mongdb-tut

• every thing in mongo is like in json
• we get a db as sqldb has as well , and then get a collection which is like a table , then we use method to

1. create a db, collection, and curd which is so-called sql boy

now let us get to start to learn how to use sql mwthods

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0. before: you need to connect a mongodb or just use mongosh, I prefer using docker
1. create a DB
   use --auto create
2. delete a DB, specified it
   db.dropDatabase() --and the current db is deleted
3. show dbs --as title say

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1. create a collection
   db.createCollection(,[options not a must])
2. show collections – as title say
3. insert into a collection --using collection name
   db..insert({“somekey”:“somevalue”,…}) – and this is more like json on method
4. delete a collection
   db..drop()
5. insert many json to a collection --using insertMany method
   db..insertMany([{“title”:“for exam”,“array”:[“I”,“dont”,“do”]},{same as before}],{with some features})
6. check collection --using find()
   db..find()[.pretty()]
7. update collection – this is more shit than js, lets look a exam
   db.col.update({‘title’:‘MongoDB 教程’},{$set:{‘title’:‘MongoDB’}})
8. remove collection key-value pairs – check a condition
   db.col.remove({‘title’:‘MongoDB 教程’})
9. conditional find from collection – just skip it, you may no going to use, but the idea is that by conditions such as and, or

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now check more thing about mothods, notice that every thing in method is more like a json

1. sort a collection by key – 1 is asc, -1 is desc – col is coll-name
   db.col.find({},{“title”:1,_id:0}).sort({“likes”:-1})
2. create index --check fast
   db.col.createIndex({“title”:1}) – so 1 is key like above, there is with options as well
3. aggregate(聚合)， view it as buildin function
   db.mycol.aggregate([{KaTeX parse error: Expected '}', got 'EOF' at end of input: …roup : {_id : "by_user", num_tutorial : {$sum : 1}}}]) – notice that every col which is called data has an field call _id, you see that $ as well,
   view it as conditional select

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some thing need to learn, we mostly is using this instead of curd

4. copy and paste, a clone of collection --for safety and reusable, once a collection is cracked, use clone data set, this is connected to cluster(集群)
5. slice is another cluster tech, that when there is huge data, a computer can’t receive, slice to multiple computers
6. dump(backup) and restore
7. db monitor, check what has happened to mongodb

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now it comes to connect to programming language

1. mostly use: java and js