Database Schema Design: ऐसे Patterns जो समय के साथ अच्छे बने रहें

-- अच्छा: consistent, readable, कोई surprises नहीं
CREATE TABLE users (
    id              BIGSERIAL PRIMARY KEY,
    email           TEXT NOT NULL,
    display_name    TEXT NOT NULL,
    password_hash   TEXT NOT NULL,
    is_active       BOOLEAN NOT NULL DEFAULT true,
    is_verified     BOOLEAN NOT NULL DEFAULT false,
    login_count     INTEGER NOT NULL DEFAULT 0,
    last_login_at   TIMESTAMPTZ,
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
-- बुरा: inconsistent casing, mixed conventions, ambiguous names
CREATE TABLE User (
    UserID          SERIAL PRIMARY KEY,
    EmailAddress    VARCHAR(255),
    name            VARCHAR(100),
    passwd          VARCHAR(255),
    active          BOOLEAN,
    verified        INT,             -- क्या यह 0/1 है? verification level?
    lastLogin       TIMESTAMP,       -- snake_case दुनिया में camelCase
    created         TIMESTAMP        -- कब created? क्या created?
);

CREATE TABLE things (
    id          BIGSERIAL PRIMARY KEY,
    -- ... domain columns ...
    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

-- API-facing resource के लिए
CREATE TABLE projects (
    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    name        TEXT NOT NULL,
    owner_id    UUID NOT NULL REFERENCES users(id),
    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
-- Internal mapping table के लिए
CREATE TABLE project_members (
    id          BIGSERIAL PRIMARY KEY,
    project_id  UUID NOT NULL REFERENCES projects(id),
    user_id     UUID NOT NULL REFERENCES users(id),
    role        TEXT NOT NULL DEFAULT 'member',
    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    UNIQUE (project_id, user_id)
);

-- हमेशा यह
created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
 
-- कभी यह नहीं
created_at  TIMESTAMP NOT NULL DEFAULT NOW()

CREATE OR REPLACE FUNCTION update_updated_at_column()
RETURNS TRIGGER AS $$
BEGIN
    NEW.updated_at = NOW();
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;
 
-- हर table पर apply करो जिसमें updated_at है
CREATE TRIGGER set_updated_at
    BEFORE UPDATE ON users
    FOR EACH ROW
    EXECUTE FUNCTION update_updated_at_column();
 
CREATE TRIGGER set_updated_at
    BEFORE UPDATE ON projects
    FOR EACH ROW
    EXECUTE FUNCTION update_updated_at_column();

CREATE TABLE customers (
    id              BIGSERIAL PRIMARY KEY,
    email           TEXT NOT NULL UNIQUE,
    display_name    TEXT NOT NULL,
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE TABLE products (
    id              BIGSERIAL PRIMARY KEY,
    sku             TEXT NOT NULL UNIQUE,
    name            TEXT NOT NULL,
    price_cents     INTEGER NOT NULL,
    is_active       BOOLEAN NOT NULL DEFAULT true,
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE TABLE orders (
    id              BIGSERIAL PRIMARY KEY,
    customer_id     BIGINT NOT NULL REFERENCES customers(id),
    status          TEXT NOT NULL DEFAULT 'pending'
                    CHECK (status IN ('pending', 'confirmed', 'shipped', 'delivered', 'cancelled')),
    total_cents     INTEGER NOT NULL,
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE TABLE order_items (
    id              BIGSERIAL PRIMARY KEY,
    order_id        BIGINT NOT NULL REFERENCES orders(id) ON DELETE CASCADE,
    product_id      BIGINT NOT NULL REFERENCES products(id),
    quantity        INTEGER NOT NULL CHECK (quantity > 0),
    unit_price_cents INTEGER NOT NULL,
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

-- Denormalized reporting table, cron job से populate
CREATE TABLE order_reports (
    id                  BIGSERIAL PRIMARY KEY,
    order_id            BIGINT NOT NULL,
    customer_email      TEXT NOT NULL,
    customer_name       TEXT NOT NULL,
    product_names       TEXT[] NOT NULL,        -- array यहां ठीक है
    item_count          INTEGER NOT NULL,
    total_cents         INTEGER NOT NULL,
    order_status        TEXT NOT NULL,
    ordered_at          TIMESTAMPTZ NOT NULL,
    report_generated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

