Detailed explanation of ORM framework SQLObject in Python

With the widespread popularity of Web applications, Python has become more and more widely used in the field of Web development. Many Python Web Frameworks today provide some ORM frameworks for operating databases. SQLObject is one of the very popular and easy-to-use ORM frameworks. This article will introduce in detail how to use the SQLObject framework.

1. Install SQLObject

Using the pip tool can easily install SQLObject:

pip install sqlobject

2. Connect to the database

First introduce the sqlobject library and use the connectionForURI method to connect to the database. The following is an example of a MySQL database connection:

import MySQLdb
from sqlobject import *


connection_string = 'mysql://user:password@localhost/database'
connection = connectionForURI(connection_string)
sqlhub.processConnection = connection

The user, password, localhost and database should be replaced with actual values.

3. Define model class

When defining a model class, you must inherit the SQLObject class. The following is a simple definition example of the Person class:

class Person(SQLObject):
    name = StringCol(length=100)
    age = IntCol(default=0)

The Person class contains two fields: name and age. name is a string type with a length of 100, and age is an integer type with an initial value of 0. SQLObject provides several different types of columns, including StringCol, IntCol, FloatCol, DecimalCol, BoolCol, DateCol, DateTimeCol and TimeCol, etc. You can also set other properties of the column, such as default value, uniqueness, index, etc.

4. Create table

To create a table in the database, just introduce the module that defines the model class in the Python shell or script and execute the createTable() method:

from models import Person


Person.createTable()

If the table already exists, it will not be created again.

5. Insert data

To insert data into the table, just create an instance of the model class and assign values ​​to each field. For example:

john = Person(name='John Smith', age=30)

To save the instance to the database, call its save() method:

john.save()

At this time, a table named person will be created in the database and a name will be inserted. Record for John Smith, age 30.

6. Querying data

SQLObject provides many methods for querying data in the database. The following are several commonly used method examples:

(1) Get all records

To get all records in the Person table, you can call the select() method of the Person class:

people = Person.select()
for person in people:
    print(person.name, person.age)

This code will iterate through each record in the Person table and output their name and age field values.

(2) Filter records by conditions

To filter records by conditions, you can pass in a SQLExpression object in the select() method. For example, the following code will get everyone whose age is 30 or above:

people = Person.select(Person.age >= 30)
for person in people:
    print(person.name, person.age)

Similarly, you can use operators such as <, <=, >, >=, ==, and != for comparison .

(3) Sort by field

To sort by field, you can pass in an OrderBy clause in the select() method. For example, the following code will sort the age field in ascending order:

people = Person.select(orderBy=Person.age)
for person in people:
    print(person.name, person.age)

To sort in descending order, you can add a minus sign before the field name, for example:

people = Person.select(orderBy=-Person.age)

7. Update data

To update data, just modify the attribute value of the model class instance and then call its save() method. For example, the following code will modify John Smith's age to 35:

john.age = 35
john.save()

8. Delete data

To delete data, simply call the destroySelf() method of the model class instance That’s it. For example, the following code will delete a record named John Smith:

john.destroySelf()

9. Summary

SQLObject is a very convenient ORM framework that can greatly simplify Python web development Operations on the database. This article introduces the basic usage of SQLObject, including connecting to the database, defining model classes, creating tables, inserting data, querying data, updating data and deleting data. I hope readers can try using SQLObject for Python web development.

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