MongoDB Basics III - Querying MongoDB

MongoDB provides various methods for querying data. Note that they are case-sensitive and need to be called exactly as written below

Query Method	Description
db.collection.find()	Performs a query on a collection and returns a cursor object.
db.collection.findAndModify()	Atomically modifies and returns a single document.
db.collection.findOne()	Performs a query and returns a single document ... the first one found by natural search order.
db.collection.findOneAndDelete()	Finds a single document and deletes it.
db.collection.findOneAndReplace()	Finds a single document and replaces it.
db.collection.findOneAndUpdate()	Finds a single document and updates it.

db.collection.find( <filter>, <projection> )

This is the basic method of querying data.
Filter and Projection are optional documents that modify the query.
Filter uses key:value pairs to restrict the Documents returned and Projection uses flagged fields to restrict the Fields returned (aka projected)

db.clients.find({ name: { last: "Musterman", first: "Max" }})
This will return all the Documents from the clients Collection with first name Max and last name Musterman

db.orders.find({ value $gt 1000 }, { company: 1, _id: 0})
This will return just the company Field for all orders valued over 1000 in the orders Collection. 1 switches a column on and 0 switches it off. The _id field must be specifically excluded

Various operators can be used. ':' means equality, but we can also use $eq

Name	Description
$eq	Matches values that are equal to a specified value.
$gt	Matches values that are greater than a specified value.
$gte	Matches values that are greater than or equal to a specified value.
$lt	Matches values that are less than a specified value.
$lte	Matches values that are less than or equal to a specified value.
$ne	Matches all values that are not equal to a specified value.
$in	Matches any of the values specified in an array.
$nin	Matches none of the values specified in an array.
$or	Joins query clauses with a logical OR returns all documents that match the conditions of either clause.
$and	Joins query clauses with a logical AND returns all documents that match the conditions of both clauses.
$not	Inverts the effect of a query expression and returns documents that do not match the query expression.
$nor	Joins query clauses with a logical NOR returns all documents that fail to match both clauses.
$exists	Matches documents that have the specified field.
$type	Selects documents if a field is of the specified type.
$mod	Performs a modulo operation on the value of a field and selects documents with a specified result.
$regex	Selects documents where values match a specified regular expression.
$text	Performs text search.
$where	Matches documents that satisfy a JavaScript expression.
$geoWithin	Selects geometries within a bounding GeoJSON geometry. The 2dsphere and 2d indexes support $geoWithin.
$geoIntersects	Selects geometries that intersect with a GeoJSON geometry. The 2dsphere index supports $geoIntersects.
$near	Returns geospatial objects in proximity to a point. Requires a geospatial index. The 2dsphere and 2d indexes support $near.
$nearSphere	Returns geospatial objects in proximity to a point on a sphere. Requires a geospatial index. The 2dsphere and 2d indexes support $nearSphere.
$all	Matches arrays that contain all elements specified in the query.
$elemMatch	Selects documents if element in the array field matches all the specified $elemMatch conditions.
$size	Selects documents if the array field is a specified size.
$bitsAllSet	Matches numeric or binary values in which a set of bit positions all have a value of 1.
$bitsAnySet	Matches numeric or binary values in which any bit from a set of bit positions has a value of 1.
$bitsAllClear	Matches numeric or binary values in which a set of bit positions all have a value of 0.
$bitsAnyClear	Matches numeric or binary values in which any bit from a set of bit positions has a value of 0.
$comment	Adds a comment to a query predicate.
$	Projects the first element in an array that matches the query condition.
$elemMatch	Projects the first element in an array that matches the specified $elemMatch condition.
$meta	Projects the document’s score assigned during $text operation.
$slice	Limits the number of elements projected from an array. Supports skip and limit slices.

Output of find is a cursor, which can be modified with various additional methods.
For instance,
db.collection.find().pretty
will return the cursor results in an easy-to-read format