Preserve nil <-> NULL between Nimrod and database.

lib/impure/db_mysql.nim

@@ -57,7 +57,7 @@ when false:
       binding: seq[MYSQL_BIND]
     discard mysql_stmt_close(stmt)
 
-proc dbQuote(s: string): string =
+proc dbQuote*(s: string): string =
   result = "'"
   for c in items(s):
     if c == '\'': add(result, "''")
@@ -69,6 +69,9 @@ proc dbFormat(formatstr: TSqlQuery, args: varargs[string]): string =
   var a = 0
   for c in items(string(formatstr)):
     if c == '?':
+      if args[a] == nil:
+        add(result, "NULL")
+      else:
         add(result, dbQuote(args[a]))
       inc(a)
     else: 
@@ -115,6 +118,9 @@ iterator fastRows*(db: TDbConn, query: TSqlQuery,
       if row == nil: break
       for i in 0..L-1: 
         setLen(result[i], 0)
+        if row[i] == nil:
+          result[i] = nil
+        else:
           add(result[i], row[i])
       yield result
     properFreeResult(sqlres, row)
@@ -132,6 +138,9 @@ proc getRow*(db: TDbConn, query: TSqlQuery,
     if row != nil: 
       for i in 0..L-1: 
         setLen(result[i], 0)
+        if row[i] == nil:
+          result[i] = nil
+        else:
           add(result[i], row[i])
     properFreeResult(sqlres, row)
 
@@ -150,7 +159,11 @@ proc getAllRows*(db: TDbConn, query: TSqlQuery,
       if row == nil: break
       setLen(result, j+1)
       newSeq(result[j], L)
-      for i in 0..L-1: result[j][i] = $row[i]
+      for i in 0..L-1:
+        if row[i] == nil:
+          result[j][i] = nil
+        else:
+          result[j][i] = $row[i]
       inc(j)
     mysql.FreeResult(sqlres)