Database Migrations Advanced

Django migrations হলো database schema changes track এবং apply করার একটি powerful system। এই গাইডে আমরা advanced migration concepts এবং techniques নিয়ে বিস্তারিত আলোচনা করব।

1. Migration Files

Migration File Structure

python

# migrations/0001_initial.py

from django.db import migrations, models

class Migration(migrations.Migration):
    
    # Migration metadata
    initial = True  # প্রথম migration কিনা
    
    # Dependencies - এই migration কোন migrations এর পর run হবে
    dependencies = [
        ('auth', '0012_alter_user_first_name_max_length'),
    ]
    
    # Operations - কী কী changes করা হবে
    operations = [
        migrations.CreateModel(
            name='Product',
            fields=[
                ('id', models.BigAutoField(primary_key=True)),
                ('name', models.CharField(max_length=200)),
                ('price', models.DecimalField(max_digits=10, decimal_places=2)),
                ('created_at', models.DateTimeField(auto_now_add=True)),
            ],
            options={
                'db_table': 'products',
                'ordering': ['-created_at'],
            },
        ),
    ]

Migration File Components

python

# migrations/0002_add_category.py

from django.db import migrations, models
import django.db.models.deletion

class Migration(migrations.Migration):
    
    # এই migration এর dependencies
    dependencies = [
        ('myapp', '0001_initial'),  # Previous migration
        ('categories', '0001_initial'),  # অন্য app এর migration
    ]
    
    # Operations list
    operations = [
        # Add field
        migrations.AddField(
            model_name='product',
            name='category',
            field=models.ForeignKey(
                on_delete=django.db.models.deletion.CASCADE,
                to='categories.category',
                null=True
            ),
        ),
        
        # Add index
        migrations.AddIndex(
            model_name='product',
            index=models.Index(
                fields=['category', '-created_at'],
                name='product_cat_created_idx'
            ),
        ),
    ]

Custom Migration Operations

python

# migrations/0003_custom_operation.py

from django.db import migrations

def create_default_categories(apps, schema_editor):
    """Custom function to create default data"""
    Category = apps.get_model('myapp', 'Category')
    
    default_categories = [
        {'name': 'Electronics', 'slug': 'electronics'},
        {'name': 'Clothing', 'slug': 'clothing'},
        {'name': 'Books', 'slug': 'books'},
    ]
    
    for cat_data in default_categories:
        Category.objects.create(**cat_data)

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0002_add_category'),
    ]
    
    operations = [
        migrations.RunPython(
            create_default_categories,
            reverse_code=migrations.RunPython.noop,
        ),
    ]

Migration File Naming

bash

# Django automatically generates migration files with sequential numbers
migrations/
├── __init__.py
├── 0001_initial.py                    # প্রথম migration
├── 0002_product_category.py           # Field addition
├── 0003_alter_product_price.py        # Field modification
├── 0004_auto_20260113_1234.py         # Auto-generated
└── 0005_custom_data_migration.py      # Custom migration

2. Migration Dependencies

Simple Dependencies

python

# migrations/0002_add_profile.py

class Migration(migrations.Migration):
    
    dependencies = [
        # এই app এর previous migration
        ('myapp', '0001_initial'),
    ]
    
    operations = [
        migrations.CreateModel(
            name='Profile',
            fields=[
                ('id', models.BigAutoField(primary_key=True)),
                ('bio', models.TextField()),
            ],
        ),
    ]

Cross-App Dependencies

python

# app1/migrations/0003_add_foreign_key.py

class Migration(migrations.Migration):
    
    dependencies = [
        ('app1', '0002_previous_migration'),
        ('app2', '0001_initial'),  # অন্য app এর migration
    ]
    
    operations = [
        migrations.AddField(
            model_name='order',
            name='customer',
            field=models.ForeignKey(
                to='app2.customer',
                on_delete=models.CASCADE,
            ),
        ),
    ]

Multiple Dependencies

python

# migrations/0005_merge_branches.py

class Migration(migrations.Migration):
    
