How to check if that data already exist in the database during update (Mongoose And Express)

Question

How to do validations before saving the edited data in mongoose?

For example, if sample.name already exists in the database, the user will receive a som

Answer 1

Typically you could use mongoose validation but since you need an async result (db query for existing names) and validators don't support promises (from what I can tell), you will need to create your own function and pass a callback. Here is an example:

var mongoose = require('mongoose'),
    Schema = mongoose.Schema,
    ObjectId = Schema.ObjectId;

mongoose.connect('mongodb://localhost/testDB');

var UserSchema = new Schema({
    name: {type:String}
});

var UserModel = mongoose.model('UserModel',UserSchema);

function updateUser(user,cb){
    UserModel.find({name : user.name}, function (err, docs) {
        if (docs.length){
            cb('Name exists already',null);
        }else{
            user.save(function(err){
                cb(err,user);
            });
        }
    });
}

UserModel.findById(req.param('sid'),function(err,existingUser){
   if (!err && existingUser){
       existingUser.name = 'Kevin';
       updateUser(existingUser,function(err2,user){
           if (err2 || !user){
               console.log('error updated user: ',err2);
           }else{
               console.log('user updated: ',user);
           }

       });
   } 
});

UPDATE: A better way

The pre hook seems to be a more natural place to stop the save:

UserSchema.pre('save', function (next) {
    var self = this;
    UserModel.find({name : self.name}, function (err, docs) {
        if (!docs.length){
            next();
        }else{                
            console.log('user exists: ',self.name);
            next(new Error("User exists!"));
        }
    });
}) ;

UPDATE 2: Async custom validators

It looks like mongoose supports async custom validators now so that would probably be the natural solution:

    var userSchema = new Schema({
      name: {
        type: String,
        validate: {
          validator: function(v, cb) {
            User.find({name: v}, function(err,docs){
               cb(docs.length == 0);
            });
          },
          message: 'User already exists!'
        }
      }
    });