Question on Array.Sum() Method , generate a n*n matrix such that there is only one 1's in a coloumn

SystemVerilog
, ,
6 

class my_array;
  rand bit[4:0] array[4][4];
  int i,j;
  rand int n;
 
//This is first constraint limiting value of each item
constraint array_item_val   {     
  foreach  (array[i]) {       // for each row
    foreach (array[,j]) {     // for each column in array
      array[i][j] inside {[0:1]};  // each element is either 0/1
        }
      }
  }

      
constraint array_col_sum  {     
  foreach  (array[i,j]) {       
    array.sum() with (item.index(2) == j ? int'(item) : 0) == 1; // col max sum is 1
 	 }
  }
    
    
    function void display();
    foreach (array[i]) begin
      foreach (array[i][j]) begin
        $write("  %d  ",array[i][j]);
      end
      $display("\n");
    end
  endfunction
 
endclass
 
module my_array_randomization;
  my_array ma;
 
  initial begin
    ma = new();
    ma.randomize();
    ma.display();   
  end
 
endmodule

this should generate sum of elements in column to 1.