Migrating from 3.x to 4.x
There are several backwards-breaking changes to be aware of when migrating from Mongoose 3 to Mongoose 4.
`findOneAndUpdate()` new field is now `false` by default
Mongoose's findOneAndUpdate(), findOneAndRemove(),
findByIdAndUpdate(), and findByIdAndRemove() functions are just
wrappers around MongoDB's
findAndModify command.
Both the MongoDB server and the MongoDB NodeJS driver set the new option
to false by default, but mongoose 3 overwrote this default. In order to be
more consistent with the MongoDB server's documentation, mongoose will
use false by default. That is,
findOneAndUpdate({}, { $set: { test: 1 } }, callback); will return the
document as it was before the $set operation was applied.
To return the document with modifications made on the update, use the new: true option.
MyModel.findOneAndUpdate({}, { $set: { test: 1 } }, { new: true }, callback);CastError and ValidationError now use kind instead of type to report error types
In Mongoose 3, CastError and ValidationError had a type field. For instance, user defined validation errors would have a type property that contained the string 'user defined'. In Mongoose 4, this property has been renamed to kind due to the V8 JavaScript engine using the Error.type property internally.
Query now has a `.then()` function
In mongoose 3, you needed to call .exec() on a query chain to get a
promise back, like MyModel.find().exec().then();. Mongoose 4 queries are
promises, so you can do MyModel.find().then() instead. Be careful if
you're using functions like
q's Q.ninvoke() or
otherwise returning a mongoose query from a promise.
More Info
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