Python Learning Day 68th: database-related operations

ORM Introduction

orm能干的事：1 创建表，修改表，删除表2 插入数据3 修改数据4 删除数据不能干：不能创建数据库类名-----》表对象------》一条数据属性-----》字段

An ORM "Object-relation-mapping" abbreviation

#sqlThe table in the #Creating table: CREATE TABLE employee (ID INT PRIMARY KEY auto_increment, Name VARCHAR, gender BITDefault 1, Birthday DATA,                                        Department VARCHAR, Salary DECIMAL (8,2) unsigned,  ); #sqlIn the table record #Add a table record: INSERT employee (name,gender,birthday,salary,department) VALUES ("Alex", 1,"1985-12-12", 8000,"Cleaning department "); #Query a table record: SELECT *From Employee WHEREage=24; #Update a table record: Update employeeSETbirthday="1989-10-24" WHEREid=1; #Delete a table record: deleteFrom Employee WHEREName="Alex"#pythonClass Employee (models. Model):Id=models. Autofield (Primary_key=true)Name=models. Charfield (MAX_LENGTH=32)Gender=models. Booleanfield () birthday=models. Datefield () department=models. Charfield (max_length=32) salary=models. Decimalfield (max_digits=8,decimal_places=2) #python Class object # Add a table record: Emp=employee (name= "Alex", gender= True,birthday= "1985-12-12", epartment= " Cleaning Department") Emp.save () # query a table record: Employee.objects.filter (age=24) # Update a table record: Employee.objects.filter (id=1). Update (birthday= "1989-10-24") # delete a table record: Employee.objects.filter (name="Alex"). Delete ()          

Using MySQL steps

0  CREATE DATABASE (Orm Cannot create DATABASE) Span class= "Hljs-number" >1  in Settings configure 2 The span class= "Zh-hans" in Zh-hans Init.py3  define classes in Models4  write attribute, corresponding to the database field 5  Execute python manage.py makemigrations (6  execute Pyhton manage.py migrate ( The table name created is App     

Settings configuration

DATABASES = {' Default ': {' ENGINE ':' Django.db.backends.mysql ',' NAME ':' Lqz ',' USER ':' Root ',' PASSWORD ': '123456 ',' HOST ': '127.0.0.1 ',' PORT ':3306,' Atomic_request ':True,' OPTIONS ': {"Init_command":"SET Storage_engine=myisam",}}}‘‘‘' NAME ':To connect to the database, you need to create a good before connecting' USER ':User name of the connection database' PASSWORD ':Connect database Password ' host ': connect host, default native ' Port ': port default 3306' atomic_request ': True, set to  True  All SQL corresponding to the unified HTTP request is executed in one transaction (either all succeeds or all fails). is a global configuration, if you want to drain an HTTP request (and then customize the transaction), you can use the non_atomic_requests decorator ' OPTIONS ': { "Init_ Command ": " Set Storage_engine=myisam ",} sets the storage engine that created the table to MyISAM, INNODB     

Query for Table

<1>All ():Query all results<2>Filter (**kwargs):It contains objects that match the filter criteria given<3>Get (**kwargs):Returns the object that matches the filter criteria given, with only one return result,If there are more than one object that meets the filter criteria or no error is thrown.<4> Exclude (**kwargs):It contains objects that do not match the filter criteria given<5> order_by (*field):Sort the results of a query<6>Reverse ():Reverse order of query results<8>Count ():Returns a matching query in the database (QuerySet)The number of objects.<9>First ():Returns the first record<10> Last (): returns the final record <11> exists (): Returns true if Queryset contains data,otherwise returns false <12> VALUES (*field): Returns a Valuequeryset-a special querysetthat is not instantiated by a series of model objects after it has been run . It's an iterative dictionary sequence <13> values_list (*field): It's   very similar to values (), it returns a tuple sequence,values  Returns a dictionary sequence <14> distinct (): rejects duplicate records from the returned results         

Table Relationship Creation

一个出版社可以出版多本书，一本书只能有一个出版社一对多（一旦确立了一对多的关系，关联字段要放在多的表里）models.ForeignKey(to=‘Publish‘,to_field=‘nid‘,on_delete=models.CASCADE)一个作者可以写多本书，一本书可以有多个作者多对多(需要第三张表)models.ManyToManyField(to=‘Author‘)一对一author和author_detail是一对一models.OneToOneField(to=‘AuthorDatail‘,to_field=‘nid‘,unique=True,on_delete=models.CASCADE)

Python Learning Day 68th: database-related operations