CREATE MATERIALIZED VIEW monthly_revenue AS
SELECT
    DATE_TRUNC('month', o.created_at) AS month,
    COUNT(DISTINCT o.id) AS order_count,
    SUM(o.total_cents) AS revenue_cents,
    COUNT(DISTINCT o.customer_id) AS unique_customers
FROM orders o
WHERE o.status != 'cancelled'
GROUP BY DATE_TRUNC('month', o.created_at)
ORDER BY month DESC;
 
-- हर रात refresh करो
REFRESH MATERIALIZED VIEW CONCURRENTLY monthly_revenue;

-- हमेशा यह करो
ALTER TABLE orders
    ADD CONSTRAINT fk_orders_customer
    FOREIGN KEY (customer_id) REFERENCES customers(id);
 
-- "Code में handle करेंगे" alternative:
-- उम्मीद। उम्मीद strategy नहीं है।

-- Customer delete नहीं हो सकता जब तक orders हैं
ALTER TABLE orders
    ADD CONSTRAINT fk_orders_customer
    FOREIGN KEY (customer_id) REFERENCES customers(id)
    ON DELETE RESTRICT;

-- Order delete करने से line items delete — अकेले meaningless हैं
ALTER TABLE order_items
    ADD CONSTRAINT fk_order_items_order
    FOREIGN KEY (order_id) REFERENCES orders(id)
    ON DELETE CASCADE;
 
-- Project delete करने से memberships delete
ALTER TABLE project_members
    ADD CONSTRAINT fk_project_members_project
    FOREIGN KEY (project_id) REFERENCES projects(id)
    ON DELETE CASCADE;

-- अगर manager छोड़ता है, reports अभी भी exist — बस unassigned
ALTER TABLE employees
    ADD CONSTRAINT fk_employees_manager
    FOREIGN KEY (manager_id) REFERENCES employees(id)
    ON DELETE SET NULL;

CREATE TABLE products (
    id              BIGSERIAL PRIMARY KEY,
    name            TEXT NOT NULL CHECK (LENGTH(name) > 0),
    price_cents     INTEGER NOT NULL CHECK (price_cents >= 0),
    discount_pct    NUMERIC(5,2) CHECK (discount_pct BETWEEN 0 AND 100),
    weight_kg       NUMERIC(10,3) CHECK (weight_kg > 0),
    status          TEXT NOT NULL CHECK (status IN ('draft', 'active', 'archived')),
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

ALTER TABLE users ADD CONSTRAINT uq_users_email UNIQUE (email);

-- प्रति user सिर्फ एक active subscription (लेकिन cancelled कितनी भी हो सकती हैं)
CREATE UNIQUE INDEX uq_active_subscription
    ON subscriptions (user_id)
    WHERE status = 'active';
 
-- प्रति user सिर्फ एक primary address
CREATE UNIQUE INDEX uq_primary_address
    ON addresses (user_id)
    WHERE is_primary = true;

CREATE TABLE users (
    id          BIGSERIAL PRIMARY KEY,
    email       TEXT NOT NULL,
    display_name TEXT NOT NULL,
    is_active   BOOLEAN NOT NULL DEFAULT true,
    deleted_at  TIMESTAMPTZ,
    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
-- Partial index: deleted rows को efficiently filter करो
CREATE INDEX idx_users_active ON users (email) WHERE deleted_at IS NULL;

-- Email unique होना चाहिए, लेकिन सिर्फ non-deleted users में
CREATE UNIQUE INDEX uq_users_email_active
    ON users (email)
    WHERE deleted_at IS NULL;

-- Soft delete: user-facing, recoverable
CREATE TABLE documents (
    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    title       TEXT NOT NULL,
    content     TEXT NOT NULL,
    owner_id    UUID NOT NULL REFERENCES users(id),
    deleted_at  TIMESTAMPTZ,
    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE INDEX idx_documents_active ON documents (owner_id) WHERE deleted_at IS NULL;
 
-- Hard delete: internal, UI से recoverable नहीं (लेकिन audited)
CREATE TABLE api_keys (
    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    user_id     UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    key_hash    TEXT NOT NULL,
    last_used_at TIMESTAMPTZ,
    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
-- Delete होने पर, gone है। audit_log record करता है कि exist करती थी।

