Datenbankschema-Design: Muster, die gut altern

-- ✅ So sieht Konsistenz aus
CREATE TABLE users (
    id              BIGSERIAL PRIMARY KEY,
    email           TEXT NOT NULL UNIQUE,
    display_name    TEXT NOT NULL,
    password_hash   TEXT NOT NULL,
    is_verified     BOOLEAN NOT NULL DEFAULT false,
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE TABLE posts (
    id              BIGSERIAL PRIMARY KEY,
    author_id       BIGINT NOT NULL REFERENCES users(id),
    title           TEXT NOT NULL,
    slug            TEXT NOT NULL UNIQUE,
    content         TEXT NOT NULL,
    status          TEXT NOT NULL DEFAULT 'draft'
                    CHECK (status IN ('draft', 'published', 'archived')),
    published_at    TIMESTAMPTZ,
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

-- ❌ Nicht normalisiert: Kundendaten in der Bestelltabelle wiederholt
CREATE TABLE orders (
    id              BIGSERIAL PRIMARY KEY,
    customer_name   TEXT NOT NULL,
    customer_email  TEXT NOT NULL,
    product_name    TEXT NOT NULL,
    product_price   INTEGER NOT NULL,
    quantity        INTEGER NOT NULL,
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
-- Problem: Wenn ein Kunde seinen Namen ändert, musst du JEDE Bestellung aktualisieren
 
-- ✅ Normalisiert: Jede Entität in ihrer eigenen Tabelle
CREATE TABLE customers (
    id              BIGSERIAL PRIMARY KEY,
    name            TEXT NOT NULL,
    email           TEXT NOT NULL UNIQUE,
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE TABLE products (
    id              BIGSERIAL PRIMARY KEY,
    name            TEXT NOT NULL,
    price_cents     INTEGER NOT NULL CHECK (price_cents >= 0),
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
CREATE TABLE orders (
    id              BIGSERIAL PRIMARY KEY,
    customer_id     BIGINT NOT NULL REFERENCES customers(id),
    total_cents     INTEGER NOT NULL CHECK (total_cents >= 0),
    status          TEXT NOT NULL DEFAULT 'pending'
                    CHECK (status IN ('pending', 'confirmed', 'shipped', 'delivered', 'cancelled')),
    created_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()
);

-- Denormalisierte Reporting-Tabelle, befüllt durch einen 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 ist hier in Ordnung
    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;
 
-- Nightly aktualisieren
REFRESH MATERIALIZED VIEW CONCURRENTLY monthly_revenue;

-- Mach immer das
ALTER TABLE orders
    ADD CONSTRAINT fk_orders_customer
    FOREIGN KEY (customer_id) REFERENCES customers(id);
 
-- Die "wir regeln das im Code"-Alternative:
-- Hoffnung. Hoffnung ist keine Strategie.

-- Kunde kann nicht gelöscht werden, solange er Bestellungen hat
ALTER TABLE orders
    ADD CONSTRAINT fk_orders_customer
    FOREIGN KEY (customer_id) REFERENCES customers(id)
    ON DELETE RESTRICT;

-- Das Löschen einer Bestellung löscht ihre Positionen — allein sind sie bedeutungslos
ALTER TABLE order_items
    ADD CONSTRAINT fk_order_items_order
    FOREIGN KEY (order_id) REFERENCES orders(id)
    ON DELETE CASCADE;
 
-- Das Löschen eines Projekts löscht seine Mitgliedschaften
ALTER TABLE project_members
    ADD CONSTRAINT fk_project_members_project
    FOREIGN KEY (project_id) REFERENCES projects(id)
    ON DELETE CASCADE;

-- Wenn ein Manager geht, existieren seine Berichte weiterhin — nur nicht zugewiesen
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);

-- Nur ein aktives Abonnement pro Nutzer (aber er kann viele gekündigte haben)
CREATE UNIQUE INDEX uq_active_subscription
    ON subscriptions (user_id)
    WHERE status = 'active';
 
-- Nur eine primäre Adresse pro Nutzer
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()
);
 
-- Der partielle Index: gelöschte Zeilen effizient herausfiltern
CREATE INDEX idx_users_active ON users (email) WHERE deleted_at IS NULL;

-- E-Mail muss eindeutig sein, aber nur unter nicht-gelöschten Nutzern
CREATE UNIQUE INDEX uq_users_email_active
    ON users (email)
    WHERE deleted_at IS NULL;

-- Soft Delete: nutzergerichtet, wiederherstellbar
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: intern, nicht von der UI wiederherstellbar (aber auditiert)
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()
);
-- Wenn gelöscht, ist es weg. Das audit_log protokolliert, dass es existierte.

