day65 from write ORM framework

ORM framework

ORM object-relational mapping, refers to the relationship between objects and databases

Why do mapping? Avoid duplication write sql statement

ORM can help us generate sql statements, execution, and get the results, and then converted to an object

object --> databases --> object

Hand line and ORM framework

The reason to write, in order to better understand the framework of the principle of realization

We automatically generate those sql statement

You can do

Create table statement

CRUD

When you want to create a table

A project corresponds to a database

A class corresponding to a table

An object corresponding to a record

A field corresponding to an attribute

We want to achieve the purpose of:

• When creating a class in a project automatically generates the table according to the type of information
  • Metaclasses to control the process of creating classes
    
  • By init method, the class learned about to create, generate a build table statement

create table user1(
    id int primary key auto_increment,
    name char(20),
    pwd char(20),
    vip tinyint default 0,
    extra float,
    utype tinyint default 0,
    islock tinyint default 0
    );

• When we create an object and save it automatically generates a record based on the information object
  • Object storage method to increase
• When we want to modify the properties of a particular object, automatically generate a modified statement
  • Object provides a method to update
• When we want to delete, delete the automatically generated statement
  • Object provides a method to delete
• When I did not need to get a certain type of data, automatically generating queries, and converts it into an object query
  • It provides a method for obtaining a class object

The difference between the timestamp and datetime

note:

• Mysql the various constraints can be controlled in python
• When the amount of data to foreign key table is too large, foreign key association is not recommended, because every time you insert data from a table when the query again will be the main table, impact on performance