mongo-docs-advanced-topic-docs-1-to-6 added

docs/MongoDB/Advanced MongoDB/_category.json

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+{
+    "label": "Advanced MongoDB",
+    "position": 25,
+    "link": {
+        "type": "generated-index",
+        "description": "Dive deeper into advanced MongoDB concepts and techniques."
+    }
+}

docs/MongoDB/Advanced MongoDB/mongodb-advanced-indexing.md

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+---
+id: mongodb-advanced-indexing
+title: MongoDB - Advanced Indexing
+sidebar_label: Advanced Indexing
+sidebar_position: 6
+tags: [mongodb, indexing, array indexing, sub-document indexing]
+description: Learn how to create advanced indexes in MongoDB, including indexing array fields and sub-document fields for optimized query performance.
+---
+
+## Indexing Array Fields
+
+We have inserted the following document in the collection named `users`:
+
+```javascript
+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.
+
+### Creating an Index on Array Fields
+
+Suppose we want to search user documents based on the user’s tags. For this, we will create an index on the `tags` array in the collection.
+
+Creating an index on an array in turn creates separate index entries for each of its fields. So in our case, when we create an index on the `tags` array, separate indexes will be created for its values `music`, `cricket`, and `blogs`.
+
+To create an index on the `tags` array, use the following code:
+
+```javascript
+db.users.createIndex({"tags":1})
+```
+
+```json
+{
+	"createdCollectionAutomatically" : false,
+	"numIndexesBefore" : 2,
+	"numIndexesAfter" : 3,
+	"ok" : 1
+}
+```
+
+After creating the index, we can search on the `tags` field of the collection like this:
+
+```javascript
+db.users.find({tags:"cricket"}).pretty()
+```
+
+```json
+{
+	"_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:
+
+```javascript
+db.users.find({tags:"cricket"}).explain()
+```
+
+This gives you the following result:
+
+```json
+{
+	"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 `"stage" : "IXSCAN", "indexName" : "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 the `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:
+
+```javascript
+db.users.createIndex({"address.city":1,"address.state":1,"address.pincode":1})
+```
+
+```json
+{
+	"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:
+
+```javascript
+db.users.find({"address.city":"Los Angeles"}).pretty()
+```
+
+```json
+{
+	"_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:
+
+```javascript
+db.users.find({"address.city":"Los Angeles","address.state":"California"}).pretty()
+```
+
+```json
+{
+	"_id" : ObjectId("5dd7c927f1dd4583e7103fdf"),
+	"address" : {
+		"city" : "Los Angeles",
+		"state" : "California",
+		"pincode" : "123"
+	},
+	"tags" : [
+		"music",
+		"cricket",
+		"blogs"
+	],
+	"name" : "Tom Benzamin"
+}
+```
+
+### Diagram (Mermaid)
+
+Here is a visual representation of the document structure and indexing process:
+
+```mermaid
+graph TD;
+    A[Document: users]
+    A --> B[Sub-document: address]
+    A --> C[Array: tags]
+    B --> D[city]
+    B --> E[state]
+    B --> F[pincode]
+    C --> G[music]
+    C --> H[cricket]
+    C --> I[blogs]
+```
+
+### Notes
+
+- Indexing array fields in MongoDB creates separate index entries for each value in the array.
+- Indexing sub-document fields allows efficient queries on nested fields.
+- Ensure the query order matches the index order to fully utilize the indexes.
+
+### Table
+
+| Field           | Type             | Indexed | Description                              |
+|-----------------|------------------|---------|------------------------------------------|
+| `address`       | Sub-document     | Yes     | Contains nested fields for address info. |
+| `address.city`  | String           | Yes     | City name in the address.                |
+| `address.state` | String           | Yes     | State name in the address.               |
+| `address.pincode`| String          | Yes     | Pincode in the address.                  |
+| `tags`          | Array of Strings | Yes     | User's tags for indexing.                |