Great topic — let’s break down MongoDB indexing and searching step by step.

1. What is Indexing in MongoDB?

• An index is a data structure (usually a B-Tree) that improves the speed of queries.

• Without an index, MongoDB performs a collection scan (checks every document).

• With indexes, MongoDB can quickly locate matching documents.

2. Creating Indexes

You create indexes with createIndex():

a) Single Field Index

db.users.createIndex({ name: 1 })

• 1 = ascending order

• -1 = descending order

• Used for queries like:

  db.users.find({ name: "Alice" })
  

b) Compound Index (Multiple Fields)

db.users.createIndex({ age: 1, name: -1 })

• Useful when queries use both fields.

• Order matters: { age: 1, name: -1 } is not the same as { name: -1, age: 1 }.

c) Unique Index

db.users.createIndex({ email: 1 }, { unique: true })

• Prevents duplicate emails.

d) Text Index (for Searching Text)

db.articles.createIndex({ content: "text", title: "text" })

• Enables text search queries:

  db.articles.find({ $text: { $search: "mongodb indexing" } })
  

e) Geospatial Index

For location-based data:

db.places.createIndex({ location: "2dsphere" })

Query with:

db.places.find({
  location: {
    $near: {
      $geometry: { type: "Point", coordinates: [40, -73] },
      $maxDistance: 5000
    }
  }
})

f) TTL (Time-to-Live) Index

Automatically deletes documents after a time:

db.sessions.createIndex({ createdAt: 1 }, { expireAfterSeconds: 3600 })

• Deletes docs 1 hour after createdAt value.

3. Searching in MongoDB

a) Equality Match

db.users.find({ name: "Alice" })

b) Range Queries

db.users.find({ age: { $gt: 20, $lt: 40 } })

c) Text Search

(Requires text index)

db.articles.find({ $text: { $search: "mongodb query api" } })

Options:

• $search: "mongodb -nosql" → exclude words

• $language: "en" → set language

• $caseSensitive: true

d) Regex Search

db.users.find({ name: { $regex: /^A/i } })

Finds names starting with "A", case-insensitive.

e) Array Search

db.orders.find({ items: { $all: ["pen", "notebook"] } })

4. Checking Index Usage

You can analyze query performance with .explain():

db.users.find({ name: "Alice" }).explain("executionStats")

• Shows whether MongoDB used an index scan (IXSCAN) or a collection scan (COLLSCAN).

5. Listing and Dropping Indexes

• List indexes:

  db.users.getIndexes()
  

• Drop one index:

  db.users.dropIndex({ name: 1 })
  

• Drop all indexes:

  db.users.dropIndexes()
  

Summary

• Indexes speed up searching in MongoDB.

• Types of indexes: single-field, compound, unique, text, geospatial, TTL.

• Searching can use equality, range, regex, arrays, text search.

• Always check with .explain() to confirm index usage.