Defining Models
Models are Python classes that represent database tables. Each attribute of the class represents a column. SQLAlchemy translates your Python code into SQL.
Example: User Model
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(20), unique=True, nullable=False)
email = db.Column(db.String(120), unique=True, nullable=False)
password = db.Column(db.String(60), nullable=False)
def __repr__(self):
return f"User('{self.username}', '{self.email}')"Common Column Types
- db.Integer – whole numbers.
- db.String(length) – text with max length.
- db.Text – long text (no max).
- db.DateTime – date and time.
- db.Boolean – True/False.
Column Constraints
- primary_key=True – unique identifier for each row.
- unique=True – no duplicate values in this column.
- nullable=False – column cannot be empty.
- default=value – default value if not provided.
Adding Models to Database
After defining your model, run `db.create_all()` again to add the new table.
Two Minute Drill
- Each model class maps to a database table.
- Each attribute (db.Column) maps to a table column.
- Primary key, unique, nullable are common constraints.
- Use `__repr__` to display object info for debugging.
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