CREATE TABLE audit_log (
    id              BIGSERIAL PRIMARY KEY,
    table_name      TEXT NOT NULL,
    record_id       TEXT NOT NULL,          -- UUID और BIGINT दोनों PKs handle करने के लिए text
    operation       TEXT NOT NULL CHECK (operation IN ('INSERT', 'UPDATE', 'DELETE')),
    old_values      JSONB,                  -- INSERT के लिए NULL
    new_values      JSONB,                  -- DELETE के लिए NULL
    changed_fields  TEXT[],                 -- कौन से columns बदले (UPDATE के लिए)
    changed_by      UUID REFERENCES users(id),
    changed_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    ip_address      INET,
    user_agent      TEXT
);
 
CREATE INDEX idx_audit_log_table_record ON audit_log (table_name, record_id);
CREATE INDEX idx_audit_log_changed_by ON audit_log (changed_by);
CREATE INDEX idx_audit_log_changed_at ON audit_log (changed_at);

CREATE OR REPLACE FUNCTION audit_trigger_function()
RETURNS TRIGGER AS $$
DECLARE
    old_data JSONB;
    new_data JSONB;
    changed  TEXT[];
    col      TEXT;
BEGIN
    IF TG_OP = 'DELETE' THEN
        old_data := to_jsonb(OLD);
        INSERT INTO audit_log (table_name, record_id, operation, old_values, changed_at)
        VALUES (TG_TABLE_NAME, OLD.id::TEXT, 'DELETE', old_data, NOW());
        RETURN OLD;
    ELSIF TG_OP = 'UPDATE' THEN
        old_data := to_jsonb(OLD);
        new_data := to_jsonb(NEW);
        -- बदले हुए fields ढूंढो
        FOR col IN SELECT key FROM jsonb_each(new_data)
        LOOP
            IF old_data->col IS DISTINCT FROM new_data->col THEN
                changed := array_append(changed, col);
            END IF;
        END LOOP;
        -- सिर्फ तभी log करो जब कुछ actually बदला हो
        IF array_length(changed, 1) > 0 THEN
            INSERT INTO audit_log (table_name, record_id, operation, old_values, new_values, changed_fields, changed_at)
            VALUES (TG_TABLE_NAME, NEW.id::TEXT, 'UPDATE', old_data, new_data, changed, NOW());
        END IF;
        RETURN NEW;
    ELSIF TG_OP = 'INSERT' THEN
        new_data := to_jsonb(NEW);
        INSERT INTO audit_log (table_name, record_id, operation, new_values, changed_at)
        VALUES (TG_TABLE_NAME, NEW.id::TEXT, 'INSERT', new_data, NOW());
        RETURN NEW;
    END IF;
    RETURN NULL;
END;
$$ LANGUAGE plpgsql;
 
-- जिन tables को audit करना है उन पर apply करो
CREATE TRIGGER audit_users
    AFTER INSERT OR UPDATE OR DELETE ON users
    FOR EACH ROW EXECUTE FUNCTION audit_trigger_function();
 
CREATE TRIGGER audit_orders
    AFTER INSERT OR UPDATE OR DELETE ON orders
    FOR EACH ROW EXECUTE FUNCTION audit_trigger_function();

-- Application में, query से पहले:
SET LOCAL app.current_user_id = 'uuid-of-current-user';
 
-- Trigger function में:
changed_by_id := current_setting('app.current_user_id', true)::UUID;

CREATE TABLE documents (
    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    title           TEXT NOT NULL,
    content         TEXT NOT NULL,
    version         INTEGER NOT NULL DEFAULT 1,
    owner_id        UUID NOT NULL REFERENCES users(id),
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE TABLE document_history (
    id              BIGSERIAL PRIMARY KEY,
    document_id     UUID NOT NULL REFERENCES documents(id) ON DELETE CASCADE,
    title           TEXT NOT NULL,
    content         TEXT NOT NULL,
    version         INTEGER NOT NULL,
    changed_by      UUID REFERENCES users(id),
    changed_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    UNIQUE (document_id, version)
);

CREATE TABLE tenants (
    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    name        TEXT NOT NULL,
    slug        TEXT NOT NULL UNIQUE,
    plan        TEXT NOT NULL DEFAULT 'free' CHECK (plan IN ('free', 'pro', 'enterprise')),
    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE TABLE projects (
    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    tenant_id   UUID NOT NULL REFERENCES tenants(id),
    name        TEXT NOT NULL,
    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE TABLE tasks (
    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    tenant_id   UUID NOT NULL REFERENCES tenants(id),
    project_id  UUID NOT NULL REFERENCES projects(id),
    title       TEXT NOT NULL,
    status      TEXT NOT NULL DEFAULT 'todo',
    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
-- हर index में tenant_id होना चाहिए query performance के लिए
CREATE INDEX idx_projects_tenant ON projects (tenant_id);
CREATE INDEX idx_tasks_tenant_project ON tasks (tenant_id, project_id);

