meteor bulk insert only inserts last item

Question

I am trying to do a bulk insert as in this method:

'createTestQuestionBatch'(limit) {
    check(limit, Number);

    if (Meteor.isServer) {
      const questionItem = {
        question: "Question will be reconstructed with a number",
        category: "n3f98f4b22v948nb4v2fg4b89",
        answer: ["Yes", "No", "Maybe", "Probably"],
        localization: "en",
        testQuestion: true,
      };

      var bulk = Question.rawCollection().initializeUnorderedBulkOp();

      for (var i = 0; i < limit; i++) {
        questionItem.question = "Is this test question number " + i + "?";
        bulk.insert(questionItem);
      }

      bulk.execute(function (err) {
        if (err) {
          throw new Meteor.Error('createTestQuestionBatch', 'Bulk update operation failed.' + err);
        } else {
          console.log("Bulk question creation operation completed. " + limit + " items has been inserted.");
        }
      });
    } else {
      console.log("Bulk operation for creating tests are running on the server. Server logs will notify when operation has completed.");
    }
  }

How come only item with number 99 gets inserted when trying to add 100 test questions? I'm running meteor 1.3.

Answer 1

The problem is that you are passing the same object to insert() across iterations.

The mongo driver does not clone the inserted document. instead, it generates an _id for it if one does not exist and adds it to its operations list.

The _id is only generated in the first iteration in your case, so MongoDB is basically instructed to insert 100 documents with the save _id . which results in only 1 actual document insertion.

To fix this, pass a fresh object in each iteration.