database

class AddIndexesToPosts < ActiveRecord::Migration[6.1]
  def change
    add_index :posts, :author_id
    add_index :posts, :published_at
    add_index :posts, [:author_id, :published_at]
    add_index :posts, :created_at, order: { created_at: :desc }

from django.db import transaction
from django.http import JsonResponse


@transaction.atomic
def transfer_funds(request):

-- Import CSV with COPY (fastest method)
COPY users (username, email, age, created_at)
FROM '/path/to/users.csv'
WITH (
  FORMAT csv,
  HEADER true,

class TransferFundsService
  def initialize(from_account:, to_account:, amount:)
    @from_account = from_account
    @to_account = to_account
    @amount = amount
  end

# Find products with specific spec value
products = Product.objects.filter(specs__weight__gte=100)

# Check if JSON key exists
products = Product.objects.filter(specs__has_key='color')

class AddConstraintsToUsers < ActiveRecord::Migration[6.1]
  def change
    # Null constraints
    change_column_null :users, :email, false
    change_column_null :users, :username, false

from products.models import Product


def import_products_bulk(product_data):
    """Import thousands of products efficiently."""
    products = [

package com.example.demo.service;

import com.example.demo.model.Order;
import com.example.demo.model.OrderItem;
import com.example.demo.model.User;
import com.example.demo.repository.OrderRepository;

class AddStatusToPosts < ActiveRecord::Migration[6.1]
  # Use change for automatic rollback
  def change
    # Add column without default to avoid table lock
    add_column :posts, :status, :string

production:
  primary:
    adapter: postgresql
    url: <%= ENV['DATABASE_URL'] %>
    pool: <%= ENV.fetch("RAILS_MAX_THREADS", 5) %>
  primary_replica:

module StatementTimeout
  extend ActiveSupport::Concern

  class TimeoutExceeded < StandardError; end

  def with_statement_timeout(milliseconds)

from django.db import migrations


def populate_slugs(apps, schema_editor):
    """Generate slugs for existing posts."""
    Post = apps.get_model('blog', 'Post')