スキーマの重大な変更の実施

use "<database-name>" // switch the current db to the db that the Task collection is stored in
collection = db.Task;
collection.aggregate([
  { $match: {} }, // match all documents in the Task collection
  {
    $addFields: { // transform the data
      _id: { $toString: "$_id" }, // change the _id field of the data to a string type
    },
  },
  { $out: "TaskV2" }, // output the data to a partner collection, TaskV2
]);

exports = function (changeEvent) {
  const db = context.services.get("mongodb-atlas").db("ExampleDB");
  const collection = db.collection("Task");
  // If the event type is "invalidate", the next const throws an error.
  // Return early to avoid this.
  if (!changeEvent.documentKey) { return; }
  // The changed document's _id as an integer:
  const changedDocId = changeEvent.documentKey._id;
  // If a document in the Task collection has been deleted, 
  // delete the equivalent object in the TaskV2 collection:
  if (changeEvent.operationType === "delete") {
    const tasksV2Collection = db.collection("TaskV2");
    // Convert the deleted document's _id to a string value 
    // to match TaskV2's schema:
    const deletedDocumentID = changedDocId.toString();
    return tasksV2Collection.deleteOne({ _id: deletedDocumentID })
  }
  // A document in the Task collection has been created, 
  // modified, or replaced, so create a pipeline to handle the change:
  const pipeline = [
    // Find the changed document data in the Task collection:
    { $match: { _id: changeEvent.documentKey._id } },
    {
      // Transform the document by changing the _id field to a string:
      $addFields: {
        _id: { $toString: "$_id" },
      },
    },
    // Insert the document into TaskV2, using the $merge operator 
    // to avoid overwriting the existing data in TaskV2:
    { $merge: "TaskV2" }]
  return collection.aggregate(pipeline);
};

exports = function (changeEvent) {
  const db = context.services.get("mongodb-atlas").db("ExampleDB");
  const collection = db.collection("TaskV2");
  // If the event type is "invalidate", the next const throws an error.
  // Return early to avoid this.
  if (!changeEvent.documentKey) { return; }
  // The changed document's _id as a string:
  const changedDocId = changeEvent.documentKey._id;
  // If a document in the TaskV2 collection has been deleted, 
  // delete the equivalent object in the Task collection
  if (changeEvent.operationType === "delete") {
    const taskCollection = db.collection("Task");
    // Convert the deleted document's _id to an integer value
    // to match Task's schema:
    const deletedDocumentID = parseInt(changedDocId);
    return taskCollection.deleteOne({ _id: deletedDocumentID })
  }
  // A document in the Task collection has been created, 
  // modified, or replaced, so create a pipeline to handle the change:
  const pipeline = [
    // Find the changed document data in the Task collection
    { $match: { _id: changedDocId } },
    {
      // Transform the document by changing the _id field
      $addFields: {
        _id: { $toInt: "$_id" },
      },
    },
    { $merge: "Task" }
  ]
  return collection.aggregate(pipeline);
};