# Core ORM
npm install drizzle-orm

# Database driver (choose one)
npm install pg            # PostgreSQL
npm install mysql2        # MySQL
npm install better-sqlite3 # SQLite

# Drizzle Kit (migrations)
npm install -D drizzle-kit

// db/schema.ts
import { pgTable, serial, text, timestamp } from 'drizzle-orm/pg-core';

export const users = pgTable('users', {
  id: serial('id').primaryKey(),
  email: text('email').notNull().unique(),
  name: text('name').notNull(),
  createdAt: timestamp('created_at').defaultNow(),
});

// db/client.ts
import { drizzle } from 'drizzle-orm/node-postgres';
import { Pool } from 'pg';
import * as schema from './schema';

const pool = new Pool({ connectionString: process.env.DATABASE_URL });
export const db = drizzle(pool, { schema });

import { db } from './db/client';
import { users } from './db/schema';
import { eq } from 'drizzle-orm';

// Insert
const newUser = await db.insert(users).values({
  email: 'user@example.com',
  name: 'John Doe',
}).returning();

// Select
const allUsers = await db.select().from(users);

// Where
const user = await db.select().from(users).where(eq(users.id, 1));

// Update
await db.update(users).set({ name: 'Jane Doe' }).where(eq(users.id, 1));

// Delete
await db.delete(users).where(eq(users.id, 1));

import { pgTable, serial, text, varchar, integer, boolean, timestamp, json, unique } from 'drizzle-orm/pg-core';

export const users = pgTable('users', {
  id: serial('id').primaryKey(),
  email: varchar('email', { length: 255 }).notNull().unique(),
  passwordHash: varchar('password_hash', { length: 255 }).notNull(),
  role: text('role', { enum: ['admin', 'user', 'guest'] }).default('user'),
  metadata: json('metadata').$type<{ theme: string; locale: string }>(),
  isActive: boolean('is_active').default(true),
  createdAt: timestamp('created_at').defaultNow().notNull(),
  updatedAt: timestamp('updated_at').defaultNow().notNull(),
}, (table) => ({
  emailIdx: unique('email_unique_idx').on(table.email),
}));

// Infer TypeScript types
type User = typeof users.$inferSelect;
type NewUser = typeof users.$inferInsert;

import { pgTable, serial, text, integer } from 'drizzle-orm/pg-core';
import { relations } from 'drizzle-orm';

export const authors = pgTable('authors', {
  id: serial('id').primaryKey(),
  name: text('name').notNull(),
});

export const posts = pgTable('posts', {
  id: serial('id').primaryKey(),
  title: text('title').notNull(),
  authorId: integer('author_id').notNull().references(() => authors.id),
});

export const authorsRelations = relations(authors, ({ many }) => ({
  posts: many(posts),
}));

export const postsRelations = relations(posts, ({ one }) => ({
  author: one(authors, {
    fields: [posts.authorId],
    references: [authors.id],
  }),
}));

// Query with relations
const authorsWithPosts = await db.query.authors.findMany({
  with: { posts: true },
});

export const users = pgTable('users', {
  id: serial('id').primaryKey(),
  name: text('name').notNull(),
});

export const groups = pgTable('groups', {
  id: serial('id').primaryKey(),
  name: text('name').notNull(),
});

export const usersToGroups = pgTable('users_to_groups', {
  userId: integer('user_id').notNull().references(() => users.id),
  groupId: integer('group_id').notNull().references(() => groups.id),
}, (table) => ({
  pk: primaryKey({ columns: [table.userId, table.groupId] }),
}));

export const usersRelations = relations(users, ({ many }) => ({
  groups: many(usersToGroups),
}));

export const groupsRelations = relations(groups, ({ many }) => ({
  users: many(usersToGroups),
}));

export const usersToGroupsRelations = relations(usersToGroups, ({ one }) => ({
  user: one(users, { fields: [usersToGroups.userId], references: [users.id] }),
  group: one(groups, { fields: [usersToGroups.groupId], references: [groups.id] }),
}));

import { eq, ne, gt, gte, lt, lte, like, ilike, inArray, isNull, isNotNull, and, or, between } from 'drizzle-orm';

// Equality
await db.select().from(users).where(eq(users.email, 'user@example.com'));

// Comparison
await db.select().from(users).where(gt(users.id, 10));

// Pattern matching
await db.select().from(users).where(like(users.name, '%John%'));

// Multiple conditions
await db.select().from(users).where(
  and(
    eq(users.role, 'admin'),
    gt(users.createdAt, new Date('2024-01-01'))
  )
);

// IN clause
await db.select().from(users).where(inArray(users.id, [1, 2, 3]));

// NULL checks
await db.select().from(users).where(isNull(users.deletedAt));

import { eq } from 'drizzle-orm';

// Inner join
const result = await db
  .select({
    user: users,
    post: posts,
  })
  .from(users)
  .innerJoin(posts, eq(users.id, posts.authorId));

// Left join
const result = await db
  .select({
    user: users,
    post: posts,
  })
  .from(users)
  .leftJoin(posts, eq(users.id, posts.authorId));

// Multiple joins with aggregation
import { count, sql } from 'drizzle-orm';

const result = await db
  .select({
    authorName: authors.name,
    postCount: count(posts.id),
  })
  .from(authors)
  .leftJoin(posts, eq(authors.id, posts.authorId))
  .groupBy(authors.id);

import { desc, asc } from 'drizzle-orm';

// Order by
await db.select().from(users).orderBy(desc(users.createdAt));

// Limit & offset
await db.select().from(users).limit(10).offset(20);

// Pagination helper
function paginate(page: number, pageSize: number = 10) {
  return db.select().from(users)
    .limit(pageSize)
    .offset(page * pageSize);
}

// Auto-rollback on error
await db.transaction(async (tx) => {
  await tx.insert(users).values({ email: 'user@example.com', name: 'John' });
  await tx.insert(posts).values({ title: 'First Post', authorId: 1 });
  // If any query fails, entire transaction rolls back
});

// Manual control
const tx = db.transaction(async (tx) => {
  const user = await tx.insert(users).values({ ... }).returning();

  if (!user) {
    tx.rollback();
    return;
  }

  await tx.insert(posts).values({ authorId: user.id });
});

// drizzle.config.ts
import type { Config } from 'drizzle-kit';

export default {
  schema: './db/schema.ts',
  out: './drizzle',
  dialect: 'postgresql',
  dbCredentials: {
    url: process.env.DATABASE_URL!,
  },
} satisfies Config;

# Generate migration
npx drizzle-kit generate

# View SQL
cat drizzle/0000_migration.sql

# Apply migration
npx drizzle-kit migrate

# Introspect existing database
npx drizzle-kit introspect

# Drizzle Studio (database GUI)
npx drizzle-kit studio

-- drizzle/0000_initial.sql
CREATE TABLE IF NOT EXISTS "users" (
  "id" serial PRIMARY KEY NOT NULL,
  "email" varchar(255) NOT NULL,
  "name" text NOT NULL,
  "created_at" timestamp DEFAULT now() NOT NULL,
  CONSTRAINT "users_email_unique" UNIQUE("email")
);