Python Learning Notes (16)-ORM Framework (SQLAlchemy)

The so-called ORM is object-relational Mapping, which maps the table results of a relational database to an object.

1. Install SQLAlchemy:

Easy_install SQLAlchemy

2. Import the SQLAlchemy and initialize the dbsession:

# import: From SQLAlchemy import Column, String, create_enginefrom sqlalchemy.orm import Sessionmakerfrom Sqlalchemy.ext.declarative Import declarative_base# creates the base class for the object: base = Declarative_base () # Defines the User object: class User (Base):    # Table Name:    __tablename__ = ' user '    # table structure:    id = column (String), primary_key=true)    name = Column ( String (20)) # Initialize database connection: # ' database type + database driver name://user name: password @ machine Address: Port number/database name ' engine = Create_engine (' Mysql+mysqlconnector://root: [Email Protected]:3306/test ') # Create dbsession type: dbsession = Sessionmaker (bind=engine)

3. Add a row of records to the database table:

# Create Session object: Session = Dbsession () # Create new User object: New_user = User (id= ' 5 ', name= ' Bob ') # Add to Session:session.add (New_user) # Commit is saved to database: Session.commit () # Close Session:session.close ()

4. Querying data from the database

# Create session:session = Dbsession () # Create a query, filter is the Where condition, and last Call one () returns a unique row, if all () is called All rows are returned: User = Session.query (user ). Filter (user.id== ' 5 '). One () # print Type and Object Name property: print ' Type: ', type (User) print ' name: ', user.name# close session: Session.close ()

5. Create a one-to-many relationship:

A person has many books: when we query a user object, the books property of the object returns a list containing several book objects

Class User (Base):    __tablename__ = ' user '    id = column (string (), primary_key=true)    name = Column (String (20 )    # One-to-many:    books = relationship (' book ') class book (Base):    __tablename__ = ' book '    id = Column (String (20), primary_key=true)    name = Column (String) # The Book    table for the "many" side is associated to the user table by a foreign key:    user_id = Column (String (20), ForeignKey (' user.id '))

Python Learning Notes (16)-ORM Framework (SQLAlchemy)