Clarified the comment on when PK is checked for autogen column property in UPSERT.

Author: seantleonard

DataGateway.Service/Services/RequestValidator.cs

@@ -217,7 +217,10 @@ public static void ValidateUpsertRequestContext(
 
             foreach (KeyValuePair<string, ColumnDefinition> column in tableDefinition.Columns)
             {
-                // Primary Key columns are validated separately.
+                // Primary Key(s) should not be present in the request body. We do not fail a request
+                // if a PK is autogenerated here, because an UPSERT request may only need to update a
+                // record. If an insert occurs on a table with autogenerated primary key,
+                // a database error will be returned.
                 if (tableDefinition.PrimaryKey.Contains(column.Key))
                 {
                     continue;