MongoDB - Advanced Indexing

We have inserted the following document in the collection named users as shown below −

db.users.insert(
	{
		"address": {
			"city": "Los Angeles",
			"state": "California",
			"pincode": "123"
		},
		"tags": [
			"music",
			"cricket",
			"blogs"
		],
		"name": "Tom Benzamin"
	}
)

The above document contains an address sub-document and a tags array.

Indexing Array Fields

Suppose we want to search user documents based on the user’s tags. For this, we will create an index on tags array in the collection.

Creating an index on array in turn creates separate index entries for each of its fields. So in our case when we create an index on tags array, separate indexes will be created for its values music, cricket and blogs.

To create an index on tags array, use the following code −

>db.users.createIndex({"tags":1})
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 2,
"numIndexesAfter" : 3,
"ok" : 1
}
>

After creating the index, we can search on the tags field of the collection like this −

> db.users.find({tags:"cricket"}).pretty()
{
	"_id" : ObjectId("5dd7c927f1dd4583e7103fdf"),
	"address" : {
		"city" : "Los Angeles",
		"state" : "California",
		"pincode" : "123"
	},
	"tags" : [
		"music",
		"cricket",
		"blogs"
	],
	"name" : "Tom Benzamin"
}
>

To verify that proper indexing is used, use the following explain command −

>db.users.find({tags:"cricket"}).explain()

This gives you the following result −

{
	"queryPlanner" : {
		"plannerVersion" : 1,
		"namespace" : "mydb.users",
		"indexFilterSet" : false,
		"parsedQuery" : {
			"tags" : {
				"$eq" : "cricket"
			}
		},
		"queryHash" : "9D3B61A7",
		"planCacheKey" : "04C9997B",
		"winningPlan" : {
			"stage" : "FETCH",
			"inputStage" : {
				"stage" : "IXSCAN",
				"keyPattern" : {
					"tags" : 1
				},
				"indexName" : "tags_1",
				"isMultiKey" : false,
				"multiKeyPaths" : {
					"tags" : [ ]
				},
				"isUnique" : false,
				"isSparse" : false,
				"isPartial" : false,
				"indexVersion" : 2,
				"direction" : "forward",
				"indexBounds" : {
					"tags" : [
						"[\"cricket\", \"cricket\"]"
					]
				}
			}
		},
		"rejectedPlans" : [ ]
	},
	"serverInfo" : {
		"host" : "Krishna",
		"port" : 27017,
		"version" : "4.2.1",
		"gitVersion" : "edf6d45851c0b9ee15548f0f847df141764a317e"
	},
	"ok" : 1
}
>

The above command resulted in "cursor" : "BtreeCursor tags_1" which confirms that proper indexing is used.

Indexing Sub-Document Fields

Suppose that we want to search documents based on city, state and pincode fields. Since all these fields are part of address sub-document field, we will create an index on all the fields of the sub-document.

For creating an index on all the three fields of the sub-document, use the following code −

>db.users.createIndex({"address.city":1,"address.state":1,"address.pincode":1})
{
	"numIndexesBefore" : 4,
	"numIndexesAfter" : 4,
	"note" : "all indexes already exist",
	"ok" : 1
}
>

Once the index is created, we can search for any of the sub-document fields utilizing this index as follows −

> db.users.find({"address.city":"Los Angeles"}).pretty()
{
	"_id" : ObjectId("5dd7c927f1dd4583e7103fdf"),
	"address" : {
		"city" : "Los Angeles",
		"state" : "California",
		"pincode" : "123"
	},
	"tags" : [
		"music",
		"cricket",
		"blogs"
	],
	"name" : "Tom Benzamin"
}

Remember that the query expression has to follow the order of the index specified. So the index created above would support the following queries −

>db.users.find({"address.city":"Los Angeles","address.state":"California"}).pretty()
{
	"_id" : ObjectId("5dd7c927f1dd4583e7103fdf"),
	"address" : {
		"city" : "Los Angeles",
		"state" : "California",
		"pincode" : "123"
	},
	"tags" : [
		"music",
		"cricket",
		"blogs"
	],
	"name" : "Tom Benzamin"
}
>

Comments

Post a Comment

Popular posts from this blog

Java : Variables Declaring

[1]. Java Variables Variables are containers for storing data values. In Java, there are different types of variables, for example: String - stores text, such as "Hello". String values are surrounded by double quotes int - stores integers (whole numbers), without decimals, such as 123 or -123 float - stores floating point numbers, with decimals, such as 19.99 or -19.99 char - stores single characters, such as 'a' or 'B'. Char values are surrounded by single quotes boolean - stores values with two states: true or false [2]. Declaring (Creating) Variables To create a variable, you must specify the type and assign it a value: Syntax type variable = value ; Where type is one of Java's types (such as int or String), and variable is the name of the variable (such as x or name). The equal sign is used to assign values to the variable. To create a variable that should store text, look at the following example: Example Create a variable called  name  of type  Stri
Read more

LINUX Move and copy files using SSH

Often you will need to move one or more files/folders or copy them to a different location. You can do so easily using an SSH connection. The commands which you would need to use are mv (short from move) and cp (short from copy). The mv command syntax looks like this: mv configuration.php-dist configuration.php By issuing the above command we will move (rename) the file configuration.php-dist to configuration.php. You can also use mv to move a whole directory and its content: mv includes/* ./ This will move all files (and folders) in the includes/ directory to the current working directory. In some cases however, we will need to only update the files and move only files that were changed, which we can do by passing ‘ -u ’ as argument to the command: mv -u includes/* admin/includes The copy (cp) command works the same way as mv, but instead of moving the files/folders it copies them. For example: cp configuration.php-dist configuration.php The command will copy the co
Read more

SQL Self JOIN

SQL Self JOIN A self JOIN is a regular join, but the table is joined with itself. Self JOIN Syntax SELECT column_name(s) FROM table1 T1, table1 T2 WHERE condition; T1 and T2 are different table aliases for the same table.
Read more