    # Multiple migration branches merge করা
    dependencies = [
        ('myapp', '0003_branch_a'),
        ('myapp', '0004_branch_b'),
    ]
    
    operations = [
        # Merge operations
    ]

Dependency Resolution

python

# migrations/0006_complex_dependencies.py

class Migration(migrations.Migration):
    
    dependencies = [
        # নিজের app
        ('myapp', '0005_merge_branches'),
        
        # অন্য apps
        ('auth', '0012_alter_user_first_name_max_length'),
        ('contenttypes', '0002_remove_content_type_name'),
        ('sessions', '0001_initial'),
    ]
    
    operations = [
        # Complex operations
    ]

3. Data Migrations

Basic Data Migration

python

# migrations/0007_populate_default_data.py

from django.db import migrations

def create_default_users(apps, schema_editor):
    """Default users create করুন"""
    User = apps.get_model('auth', 'User')
    
    users_data = [
        {'username': 'admin', 'email': 'admin@example.com', 'is_staff': True},
        {'username': 'user1', 'email': 'user1@example.com', 'is_staff': False},
    ]
    
    for user_data in users_data:
        User.objects.create(**user_data)

def delete_default_users(apps, schema_editor):
    """Reverse operation"""
    User = apps.get_model('auth', 'User')
    User.objects.filter(username__in=['admin', 'user1']).delete()

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0006_complex_dependencies'),
        ('auth', '0012_alter_user_first_name_max_length'),
    ]
    
    operations = [
        migrations.RunPython(
            create_default_users,
            reverse_code=delete_default_users,
        ),
    ]

Data Transformation Migration

python

# migrations/0008_transform_data.py

from django.db import migrations

def transform_prices(apps, schema_editor):
    """Prices কে USD থেকে BDT তে convert করুন"""
    Product = apps.get_model('myapp', 'Product')
    
    # Bulk update for better performance
    products = Product.objects.all()
    
    for product in products:
        # USD to BDT conversion (1 USD = 110 BDT)
        product.price = product.price * 110
    
    # Bulk update
    Product.objects.bulk_update(products, ['price'])

def reverse_transform_prices(apps, schema_editor):
    """Reverse: BDT থেকে USD"""
    Product = apps.get_model('myapp', 'Product')
    
    products = Product.objects.all()
    
    for product in products:
        product.price = product.price / 110
    
    Product.objects.bulk_update(products, ['price'])

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0007_populate_default_data'),
    ]
    
    operations = [
        migrations.RunPython(
            transform_prices,
            reverse_code=reverse_transform_prices,
        ),
    ]

Complex Data Migration

python

# migrations/0009_migrate_user_profiles.py

from django.db import migrations

def migrate_user_profiles(apps, schema_editor):
    """
    Old UserProfile থেকে new Profile model এ data migrate করুন
    """
    OldProfile = apps.get_model('myapp', 'UserProfile')
    NewProfile = apps.get_model('myapp', 'Profile')
    User = apps.get_model('auth', 'User')
    
    # Batch processing for better performance
    batch_size = 1000
    old_profiles = OldProfile.objects.all()
    
    new_profiles = []
    
    for old_profile in old_profiles.iterator(chunk_size=batch_size):
        new_profile = NewProfile(
            user_id=old_profile.user_id,
            bio=old_profile.biography or '',
            avatar=old_profile.profile_picture,
            phone=old_profile.contact_number,
            # Data transformation
            full_name=f"{old_profile.first_name} {old_profile.last_name}",
        )
        new_profiles.append(new_profile)
        
        # Bulk create in batches
        if len(new_profiles) >= batch_size:
            NewProfile.objects.bulk_create(new_profiles)
            new_profiles = []
    
    # Create remaining profiles
    if new_profiles:
        NewProfile.objects.bulk_create(new_profiles)

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0008_transform_data'),
    ]
    
    operations = [
        migrations.RunPython(
            migrate_user_profiles,
            reverse_code=migrations.RunPython.noop,
        ),
    ]

Conditional Data Migration

python

# migrations/0010_conditional_migration.py

from django.db import migrations

def conditional_data_update(apps, schema_editor):
    """
    শুধুমাত্র specific conditions এ data update করুন
    """
    Product = apps.get_model('myapp', 'Product')
    
