mongodb Insert 、 remove 、操作原子性（atomicity）

insert methods

db.collection.insertOne()
db.collection.insertMany()
db.collection.insert()

db.collection.insert()

inserts a single document or multiple documents into a collection.
To insert a single document, pass a document to the method; to insert multiple documents, pass an array of documents to the method.

db.collection.insert(
   <document or array of documents>,
   {
     writeConcern: <document>,
     ordered: <boolean>
   }
)

db.collection.insertMany(
   [ <document 1> , <document 2>, ... ],
   {
      writeConcern: <document>,
      ordered: <boolean>
   }
)

about ordered（Defaults to true）

Optional.
If true, perform an ordered insert of the documents in the array, and if an error occurs with one of documents, MongoDB will return without processing the remaining documents in the array.

If false, perform an unordered insert, and if an error occurs with one of documents, continue processing the remaining documents in the array.

Delete methods

db.collection.remove()    Delete a single document or all documents that match a specified filter.
db.collection.deleteOne() 	
db.collection.deleteMany()

remove()

db.users.remove( { status : "P" } )

删除集合、数据库

db.COLLECTION_NAME.drop()
db.dropDatabase()

Atomicity

In MongoDB, a write operation is atomic on the level of a single document, even if the operation modifies multiple embedded documents within a single document.

$isolated

Using the $isolated operator, a write operation that affects multiple documents can prevent other processes from interleaving once the write operation modifies the first document. This ensures that no client sees the changes until the write operation completes or errors out.

db.foo.update(
    { status : "A" , $isolated : 1 },
    { $inc : { count : 1 } },
    { multi: true }
)

Without the $isolated operator, the multi-update operation will allow other operations to interleave(交错) with its update of the matched documents.