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How does MongoDB index arrays?
MongoDB indexes every value of an array so that you can query for single elements.
To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −
> db.indexingForArrayElementDemo.insertOne({"StudentFavouriteSubject":["MongoDB","MySQL"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8acdca6cea1f28b7aa0816")
}Display all documents from a collection with the help of find() method. The query is as follows −
> db.indexingForArrayElementDemo.find().pretty();
The following is the output −
{
"_id" : ObjectId("5c8acdca6cea1f28b7aa0816"),
"StudentFavouriteSubject" : [
"MongoDB",
"MySQL"
]
}Here is the query by which MongoDB index array &minus ;
> db.indexingForArrayElementDemo.ensureIndex({"StudentFavouriteSubject":1});The following is the output −
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}Here is the query for individual array elements −
> db.indexingForArrayElementDemo.find({"StudentFavouriteSubject":"MongoDB"}).pretty();The following is the output −
{
"_id" : ObjectId("5c8acdca6cea1f28b7aa0816"),
"StudentFavouriteSubject" : [
"MongoDB",
"MySQL"
]
}Let us see another example. The query is as follows −
> db.indexingForArrayElementDemo.find({"StudentFavouriteSubject":"MySQL"}).pretty();The following is the output −
{
"_id" : ObjectId("5c8acdca6cea1f28b7aa0816"),
"StudentFavouriteSubject" : [
"MongoDB",
"MySQL"
]
}
Updated on: 30-Jul-2019
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