MongoDB (a) Basic introduction

What is MongoDB?

MongoDB is written by the C + + language and is an open source database system based on distributed file storage.
In the case of high load, adding more nodes can guarantee the performance of the server.
MongoDB is designed to provide scalable, high-performance data storage solutions for Web applications.
MongoDB stores data as a document and data structures consist of key-value (key=>value) pairs. A MongoDB document is similar to a JSON object. Field values can contain other documents, arrays, and array of documents.

MongoDB Features

• MongoDB provides a document-oriented storage that is simple and easy to operate.
• You can set the index of any property in the MongoDB record (for example: Firstname= "Sameer", address= "8 Gandhi Road") for faster sorting.
• You can create data mirroring either locally or on the network, which makes MongoDB more extensible.
• If the load increases (requiring more storage space and greater processing power), it can be distributed across other nodes in the computer network which is called a shard.
• The MONGO supports rich query expressions. Query directives use a JSON-style tag to easily query objects and arrays embedded in the document.
• MongoDb uses the update () command to implement a replacement of the completed document (data) or some specified data fields.
• The map/reduce in MongoDB is primarily used for batch processing and aggregation of data.
• Map and reduce. The map function calls emit (Key,value) to traverse all records in the collection, passing key and value to the reduce function for processing.
• The map function and the reduce function are written in JavaScript and can be executed with the Db.runcommand or MapReduce command.
• Gridfs is a built-in feature in MongoDB that can be used to store a large number of small files.
• MongoDB allows you to execute scripts on the server, write a function in JavaScript, execute directly on the server, or store the definition of the function on the server, next time you call it directly.
• MongoDB supports a variety of programming languages: ruby,python,java,c++,php,c# and many more languages.
• MongoDB installation is simple.

MongoDB Concept Analysis

RDBMS Terminology	MongoDB Terminology	explain
Database	Database	Database
Table	Collection	Database Tables/Collections
Row	Document	Data Logging hang/Documentation
Column	Field	Data fields/Fields
Index	Index	Index
Tables joins		Table Connection/mongodb not supported
Primary key	Primary key	Primary key/mongodb automatically sets the _id field as the primary key

Database

// 显示所有数据的列表show dbs// 显示当前数据库对象或集合db// 运行 use 命令，连接到一个指定数据库

Document

A document is a set of key-value (Key-value) pairs (that is, Bson). MongoDB documents do not need to set the same field, and the same field does not require the same data type, which is very different from the relational database, is also a very prominent MongoDB features.

Collection

A collection is a MongoDB document group, similar to a table in an RDBMS (relational database management system: Relational databases Management systems).
The collection exists in the database, the collection does not have a fixed structure, which means that you can insert data in different formats and types on the collection, but usually we have some relevance to the data that we insert into the collection.

Meta data

The information for the database is stored in the collection. They use the system's namespace:

dbname.system.*

MongoDB data type

Data Type	Description
String	String. Data types commonly used to store data. In MongoDB, the UTF-8 encoded string is legal.
Integer	Integer value. Used to store numeric values. Depending on the server you are using, it can be divided into 32-bit or 64-bit.
Boolean	Boolean value. Used to store Boolean values (True/false).
Double	Double-precision floating-point value. Used to store floating-point values.
Min/max keys	Compares a value to the lowest and highest value of a BSON (binary JSON) element.
Arrays	Used to store an array or list or multiple values as a single key.
Timestamp	Time stamp. Record when the document was modified or added.
Object	Used for inline documents.
Null	Used to create a null value.
Symbol	Symbol. The data type is basically the same as the string type, but unlike it, it is typically used in languages with special symbol types.
Date	Date time. Use the UNIX time format to store the current date or time. You can specify your own datetime: Create a Date object and pass in the month-date information.
Object ID	The object ID. The ID used to create the document.
Binary Data	Binary data. Used to store binary data.
Code	The code type. Used to store JavaScript code in a document.
Regular expression	The regular expression type. Used to store regular expressions.

MongoDB (i) Basic introduction