python-mysqlHow do I use Python to create a MySQL Object-Relational Mapping?

Object-Relational Mapping (ORM) is a technique that allows developers to interact with databases using objects. To use Python to create an ORM, the developer must first install the Python package SQLAlchemy. This package provides an interface to interact with various database systems, including MySQL.

Once SQLAlchemy is installed, the developer must create a database engine. This can be done by providing the connection string to the database. For example, to create a MySQL engine, the following code can be used:

from sqlalchemy import create_engine
engine = create_engine('mysql+pymysql://username:password@hostname/database')

Next, the developer must create a Declarative Base object, which will be used to define the classes that will interact with the database. The Declarative Base must be passed the engine created in the previous step.

from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base(engine)

Finally, the developer must define the classes that will be used to interact with the database. Each class must be a subclass of the Base object created in the previous step. For example, to create a table called users with columns id and name, the following code can be used:

from sqlalchemy import Column, Integer, String

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)

Once the classes have been created, the developer can create the database tables by calling the create_all method on the Base object.

Base.metadata.create_all()

Finally, the developer can use the classes to interact with the database. For example, to insert a new user into the database, the following code can be used:

from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind=engine)
session = Session()

user = User(name='John Doe')
session.add(user)
session.commit()

The above code will insert a new user into the users table with the name John Doe.

List of Code Parts with Explanation

• from sqlalchemy import create_engine: This imports the create_engine function from the sqlalchemy package, which is used to create a database engine.
• engine = create_engine('mysql+pymysql://username:password@hostname/database'): This creates a database engine using the connection string provided.
• from sqlalchemy.ext.declarative import declarative_base: This imports the declarative_base function from the sqlalchemy.ext.declarative package, which is used to create a Declarative Base object.
• Base = declarative_base(engine): This creates a Declarative Base object using the engine created in the previous step.
• class User(Base):: This creates a class called User which is a subclass of the Base object.
• __tablename__ = 'users': This specifies the name of the table that the class will interact with.
• id = Column(Integer, primary_key=True): This creates a column called id in the users table with the data type Integer and sets it as the primary key.
• name = Column(String): This creates a column called name in the users table with the data type String.
• Base.metadata.create_all(): This creates the tables in the database based on the classes created.
• from sqlalchemy.orm import sessionmaker: This imports the sessionmaker function from the sqlalchemy.orm package, which is used to create a Session object.
• Session = sessionmaker(bind=engine): This creates a Session object using the engine created in the first step.
• session = Session(): This creates a Session object using the Session object created in the previous step.
• user = User(name='John Doe'): This creates a User object with the name John Doe.
• session.add(user): This adds the User object to the Session.
• session.commit(): This commits the changes to the database.

Relevant Links

• SQLAlchemy Documentation
• SQLAlchemy Tutorial

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