MongoDB atomic operations

mongodb does not support transactions, therefore, in the application of your project, pay attention to this point. Whatever the design, we do not ask mongodb ensure data integrity.

But mongodb provides many atomic operations, such as saving a document, modify, delete, etc., are atomic operations.

Either this is the so-called atomic operation to save the document to Mongodb, or not saved to Mongodb, the document does not have to query intact will not happen.

Atomic data model

Consider the following example, library books and transaction information.

In one example illustrates how to ensure that the same document embedded fields related atomic operations (update: update) fields are synchronized.

book = {
          _id: 123456789,
          title: "MongoDB: The Definitive Guide",
          author: [ "Kristina Chodorow", "Mike Dirolf" ],
          published_date: ISODate("2010-09-24"),
          pages: 216,
          language: "English",
          publisher_id: "oreilly",
          available: 3,
          checkout: [ { by: "joe", date: ISODate("2012-10-15") } ]
        }

You can use db.collection.findAndModify () method to determine whether books can be updated with new settlement and billing information.

Embedded in the same document available and checkout fields to ensure that these fields are synchronized update:

db.books.findAndModify ( {
   query: {
            _id: 123456789,
            available: { $gt: 0 }
          },
   update: {
             $inc: { available: -1 },
             $push: { checkout: { by: "abc", date: new Date() } }
           }
} )

Atomic operations commonly used commands

$ Set

It is used to specify a key and update the key, if the key does not exist and create.

{ $set : { field : value } }

$ Unset

To remove a key.

{ $unset : { field : 1} }

$ Inc

$ Inc can be a numeric value of the document (only to meet the requirements of digital) keys to increase or decrease operations.

{ $inc : { field : value } }

$ Push

usage:

{ $push : { field : value } }

The value added to the field to go inside, it must be an array type field job, if the field does not exist, a new array type added.

$ PushAll

With $ push, but once you can append multiple values ​​into an array field.

{ $pushAll : { field : value_array } }

$ Pull

To delete a field from an array of value equal value.

{ $pull : { field : _value } }

$ AddToSet

Adding a value into the array, and only when the value is not within the array to increase.

$ Pop

The first or the last element of the array of deleted

{ $pop : { field : 1 } }

$ Rename

Modify the field name

{ $rename : { old_field_name : new_field_name } }

$ Bit

Bit operations, integer type

{$bit : { field : {and : 5}}}

Shift operator

> t.find() { "_id" : ObjectId("4b97e62bf1d8c7152c9ccb74"), "title" : "ABC", "comments" : [ { "by" : "joe", "votes" : 3 }, { "by" : "jane", "votes" : 7 } ] }
 
> t.update( {'comments.by':'joe'}, {$inc:{'comments.$.votes':1}}, false, true )
 
> t.find() { "_id" : ObjectId("4b97e62bf1d8c7152c9ccb74"), "title" : "ABC", "comments" : [ { "by" : "joe", "votes" : 4 }, { "by" : "jane", "votes" : 7 } ] }