Python
Defining models
Learn to define models with declarative_base.
Defining models
In SQLAlchemy, models derive from a base class created by declarative_base(). Each model represents a database table; the __tablename__ attribute sets the table name.
from sqlalchemy.orm import declarative_base
Base = declarative_base()
class User(Base):
__tablename__ = "users"
id = Column(Integer, primary_key=True)
name = Column(String)
The model class defines the table structure as a Python class. This lets you create tables without writing SQL.
The __tablename__ attribute
In each model class, the __tablename__ attribute sets the table name as a string. This is the name of the actual table in the database.
class Product(Base):
__tablename__ = "products"
# columns...
Table names are usually plural and lowercase (e.g. users, products). The model class is singular and starts with uppercase (e.g. User, Product).
Exercise Define a User model
Start with from sqlalchemy import create_engine, Column, Integer, String and from sqlalchemy.orm import declarative_base. Define Base = declarative_base(). Inside class User(Base): add __tablename__ = "users". Add columns id = Column(Integer, primary_key=True) and name = Column(String). Print the table name with print(User.__tablename__).
Show example solution
from sqlalchemy import create_engine, Column, Integer, String
from sqlalchemy.orm import declarative_base
Base = declarative_base()
class User(Base):
__tablename__ = "users"
id = Column(Integer, primary_key=True)
name = Column(String)
print(User.__tablename__)
Test yourself
-
Match the model concepts
- declarative_base
- Gives the base class
- __tablename__
- Sets the table name
- class User(Base)
- Defines a model
- Column
- Creates a column
-
What does the __tablename__ attribute set?
- The class name
- The table name
- The connection string
- The column type
Show answer
The table name — __tablename__ sets the name of the table in the database.
-
Complete the __tablename__ assignment
class User(Base):
____ = "users"
Show answer
class User(Base):
__tablename__ = "users"
Next lesson: Column and type
