SQLSTATE[42S22]: Column not found: 1054 Unknown column '0' in 'field list'

I write a lumen code to update my table fields, this is my code -

$field='';
        if($request->input('category')){
            $val=$request->input('category');
            $field="'category' => '$val'";
        }
        if($request->input('subcategory')){
            $val=$request->input('subcategory');
            if($field==''){
                $field="'sub_category' => '$val'";
            }else{
                $field.=",'sub_category' => '$val'";
            }
        }
      // return $field;

        $Expence=DB::table('expencedetails')->where('id',$request->input('id'))->update(['$field']);

the value of $filed is 'category' => 'fgfg','sub_category' => 'ggg'.

when I run the code it shows an error SQLSTATE[42S22]: Column not found: 1054 Unknown column '0' in 'field list' (SQL: update expencedetails set 0 = $field where id = 1)

from Newest questions tagged laravel-5 - Stack Overflow http://ift.tt/2DWYJ5l
via IFTTT