Finding Documents in MongoDB

Introduction

In MongoDB, finding documents is done using the find() method, which retrieves documents from a collection based on specified criteria. This tutorial will guide you through the various ways to find documents in a MongoDB collection using mongosh.

Prerequisites

• MongoDB installed and running on your machine.

• Access to mongosh and a populated database.

Step 1: Start mongosh

1. Open Terminal/Command Prompt:

   • Launch your terminal (macOS/Linux) or command prompt (Windows).

2. Start mongosh:

   • Type the following command and press Enter:

     mongosh

Step 2: Switch to the Database

Switch to the database where your collection is located.

1. Use a Database:

   use myNewDatabase

Step 3: Finding Documents

1. Find All Documents

To retrieve all documents in a collection, use the find() method without any parameters.

db.users.find()

• This will return all documents in the users collection.

2. Find Documents with Criteria

You can specify criteria to filter the documents returned by the find() method.

1. Find Documents by Field Value:

   • To find documents where the name is "Pankaj":

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

2. Find Documents by Multiple Fields:

   • To find documents where the age is 30 and the city is "Indore":

   db.users.find({ age: 30, city: "Indore" })

3. Find Documents with Comparison Operators

MongoDB supports various comparison operators that you can use in your queries.

1. Find Documents with $gt (Greater Than):

   • To find users older than 25:

   db.users.find({ age: { $gt: 25 } })

2. Find Documents with $lt (Less Than):

   • To find users younger than 30:

   db.users.find({ age: { $lt: 30 } })

3. Find Documents with $ne (Not Equal):

   • To find users not living in "Mumbai":

   db.users.find({ city: { $ne: "Mumbai" } })

4. Find Documents with Logical Operators

MongoDB allows you to combine multiple criteria using logical operators.

1. Using $or:

   • To find users who are either from "Delhi" or "Mumbai":

   db.users.find({ $or: [{ city: "Delhi" }, { city: "Mumbai" }] })

2. Using $and:

   • To find users who are older than 25 and from "Indore":

   db.users.find({ $and: [{ age: { $gt: 25 } }, { city: "Indore" }] })

5. Find Documents with Projection

You can limit the fields returned by the query using projection.

1. Find Specific Fields:

   • To find all users but only return their names and cities:

   db.users.find({}, { name: 1, city: 1 })

6. Find One Document

To find a single document that matches the criteria, use the findOne() method.

db.users.findOne({ name: "Pankaj" })

• This will return the first document that matches the criteria.

Step 4: Sort and Limit Results

You can sort and limit the results returned by your queries.

1. Sort Results:

   • To find all users sorted by age in ascending order:

   db.users.find().sort({ age: 1 })

2. Limit Results:

   • To limit the results to the first 2 documents:

   db.users.find().limit(2)

Conclusion

You have learned how to find documents in MongoDB using mongosh. You can retrieve all documents, filter them based on specific criteria, use comparison and logical operators, project specific fields, and sort and limit the results.

Feel free to reach out with any questions or for further guidance!

---