Only the first sub-document added to MongoDB model

Question

I have a Mongoose model that looks like this:

var ProjectSchema = new Schema({
    name: String,
    slug: String,
    dateCreated: { type: Date, default: new Date() },
    dateUpdated: { type: Date, default: new Date() },
    createdByUserId: Schema.Types.ObjectId,
    screens: [Schema.Types.Mixed]
});

I have a class method that looks like this:

ProjectSchema.statics.saveElementProperties = function(slugName, screenIndex, elementId, props, callback) {
    var Project = mongoose.model('Project');

    var updateProject = function(project) {
        // Init empty objects if missing
        project.screens[screenIndex] = project.screens[screenIndex] || {};
        project.screens[screenIndex].elements = project.screens[screenIndex].elements || {};
        project.screens[screenIndex].elements[elementId] = project.screens[screenIndex].elements[elementId] || {};
        // Apply properties
        project.screens[screenIndex].elements[elementId] = "Dummy Project Data";
        console.log('elements before save:', project.screens[screenIndex].elements);
        project.save(callback);
    };

    Project.findOne({ slug: slugName }, function(err, project) {
        if (!project) {
            project = new Project({ name: slugName, slug: slugName });
        }
        updateProject(project);
    });
};

This happens when I call the method saveElementProperties:

1. The first time I run this method, it works like it should; a new object is added to project.screens[screenIndex].elements both in runtime (the 'elements before save:' log statement) and when checking the MongoDB database with the mongo client.
2. The second time, a 2nd object is added to project.screens[screenIndex].elements in runtime, but this object is never persisted to MongoDB.
3. The third time, object 1 and 3 are visible in project.screens[screenIndex].elements in runtime, but the 3rd object is never persisted to MongoDB.

What causes this behavior?

MAJOR UPDATE: I rewrote the entire persistence mechanism to run less frequently, and instead replace the entire project.screens[screenIndex].elements object with an updated structure:

ProjectSchema.statics.saveScreenProperties = function(slugName, screenIndex, elements, callback) {
    console.log('saveScreenProperties:', slugName, screenIndex);
    var Project = mongoose.model('Project');

    var updateProject = function(project) {
        // Init empty objects if missing
        project.screens[screenIndex] = project.screens[screenIndex] || {};
        project.screens[screenIndex].elements = elements;
        // Mark as modified and save
        project.markModified('screens.' + screenIndex);
        project.save(callback);
    };

    Project.findOne({ slug: slugName }, function(err, project) {
        if (!project) {
            project = new Project({ name: slugName, slug: slugName });
            console.log('  creating new project');
        }
        updateProject(project);
    });
};

However, it still shows the same behavior - it stores the initial elements object, but not later changes to it.

Answer 1

The problem is that you are manipulating the objects just as you would in standard code but mongoose is not a 'persistence engine` it's an ODM. As such you need to use the provided methods to update the datastore.

You will need to use the update operators to $push onto the array. Mongoose has some analogous methods as well. The most explainatory docs are on the MongoDB site.

http://docs.mongodb.org/manual/reference/operator/update-array/

http://docs.mongodb.org/manual/reference/operator/update/

http://docs.mongodb.org/manual/reference/method/db.collection.update/#db.collection.update