Dp Active Record

DodaTech 1 min read

In this tutorial, you'll learn about How to Fix Active Record Errors. We cover key concepts, practical examples, and best practices.

Fix active record errors when business logic and persistence coupled or SQL in domain objects.

Quick Fix

Wrong

class User:
    def __init__(self,name,email):
        self.name=name; self.email=email
    def save(self):
        # Auto-generates: INSERT INTO users(name,email) VALUES(?,?)
        db.execute('INSERT INTO users VALUES (?,?)',self.name,self.email)

Magic save() couples domain object to database schema. Hard to test without DB.

Right

class User:
    def __init__(self,name,email):
        self.name=name; self.email=email
    def validate(self):
        if '@' not in self.email: raise ValueError()
class UserMapper:
    def save(self,user):
        user.validate()
        db.execute('INSERT INTO users(name,email) VALUES(?,?)',user.name,user.email)
    def find(self,uid):
        row=db.execute('SELECT name,email FROM users WHERE id=?',uid).fetchone()
        return User(row[0],row[1]) if row else None
mapper=UserMapper(); mapper.save(User('Alice','a@b.com'))

Domain object pure. Persistence separated in Mapper. Domain testable without DB.

Prevention

Active Record combines domain and persistence. Data Mapper separates them. Choose based on complexity.

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FAQ

What is Active Record?

Object wraps DB row. Domain logic + persistence in one class.

When to use?

Simple CRUD. Small projects. Prototypes. Rails-style development.

vs Data Mapper?

Active Record: simpler, couples domain to DB. Data Mapper: decoupled, more complex.

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