    # শুধু inactive products এর price update করুন
    inactive_products = Product.objects.filter(is_active=False)
    
    for product in inactive_products:
        # 20% discount apply করুন
        product.price = product.price * 0.8
        product.discount_applied = True
    
    Product.objects.bulk_update(
        inactive_products,
        ['price', 'discount_applied']
    )

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0009_migrate_user_profiles'),
    ]
    
    operations = [
        migrations.RunPython(
            conditional_data_update,
            reverse_code=migrations.RunPython.noop,
        ),
    ]

4. RunPython Operations

Basic RunPython

python

# migrations/0011_runpython_basic.py

from django.db import migrations

def forward_func(apps, schema_editor):
    """Forward migration logic"""
    MyModel = apps.get_model('myapp', 'MyModel')
    # Operations
    pass

def reverse_func(apps, schema_editor):
    """Reverse migration logic"""
    MyModel = apps.get_model('myapp', 'MyModel')
    # Reverse operations
    pass

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0010_conditional_migration'),
    ]
    
    operations = [
        migrations.RunPython(
            forward_func,
            reverse_code=reverse_func,
        ),
    ]

RunPython with Database Router

python

# migrations/0012_runpython_with_router.py

from django.db import migrations

def update_analytics_data(apps, schema_editor):
    """
    Specific database এ data update করুন
    """
    # Database alias check করুন
    if schema_editor.connection.alias != 'analytics':
        return
    
    AnalyticsData = apps.get_model('myapp', 'AnalyticsData')
    
    # Analytics database এ operations
    AnalyticsData.objects.using('analytics').update(
        processed=True
    )

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0011_runpython_basic'),
    ]
    
    operations = [
        migrations.RunPython(
            update_analytics_data,
            reverse_code=migrations.RunPython.noop,
        ),
    ]

RunPython with Hints

python

# migrations/0013_runpython_hints.py

from django.db import migrations

def complex_operation(apps, schema_editor):
    """
    Complex operation with database hints
    """
    Product = apps.get_model('myapp', 'Product')
    Category = apps.get_model('myapp', 'Category')
    
    # Get database alias from schema_editor
    db_alias = schema_editor.connection.alias
    
    # Use specific database
    products = Product.objects.using(db_alias).all()
    
    for product in products:
        # Complex logic
        pass

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0012_runpython_with_router'),
    ]
    
    operations = [
        migrations.RunPython(
            complex_operation,
            hints={'target_db': 'default'},
        ),
    ]

RunPython with Atomic

python

# migrations/0014_runpython_atomic.py

from django.db import migrations, transaction

def atomic_operation(apps, schema_editor):
    """
    Atomic operation - সব success হবে অথবা সব rollback হবে
    """
    Product = apps.get_model('myapp', 'Product')
    
    with transaction.atomic():
        # All or nothing
        products = Product.objects.all()
        
        for product in products:
            product.updated = True
            product.save()

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0013_runpython_hints'),
    ]
    
    # atomic=False করলে migration non-atomic হবে
    atomic = True
    
    operations = [
        migrations.RunPython(
            atomic_operation,
            reverse_code=migrations.RunPython.noop,
            atomic=True,  # এই operation atomic
        ),
    ]

5. Reversible Migrations

Fully Reversible Migration

python

# migrations/0015_reversible.py

from django.db import migrations, models

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0014_runpython_atomic'),
    ]
    
    operations = [
        # AddField - automatically reversible
        migrations.AddField(
            model_name='product',
            name='sku',
            field=models.CharField(max_length=50, null=True),
        ),
        
        # RemoveField - automatically reversible
        migrations.RemoveField(
            model_name='product',
            name='old_field',
        ),
        
        # AlterField - automatically reversible
        migrations.AlterField(
            model_name='product',
            name='price',
            field=models.DecimalField(max_digits=12, decimal_places=2),
        ),
    ]

