UserNames = "";  // this is the text we save to the log
var UsersData = []; // this is the data we put back in the row for the redraw of the table

$('#CURRENT_USER_LIST option').each(function(){
    UsersSelected.push(parseInt($(this).val()));
    UserNames += $(this).text() + ", ";
    UsersData.push({
        Id: parseInt($(this).val()),
        Title: $(this).text()
    });
});

var ItemProperties = {};

ItemProperties[ThisColumn] = {
    'results': UsersSelected
};

if(UsersSelected.length > 0){
    //we have at least one user assigned
    ThisPhase[ThisColumn] = {
        "results": UsersSelected
    };
}
else{
    //nobody assigned
    ThisPhase[ThisColumn] = {
        "results": null
    };
};

updateListItem(_spPageContextInfo.webAbsoluteUrl,'PROJECT%20PHASES',ThisPhase.Id,ItemProperties,
    function(data){//successfully updated.
        if(UsersData.length > 0){
            UserNames = "";
            for (var c = 0; c < UsersData.length; c++) {
                UserNames += UsersData[c].Title + (UsersData.length > c+1 ? ", ": "");
            };
        };

        $(ControlToUpdate).html(UserNames);

    },logError);

The problem comes when I attempt to pass a null value back on a single user column. when I pass a null value into the "ThisColumn" (which is a single user column):

var UserSelected = 0;  //this is the array we save back to sharepoint.
var UserName = "";  // this is the text we save to the user log
var UsersData; // this is the data we put back in the row for the redraw of the table

UserSelected = $('#SINGLE_NEW_USER_LIST').val() || null;
UserName = UserSelected ? $('#SINGLE_NEW_USER_LIST :selected').text() : "";
UserData = {
    Title: UserName
};

var ItemProperties = {};
ItemProperties[ThisColumn] = UserSelected;

updateListItem(_spPageContextInfo.webAbsoluteUrl,'PROJECT%20PHASES',ThisPhase.Id,ItemProperties,
    function(data){ //successfully added information
        ThisPhase[ThisColumn] = UserSelected;

        UserName = UserSelected ? UserName : "[CLICK TO ADD "+ColumnToDisplayText+"]";

        $(ControlToUpdate).html(UserName);
    },
    function(err){
        console.log(err);
    }
);

I get the following error back from SharePoint :

"Cannot convert a primitive value to the expected type 'Edm.Int32'. See the inner exception for more details."

I've been searching for quite a while, but I can't seem to find any answers on how to use a POST request to REMOVE an ID from a Single-user field in SharePoint .

Any help would be much appreciated.

Answer 1

Make sure the user field value is specified as <FieldName>Id: null in request, for example:

url: <webUrl>/_api/web/lists/getbytitle('<listTitle>')/items(<itemId>)  
method: POST
headers:
      "X-HTTP-Method": "MERGE",
      "If-Match": "*"
body: {
       "__metadata": { "type": "SP.Data.TasksListItem" },
       "ApproverId": null
      }

where

ApproverId corresponds to single-user field named Assigned

---

Assume a Tasks list with single-user field named Assigned, then the following example demonstrates how to remove its value:

var listTitle = "Tasks";
var itemProperties = {
    '__metadata': { "type": "SP.Data.TasksListItem" },
    "AssignedToId": null
};
var itemId = 1;
var webUrl = _spPageContextInfo.webServerRelativeUrl;


updateListItem(webUrl,listTitle,itemId,itemProperties)
.done(function(item)
{
    console.log('List item has been updated');
})
.fail(function(error){
    console.log(JSON.stringify(error));
});

where

function executeJson(options) 
{
    var headers = options.headers || {};
    var method = options.method || "GET";
    headers["Accept"] = "application/json;odata=verbose";
    if(options.method == "POST") {
        headers["X-RequestDigest"] = $("#__REQUESTDIGEST").val();
    }   

    var ajaxOptions = 
    {       
       url: options.url,   
       type: method,  
       contentType: "application/json;odata=verbose",
       headers: headers
    };
    if("data" in options) {
      ajaxOptions.data = JSON.stringify(options.data);
    }  

    return $.ajax(ajaxOptions);
}


function updateListItem(webUrl,listTitle,itemId,itemPayload)
{
     var options ={
        url: webUrl + "/_api/web/lists/getbytitle('" + listTitle + "')/items(" + itemId + ")",  
        method: "POST",
        headers : {
         "X-HTTP-Method": "MERGE",
          "If-Match": "*"
        },
        data: itemPayload    
     };     
     return executeJson(options);
}

Answer 2

I figured out the fix.

Rather than posting a null value to the id field, set the field to zero.

ItemProperties = {
    AssignedToId: 0
}