Changing schemas in mongoDB/mongoose

Question

I am getting started with mongoDB and mongoose. I was wondering how people manage evolving schemas. For example if i started with a schema like this:

user_ID : 123,
user_firstName : 'bob',
user_lastName : 'smith'

And evolved it to something like this:

user_ID: 123,
user_name: [first:'bob', last:'smith']

How could I update or manage old records that were established using the old schema design?

Answer 1

One approach to migrating document schemas involving simple data transformations would be to use $exists to find documents that are missing the new fields and migrate them.

For example, transforming firstName and lastName into a new user_name field:

db.mycollection.find( { user_name : { $exists : false } } ).forEach(
    function (doc) {
        doc.user_name = {'first': doc.user_firstName, 'last': doc.user_lastName};

        // Remove old properties
        delete doc.user_firstName;
        delete doc.user_lastName;

        // Save the updated document
        db.mycollection.save(doc);
    }
)

For more complex migrations some tools that could be helpful are:

• schema.js or variety for analyzing the current schema of a collection
• JSV: JSON Schema Validator for validating documents