Reversible Data Migration

python

# migrations/0016_reversible_data.py

from django.db import migrations

def set_default_status(apps, schema_editor):
    """Forward: Set default status"""
    Order = apps.get_model('myapp', 'Order')
    Order.objects.filter(status__isnull=True).update(status='pending')

def clear_default_status(apps, schema_editor):
    """Reverse: Clear status"""
    Order = apps.get_model('myapp', 'Order')
    Order.objects.filter(status='pending').update(status=None)

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0015_reversible'),
    ]
    
    operations = [
        migrations.RunPython(
            set_default_status,
            reverse_code=clear_default_status,  # Reversible
        ),
    ]

Irreversible Migration

python

# migrations/0017_irreversible.py

from django.db import migrations

def delete_old_data(apps, schema_editor):
    """Delete old data - cannot be reversed!"""
    OldModel = apps.get_model('myapp', 'OldModel')
    OldModel.objects.all().delete()

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0016_reversible_data'),
    ]
    
    operations = [
        migrations.RunPython(
            delete_old_data,
            reverse_code=migrations.RunPython.noop,  # Irreversible
        ),
        
        # অথবা explicitly irreversible mark করুন
        migrations.RunPython(
            delete_old_data,
            reverse_code=None,  # None = irreversible
        ),
    ]

Testing Reversibility

bash

# Migration apply করুন
python manage.py migrate myapp 0017

# Migration reverse করুন
python manage.py migrate myapp 0016

# যদি irreversible হয় তাহলে error দেবে
# IrreversibleError: Operation RunPython is not reversible

6. Squashing Migrations

Why Squash Migrations?

bash

# অনেক migrations থাকলে slow হয়
migrations/
├── 0001_initial.py
├── 0002_add_field.py
├── 0003_alter_field.py
├── 0004_remove_field.py
├── ... (100+ migrations)
└── 0150_latest.py

# Squashing করে optimize করুন

Squash Command

bash

# Squash migrations from 0001 to 0050
python manage.py squashmigrations myapp 0001 0050

# Output: 0001_squashed_0050_auto.py

Squashed Migration Example

python

# migrations/0001_squashed_0050_auto.py

from django.db import migrations, models

class Migration(migrations.Migration):
    
    # Squashed migration marker
    replaces = [
        ('myapp', '0001_initial'),
        ('myapp', '0002_add_field'),
        ('myapp', '0003_alter_field'),
        # ... all replaced migrations
        ('myapp', '0050_latest'),
    ]
    
    initial = True
    
    dependencies = [
        ('auth', '0012_alter_user_first_name_max_length'),
    ]
    
    operations = [
        # Optimized operations
        migrations.CreateModel(
            name='Product',
            fields=[
                ('id', models.BigAutoField(primary_key=True)),
                ('name', models.CharField(max_length=200)),
                ('price', models.DecimalField(max_digits=12, decimal_places=2)),
                ('sku', models.CharField(max_length=50)),
                # Final state of all fields
            ],
        ),
    ]

Squashing Workflow

bash

# Step 1: Squash migrations
python manage.py squashmigrations myapp 0001 0050

# Step 2: Test squashed migration
python manage.py migrate myapp 0001_squashed_0050_auto

# Step 3: যদি সব ঠিক থাকে, old migrations delete করুন
# (শুধু যদি সব environments এ squashed migration applied হয়)

# Step 4: replaces attribute remove করুন
# এখন এটি একটি normal migration

Manual Squashing

python

# migrations/0001_squashed_manual.py

from django.db import migrations, models

class Migration(migrations.Migration):
    """
    Manually squashed migration
    0001 থেকে 0050 পর্যন্ত সব migrations এর final state
    """
    
    replaces = [
        ('myapp', '0001_initial'),
        ('myapp', '0002_add_category'),
        # ... list all replaced migrations
    ]
    
    initial = True
    
    dependencies = []
    
    operations = [
        # শুধু final state define করুন
        migrations.CreateModel(
            name='Product',
            fields=[
                # All fields in their final state
            ],
        ),
        
        migrations.CreateModel(
            name='Category',
            fields=[
                # All fields in their final state
            ],
        ),
        