-- Table पर RLS enable करो
ALTER TABLE projects ENABLE ROW LEVEL SECURITY;
 
-- Session variable पर based policy बनाओ
CREATE POLICY tenant_isolation ON projects
    USING (tenant_id = current_setting('app.current_tenant_id')::UUID);
 
-- Table owners के लिए भी RLS force करो
ALTER TABLE projects FORCE ROW LEVEL SECURITY;

-- Application के connection middleware में:
SET LOCAL app.current_tenant_id = 'tenant-uuid-here';
 
-- अब RLS-enabled tables पर सभी queries automatically filter होती हैं
SELECT * FROM projects;
-- PostgreSQL internally add करता है: WHERE tenant_id = 'tenant-uuid-here'

-- हर tenant के लिए schema बनाओ
CREATE SCHEMA tenant_acme;
CREATE SCHEMA tenant_globex;
 
-- Tables tenant के schema में रहती हैं
CREATE TABLE tenant_acme.projects (
    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    name        TEXT NOT NULL,
    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
-- Current tenant के लिए search_path set करो
SET search_path TO tenant_acme, public;
 
-- अब unqualified queries tenant का schema hit करती हैं
SELECT * FROM projects;  -- tenant_acme.projects query करता है

CREATE TABLE products (
    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    name            TEXT NOT NULL,
    category_id     UUID NOT NULL REFERENCES categories(id),
    price_cents     INTEGER NOT NULL CHECK (price_cents >= 0),
    attributes      JSONB NOT NULL DEFAULT '{}',
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
-- Example data:
-- Shoe: {"size": "10", "color": "black", "material": "leather"}
-- Laptop: {"ram_gb": 16, "storage_gb": 512, "screen_inches": 14.0}

CREATE TABLE user_settings (
    user_id     UUID PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
    preferences JSONB NOT NULL DEFAULT '{
        "theme": "system",
        "notifications": {"email": true, "push": false},
        "locale": "en",
        "timezone": "UTC"
    }',
    updated_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

-- पूरे JSONB column पर index (@> containment queries के लिए अच्छा)
CREATE INDEX idx_products_attributes ON products USING GIN (attributes);
 
-- Query: सभी black color products ढूंढो
SELECT * FROM products
WHERE attributes @> '{"color": "black"}';
 
-- Query: इनमें से कोई attribute वाले products ढूंढो
SELECT * FROM products
WHERE attributes ?| ARRAY['color', 'size'];

-- Specific path index करो
CREATE INDEX idx_products_color ON products ((attributes->>'color'));
 
-- अब यह regular B-tree lookup है
SELECT * FROM products
WHERE attributes->>'color' = 'black';

-- नया column add करना: clean, atomic, एक statement
ALTER TABLE products ADD COLUMN weight_kg NUMERIC(10,3);
 
-- नया JSONB field add करना: messy, backfill चाहिए
UPDATE products
SET attributes = attributes || '{"weight_kg": null}'
WHERE NOT (attributes ? 'weight_kg');
-- Plus application code update करो missing weight_kg handle करने के लिए
-- Plus validation logic update करो
-- Plus हर API response update करो जो attributes include करता है

-- SAFE: metadata-only, instant (PostgreSQL 11+)
ALTER TABLE users ADD COLUMN bio TEXT;
ALTER TABLE users ADD COLUMN is_premium BOOLEAN NOT NULL DEFAULT false;
 
-- खतरनाक: पूरी table rewrite करता है, full table lock
ALTER TABLE users ALTER COLUMN email TYPE VARCHAR(500);
ALTER TABLE users ADD COLUMN score INTEGER NOT NULL DEFAULT compute_score();
 
-- खतरनाक: validate करने के लिए पूरी table scan करता है
ALTER TABLE orders ADD CONSTRAINT check_total CHECK (total_cents >= 0);

-- यह table lock करता है और rewrite करता है। बड़ी table पर मत करो।
ALTER TABLE users ADD COLUMN avatar_url TEXT NOT NULL DEFAULT 'https://example.com/default.png';

