Re: Insert 'NULL' value in Postgres with Nim 0.19.1 without 'nil'

[ThomasTJdev]

**Second attempt (working)**
    
    
     # Custom object with predefined global null: dbNullVal
    # exec(db, sql"UPDATE myTable SET age = ? WHERE name = ?", dbNullVal, 
"John")
    
    # lib/impure/db_postgres.nim
    
    # __ New
    type
      ArgObj = object
        val: string
        isNull: bool
    
    var arg: ArgObj
    var dbNullVal*: ArgObj
    dbNullVal.isNull = true
    
    proc argType*(v: ArgObj): ArgObj =
      return dbNullVal
    
    proc argType*(v: string | int): ArgObj =
      arg.val = $v
      arg.isNull = false
      return arg
    
    # __ Changes to existing
    proc dbFormat[T](formatstr: SqlQuery, args: varargs[T, argType]): string =
      # varargs[string, `$`] => varargs[T, argType]
      result = ""
      var a = 0
      if args.len > 0 and not string(formatstr).contains("?"):
        dbError("""parameter substitution expects "?" """)
      if args.len == 0:
        return string(formatstr)
      else:
        for c in items(string(formatstr)):
          if c == '?':
            # Check bool on arg
            if args[a].isNull:
              add(result, "NULL")
            else:
              # Use args.val instead
              add(result, dbQuote(args[a].val))
            inc(a)
          else:
            add(result, c)
    
    # varargs[string, `$`] for all is just replaced with varargs[T, argType]
    proc exec*[T](db: DbConn, query: SqlQuery, args: varargs[T, argType]) {.
      tags: [ReadDbEffect, WriteDbEffect].} =
      ## executes the query and raises EDB if not successful.
      var res = pqexecParams(db, dbFormat(query, args), 0, nil, nil,
                            nil, nil, 0)
      if pqresultStatus(res) != PGRES_COMMAND_OK: dbError(db)
      pqclear(res)
    
    
    Run