        # Indexes, constraints etc.
        migrations.AddIndex(
            model_name='product',
            index=models.Index(fields=['category']),
        ),
    ]

7. Zero Downtime Migrations

Strategy 1: Add Field with Default

python

# Step 1: Add nullable field
# migrations/0020_add_field_step1.py

class Migration(migrations.Migration):
    operations = [
        migrations.AddField(
            model_name='product',
            name='new_price',
            field=models.DecimalField(
                max_digits=10,
                decimal_places=2,
                null=True,  # Nullable - no downtime
            ),
        ),
    ]

# Step 2: Populate data
# migrations/0021_populate_new_price.py

def populate_new_price(apps, schema_editor):
    Product = apps.get_model('myapp', 'Product')
    Product.objects.update(new_price=models.F('old_price'))

class Migration(migrations.Migration):
    operations = [
        migrations.RunPython(populate_new_price),
    ]

# Step 3: Make field non-nullable
# migrations/0022_make_field_required.py

class Migration(migrations.Migration):
    operations = [
        migrations.AlterField(
            model_name='product',
            name='new_price',
            field=models.DecimalField(
                max_digits=10,
                decimal_places=2,
                null=False,  # এখন required
            ),
        ),
    ]

# Step 4: Remove old field
# migrations/0023_remove_old_field.py

class Migration(migrations.Migration):
    operations = [
        migrations.RemoveField(
            model_name='product',
            name='old_price',
        ),
    ]

Strategy 2: Rename Field Safely

python

# Step 1: Add new field
class Migration(migrations.Migration):
    operations = [
        migrations.AddField(
            model_name='user',
            name='full_name',
            field=models.CharField(max_length=200, null=True),
        ),
    ]

# Step 2: Dual write (application code)
# models.py
class User(models.Model):
    name = models.CharField(max_length=100)  # Old field
    full_name = models.CharField(max_length=200, null=True)  # New field
    
    def save(self, *args, **kwargs):
        # Write to both fields
        if self.name and not self.full_name:
            self.full_name = self.name
        super().save(*args, **kwargs)

# Step 3: Backfill data
def backfill_full_name(apps, schema_editor):
    User = apps.get_model('myapp', 'User')
    User.objects.filter(full_name__isnull=True).update(
        full_name=models.F('name')
    )

# Step 4: Switch application code to use new field

# Step 5: Remove old field
class Migration(migrations.Migration):
    operations = [
        migrations.RemoveField(
            model_name='user',
            name='name',
        ),
    ]

Strategy 3: Add Index Without Locking

python

# PostgreSQL: CONCURRENT index creation

from django.contrib.postgres.operations import AddIndexConcurrently
from django.db import migrations, models

class Migration(migrations.Migration):
    
    atomic = False  # CONCURRENT operations require non-atomic migration
    
    operations = [
        AddIndexConcurrently(
            model_name='product',
            index=models.Index(
                fields=['category', 'created_at'],
                name='product_cat_created_idx'
            ),
        ),
    ]

Strategy 4: Large Table Alterations

python

# For large tables, use multiple small migrations

# Step 1: Add new table
class Migration(migrations.Migration):
    operations = [
        migrations.CreateModel(
            name='ProductNew',
            fields=[
                # New schema
            ],
        ),
    ]

# Step 2: Gradually copy data
def copy_data_batch(apps, schema_editor):
    Product = apps.get_model('myapp', 'Product')
    ProductNew = apps.get_model('myapp', 'ProductNew')
    
    # Copy in batches
    batch_size = 1000
    products = Product.objects.all()[:batch_size]
    
    new_products = [
        ProductNew(**product.__dict__)
        for product in products
    ]
    
    ProductNew.objects.bulk_create(new_products)

# Step 3: Switch application to new table

# Step 4: Rename tables
class Migration(migrations.Migration):
    operations = [
        migrations.RenameModel('Product', 'ProductOld'),
        migrations.RenameModel('ProductNew', 'Product'),
    ]

