防止重复插入文档

Question

I'm building a web hook that will receive POST requests from Facebook. In each request, there's a facebookId field that will be used to insert a new record in database. facebookId should be unique in the database (meaning no two records should have the same facebookId ). The prototype code is something like this

postRequestHandler(req) {
  const facebookId = req.body.facebookId;
  if (!Meteor.users.findOne({ facebookId })) {
    Meteor.users.insert({ 
      facebookId,
      // some other fields
    })
  }    
}

The problem is, sometimes when there are many requests (yes, they have different meaning) containing the same new facebookId (which is not existed in the database) and they come almost at the same time . This will make the !Meteor.users.findOne({ facebookId }) check failed, and multiple records with same facebookId field will be inserted to the database. How do I prevent this ?

Answer 1

You should create a unique index on your facebookId field to have MongoDB guarantee uniqueness across your data and then add some exception handling code around your the callback that your insert call returns (documentation here ). You will need to judge based on your business requirements what the right exception handling code should look like.

Meteor.users.insert({ 
    facebookId,
    // some other fields
}, function(error, id) { 
    if ( error ) {
        /* add exception handling code here, e.g. return an error message to the client */
    } else {
        /* add code for successful case here, 'id' will be your newly inserted document's '_id' */
    }
});