##Insert
- db.collection.insertOne()
- db.collection.insertMany()
- db.collection.insert()
如果没有 _id字段，mongo会自动加一个
##Update
The updateOne(), updateMany(), and replaceOne() operations accept the upsert parameter. When upsert : true, if no document in the collection matches the filter, a new document is created based on the information passed to the operation.
- db.collection.updateOne()
- db.collection.updateMany()
- db.collection.replaceOne()
- db.collection.update()
db.collection.update() method can accept query criteria to determine which documents to update as well as an options document that affects its behavior, such as the multi option to update multiple documents.
- The $set operator replaces the value of a field with the specified value.
- $unset replaces the matching element with null
- The $rename operator updates the name of a field
##Delete
- db.collection.deleteOne()
- db.collection.deleteMany()
- db.collection.remove()
—Bulk Write—
- db.collection.bulkWrite()
写操作对于每个document都是原子操作，bulk里操作单个document的也是原子
当一个操作要改变多个document的时候，每个document的变化是原子的，但整个批量操作不是原子的。这时候需要isolateddb.foo.update(
{ status : "A" , $isolated : 1 },
{ $inc : { count : 1 } },
{ multi: true }
)
当你要把不同的多个操作 变成一个原子操作，你需要Transaction
https://docs.mongodb.org/manual/tutorial/perform-two-phase-commits/
##Concurrency Control
需要有唯一的字段，让mongo知道重复了
##Performance