تصميم مخططات قواعد البيانات: أنماط تصمد مع الزمن

-- Good: consistent, readable, no surprises
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()
);
 
-- Bad: 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,             -- is this 0/1? a verification level?
    lastLogin       TIMESTAMP,       -- camelCase in a snake_case world
    created         TIMESTAMP        -- created what? when?
);

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

-- For an API-facing resource
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()
);
 
-- For an internal mapping table
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)
);

-- Always this
created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
 
-- Never this
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;
 
-- Apply to every table that has updated_at
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, populated by a cron job
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 is fine here
    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;
 
-- Refresh it nightly
REFRESH MATERIALIZED VIEW CONCURRENTLY monthly_revenue;

-- Always do this
ALTER TABLE orders
    ADD CONSTRAINT fk_orders_customer
    FOREIGN KEY (customer_id) REFERENCES customers(id);
 
-- The "we'll handle it in code" alternative:
-- Hope. Hope is not a strategy.

-- Customer can't be deleted while they have orders
ALTER TABLE orders
    ADD CONSTRAINT fk_orders_customer
    FOREIGN KEY (customer_id) REFERENCES customers(id)
    ON DELETE RESTRICT;

-- Deleting an order deletes its line items — they're meaningless alone
ALTER TABLE order_items
    ADD CONSTRAINT fk_order_items_order
    FOREIGN KEY (order_id) REFERENCES orders(id)
    ON DELETE CASCADE;
 
-- Deleting a project deletes its memberships
ALTER TABLE project_members
    ADD CONSTRAINT fk_project_members_project
    FOREIGN KEY (project_id) REFERENCES projects(id)
    ON DELETE CASCADE;

-- If a manager leaves, their reports still exist — just 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);

-- Only one active subscription per user (but they can have many cancelled ones)
CREATE UNIQUE INDEX uq_active_subscription
    ON subscriptions (user_id)
    WHERE status = 'active';
 
-- Only one primary address per user
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()
);
 
-- The partial index: filter out deleted rows efficiently
CREATE INDEX idx_users_active ON users (email) WHERE deleted_at IS NULL;

-- Email must be unique, but only among non-deleted users
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, not recoverable from UI (but 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()
);
-- When deleted, it's gone. The audit_log records that it existed.

CREATE TABLE audit_log (
    id              BIGSERIAL PRIMARY KEY,
    table_name      TEXT NOT NULL,
    record_id       TEXT NOT NULL,          -- text to handle both UUID and BIGINT PKs
    operation       TEXT NOT NULL CHECK (operation IN ('INSERT', 'UPDATE', 'DELETE')),
    old_values      JSONB,                  -- NULL for INSERT
    new_values      JSONB,                  -- NULL for DELETE
    changed_fields  TEXT[],                 -- which columns changed (for UPDATE)
    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 $$
DECLARE
    old_data JSONB;
    new_data JSONB;
    changed  TEXT[];
    col      TEXT;
BEGIN
    IF TG_OP = 'DELETE' THEN
        old_data := to_jsonb(OLD);
        INSERT INTO audit_log (table_name, record_id, operation, old_values, changed_at)
        VALUES (TG_TABLE_NAME, OLD.id::TEXT, 'DELETE', old_data, NOW());
        RETURN OLD;
    ELSIF TG_OP = 'UPDATE' THEN
        old_data := to_jsonb(OLD);
        new_data := to_jsonb(NEW);
        -- Find changed fields
        FOR col IN SELECT key FROM jsonb_each(new_data)
        LOOP
            IF old_data->col IS DISTINCT FROM new_data->col THEN
                changed := array_append(changed, col);
            END IF;
        END LOOP;
        -- Only log if something actually changed
        IF array_length(changed, 1) > 0 THEN
            INSERT INTO audit_log (table_name, record_id, operation, old_values, new_values, changed_fields, changed_at)
            VALUES (TG_TABLE_NAME, NEW.id::TEXT, 'UPDATE', old_data, new_data, changed, NOW());
        END IF;
        RETURN NEW;
    ELSIF TG_OP = 'INSERT' THEN
        new_data := to_jsonb(NEW);
        INSERT INTO audit_log (table_name, record_id, operation, new_values, changed_at)
        VALUES (TG_TABLE_NAME, NEW.id::TEXT, 'INSERT', new_data, NOW());
        RETURN NEW;
    END IF;
    RETURN NULL;
END;
$$ LANGUAGE plpgsql;
 
-- Apply to tables you want audited
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();

-- In your application, before the query:
SET LOCAL app.current_user_id = 'uuid-of-current-user';
 
-- In the trigger function:
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()
);
 
-- Every index should include tenant_id for query performance
CREATE INDEX idx_projects_tenant ON projects (tenant_id);
CREATE INDEX idx_tasks_tenant_project ON tasks (tenant_id, project_id);

