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Basic MongoDB operations using Mongo Shell

1. Start Mongo Shell (Skip while using MongoDB Compass)

mongo
- Opens the Mongo Shell where you can run MongoDB commands.

2. Select a Database

  • Command: 
    use <database_name>
  • Example: 
    use myDatabase
  • Details: If the database doesn’t exist, MongoDB will create it when you add data.

3. Create a Collection

  • Command: 
    db.createCollection("<collection_name>")
  • Example: 
    db.createCollection("movies")
  • Details: Collections are created automatically when you first insert data, but you can create them manually if needed.

4. Insert Documents

  • Command: 
    db.<collection_name>.insertOne(<document>)
db.<collection_name>.insertMany([<document1>, <document2>])
  • Examples: 
    db.movies.insertOne({ title: "Inception", year: 2010, genre: "Sci-Fi" })
db.movies.insertMany([
  { title: "The Matrix", year: 1999, genre: "Sci-Fi" },
  { title: "Interstellar", year: 2014, genre: "Sci-Fi" }
])
  • Details: insertOne() adds a single document, insertMany() adds multiple documents.

5. Find Documents

  • Command: 
    db.<collection_name>.find(<query>)
db.<collection_name>.findOne(<query>)
  • Examples: 
    db.movies.find() // Retrieve all documents in the collection
db.movies.find({ genre: "Sci-Fi" }) // Find all Sci-Fi movies
db.movies.findOne({ title: "Inception" }) // Find a single document matching the query
  • Details:
    • find() retrieves multiple documents
    • findOne() retrieves a single document

6. Update Documents

  • Command: 
    db.<collection_name>.updateOne(<query>, <update>)
db.<collection_name>.updateMany(<query>, <update>)
  • Examples: 
    db.movies.updateOne({ title: "Inception" }, { $set: { year: 2011 } }) // Update a single document
db.movies.updateMany({ genre: "Sci-Fi" }, { $set: { genre: "Science Fiction" } }) // Update multiple documents
  • Details:
    • $set updates the specified fields.
    • Other update operators include:
      • $inc for incrementing
      • $push for adding items to arrays

7. Delete Documents

  • Command: 
    db.<collection_name>.deleteOne(<query>)
db.<collection_name>.deleteMany(<query>)
  • Examples: 
    db.movies.deleteOne({ title: "Inception" }) // Delete a single document
db.movies.deleteMany({ genre: "Sci-Fi" }) // Delete multiple documents
  • Details:
    • deleteOne() removes one document
    • deleteMany() removes all documents matching the query.

8. Drop a Collection (DANGER)

  • Command: 
    db.<collection_name>.drop()
  • Example: 
    db.movies.drop()
  • Details: Removes the entire collection and all its documents.

9. List All Databases

  • Command: 
    show dbs
  • Details: Lists all databases on the server.

10. List Collections in a Database

  • Command: 
    show collections
  • Details: Lists all collections in the currently selected database.

11. Count Documents

  • Command: 
    db.<collection_name>.countDocuments(<query>)
  • Example: 
    db.movies.countDocuments({ genre: "Sci-Fi" })
  • Details: Counts the number of documents matching the query. (If query isnt provided, it returns count of all documents)

12. Basic Aggregation

  • Command: 
    db.<collection_name>.aggregate([<pipeline_stage1>, <pipeline_stage2>])
  • Example: 
    db.movies.aggregate([
  { $match: { genre: "Sci-Fi" } },
  { $group: { _id: "$year", count: { $sum: 1 } } }
])
  • Details: Performs complex queries involving multiple stages like $match, $group, and $sort.

Summary Table

Operation Command Example Description
Start Mongo Shell mongo Opens the MongoDB Shell.
Select a Database use myDatabase Switches to the specified database.
Create a Collection db.createCollection("movies") Creates a new collection.
Insert Documents db.movies.insertOne({ title: "Inception", year: 2010 }) Adds new documents to a collection.
Find Documents db.movies.find({ genre: "Sci-Fi" }) Retrieves documents from a collection.
Update Documents db.movies.updateOne({ title: "Inception" }, { $set: { year: 2011 } }) Updates existing documents.
Delete Documents db.movies.deleteOne({ title: "Inception" }) Deletes documents from a collection.
Drop a Collection db.movies.drop() Deletes the entire collection.
List All Databases show dbs Lists all databases.
List Collections show collections Lists all collections in the current database.
Count Documents db.movies.countDocuments({ genre: "Sci-Fi" }) Counts documents matching a query.
Basic Aggregation db.movies.aggregate([ { $match: { genre: "Sci-Fi" } } ]) Performs advanced queries with aggregation stages.

Additional Resources