• What’s special about blink? Rookie supply chain scenario best practices


    Author: Chensheng, YuanqiaoRookie supply chain has a long business link, many nodes and many entities, which makes the technical team face many challenges in the process of building a real-time warehouse in the supply chain, such as: how to realize real-time variable key statistics? How to realize real-time timeout statistics? How to optimize resources effectively? […]

  • MySQL foundation 04 query


    Relational query 1. Internal connection: realize a ∩ B Select field list From a table inner join b table On Association condition Where and other clauses; 2. Left outer connection #The query result is a Select field list From a table left join b table On Association condition Where and other clauses; #Realize a – […]

  • 1. Teach you how to use js to operate the database mysql ORM learning notes


    Node.js ORM – Sequelize basic Summary: ORM (object relation mapping) based on promise supports multiple databases, transactions, associations, etcinstall: npm i sequelize mysql2 -S Basic use: const Sequelize = require(“sequelize”); //Establish a connection const sequelize = new Sequelize(“kaikeba”, “root”, “admin”, { host: “localhost”, dialect: “mysql”, operatorsAliases: false }); //Define model const Fruit = sequelize.define(“Fruit”, { […]

  • IOS — possible crash caused by objc, association and design


    //Objc assignment is similar to our commonly used assignment. The feature of the assignment strategy is that after the object is released, it will not actively set the application object as nil, which will lead to the risk of application crash due to accessing the zombie object. To solve this problem: we can create a […]

  • Alibaba specification does not recommend multi table join, but how to write this SQL?


    For the description of Alibaba development manual, multi table join is prohibited: The manual says “mandatory”. I believe that the code in many students’ projects does not meet this requirement. But the key problem is: how to write SQL without join?! Decompose associated query That is to say, a single table query is made for […]

  • integrity constraint


    integrity constraint I. Introduction Constraints are optional parameters, just like the width of the data type Function: used to ensure the integrity and consistency of data It is mainly divided into: Primary key (PK) indicates that the field is the primary key of the table and can uniquely identify the record Foreign key (FK) indicates […]

  • Oracle error column type inconsistent with referenced column type


    Appears when a foreign key is associatedBecause the field type is inconsistent with the primary key type of another table

  • /usr/local/lib/ruby/gems/2.4.0/gems/cocoapods-1.5.3/lib/cocoapods/command.rb:118:in `git_version’: Failed to extract git version from `git –version`


    Problems and analysis When I was working on the project today, the following error message was reported when I executed the pod update: /usr/local/lib/ruby/gems/2.4.0/gems/cocoapods-1.5.3/lib/cocoapods/command.rb:118:in git_version’: Failed to extract git version fromgit –version(“xcrun: error: active developer path (\”/Users/feiwei/Desktop/Xcode.app/Contents/Developer\”) does not exist\nUsesudo xcode-select –switch path/to/Xcode.appto specify the Xcode that you wish to use for command line developer […]

  • Mongodb v4.0 command


    Mongodb v4.0 command Official documents > Click here< Operating system library #Operation administrator Library use admin The right to identify db.auth(“root”,”admin”); #User view (format beautification) db.system.users.find().pretty(); #New users db.createUser({ user: ‘root1’, pwd: ‘admin1’, roles: [ { role: “dbOwner”, db: “yapi” }] }); #Update user information / password / permission db.updateUser(“root1”,{ pwd: “admin2”, roles: [{ role: […]

  • Service of four Android components


    Preface Hi, Hello everyone. In the last issue, we talked about how to use the broadcastreceiver. In this issue, we talked about the service related knowledge of the four components of Android. Every day a technical dry goods, every day we progress together. Patience and concentration are not only virtues, but also wealth.   1. […]

  • Feel the difference between using lambda and LINQ to filter data sets in. net


    lambda: ids.Add( _hahahacontext .hahahamodel .FirstOrDefault(    A=>//lambda has been filtered A. name == “Zhang Hongwei” && a.age== 18 ) .id .ToString() );   linq: ids.Add(( Query filtering from R in_hahahacontext.hahahamodel//linq Where (r. name = Zhang Hongwei & & R. age = 18) select r.id ).FirstOrDefault() .ToString() );   When it comes to multi-table joint checking, […]

  • Php json_encode() function returns object and array problems


    The PHP json_encode() function formats different types of JSON data according to different array types  When indexing arrays <?php $arr = [1,2,3,4,5]; (json_encode($arr)); //输出 [1,2,3,4,5]  When associating arrays “Bob”, “job”=>”IT” ]; (json_encode($arr)); // Output {name”:”Bob”,”job”:”IT”}  Empty array <?php $arr = []; (json_encode($arr)); //输出 [] When indexing arrays, data of array type is generated, data of […]