-- Migration 1: nullable column add करो
ALTER TABLE users ADD COLUMN normalized_email TEXT;

-- Migration 2: batches में backfill करो (बड़ी tables के लिए एक statement में मत करो)
UPDATE users SET normalized_email = LOWER(TRIM(email))
WHERE normalized_email IS NULL
LIMIT 10000;
-- सब rows backfill होने तक repeat करो

-- Migration 3: Constraint add करो (full table scan बचाने के लिए NOT VALID इस्तेमाल करो, फिर अलग से validate करो)
ALTER TABLE users ADD CONSTRAINT users_normalized_email_not_null
    CHECK (normalized_email IS NOT NULL) NOT VALID;
 
-- Migration 4: Constraint validate करो (ShareUpdateExclusiveLock लेता है, AccessExclusiveLock नहीं)
ALTER TABLE users VALIDATE CONSTRAINT users_normalized_email_not_null;

-- WRITES BLOCK करता है: live table पर मत करो
CREATE INDEX idx_users_email ON users (email);
 
-- NON-BLOCKING: इसकी जगह यह इस्तेमाल करो
CREATE INDEX CONCURRENTLY idx_users_email ON users (email);

-- Comma-separated values इस तरह query करते हैं। यह मत करो।
SELECT * FROM posts WHERE tags LIKE '%react%';
-- यह "react-native" और "preact" को भी match करता है
 
-- मुझे यह करना चाहिए था:
CREATE TABLE post_tags (
    post_id     UUID NOT NULL REFERENCES posts(id) ON DELETE CASCADE,
    tag_id      UUID NOT NULL REFERENCES tags(id) ON DELETE CASCADE,
    PRIMARY KEY (post_id, tag_id)
);

CREATE TABLE posts (
    id      UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    title   TEXT NOT NULL,
    tags    TEXT[] NOT NULL DEFAULT '{}',
    -- ...
);
 
CREATE INDEX idx_posts_tags ON posts USING GIN (tags);
 
-- Clean queries
SELECT * FROM posts WHERE 'react' = ANY(tags);
SELECT * FROM posts WHERE tags @> ARRAY['react', 'nextjs'];

-- उस समय ठीक लगा
CREATE TABLE notifications (
    id      BIGSERIAL PRIMARY KEY,
    type    TEXT NOT NULL,  -- "email", "sms", "push"
    -- ...
);
 
-- फिर किसी भी ORM में query करो:
-- notification.type  ← हर language के type system से conflict
-- "type" ज़्यादातर SQL dialects में reserved word है
-- हर जगह quote करना पड़ता है: SELECT "type" FROM notifications

-- Extensions
CREATE EXTENSION IF NOT EXISTS "pgcrypto";  -- gen_random_uuid() के लिए
 
-- Updated_at trigger function (reusable)
CREATE OR REPLACE FUNCTION update_updated_at_column()
RETURNS TRIGGER AS $$
BEGIN
    NEW.updated_at = NOW();
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;
 
-- Tenants
CREATE TABLE tenants (
    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    name            TEXT NOT NULL CHECK (LENGTH(name) > 0),
    slug            TEXT NOT NULL UNIQUE CHECK (slug ~ '^[a-z0-9-]+$'),
    plan            TEXT NOT NULL DEFAULT 'free'
                    CHECK (plan IN ('free', 'pro', 'enterprise')),
    settings        JSONB NOT NULL DEFAULT '{}',
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE TRIGGER set_updated_at BEFORE UPDATE ON tenants
    FOR EACH ROW EXECUTE FUNCTION update_updated_at_column();
 
-- Users
CREATE TABLE users (
    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    tenant_id       UUID NOT NULL REFERENCES tenants(id),
    email           TEXT NOT NULL,
    display_name    TEXT NOT NULL CHECK (LENGTH(display_name) > 0),
    password_hash   TEXT NOT NULL,
    is_active       BOOLEAN NOT NULL DEFAULT true,
    is_verified     BOOLEAN NOT NULL DEFAULT false,
    last_login_at   TIMESTAMPTZ,
    deleted_at      TIMESTAMPTZ,
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE UNIQUE INDEX uq_users_email_per_tenant
    ON users (tenant_id, email)
    WHERE deleted_at IS NULL;
 
CREATE INDEX idx_users_tenant ON users (tenant_id) WHERE deleted_at IS NULL;
 