# Step 5: Drop old table

8. Migration Conflicts

Detecting Conflicts

bash

# Migration conflicts detect করুন
python manage.py makemigrations --check

# Output যদি conflict থাকে:
# CommandError: Conflicting migrations detected; multiple leaf nodes in the migration graph

Conflict Scenario

bash

# Developer A creates:
migrations/0005_add_field_a.py

# Developer B creates (same time):
migrations/0005_add_field_b.py

# Conflict! দুটি 0005 migration

Resolving Conflicts - Method 1: Merge Migration

bash

# Django automatically merge migration create করবে
python manage.py makemigrations --merge

# Output: 0006_merge_0005_add_field_a_0005_add_field_b.py

python

# migrations/0006_merge.py

class Migration(migrations.Migration):
    
    # দুটি conflicting migrations এর উপর depend করে
    dependencies = [
        ('myapp', '0005_add_field_a'),
        ('myapp', '0005_add_field_b'),
    ]
    
    operations = [
        # Usually empty - just merges the branches
    ]

Resolving Conflicts - Method 2: Manual Resolution

bash

# Step 1: Rename one migration
mv migrations/0005_add_field_b.py migrations/0006_add_field_b.py

# Step 2: Update dependencies in 0006

python

# migrations/0006_add_field_b.py

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0005_add_field_a'),  # Updated dependency
    ]
    
    operations = [
        # Original operations
    ]

Preventing Conflicts

bash

# Best practices:

# 1. Always pull latest code before creating migrations
git pull origin main
python manage.py makemigrations

# 2. Communicate with team about migrations

# 3. Use feature branches
git checkout -b feature/add-new-field
python manage.py makemigrations
git push origin feature/add-new-field

# 4. Merge conflicts early
git merge main
python manage.py makemigrations --merge

Complex Conflict Resolution

python

# যদি merge migration এ operations প্রয়োজন হয়

# migrations/0007_merge_complex.py

from django.db import migrations

def resolve_conflict(apps, schema_editor):
    """
    Conflicting changes resolve করুন
    """
    Product = apps.get_model('myapp', 'Product')
    
    # দুটি migration এর effects reconcile করুন
    products = Product.objects.all()
    
    for product in products:
        # Conflict resolution logic
        pass

class Migration(migrations.Migration):
    
    dependencies = [
        ('myapp', '0005_branch_a'),
        ('myapp', '0006_branch_b'),
    ]
    
    operations = [
        migrations.RunPython(
            resolve_conflict,
            reverse_code=migrations.RunPython.noop,
        ),
    ]

Best Practices

1. Migration Organization

bash

# ✅ Good: Descriptive names
0001_initial.py
0002_add_product_category.py
0003_add_product_sku_index.py
0004_populate_default_categories.py

# ❌ Bad: Auto-generated names only
0001_auto_20260113_1234.py
0002_auto_20260113_1456.py

2. Keep Migrations Small

python

# ✅ Good: One logical change per migration
# migrations/0005_add_category_field.py
operations = [
    migrations.AddField(
        model_name='product',
        name='category',
        field=models.ForeignKey(...),
    ),
]

# ❌ Bad: Multiple unrelated changes
operations = [
    migrations.AddField(...),  # Add category
    migrations.AlterField(...),  # Change price
    migrations.CreateModel(...),  # Create new model
    migrations.RunPython(...),  # Data migration
]

3. Test Migrations

python

# tests/test_migrations.py

from django.test import TestCase
from django.db.migrations.executor import MigrationExecutor
from django.db import connection

class MigrationTestCase(TestCase):
    
    def test_migration_0008_forward_backward(self):
        """Test migration can be applied and reversed"""
        executor = MigrationExecutor(connection)
        
        # Go to migration 0007
        executor.migrate([('myapp', '0007_previous')])
        
        # Apply migration 0008
        executor.migrate([('myapp', '0008_target')])
        
        # Reverse migration
        executor.migrate([('myapp', '0007_previous')])

4. Document Complex Migrations

python

# migrations/0010_complex_data_migration.py

"""
Migration: Complex Data Transformation

Purpose:
    - Migrate user profiles from old schema to new schema
    - Transform phone numbers to international format
    - Merge duplicate user accounts

