dropCollection不会删除集合

Question

mongoose 4.0.3
node 0.10.22
mongod db version 3.0.1

I'm trying to drop a collection using moongoose, but it isn't working

run: function() {
    return Q(mongoose.connect('mongodb://127.0.0.1:27017/test',opts))
    .then(function(data){
        return Q(mongoose.connection.db.dropCollection('departments'))
        .then(function(data2){
            console.log('data2 is ',data2);
            return Q(true);
        }).catch(function(err){
            console.log('err is',err);
            return Q(false);
        });
    }).catch(function(err){
        console.log('err is', err);
        return Q(false);
    });
}

This returns data2 is undefined

I tried to follow the answers based on this question : Mongoose.js: remove collection or DB

Answer 1

I think you misunderstand the way mongoose, db and Q can interact.

you can try (not tested)

run: function() {
  return Q(mongoose.connect('mongodb://127.0.0.1:27017/test',opts).exec())
  .then(function(){
    var db = mongoose.connection.db;
    var drop = Q.nbind(db.dropCollection, db);
    return drop('departments')
           .then(function(data2){
             console.log('data2 is ',data2);
             return true;
            }).catch(function(err){
             console.log('err is',err);
             return false;
             });
}).catch(function(err){
    console.log('err is', err);
    return false;
});

}

a mongoose function needs to be called with exec() in order to return a Promise.

this does not extend to the dropCollection method as far as I know so you need to de-nodeify it.

Answer 2

I don't think you can use Q this way.

Q() turns anything you pass to it into a promise. When you pass in a function call the way you do it, you effectively pass in that function's return value. In other words, just like Q(3) will resolve to 3 , Q(nodefunc(args)) will resolve to whatever nodefunc(args) returns - and in case of asynchronous functions that isn't particularly much.

I suppose you want to use ninvoke (aka nsend ) instead.

Q.ninvoke(object, methodName, ...args)

Alias: Q.nsend

Calls a Node.js-style method with the given variadic arguments, returning a promise that is fulfilled if the method calls back with a result, or rejected if it calls back with an error (or throws one synchronously).

The mongoose API docs say that connect is a synchronous method that returns nothing. Its close cousin createConnection will return a connection object and might be a better fit for the use case.

The following code has both - a call to Q for a synchronous method that returns an actual value, and a call to Q.nsend for an asynchronous method that works with callbacks.

run: function() {
    return Q(mongoose.createConnection('mongodb://127.0.0.1:27017/test', opts))
    .then(function(connection){
        return Q.nsend(connection.db, 'dropCollection', 'departments')
        .then(function(data){
            console.log('data is ', data);
            return data;
        });
    }).catch(function(err){
        console.log('err is', err);
    });
}

(untested code)