Unable to retrieve Dictionary value when used in LINQ -

i trying update 'name' datacolumn based on 'id' datacolumn in datatable. 'id'-'name' pairs stored in dictionary, created using datatable extension method follows:

public static dictionary<object, object> todictionary(this datatable datatable, string keycolumn, string valuecolumn)     {         dictionary<object, object> resultdict = new dictionary<object, object>();          if (datatable.columns.contains(keycolumn) && datatable.columns.contains(valuecolumn))         {             foreach (datarow dr in datatable.rows)                 if (resultdict.containskey(dr[keycolumn]) == false)                     resultdict.add(dr[keycolumn], dr[valuecolumn]);         }          return resultdict;     } 

i using following linq syntax update datacolumn:

misuserdetailsdt.asenumerable().tolist().foreach(row => row.setfield("departmentname", deptdict[row["departmentid"]].tostring())); 

here 'misuserdetailsdt' datatable containing filled column 'departmentid' , empty column 'departmentname'-which trying update.

i have seperate method generates dictionary follows:

var deptdict = departmentdt.todictionary("deptid", "deptname"); 

where 'departmentdt' datatable containing columns 'deptid' , 'deptname'.

now when execute linq code give 'keynotfoundexception'. have thoroughly checked 'departmentdt' table 'deptdict' have keys(departmentids) 'misuserdetailsdt' table. 'departmentdt' has been generated distinct ids of 'misuserdetailsdt' table.

i think there issue figuring out appropriate type of dictionary keys. tried casting int16, didn't work out. please me figure out solution.

i have figured out problem. code works when dictionary values casted int32. @timschmelter giving useful info. changing code make use of foreach loop instead.