Data integrity is concerned with storing data accurately, ensuring that if a row should not have an empty name that we don’t store it in the database, or that we don’t store a negative price value or any number of same constraints like that.

Column constraints ensure that we apply rules of consistency and validation consistently. That means that if one record has certain rules that make it valid, then we should apply those rules to all records and all changes that are sent to the database, treating all rules of consistency for all records the same.

• Column constraints ensure data integrity across our database, allowing for database accuracy and consistency.
• Constraints are conditions on your column, that provide checks on the data’s validity. It does not allow data that violates constraints to be inserted into the database (it will raise an error if you attempt to).
• In SQLAlchemy, constraints are set in db.Column() after setting the data type.
  • nullable=False is equivalent to NOT NULL in SQL
  • unique=True is equivalent to UNIQUE in SQL

# 例子
class User(db.Model):
	name = db.Column(db.String(), nullable=False)
	title = db.Column(db.String(), unique=True)
	title = db.Column(db.String(), unique=True, nullable=False)

Implement a check constraint

class Product(db.Model):
	# This ensures that no product goes into the table with a nonpositive price value
	price = db.Column(db.Float, db.CheckConstraint('price>0'))