CREATE TRIGGER set_updated_at BEFORE UPDATE ON users
    FOR EACH ROW EXECUTE FUNCTION update_updated_at_column();
 
-- RLS Enable करो
ALTER TABLE users ENABLE ROW LEVEL SECURITY;
CREATE POLICY tenant_isolation ON users
    USING (tenant_id = current_setting('app.current_tenant_id')::UUID);
 
-- Projects
CREATE TABLE projects (
    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    tenant_id       UUID NOT NULL REFERENCES tenants(id),
    name            TEXT NOT NULL CHECK (LENGTH(name) > 0),
    description     TEXT NOT NULL DEFAULT '',
    status          TEXT NOT NULL DEFAULT 'active'
                    CHECK (status IN ('active', 'archived', 'deleted')),
    owner_id        UUID NOT NULL REFERENCES users(id),
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE INDEX idx_projects_tenant ON projects (tenant_id);
CREATE INDEX idx_projects_owner ON projects (owner_id);
 
CREATE TRIGGER set_updated_at BEFORE UPDATE ON projects
    FOR EACH ROW EXECUTE FUNCTION update_updated_at_column();
 
ALTER TABLE projects ENABLE ROW LEVEL SECURITY;
CREATE POLICY tenant_isolation ON projects
    USING (tenant_id = current_setting('app.current_tenant_id')::UUID);
 
-- Tasks
CREATE TABLE tasks (
    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    tenant_id       UUID NOT NULL REFERENCES tenants(id),
    project_id      UUID NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
    title           TEXT NOT NULL CHECK (LENGTH(title) > 0),
    description     TEXT NOT NULL DEFAULT '',
    status          TEXT NOT NULL DEFAULT 'todo'
                    CHECK (status IN ('todo', 'in_progress', 'review', 'done')),
    priority        INTEGER NOT NULL DEFAULT 0 CHECK (priority BETWEEN 0 AND 4),
    assignee_id     UUID REFERENCES users(id) ON DELETE SET NULL,
    due_at          TIMESTAMPTZ,
    completed_at    TIMESTAMPTZ,
    sort_order      INTEGER NOT NULL DEFAULT 0,
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE INDEX idx_tasks_tenant_project ON tasks (tenant_id, project_id);
CREATE INDEX idx_tasks_assignee ON tasks (assignee_id) WHERE assignee_id IS NOT NULL;
CREATE INDEX idx_tasks_status ON tasks (tenant_id, status) WHERE status != 'done';
 
CREATE TRIGGER set_updated_at BEFORE UPDATE ON tasks
    FOR EACH ROW EXECUTE FUNCTION update_updated_at_column();
 
ALTER TABLE tasks ENABLE ROW LEVEL SECURITY;
CREATE POLICY tenant_isolation ON tasks
    USING (tenant_id = current_setting('app.current_tenant_id')::UUID);
 
-- Task comments
CREATE TABLE task_comments (
    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    tenant_id       UUID NOT NULL REFERENCES tenants(id),
    task_id         UUID NOT NULL REFERENCES tasks(id) ON DELETE CASCADE,
    author_id       UUID NOT NULL REFERENCES users(id),
    body            TEXT NOT NULL CHECK (LENGTH(body) > 0),
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE INDEX idx_task_comments_task ON task_comments (task_id);
 
CREATE TRIGGER set_updated_at BEFORE UPDATE ON task_comments
    FOR EACH ROW EXECUTE FUNCTION update_updated_at_column();
 
ALTER TABLE task_comments ENABLE ROW LEVEL SECURITY;
CREATE POLICY tenant_isolation ON task_comments
    USING (tenant_id = current_setting('app.current_tenant_id')::UUID);
 
-- Audit log (कोई RLS नहीं — admin-only table)
CREATE TABLE audit_log (
    id              BIGSERIAL PRIMARY KEY,
    tenant_id       UUID NOT NULL REFERENCES tenants(id),
    table_name      TEXT NOT NULL,
    record_id       TEXT NOT NULL,
    operation       TEXT NOT NULL CHECK (operation IN ('INSERT', 'UPDATE', 'DELETE')),
    old_values      JSONB,
    new_values      JSONB,
    changed_fields  TEXT[],
    changed_by      UUID REFERENCES users(id),
    changed_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE INDEX idx_audit_log_tenant_table ON audit_log (tenant_id, table_name, record_id);
CREATE INDEX idx_audit_log_changed_at ON audit_log (changed_at);