Migrations - potatoscript/django GitHub Wiki

Migrations in Django are step-by-step instructions that Django writes to help your database stay in sync with the changes you make in your models.py.

🧠 Why Do We Need Migrations?

Imagine you're building with LEGO 🧱
You decide to:

• Add a new block (new model or field)
• Remove a block (delete a model or field)
• Rename a block (rename a model or field)

You need a way to tell your LEGO box (database) that something has changed. That's what migrations do!

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🪄 Step-by-Step: Making and Applying Migrations

✅ 1. Make a Change in Your Model

For example, let’s add a brand to our Toy model.

📄 models.py

class Toy(models.Model):
    name = models.CharField(max_length=100)
    brand = models.CharField(max_length=100, default="No Brand")
    ...

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🧙‍♂️ 2. Run makemigrations

In your terminal:

python manage.py makemigrations

🎉 Django will detect the change and create a new file in migrations/.

🗂 You’ll see something like:

Migrations for 'myapp':
  myapp/migrations/0002_toy_brand.py

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🧱 3. Run migrate to Apply It to the Database

python manage.py migrate

This will actually update your database structure to match the model.

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📦 Let’s Do a Full Example

Step 1: Original Model

class Toy(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimalField(max_digits=6, decimal_places=2)

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Step 2: Modify the Model (Add Field)

class Toy(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimalField(max_digits=6, decimal_places=2)
    rating = models.FloatField(default=5.0)  # new!

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Step 3: Make Migrations

python manage.py makemigrations

Output:

Migrations for 'myapp':
  myapp/migrations/0002_toy_rating.py
    - Add field rating to toy

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Step 4: Apply Migrations

python manage.py migrate

Output:

Applying myapp.0002_toy_rating... OK

🎉 The database now has a new rating column!

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📚 Extra Commands You Should Know

Command	What It Does
python manage.py showmigrations	Lists all migrations and their status ✅
python manage.py sqlmigrate myapp 0002	Shows the SQL Django will run
python manage.py migrate myapp 0002	Runs a specific migration
python manage.py makemigrations myapp	Only make migrations for one app

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🔙 Rolling Back Migrations

Oops? Want to undo the last one?

python manage.py migrate myapp 0001

This rolls your app back to before migration 0002.

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🧁 Best Practices

✅ Always run makemigrations after editing models.py
✅ Then run migrate right after
✅ Don’t manually edit migration files unless you know what you’re doing
✅ Keep migrations in version control (like Git!)

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🔍 Advanced Tip: Checking Migration Files

Go to your app folder:

📁 myapp/migrations/0002_toy_rating.py

You’ll see something like this:

class Migration(migrations.Migration):

    dependencies = [
        ('myapp', '0001_initial'),
    ]

    operations = [
        migrations.AddField(
            model_name='toy',
            name='rating',
            field=models.FloatField(default=5.0),
        ),
    ]

It’s like a history book 📖 for your model!

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🎯 Summary

Step	Action
✍️ 1	Change your model in models.py
🪄 2	Run python manage.py makemigrations
🏗️ 3	Run python manage.py migrate
🔁 4	Check with showmigrations or rollback if needed

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