Column and type
- Python course
- Advanced
- Lesson 46/83
- 5 min
Learn column types with Column(Integer), Column(String).
Column and types
Column defines a table column. It takes a type as its first parameter: Integer, String, Float, Boolean, DateTime and so on.
class Product(Base):
__tablename__ = "products"
id = Column(Integer, primary_key=True)
name = Column(String)
price = Column(Float)
in_stock = Column(Boolean)primary_key=True marks a primary key, nullable=False marks a non-null column. A length can be given as in String(50).
Meaning of types
Each column type maps to a corresponding type in the database. Integer stores integers, String stores text, Float stores decimals, Boolean stores true/false.
amount = Column(Integer) # integer
label = Column(String(50)) # text up to 50 chars
ratio = Column(Float) # decimal
active = Column(Boolean) # true/falseChoosing the right type matters for validation and efficiency. A wrong type can cause data loss.
Practice Define a Product model
Start with from sqlalchemy import create_engine, Column, Integer, String, Float and from sqlalchemy.orm import declarative_base. Define Base = declarative_base(). Inside class Product(Base): add __tablename__ = "products". Add columns id = Column(Integer, primary_key=True), name = Column(String) and price = Column(Float). Print the table name with print(Product.__tablename__).
Starter code
# bring in create_engine, Column, Integer, String, Float from sqlalchemy
# bring in declarative_base
# define Base
# define Product class (derive from Base, set table name to 'products')
# add id, name and price columns
# print Product.__tablename__Sample solution
from sqlalchemy import create_engine, Column, Integer, String, Float
from sqlalchemy.orm import declarative_base
Base = declarative_base()
class Product(Base):
__tablename__ = "products"
id = Column(Integer, primary_key=True)
name = Column(String)
price = Column(Float)
print(Product.__tablename__)Expected output
products
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does Column(Integer, primary_key=True) specify?
- An auto-increment column
- A foreign key column
- A nullable column
- A primary key column Correct answer
Explanation: primary_key=True marks the column as a primary key.
2 Complete the String column definition
class Product(Base):
__tablename__ = "products"
name = Column(____)class Product(Base):
__tablename__ = "products"
name = Column(String)Explanation: Column(String) defines a text column.
3 Match the type concepts
| Term | Meaning |
|---|---|
Integer |
Stores integers |
String |
Stores text |
Float |
Stores decimals |
Boolean |
Stores true/false |