Querying several MongoDb collections and performing the same operation

Question

I have two parameters I need to search my mongo collections on, say A and B. This query will return be guaranteed to return a result from one of the 3 collections, 'History', 'Current' or 'Draft'.

I want to find the collection that contains a record that matches parameters A and B, and use a promise to perform a task on that record regardless of which collection the data was found in

This is the singular version of the code:

app.models.Current.find(_id: ObjectId('A'), version: 'B').exec(function(err, current) {
    //Amend the record
    ...
})
.then(function() {
    //Do stuff with the new record
    ...
})

Is there a way of doing this without wrapping it in a giant if statement?

Tyler Kirby · Accepted Answer · 2017-03-24 20:19:15Z

I don't believe that you can query multiple collections in a single database call, but you can create a single promise that will resolve after the document is found in one of the three collections. It will be similar to the following:

let promise = new Promise(
   function(resolve, reject){
     app.models.Current.find(_id: ObjectId('A'), version: 'B')
        .exec(function(err,current) {
           //Amend the record
            ...
            // If record exists and was amended, resolve with that record.
            resolve(current);
         });

     app.models.History.find(_id: ObjectId('A'), version: 'B')
        .exec(function(err,history) {
           //Amend the record
            ...
            // If record exists and was amended, resolve with that record.
            resolve(history);
         });
     ...(repeat for other collections)...
   }
).then(function(record){
   //Do something with the amended record
}

Hope this helps!

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