Defining models
- Python course
- Advanced
- Lesson 45/83
- 5 min
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).
Practice 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__).
Starter code
# bring in create_engine, Column, Integer, String from sqlalchemy
# bring in declarative_base
# define Base
# define User class (derive from Base, set table name to 'users')
# add id and name columns
# print User.__tablename__Sample 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__)Expected output
users
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the model concepts
| Term | Meaning |
|---|---|
declarative_base |
Gives the base class |
__tablename__ |
Sets the table name |
class User(Base) |
Defines a model |
Column |
Creates a column |
2 What does the __tablename__ attribute set?
- The class name
- The table name Correct answer
- The connection string
- The column type
Explanation: __tablename__ sets the name of the table in the database.
3 Complete the __tablename__ assignment
class User(Base):
____ = "users"class User(Base):
__tablename__ = "users"Explanation: The __tablename__ attribute sets the table name.