Update PostgresStorageAdapter.js (#2094)

this isn't just a simplification, but also fixing a bug: the result of `count(*)` is always returned as a string that needs conversion, not as a number, because it is 64-bit, and all 64-bit numbers are returned as strings. So, the previous `=== 0` would have never worked.

Author: vitaly-t

src/Adapters/Storage/Postgres/PostgresStorageAdapter.js

@@ -286,12 +286,12 @@ export class PostgresStorageAdapter {
   // If no objects match, reject with OBJECT_NOT_FOUND. If objects are found and deleted, resolve with undefined.
   // If there is some other error, reject with INTERNAL_SERVER_ERROR.
   deleteObjectsByQuery(className, schema, query) {
-    return this._client.query(`WITH deleted AS (DELETE FROM $<className:name> RETURNING *) SELECT count(*) FROM deleted`, { className })
-    .then(result => {
-      if (result[0].count === 0) {
+    return this._client.one(`WITH deleted AS (DELETE FROM $<className:name> RETURNING *) SELECT count(*) FROM deleted`, { className }, res=>parseInt(res.count))
+    .then(count => {
+      if (count === 0) {
         throw new Parse.Error(Parse.Error.OBJECT_NOT_FOUND, 'Object not found.');
       } else {
-        return result[0].count;
+        return count;
       }
     });
   }