CODEWITHSUNDEEP
mongodbdatabase-designmeteor
Steve Ross
Steve Ross

Reputation: 4144

Meteor: Relating Items

I'm using Meteor and MongoDB, as suggested by the documentation. Coming from a relational database background, I want to understand strategies for modeling data in NOSQL stores.

The scenario is I have users, and each user has one vin. All pretty standard and possible with one collection. But if I want to find the highest vin to display some anonymous information about the most recently purchased car, do I just construct a find like:

Users.find({}, sort: {vin_number: -1})

or is there a better way to model it? What if a given user has more than one vin? In a relational world, that's a "has many" relationship. But if I embed an array of vins in a user document, how could I extract the highest number.

As you can see, I am wrestling with the fundamental shift from modeling things as tables to embedded documents.

Any help is appreciated, and (although I know it's not the SO way) I'd love any pointers to places for a gentle migration from the relational modeling patterns to schema-less ones.

Upvotes: 1

Views: 275

Answers (2)

Denis
Denis

Reputation: 7343

For array fields you can use instruction $unwind at aggregation framework. It create different items from your one and you can easily filtrate it as usual.

Aggregation framework

For example you have item similar to this one:

{_id: 'KJDKDSJKSJDK', type: 'car', manufacturer: 'opel', model: 'vectra', vins: [1234,5678]}

unwind will create two new items for this projection:

{_id: 'KJDKDSJKSJDK', type: 'car', manufacturer: 'opel', model: 'vectra', vins: 1234}

{_id: 'KJDKDSJKSJDK', type: 'car', manufacturer: 'opel', model: 'vectra', vins: 5678}

As you can see array field changed to int.

Upvotes: 1

Tarang
Tarang

Reputation: 75945

You could use a transform to get the highest vin from the list of vins:

Users.find({}, {sort: {vin_number: -1}, transform: function(doc) {
    doc.vin_number = _.max(doc.vin_number_array);
    return doc;
}})

I've never tried this, i'm a bit unsure of whether the transform or the sort comes first. But if you had an array of vin numbers in vin_number_array in your document, the vin_number would end up as the highest of those using underscore's max function.

Upvotes: 1

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