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Select documents: find(), pretty(), count(), distinct()

We use find() to get all fields from all documents (and pretty() to return data in a format that is easier for humans to parse):

> db.movies.find().pretty()

We use projections when we want to retrieve only some fields. In the following code, first query returns _id and title, as _id is always returned unless explicitly excluded. Second query returns only title as _id has been explicitly excluded. Third query returns all fields except the three explicitly excluded.

> db.movies.find({}, {title: 1})
> db.movies.find({}, {title: 1, _id: 0})
> db.movies.find({}, {_id: 0, cast: 0, plot: 0})

We use distinct() to get all distinct values for a field in a collection:

> db.movies.distinct("year")

We specify filtering criteria using standard JSON notation:

> db.movies.find({mpaaRating: "PG-13", year: 2009}).pretty()

When dealing with arrays (in this example, the cast field), we may want a total coincidence (all elements in the exact same order):

> db.movies.find({cast: ["Jeff Bridges", "Tim Robbins"]})

Or we may want to be sure the array contains one specific element (maybe among others):

> db.movies.find({cast: "Jeff Bridges"})

We could also want the array to contain one specific element in one exact position (again, we don't care about other elements in the array):

> db.movies.find({"cast.0": "Jeff Bridges"})

Some examples of filters using operators:

{"birth year": {$gte: 1965, $lt: 1970}}
{coordinates: {$geoWithin: {$centerSphere: [[-117.1747, 52.6871], 0.6951]}}}

Finally, we use count() to know how many documents match all our filters:

> db.movies.find({"awards.wins": 2, "awards.nominations": 6}).count()
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