When we need to use $And in MongoDb Query?

 By default, MongoDb has the $and operator in find query. 

For example of this:

db.products.find({$and: [{name:"Mazda 3"}, {manufacturer:"Mazda"}]});

You can shortcut to:

db.products.find({name:"Mazda 3", manufacturer:"Mazda"});

So why still $and operator?

MongoDb builds using Javascript engine, when you search the same fields, the last search criteria will overwrite all. For example below

db.products.find({parts:"Seats", parts:"Doors"});

is equivalent to

db.products.find({parts:"Doors"});

The correct way to search the same fields is using $and operator.

db.products.find({$and:[{parts:"Seats"}, {parts:"Doors"}]});