I am aware of [Collation](https://docs.mongodb.com/manual/reference/collation/) in mongodb but can't use it since our production isn't running at 3.4

Having said that, my only other option is using [$toLower](https://docs.mongodb.com/manual/reference/operator/aggregation/toLower/) aggregation pipeline in combination with sort.

The parent table is **User** and each user has a role reference in **Role** model.

```
User: _id: 123, role_id: 'role_1', name: 'Jai'
Role: _id: 'role_1', name: 'Role One'

```

My query looks like this, but i can't even get the projection working:

```
> db.User.aggregate([{'$lookup': {"from": "Role", "localField": "role", "foreignField": "_id", "as": "role"}}, {'$project': {'role_lower': {'$toLower': '$role.name'}}}]).pretty()

```

Getting error: *"can't convert from BSON type array to String"*

Am i doing something wrong or its not achievable?