[mongodb] Collection.find() & .aggregate() cursor generics

[hinell]

Description

Featuring generics on the Cursor, AggregateCursor,
Collection.find() and Collection.aggregate() methods respectively.

Now we can do things like this:

interface USER{ _id: ObjectID; name: string;}
let users_col   = db.collection('col_name');
    users.find<USER>()        // Cursor returned
    .forEach(function(currentuser){
       console.log(user.name) // checking USER type
});

interface SUMMARY { id_: ObjectID,  total: number }
let payments = db.collection('payments');
    payments.aggregate<SUMMARY>() // AggregateCursor returned
    .toArray(function(err,sum){
      console.log(sum.total)
  })

Q: Why not to just declare the generic right on the db.collection() method and Collection interface as proposed by #13731?

Cause there are only a few methods that use the type that generic variable provides and also this would be sort of extra job creating mess and confusing users. So if you feel that you need another one extra generic-typed method like these one then just let me know.

Template

• Make your PR against the master branch.
• Use a meaningful title for the pull request. Include the name of the package modified.
• Test the change in your own code. (Compile and run.)
• Follow the advice from the readme.
• Avoid common mistakes.
• Run tsc without errors.
• Run npm run lint package-name if a tslint.json is present.

[dt-bot]

mongodb/index.d.ts

to author (@CaselIT). Could you review this PR?
👍 or 👎?

Checklist

• pass the Travis CI test?

[hinell]

Attention is needed guys. @CaselIT @beary

[CaselIT]

This will break backward compatibility.
As I mentioned #13731 (comment) I do not think there is a solution that maintains it until the issue microsoft/TypeScript#2175 is fixed.

If you want to use a typed version manually install it from the typings repo

typings i github:Think7/typings-mongodb#generics

[hinell]

@CaselIT

This will break backward compatibility.

You need to explain it more precisely and what the interface it will break exactly before considering pr to close.

[CaselIT]

If you used any of the classes that are now generic as a type annotation you will now have an error of the type error TS2314: Generic type '...' requires 1 type argument(s).

Example if you had:

let c: Cursor;

Typescript will not output error TS2314: Generic type 'Cursor' requires 1 type argument(s).

[hinell]

let c: Cursor;

Just use any type

let c: Cursor<any>;

Now NO backward compatibility is broken.

[CaselIT]

@hinell that is exactly the problem. If you have an existing project that uses the current definition that would break and you would need to go and modify all the types that are now generics.

[hinell]

@CaselIT
As you can see below travis show us no errros.
And meanwhile whoever need to use the Cursor type directly when it is already defined by collection.find<T>() method with T set to any by default?
Existing projects that depend on new interface won't have broke their compatibility if they use this method.

[CaselIT]

I'll let the maintainers decide.
I'm not for breaking existing code.

[hinell]

@CaselIT
It's fine but you have to show where the backward incompatibility is taking place before I consider this PR as useless.

Well guys what about if I'll extract generics into a separate interface?
upd: stupid idea

[bowdenk7]

@hinell Looks like there are some merge conflicts. Please refresh the PR so we can merge.

[hinell]

@bowdenk7 Here we go...

[aozgaa]

Please remove TODO.

[aozgaa]

Please remove comment.