Create Document with unique property in Mongoose

Question

Create Document with unique property in Mongoose

I'm trying to save a document with a unique property across the collection.

So if someone tries to save a kitten with {name: 'kitty'} and that name already exisits it fails and retries with {name: 'kitty1'} (then 'kitty2' etc).

I really can't figure out a good way to do this, any ideas?

Here's what I have so far (doesn't work).

var kittenSchema = new Schema ({
    name: {type: String, index: {unique: true}}
})

var Kitten = mongoose.model('Kitten', kittenSchema);

var kitten = new Kitten({
    name: 'kitty'
});

kitten.save(function(err, kitten){
    if (err){
        saveKitten(kitten, 1, function(err, kitten){
            if (err){
                console.log("Damn, no kitten");
            } else {
                console.log("New kitten " + kitten.name + "saved.");
            });
    } else {
        console.log("New kitten " + kitten.name + "saved.");
    }
}));

function saveKitten(kitten, count, callback){
    kitten.name = kitten.name + count;

    kitten.save(function(err, newKitten){
        if (err){
            if (count > 100){
                // Give up!
                callback(err, null);
            }

            saveKitten(kitten, count + 1, callback);
        } else {
            callback(null, newKitten);
        }
    }));
}

node.js
mongodb
mongoose

Answer 1

Your example almost works as is, but with a few typos and a scoping issue.

The first time you call kitten.save, your callback's argument is kitten. The problem is that the local kitten argument shadows the external kitten, and in the case of an error, the local kitten is undefined.

var kittenSchema = new mongoose.Schema ({
    name: {type: String, index: {unique: true}}
})

var Kitten = mongoose.model('Kitten', kittenSchema);

var kitten = new Kitten({
    name: 'kitty'
});

kitten.save(function(err, newKitten){
    if (err){
        saveKitten(kitten, 1, function(err, newKitten){
            if (err){
                console.log("Damn, no kitten");
            } else {
                console.log("New kitten " + newKitten.name + " saved.");
            }
        });
    } else {
        console.log("New kitten " + newKitten.name + " saved.");
    }
});

function saveKitten(kitten, count, callback){
    kitten.name = kitten.name + count;

    kitten.save(function(err, newKitten){
        if (err){
            if (count > 100){
                // Give up!
                callback(err, null);
            }

            saveKitten(kitten, count + 1, callback);
        } else {
            callback(null, newKitten);
        }
    });
}

Also note that the way you are using '+' here means this code will insert "kitten", "kitten1", "kitten12", "kitten123", etc.

Answer 2

After a pointer from NilsH I think I might try to pull back all possible name clashes and look for a new name locally.

Something like this:

var Kitten = mongoose.model('Kitten', kittenSchema);

var kitten = new Kitten({
    name: 'kitty'
});

Kitten.find({name: new RegExp('^'+ kitten.name +'*', "i")}, 'name').exec(function(err, docs){
    var tryName = name;
    var count = 0;

    while (True){
        if (_.indexOf(docs, tryName) != -1){
            break;
        } else {
            tryName = name + count;
        }
    }

    kitten.name = tryName;

    kitten.save(function(err, kitten){
        if (err){
            console.log("Damn, no kitten");
        } else {
            console.log("New kitten " + kitten.name + "saved.");
        }
    }));    
});

There's a possible race condition between finding the name and using it but I think I can live with that.