Add case insensitive indexes support

[angfal]

Description

MongoDB allows to create and search by case insensitive indexes. The problem to support this feature it's required to execute separate "collation" function for a MongoDB cursor which is hidden by loopback and no way to receive access to it. As the result, no a reasonable way somehow wrap loopback functions to use such functionality via loopback.

Ideally, it would be great to add the support of this parameter for loopback MongoDB connector. For example using filter:

Model.find({
    where: {...}, 
    collation: {
        locale : <locale>,
        strength : <strength>
    }
});

// mongodb.js:
MongoDB.prototype.all = function all(model, filter, options, callback) {
    ...
    function processResponse(err, cursor) {
        ...
       if (filter.collation) {
           cursor.collation(filter.collation)
       }
        ...
    }
}

or using options (to not corrupt filter schema which common for all datasource)

Model.find({where: {...}}, {
    collation: {
        locale : <locale>,
        strength : <strength>
    }
});

Links:

• https://docs.mongodb.com/manual/core/index-case-insensitive

[kjdelisle]

@angfal Pull requests are welcome. My experience with mongodb is somewhat limited, though your 2nd proposal sounds solid to me. If you're willing to make a PR with test coverage, I'll review it and help you land it. :)

[angfal]

@kjdelisle Great! I will make the required fixes

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[angfal]

Please, somebody review my pr

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[angfal]

Additional info in the PR

[barocsi]

ok so how to use it within a query?

[ryan-open]

@barocsi https://github.com/strongloop/loopback-connector-mongodb/blob/260733d21e6d9cf73947c3dc08a53e650f37f766/test/mongodb.test.js#L2714