How to use array operators in MongoDB to filter data
MongoDB provides array operators to perform different queries on the arrays. There are three array operators:
$all$size$elemMatch
Let's perform different logical operators on the following database, named educative, with a collection named courses.
use educative //selecting our databasedb.courses.find({}) //showing all the documents of "courses"[{ _id: 10, course_name: 'python', hours: [10,14,20] },{ _id: 11, course_name: 'C++', hours: [10,15] },{ _id: 12, course_name: 'java', hours: [10,11,12] }]
{<field>:{$all: [ <value1> , <value2> ... ]}}
Example
An example of the $all operator is given below:
//querydb.courses.find({"hours": { $all: [10, 11]}}).pretty()//output[ { _id: 12, course_name: 'java', hours: [ 10, 11, 12 ] } ]
As we can see, the $all operator returns only those hours values that have both values 10 and 11.
Note: The
$alloperator is equivalent to an$andoperation of the specified values.
The $size operator
This operator is used to find the documents with an array field whose size equals the specified size in a query clause.
Syntax
Here's the syntax of the $size operator:
{<field>:{$size: value}}
Example
An example of the $size operator is given below:
//querydb.courses.find({ "hours": { $size: 3}}).pretty()//output[{ _id: 10, course_name: 'python', hours: [ 10, 14, 20 ] },{ _id: 12, course_name: 'java', hours: [ 10, 11, 12 ] }]
As we can see, the $size operator returns only those hours values that have three elements.
The $elemMatch operator
The $elemMatch operator matches documents with an array field with at least one element that satisfies all the specified query criteria.
Syntax
Here's the syntax of $elemMatch operator:
{<field>:{$elemMatch:{<query1>, <query2>, ...}}}
Example
An example of the $elemMatch operator is given below:
//querydb.courses.find({ "hours": { $elemMatch: {$gte: 11, $lt: 15}}}).pretty()//output[{ _id: 10, course_name: 'python', hours: [ 10, 14, 20 ] },{ _id: 12, course_name: 'java', hours: [ 10, 11, 12 ] }]
As we can see, the $elemMatch query in the example returns only those hours values that are greater than or equal to 11 and less than 15.
Run your queries
You can run all the aforementioned MongoDB queries in the terminal below:
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