convex-backend PR 59: Improve .unique() error message: print document _ids (#35342)

Makes the error message thrown by `.unique()` more useful. The `_id`'s of the first two documents returned by the `unique()` query are printed in the error message. This is very helpful to the user in identifying and resolving incorrect data.

Feel free to change my wording in the error message - but in my opinion it should be clear that the document id's printed are *not* all the documents returned by the `unique()` query but just the first two.

I [built the Convex backend locally](https://github.com/get-convex/convex-backend/blob/ad552652f4aaa0225e977ed7f5d92a35108b85d4/BUILD.md), made this change locally, and ran the tutorial demo to verify that it works as expected.

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Co-authored-by: Jan Balin <[email protected]>
GitOrigin-RevId: 816362f3274acabe1440eda6c6d993a94160009e

Author: 2 people

Diff for: npm-packages/convex/src/server/impl/query_impl.ts

@@ -326,7 +326,8 @@ export class QueryImpl implements Query<GenericTableInfo> {
       return null;
     }
     if (first_two_array.length === 2) {
-      throw new Error("unique() query returned more than one result");
+      throw new Error(`unique() query returned more than one result: 
+ [${first_two_array[0]._id}, ${first_two_array[1]._id}, ...]`);
     }
     return first_two_array[0];
   }