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Millie Molotov
Millie Molotov

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MongoDB Command Shortcuts: The Ultimate Guide

#mongodb #nosql #database #programming

This post is a comprehensive guide to the most important MongoDB commands and operations. It covers basic queries, CRUD operations, indexing, aggregation, and more advanced concepts.

1. MongoDB Basics

Connecting to MongoDB 

mongo --host <hostname> --port <port> -u <username> -p <password> --authenticationDatabase <authDB>
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Show Databases 

show dbs;
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Use a Database 

use myDatabase;
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Show Collections 

show collections;
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2. CRUD Operations

Create a Collection 

db.createCollection("myCollection");
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Insert Documents 

db.myCollection.insertOne({ name: "John", age: 30 }); db.myCollection.insertMany([{ name: "Jane", age: 25 }, { name: "Doe", age: 22 }]);
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Read Documents 

db.myCollection.find(); db.myCollection.find({ name: "John" });
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Update Documents 

db.myCollection.updateOne({ name: "John" }, { $set: { age: 31 } }); db.myCollection.updateMany({ age: { $lt: 30 } }, { $set: { status: "young" } });
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Delete Documents 

db.myCollection.deleteOne({ name: "John" }); db.myCollection.deleteMany({ age: { $lt: 25 } });
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3. Querying Documents

Basic Queries 

db.myCollection.find({ name: "John" }); db.myCollection.find({ age: { $gt: 25 } });
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Projection 

db.myCollection.find({}, { name: 1, age: 1 });
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Sorting 

db.myCollection.find().sort({ age: -1 });
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Limiting and Skipping 

db.myCollection.find().limit(5); db.myCollection.find().skip(5).limit(5);
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4. Updating Documents

Update Operators

  • $set: Sets the value of a field 
db.myCollection.updateOne({ name: "John" }, { $set: { age: 31 } });
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  • $unset: Removes a field 
db.myCollection.updateOne({ name: "John" }, { $unset: { age: "" } });
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  • $inc: Increments the value of a field 
db.myCollection.updateOne({ name: "John" }, { $inc: { age: 1 } });
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  • $push: Adds an item to an array 
db.myCollection.updateOne({ name: "John" }, { $push: { hobbies: "reading" } });
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5. Deleting Documents

Delete Operators

  • deleteOne: Deletes a single document 
db.myCollection.deleteOne({ name: "John" });
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  • deleteMany: Deletes multiple documents 
db.myCollection.deleteMany({ age: { $lt: 25 } });
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6. Indexes

Creating Indexes 

db.myCollection.createIndex({ name: 1 });
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Viewing Indexes 

db.myCollection.getIndexes();
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Dropping Indexes 

db.myCollection.dropIndex("name_1");
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7. Aggregation

Basic Aggregation 

db.myCollection.aggregate([ { $match: { status: "active" } }, { $group: { _id: "$age", total: { $sum: 1 } } } ]);
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Common Aggregation Stages

  • $match: Filters documents 
{ $match: { status: "active" } }
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  • $group: Groups documents by a specified field 
{ $group: { _id: "$age", total: { $sum: 1 } } }
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  • $sort: Sorts documents 
{ $sort: { total: -1 } }
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  • $project: Reshapes documents 
{ $project: { name: 1, age: 1 } }
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8. Data Modeling

Embedding Documents 

let post = { title: "Post Title", content: "Post Content", comments: [ { user: "John", comment: "Great post!" }, { user: "Jane", comment: "Thanks for sharing!" } ] };
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Referencing Documents 

let user = { name: "John" }; let post = { title: "Post Title", content: "Post Content", userId: user._id };
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9. Replication

Setting Up a Replica Set 

rs.initiate(); rs.add("mongodb1.example.net:27017"); rs.add("mongodb2.example.net:27017"); rs.add("mongodb3.example.net:27017");
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Checking Replica Set Status 

rs.status();
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10. Sharding

Enabling Sharding 

sh.enableSharding("myDatabase");
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Sharding a Collection 

sh.shardCollection("myDatabase.myCollection", { shardKey: 1 });
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11. Transactions

Starting a Transaction 

const session = db.getMongo().startSession(); session.startTransaction();
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Committing a Transaction 

session.commitTransaction(); session.endSession();
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Aborting a Transaction 

session.abortTransaction(); session.endSession();
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12. Security

Creating a User 

db.createUser({ user: "myUser", pwd: "myPassword", roles: [{ role: "readWrite", db: "myDatabase" }] });
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Authenticating a User 

db.auth("myUser", "myPassword");
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13. Best Practices

  • Use Indexes: Ensure that your queries are efficient by using indexes.
  • Data Modeling: Choose the right data model (embedding vs. referencing) based on your use case.
  • Backup Regularly: Regularly backup your data to prevent data loss.
  • Monitor Performance: Use monitoring tools to keep an eye on the performance of your MongoDB instance.
  • Secure Your Database: Implement proper authentication and authorization mechanisms.

Conclusion

This post summarizes key concepts, commands, and operations for working with MongoDB. Keep this as a quick reference while you're working with MongoDB!

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