db_postgres.getRow proc issues warning when SQL returns 0 rows

[chrisheller]

When calling getRow and no results are returned, postgres will issue a warning message to stderr : "row number 0 is out of range 0..-1". Other than the warning, there doesn't appear to be any problems caused by this, so its a minor issue.

let row = db.getRow(sql"select * from some_table where 1 = 2")
# "row number 0 is out of range 0..-1" printed to stderr

This is happening because setRow is called without checking if there are any rows returned. The following changes resolve the issue by calling pqntuples to check how many rows were returned.

--- /tmp/original_db_postgres.nim	2019-07-24 16:35:38.000000000 -0700
+++ /nim-0.20.0/lib/impure/db_postgres.nim	2019-07-24 16:36:44.000000000 -0700
@@ -392,7 +392,8 @@
   var res = setupQuery(db, query, args)
   var L = pqnfields(res)
   result = newRow(L)
-  setRow(res, result, 0, L)
+  if pqntuples(res) > 0:
+    setRow(res, result, 0, L)
   pqclear(res)
 
 proc getRow*(db: DbConn, stmtName: SqlPrepared,
@@ -400,7 +401,8 @@
   var res = setupQuery(db, stmtName, args)
   var L = pqNfields(res)
   result = newRow(L)
-  setRow(res, result, 0, L)
+  if pqntuples(res) > 0:
+    setRow(res, result, 0, L)
   pqClear(res)
 
 proc getAllRows*(db: DbConn, query: SqlQuery,

If no one sees any issues with that, I will make a pull request for this.