Introduction to mongodb

1、MongoDB summary

from C++ Language writing , Open source and based on distributed file storage ; Under high load , Ensure server performance by adding more nodes ; For the purpose of WEB Applications provide scalable, high-performance data storage solutions ; Store data as a document , Data structure consists of key value pairs (key / value);
Its documents are similar JSON object , Field values can contain other documents 、 Arrays and document arrays .

2、MongoDB characteristic

 •   Scalable 、 High performance next generation database ;
 •   Easy to deploy 、 Easy to use 、 It's convenient to store data ;
 •   Document oriented （json Format ） Storage , Easy to read 、 Efficient ;  
 •   Model freedom , Support dynamic query 、 Full index , Modeless ;  
 •   Efficient data storage , Increased efficiency ; 
 •   Support for replication and recovery ;
 •   To support cloud level scalability , Support horizontal database clustering , Additional servers can be added dynamically ;

3、MongoDB The elements of

MongoDB By Library （database）、 aggregate （collection）、 Document object （documen） Three levels make up , Similar to the traditional relational database, the database （database）、 surface （table）、 Record （record） Three levels of composition . among , The document is similar to json The key/value pair , for example ：{“name”:“tom”,“age”:23}, A collection is a collection of documents , A library is a collection of sets .

4、MongoDB Support language

5、MongoDB Of “ObjectId”

Different machines can easily generate it with the same method that is globally unique .ObjectId Use 12 Byte storage space , The generation method is as follows ：

 example ：
4e931cb61e19edcd8800017f        
 Time stamp   machine ID PID  Counter         

 notes ：
 •   Timestamp can guarantee the uniqueness of seconds ;
 •   machine ID It can ensure that the distributed design is considered , Avoid clock synchronization ;
 •  PID It can ensure that the same server runs multiple mongod Uniqueness when instance ;
 •   The counter can guarantee the uniqueness in the same second ;

6、MongoDB data type

data type	give an example
Null value	null
Boolean	ture & false
Integers	123
floating-point	12.3
character string	“hello world”
object ID	use new ObjectId（） To claim
date	use new Date（） To declare the timestamp
Array	[“apple”,”blanan”,”pear”]
Embedded documents	{“username” : “jone”, “age”: 13, “contact” : {“home”:”123”,”moblie”:”456”}}
RegExp（ Regular expressions ）	/[a-z]/

7、MongoDB And TRDB Comparison of basic concepts of database

MongoDB	TRDB	Than a say bright
library DB	library DB	Have the concept of Library , You need to use the command to create the library name . For example, two database names are established according to different projects , One for test library , Used for testing , One for goodsdb library , Used for formal business data storage and operation
aggregate	surface	A set corresponds to a table . MongoDB There is no need to define the set structure in advance , TRDB The table structure must be forcibly defined in advance
file	That's ok	Every document has a special _id,_id The value is unique in the collection to which the document belongs , Default by MongoDB Self maintenance , Of course, it can also be specified by the programmer . One “ file ” similar TRDB Of —“ That's ok ” Record ,“ file ” Avoid the relationship between different sets （ Join ) ,; And then “ That's ok ” On the basis of TRDB Emphasize the relationship
Key value pair	field value	MongoDB“ file ” One of the “ Key value pair ” similar TRDB One of them “ field value ”, however “ file ” Inside “ Key value pair ” More complex data structures can be embedded