Added mongodb cheatsheet

mongodb.md

@@ -0,0 +1,147 @@
+---
+title: mongodb
+updated:  2024-02-15
+layout: 2017/sheet
+category: Databases
+---
+
+## Connect to MongoDB
+mongosh connects to mongodb://127.0.0.1:27017 by default
+```js
+mongosh "mongodb://user:password@host:port/dbname"
+```
+
+## Databases and Collections
+### Show Databases
+```js
+show dbs
+```
+
+### Use Database
+```js
+use <database_name>
+```
+
+### Show Collections
+```js
+show collections
+```
+
+## CRUD Operations
+### Create
+```js
+db.collection.insertOne({ key: "value" }) // Insert a single document
+db.collection.insertMany([{ key: "value" }, ...]) // Insert multiple documents
+```
+
+### Read
+```js
+db.collection.find({}) // Find all documents
+db.collection.findOne({ key: "value" }) // Find one document by key
+```
+
+### Complex Queries
+```js
+db.collection.find({ age: { $gt: 18, $lt: 65 }}) // Find documents with age between 18 and 65 (gt = greater than, lt = less than)
+db.collection.find({ status: { $in: ["A", "B"] }}) // Find documents with status A or B
+```
+
+### Update
+```js
+// Upsert example
+db.collection.updateOne(
+  { key: "unique_value" },
+  { $set: { key: "new value" } },
+  { upsert: true }
+)
+```
+
+### Delete
+```js
+db.collection.deleteOne({ key: "value" }) // Delete a single document
+db.collection.deleteMany({ key: "value" }) // Delete multiple documents
+```
+
+## Indexes
+### Create Index
+```js
+db.collection.createIndex({ key: 1 }) // Create an ascending index (1 = ascending, -1 = descending)
+db.collection.createIndex({ email: 1 }, { unique: true }) // Create a unique index useful for email, username, etc. You can't have two documents with the same email
+```
+
+### List Indexes
+```js
+db.collection.getIndexes()
+```
+
+### Aggregation
+```js
+db.collection.aggregate([
+{ $match: { key: "value" } },
+{ $group: { _id: "$key", count: { $sum: 1 } } }
+])
+```
+
+### Expanded Aggregation
+```js
+db.collection.aggregate([
+  { $match: { status: "A" } },
+  { $group: { _id: "$cust_id", total: { $sum: "$amount" } } },
+  { $sort: { total: -1 } },
+  { $limit: 5 }
+])
+```
+
+## Replication and Sharding
+### Replica Sets
+```js
+rs.initiate()
+rs.status()
+```
+
+### Sharding
+```js
+sh.addShard("shard0000/mongodb0.example.net:27017")
+sh.status()
+```
+
+## Administration
+### Create User
+```js
+db.createUser({ user: "username", pwd: "password", roles: ["readWrite", "dbAdmin"]})
+```
+
+### Backup and Restore
+MongoDB uses `mongodump` and `mongorestore` for backup and restoration.
+```bash
+mongodump --db <database_name> # Backup a database
+mongorestore --db <database_name> <path_to_backup> # Restore a database
+```
+
+### Performance Monitoring
+```js
+db.currentOp() # Show current operations
+db.stats() # Database statistics
+```
+
+## Security
+### Enable Authentication
+```js
+mongod --auth
+```
+
+## Miscellaneous
+### Run JavaScript File
+```js
+load("/path/to/script.js")
+```
+
+### Set Profiling Level
+```js
+db.setProfilingLevel(level, slowms) // level = 0 (off), 1 (slow operations), 2 (all operations)
+```
+
+### Change Streams
+```js
+db.collection.watch() // Watch for changes in a collection
+```