-- Enable RLS on the table
ALTER TABLE projects ENABLE ROW LEVEL SECURITY;
 
-- Create a policy based on a session variable
CREATE POLICY tenant_isolation ON projects
    USING (tenant_id = current_setting('app.current_tenant_id')::UUID);
 
-- Force RLS even for table owners
ALTER TABLE projects FORCE ROW LEVEL SECURITY;

-- In your application's connection middleware:
SET LOCAL app.current_tenant_id = 'tenant-uuid-here';
 
-- Now all queries on RLS-enabled tables are automatically filtered
SELECT * FROM projects;
-- PostgreSQL internally adds: WHERE tenant_id = 'tenant-uuid-here'

-- Create a schema for each tenant
CREATE SCHEMA tenant_acme;
CREATE SCHEMA tenant_globex;
 
-- Tables live in the tenant's schema
CREATE TABLE tenant_acme.projects (
    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    name        TEXT NOT NULL,
    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
-- Set the search_path for the current tenant
SET search_path TO tenant_acme, public;
 
-- Now unqualified queries hit the tenant's schema
SELECT * FROM projects;  -- queries tenant_acme.projects

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()
);

-- Index the entire JSONB column (good for @> containment queries)
CREATE INDEX idx_products_attributes ON products USING GIN (attributes);
 
-- Query: find all products with color = "black"
SELECT * FROM products
WHERE attributes @> '{"color": "black"}';
 
-- Query: find products with any of these attributes
SELECT * FROM products
WHERE attributes ?| ARRAY['color', 'size'];

-- Index a specific path
CREATE INDEX idx_products_color ON products ((attributes->>'color'));
 
-- Now this is a regular B-tree lookup
SELECT * FROM products
WHERE attributes->>'color' = 'black';

-- Adding a new column: clean, atomic, one statement
ALTER TABLE products ADD COLUMN weight_kg NUMERIC(10,3);
 
-- Adding a new JSONB field: messy, requires a backfill
UPDATE products
SET attributes = attributes || '{"weight_kg": null}'
WHERE NOT (attributes ? 'weight_kg');
-- Plus update application code to handle missing weight_kg
-- Plus update validation logic
-- Plus update every API response that includes attributes

-- 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;
 
-- DANGEROUS: rewrites the entire table, full table lock
ALTER TABLE users ALTER COLUMN email TYPE VARCHAR(500);
ALTER TABLE users ADD COLUMN score INTEGER NOT NULL DEFAULT compute_score();
 
-- DANGEROUS: scans the entire table to validate
ALTER TABLE orders ADD CONSTRAINT check_total CHECK (total_cents >= 0);

-- This locks the table and rewrites it. Don't do this on a big table.
ALTER TABLE users ADD COLUMN avatar_url TEXT NOT NULL DEFAULT 'https://example.com/default.png';

-- Migration 1: Add the nullable column
ALTER TABLE users ADD COLUMN normalized_email TEXT;

-- Migration 2: Backfill in batches (don't do this in one statement for large tables)
UPDATE users SET normalized_email = LOWER(TRIM(email))
WHERE normalized_email IS NULL
LIMIT 10000;
-- Repeat until all rows are backfilled

-- Migration 3: Add constraint (use NOT VALID to avoid full table scan, then validate separately)
ALTER TABLE users ADD CONSTRAINT users_normalized_email_not_null
    CHECK (normalized_email IS NOT NULL) NOT VALID;
 
-- Migration 4: Validate the constraint (takes a ShareUpdateExclusiveLock, not an AccessExclusiveLock)
ALTER TABLE users VALIDATE CONSTRAINT users_normalized_email_not_null;

-- BLOCKS WRITES: don't do this on a live table
CREATE INDEX idx_users_email ON users (email);
 
-- NON-BLOCKING: use this instead
CREATE INDEX CONCURRENTLY idx_users_email ON users (email);

-- This is how you query comma-separated values. Don't do this.
SELECT * FROM posts WHERE tags LIKE '%react%';
-- This also matches "react-native" and "preact"
 
-- What I should have done:
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'];

-- Seemed fine at the time
CREATE TABLE notifications (
    id      BIGSERIAL PRIMARY KEY,
    type    TEXT NOT NULL,  -- "email", "sms", "push"
    -- ...
);
 
-- Then you try to query it in literally any ORM:
-- notification.type  ← conflicts with every language's type system
-- "type" is a reserved word in most SQL dialects
-- You end up quoting it everywhere: SELECT "type" FROM notifications

-- Extensions
CREATE EXTENSION IF NOT EXISTS "pgcrypto";  -- for gen_random_uuid()
 
-- 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();
 
-- Enable RLS
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 (no RLS — 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);