Mongodb (III) - CRUD

Hello everyone , I meet you again , I'm the king of the whole stack .

MongoDB As a non relational database . There is a big difference between the addition, deletion and modification of the traditional database . Here is just a summary of the knowledge points , In practice . We Baidu specific use method can .

Let's look at the major aspects first ：

One . I won't go into too much detail about the insertion and deletion inside . Relatively speaking, there are few knowledge points .

Let's take a look at the update , It's very practical to use the operation often , We need to use it flexibly according to the actual situation , Here is just a knowledge point , Baidu needs to give examples to learn and use ：

2, It's the same with queries , Take a look at the summary of knowledge points . In fact, use a few . There are still rules . Compare easy Records of the ：

3, Look at the fixed set Capped Collection: As the name suggests, it is a set with a fixed size . Its advantage is its excellent performance , With LRU（Least Recently Used Use at least in the near future ） Rules and insertion order age-out( To remove from ) Handle .

Because the size of the collection space must be , When space runs out . The newly added object will replace the oldest object in the collection . Always keep the latest object .

characteristic ： Inserting a fixed set is extremely fast ; The query output speed according to the insertion order is extremely fast ; When inserting the latest data , Eliminate the first data .

Usage method ： Store log information , Most suitable for just . Cache a few documents ……

establish :db.createCollection(“my_collection”,{capped:true,size:100000})

Convert a normal set to a fixed set ：db.runCommand({convertTocapped:”test”,size:100000})

4, Large file set （GridFS）:

GridFS It's a kind of MongoDB The mechanism of storing large binary files in . such as ： Store huge files , Like video , High definition pictures, etc ;GridFS Will directly use the established replication or fragmentation mechanism , Fault recovery and expansion are very easy; The file system that can prevent users from uploading content fails ; It does not generate disk fragments .

GridFS Use two tables to store data , Default fs.files: Including metadata objects .fs.chunks A binary block that contains information about a file . By using bin Under folder mongofiles To operate , Its put( Storage ),get( obtain ) and list（ list ） Three commands .

Very simple. .

Okay , Just to put it briefly MongoDB Addition, deletion and modification of , Specific operation examples are not given , Just check it with time . We need to know these things , Fixed set and large file set . Is a very good idea , It deserves our special attention .

Suddenly I think of the past series of looking at pictures and thinking , It seems that it can be here . Look at these pictures , Just tell it all . In this way, you almost learn the same .

Copyright notice ： This article is the original article of the blogger , Blog , Do not reprint without permission .

Publisher ： Full stack programmer stack length , Reprint please indicate the source ：https://javaforall.cn/117045.html Link to the original text ：https://javaforall.cn