MongoDB
## Links
- [3t](https://studio3t.com/knowledge-base/articles/mongodb-aggregation-framework/#mongodb-project)
- [runnob](https://www.runoob.com/mongodb/mongodb-aggregate.html)
- [mongodb for mac](https://www.mongodb.com/docs/manual/tutorial/install-mongodb-on-os-x/)
## Initialize MongoDB
### Install and Uninstall mongoDB
```
brew tap MongoDB/brew
brew install mongodb-community
brew uninstall mongodb-community
```
### Check services
```
brew services list
```
### Start services
```
brew services start mongodb-community
brew services stop mongodb-community
```
### Verify the MongoDB service
```
brew services list | grep mongodb
```
### Connect to the shell
```
mongosh
```
## Use of MongoDB
### show dbs
```
show dbs
```
### Enter a database
```
use shopDB
```
### show and drop collections
```
show collections
db.products.drop()
```
### To see which database you are in
```
> db
```
### Insert
```
db.products.insertOne({
name: 'orange', qty: 13, type: 'fruit', price: 8
})
db.products.insertMany([
{name: 'pear', qty: 20, type: 'fruit'},
{name: 'watermelon', qty: 10, type: 'fruit'}
])
```
### Find
```
db.products.find() # all
db.products.find({qty: 10}) # qty == 10
db.products.find({qty: 10, type: 'it'}) # and
db.products.find({$or: [{name: 'apple'}, {name: 'orange'}]}) # or
db.products.find({qty: {$gt: 15}}) # >
db.products.find({qty: {$gte: 15}}) # >=
db.products.find({qty: {$lte: 15}}) # <=
```
### Update
```
db.products.updateMany({name: 'watermelon'},{$set: {qty: 100}})
db.products.updateMany(
{name: 'mango'},{$set: {qty: 100}}, {upsert: true}
) # insert one if the document doesn't exist
```
### Delete
```
db.products.deleteOne({type: 'stationery'})
db.products.deleteMany({type: 'stationery'})
```
### Sort
```
db.products.find({type: 'fruit'}).sort({name: -1})
```
### Index
```
db.products.createIndex({name: -1})
db.products.getIndices()
db.products.dropIndex('name_-1')
```
### Group
| Expressions | Descriptions | Examples |
| --------- | ------------------------------------------------------------ | ------------------------------------------------------------ |
| $sum | 计算总和。 | db.mycol.aggregate([{$group : {_id : "$by_user", num_tutorial : {$sum : "$likes"}}}]) |
| $avg | 计算平均值 | db.mycol.aggregate([{$group : {_id : "$by_user", num_tutorial : {$avg : "$likes"}}}]) |
| $min | 获取集合中所有文档对应值得最小值。 | db.mycol.aggregate([{$group : {_id : "$by_user", num_tutorial : {$min : "$likes"}}}]) |
| $max | 获取集合中所有文档对应值得最大值。 | db.mycol.aggregate([{$group : {_id : "$by_user", num_tutorial : {$max : "$likes"}}}]) |
| $push | 将值加入一个数组中，不会判断是否有重复的值。 | db.mycol.aggregate([{$group : {_id : "$by_user", url : {$push: "$url"}}}]) |
| $addToSet | 将值加入一个数组中，会判断是否有重复的值，若相同的值在数组中已经存在了，则不加入。 | db.mycol.aggregate([{$group : {_id : "$by_user", url : {$addToSet : "$url"}}}]) |
| $first | 根据资源文档的排序获取第一个文档数据。 | db.mycol.aggregate([{$group : {_id : "$by_user", first_url : {$first : "$url"}}}]) |
| $last | 根据资源文档的排序获取最后一个文档数据 | db.mycol.aggregate([{$group : {_id : "$by_user", last_url : {$last : "$url"}}}]) |