Dependencies:
    - Requires 0009_add_profile_fields to be applied first

Reversibility:
    - This migration is irreversible due to data merging

Performance:
    - Processes ~100,000 records
    - Estimated time: 5-10 minutes
    - Uses batch processing for efficiency

Author: John Doe
Date: 2026-01-13
"""

from django.db import migrations

def complex_transformation(apps, schema_editor):
    # Implementation
    pass

class Migration(migrations.Migration):
    # Migration definition
    pass

সারসংক্ষেপ

Django migrations advanced features ব্যবহার করে complex database changes safely manage করুন:

Key Points:

Migration Files: Structure, components, naming conventions বুঝুন
Dependencies: Simple, cross-app, multiple dependencies manage করুন
Data Migrations: Data transformation, population, migration করুন
RunPython: Custom Python code migrations এ execute করুন
Reversible Migrations: Forward এবং reverse operations define করুন
Squashing: অনেক migrations কে optimize করুন
Zero Downtime: Production এ downtime ছাড়া migrations apply করুন
Conflicts: Migration conflicts detect এবং resolve করুন

Migrations properly manage করা production applications এর জন্য critical! 🚀💾

Database Migrations Advanced ​

1. Migration Files ​

Migration File Structure ​

Migration File Components ​

Custom Migration Operations ​

Migration File Naming ​

2. Migration Dependencies ​

Simple Dependencies ​

Cross-App Dependencies ​

Multiple Dependencies ​

Dependency Resolution ​

3. Data Migrations ​

Basic Data Migration ​

Data Transformation Migration ​

Complex Data Migration ​

Conditional Data Migration ​

4. RunPython Operations ​

Basic RunPython ​

RunPython with Database Router ​

RunPython with Hints ​

RunPython with Atomic ​

5. Reversible Migrations ​

Fully Reversible Migration ​

Reversible Data Migration ​

Irreversible Migration ​

Testing Reversibility ​

6. Squashing Migrations ​

Why Squash Migrations? ​

Squash Command ​

Squashed Migration Example ​

Squashing Workflow ​

Manual Squashing ​

7. Zero Downtime Migrations ​

Strategy 1: Add Field with Default ​

Strategy 2: Rename Field Safely ​

Strategy 3: Add Index Without Locking ​

Strategy 4: Large Table Alterations ​

8. Migration Conflicts ​

Detecting Conflicts ​

Conflict Scenario ​

Resolving Conflicts - Method 1: Merge Migration ​

Resolving Conflicts - Method 2: Manual Resolution ​

Preventing Conflicts ​

Complex Conflict Resolution ​

Best Practices ​

1. Migration Organization ​

2. Keep Migrations Small ​

3. Test Migrations ​

4. Document Complex Migrations ​

সারসংক্ষেপ ​

Key Points: ​

Database Migrations Advanced

1. Migration Files

Migration File Structure

Migration File Components

Custom Migration Operations

Migration File Naming

2. Migration Dependencies

Simple Dependencies

Cross-App Dependencies

Multiple Dependencies

Dependency Resolution

3. Data Migrations

Basic Data Migration

Data Transformation Migration

Complex Data Migration

Conditional Data Migration

4. RunPython Operations

Basic RunPython

RunPython with Database Router

RunPython with Hints

RunPython with Atomic

5. Reversible Migrations

Fully Reversible Migration

Reversible Data Migration

Irreversible Migration

Testing Reversibility

6. Squashing Migrations

Why Squash Migrations?

Squash Command

Squashed Migration Example

Squashing Workflow

Manual Squashing

7. Zero Downtime Migrations

Strategy 1: Add Field with Default

Strategy 2: Rename Field Safely

Strategy 3: Add Index Without Locking

Strategy 4: Large Table Alterations

8. Migration Conflicts

Detecting Conflicts

Conflict Scenario

Resolving Conflicts - Method 1: Merge Migration

Resolving Conflicts - Method 2: Manual Resolution

Preventing Conflicts

Complex Conflict Resolution

Best Practices

1. Migration Organization

2. Keep Migrations Small

3. Test Migrations

4. Document Complex Migrations

সারসংক্ষেপ

Key Points: