Why does using mongoose callback result in saving data twice?

问题

I have been wondering why adding a callback to the mongoose findOneAndUpdate function results in saving the data twice to the DB?

public async addPersonAsFavorite(userId: string, friendId: string) {
    if (!await this.isPersonAlreadyFriend(userId, friendId)) {
      const friendList = FriendsList.findOneAndUpdate(
        { _id: userId },
        { $push: { friendsList: friendId } },
        { upsert: true, new: true },
        (err, data) => {
         if (err) console.error(err);
         return data;
        }
      );
      return friendList;
    }}

  public async isPersonAlreadyFriend(userId: string, friendId: string) {
    let isFriendFound = false;
    await FriendsList.findById(userId, (err, data) => {
      if (data) {
        console.log(data.friendsList);
      }
      if (err) console.error(err);
      if (data && data.friendsList.indexOf(friendId) > -1) {
        isFriendFound = true;
        console.log('already friend');
      } else {
        console.log('not friend');
        isFriendFound = false;
      }
    })
    return isFriendFound;
  }

If i remove the callback, the data only gets saved once.

EDIT: added second piece of code and new question. If someone spams the button to add friend. The friend will be added multiple times because before the first friend is added and the check can be done to prevent this it has already added the person multiple times.

How can i make sure that it completes the write to the DB before allowing the function to be called again?

回答1:

Maybe the problem is in isPersonAlreadyFriend method, because you are trying to call it using async await but then you are passing a callback, what makes the method not return a promise. The rigth way to use promises with mongodb should be something like this:

public async isPersonAlreadyFriend(userId: string, friendId: string) {
    let isFriendFound = false;
    const data = await FriendsList.findById(userId);
    if (data) {
      console.log(data.friendsList);
    }
    if (data && data.friendsList.indexOf(friendId) > -1) {
      isFriendFound = true;
      console.log('already friend');
    } else {
      console.log('not friend');
      isFriendFound = false;
    }
    return isFriendFound;
  }

Try with this and let me know if it helps

来源：https://stackoverflow.com/questions/54195550/why-does-using-mongoose-callback-result-in-saving-data-twice

标签

javascript

mongodb

express

mongoose