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Introduction to MongoDB

Summary: MongoDB is an open source database system based on distributed file storage, which is based on documents (document, that is, the concept of rows in a relational database) and is stored in the form of key= > value, similar to the format of JSON. Mongodb is a document-based non-relational database, which is open source, high-performance, highly available and extensible.

Comparison between MongoDB and Relational Database

The following figure shows a comparison between sql terms and mongodb terms:

Document

Document is the basic unit of data in MongoDB. It is very simple to understand that a group of data put together in an orderly manner is a document.

For example:

Single key value document {"userName": "Bertram"}

Multi-key value document {"_ id": ObjectId ("ff4a0ead0c5fc752b13f2af441b7da12"), "name": "Bertram", "countryName": "Japan"}

Set

Putting multiple documents together is a collection.

Database

Multiple collections are put together to form a database.

Shell partial command table

1) show dbs displays all databases

> show dbs / / the newly created database will not be displayed. Some data needs to be written before it can be displayed. Admin (empty) local 0.078GBtest 0.078GBservice 0.058GB >

2) db displays the current database

> db test

3) use switch or create database

> use local / / if the database does not exist, create the database, otherwise switch to the specified database. Basic operations of databases, collections and documents of switched to dblocal > dblocal > MongoDB

1.MongoDB creates database and deletes database

1) create the database: use DATABASE_NAME if the database does not exist, create the database, otherwise switch to the specified database 2) delete the database: db.dropDatabase ()

two。 Create and delete collections

1) create a collection: db.createCollection (name, options) Parameter description: name: name of the collection to be created options: optional parameter, specify options for memory size and index 2) Collection deletion: db.collection.drop () 3) if you want to view an existing collection You can use the show collections or show tables command: > show collections or show tables4) example: here is the use of createCollection () with several key parameters: create a collection (the entire collection space size 10240KB, the maximum number of documents is 17855200.) > db.createCollection ('replicationColletion', {' capped':true, 'size':10240,' max':17855200}) {"ok": 1} > in MongoDB, you do not need to create a collection. When you insert some documents, MongoDB automatically creates collections. > db.curriculum.insert ({"name": "English"}) > show collectionscurriculum

3. Insert document

1) insert document: MongoDB inserts a document into the collection using the insert () or save () method The syntax is as follows: db.serviceLECTION_NAME.insert (document) example: the following documents can be stored in the service collection of MongoDB's runoob database: > db.service.insert ({title: 'MongoDB learning', description: 'MongoDB is a Nosql database', by: '51CTO blog', url: 'https://docs.mongodb.com', tags: [' mongodb', 'database',' NoSQL'] Likes: 100}) in the above example, service is the collection name If the collection is not in the database, MongoDB automatically creates the set and inserts the document. 2) View the inserted document: > db.service.find () {"_ id": ObjectId ("5e143d32183a994d1b71c06a"), "title": "MongoDB Learning", "description": "MongoDB is a Nosql Database", "by": "51CTO blog", "url": "https://docs.mongodb.com"," tags ": [" mongodb "," database "," NoSQL "] "likes": 100}-3) We can also define the data as a variable As follows: > document= ({title: 'MongoDB Learning', description: 'MongoDB is a Nosql database', by: '51CTO blog', url: 'https://docs.mongodb.com', tags: [' mongodb', 'database',' NoSQL'], likes: 100}) The results displayed after execution are as follows: {"title": "MongoDB Learning", "description": "MongoDB is a Nosql database", "by": "51CTO blog", "url": "https://docs.mongodb.com"," tags ": [" mongodb "," database "," NoSQL "] "likes": 100} perform insert operation: > db.service.insert (document) WriteResult ({"nInserted": 1}) insert the document you can also use the db.service.save (document) command. If you do not specify the _ id field, the save () method is similar to the insert () method. If you specify the _ id field, the data for that _ id is updated.

4. Query document

-- MongoDB queries documents using the find () method. The find () method displays all documents in an unstructured manner. -- MongoDB Limit () method if you need to read a specified number of data records in MongoDB, you can use the Limit method of MongoDB, and the limit () method accepts a numeric parameter that specifies the number of records to read from MongoDB. -- count query the number of records-- the MongoDB Skip () method can not only use the limit () method to read a specified amount of data, but also use the skip () method to skip the specified amount of data. The skip method also accepts a numeric parameter as the number of skipped records. Example: > db.service.find () {"_ id": ObjectId ("5e143d32183a994d1b71c06a"), "title": "MongoDB Learning", "description": "MongoDB is a Nosql database", "by": "51CTO blog", "url": "https://docs.mongodb.com"," tags ": [" mongodb "," database "," NoSQL "]," likes ": 100 > db.service.find ({}) {"title": "0", "_ id": "1"}) .limit (1) {"_ id": ObjectId ("5e143d32183a994d1b71c06a"), "title": "MongoDB Learning"} > db.service.find (). Limit (2) {"_ id": ObjectId ("5e143edc183a994d1b71c06b"), "title": "Python tutorial", "description": "Python is a programming language", "by": "51CTO blog" "url": "https://www.python.org"," tags ": [" Python "," programme "," language "]," likes ": 120} Note: if the query find does not specify parameters in the limit () method, all data in the collection is displayed. > db.service.find () .count () / / query and count the number of result records > db.service.count () / / Statistics the following examples only show the second document data > db.service.find ({}, {"title": "1", _ id:0}) .limit (1) .skip (1) {"title": "Python tutorial"}

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