add a beforeCount hook

[matthewheck]

This provides a solution to #4683. This provides a beforeCount hook to the count query, allowing for the user to change the options of count before the database is queried.

I attempted to add an afterCount hook but, because the count is not attached to the model itself, changing it after the database return would require more substantial (probably breaking) changes. Additionally, can't think of a good use case for changing the count after we have queried the database.

Long time user, first time contributor. Hoping to give back more to this great community!

[mickhansen]

You can clean up assertions a bit by using stuff like:

return expect(this.User.count({where: {username: 'joe'}})).to.eventually.equal(1);
return expect(this.User.count({where: {username: 'joe'}})).to.be.rejectedWith('Oops!');

[matthewheck]

Thanks for the tip. Clean up done!

[mickhansen]

LGTM, @janmeier?

[janmeier]

Yep, LGTM as well - thanks a lot @matthewheck , and sorry for leaving you waiting for so long

[emersonmsantos7]

BeforeCount is not in the documentation: http://docs.sequelizejs.com/en/v3/api/hooks/

[josephgrossberg]

Update: still no mention in the docs http://docs.sequelizejs.com/

This is a cool feature that merits documenting. How can I help? ping @sdepold

[aat2703]

Why not just firing beforeFind hook? It seems odd