CREATE TABLE audit_log (
    id              BIGSERIAL PRIMARY KEY,
    table_name      TEXT NOT NULL,
    record_id       TEXT NOT NULL,          -- Text, um sowohl UUID als auch BIGINT PKs zu handhaben
    operation       TEXT NOT NULL CHECK (operation IN ('INSERT', 'UPDATE', 'DELETE')),
    old_values      JSONB,                  -- NULL bei INSERT
    new_values      JSONB,                  -- NULL bei DELETE
    changed_fields  TEXT[],                 -- welche Spalten sich geändert haben (bei 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 $$
DECLARE
    old_data JSONB;
    new_data JSONB;
    changed  TEXT[];
    col      TEXT;
BEGIN
    IF TG_OP = 'DELETE' THEN
        old_data := to_jsonb(OLD);
        INSERT INTO audit_log (table_name, record_id, operation, old_values, changed_at)
        VALUES (TG_TABLE_NAME, OLD.id::TEXT, 'DELETE', old_data, NOW());
        RETURN OLD;
    ELSIF TG_OP = 'UPDATE' THEN
        old_data := to_jsonb(OLD);
        new_data := to_jsonb(NEW);
        -- Geänderte Felder finden
        FOR col IN SELECT key FROM jsonb_each(new_data)
        LOOP
            IF old_data->col IS DISTINCT FROM new_data->col THEN
                changed := array_append(changed, col);
            END IF;
        END LOOP;
        -- Nur loggen, wenn sich tatsächlich etwas geändert hat
        IF array_length(changed, 1) > 0 THEN
            INSERT INTO audit_log (table_name, record_id, operation, old_values, new_values, changed_fields, changed_at)
            VALUES (TG_TABLE_NAME, NEW.id::TEXT, 'UPDATE', old_data, new_data, changed, NOW());
        END IF;
        RETURN NEW;
    ELSIF TG_OP = 'INSERT' THEN
        new_data := to_jsonb(NEW);
        INSERT INTO audit_log (table_name, record_id, operation, new_values, changed_at)
        VALUES (TG_TABLE_NAME, NEW.id::TEXT, 'INSERT', new_data, NOW());
        RETURN NEW;
    END IF;
    RETURN NULL;
END;
$$ LANGUAGE plpgsql;
 
-- Auf zu auditierende Tabellen anwenden
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 deiner Anwendung, vor der Abfrage:
SET LOCAL app.current_user_id = 'uuid-of-current-user';
 
-- In der Trigger-Funktion:
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()
);
 
-- Jeder Index sollte tenant_id für Abfrageleistung enthalten
CREATE INDEX idx_projects_tenant ON projects (tenant_id);
CREATE INDEX idx_tasks_tenant_project ON tasks (tenant_id, project_id);

-- RLS auf der Tabelle aktivieren
ALTER TABLE projects ENABLE ROW LEVEL SECURITY;
 
-- Eine Policy basierend auf einer Session-Variable erstellen
CREATE POLICY tenant_isolation ON projects
    USING (tenant_id = current_setting('app.current_tenant_id')::UUID);
 
-- RLS auch für Tabellenbesitzer erzwingen
ALTER TABLE projects FORCE ROW LEVEL SECURITY;

-- In der Connection-Middleware deiner Anwendung:
SET LOCAL app.current_tenant_id = 'tenant-uuid-here';
 
-- Jetzt werden alle Abfragen auf RLS-aktivierten Tabellen automatisch gefiltert
SELECT * FROM projects;
-- PostgreSQL fügt intern hinzu: WHERE tenant_id = 'tenant-uuid-here'

-- Ein Schema für jeden Mandanten erstellen
CREATE SCHEMA tenant_acme;
CREATE SCHEMA tenant_globex;
 
-- Tabellen leben im Schema des Mandanten
CREATE TABLE tenant_acme.projects (
    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    name        TEXT NOT NULL,
    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
);
 
-- Den search_path für den aktuellen Mandanten setzen
SET search_path TO tenant_acme, public;
 
-- Jetzt treffen unqualifizierte Abfragen das Schema des Mandanten
SELECT * FROM projects;  -- fragt tenant_acme.projects ab

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()
);
 
-- Beispieldaten:
-- Schuh: {"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()
);

-- Die gesamte JSONB-Spalte indizieren (gut für @> Containment-Abfragen)
CREATE INDEX idx_products_attributes ON products USING GIN (attributes);
 
-- Abfrage: Alle Produkte mit color = "black" finden
SELECT * FROM products
WHERE attributes @> '{"color": "black"}';
 
-- Abfrage: Produkte mit einem dieser Attribute finden
SELECT * FROM products
WHERE attributes ?| ARRAY['color', 'size'];

-- Einen bestimmten Pfad indizieren
CREATE INDEX idx_products_color ON products ((attributes->>'color'));
 
-- Jetzt ist das ein regulärer B-Tree-Lookup
SELECT * FROM products
WHERE attributes->>'color' = 'black';

-- Eine neue Spalte hinzufügen: sauber, atomar, ein Statement
ALTER TABLE products ADD COLUMN weight_kg NUMERIC(10,3);
 
-- Ein neues JSONB-Feld hinzufügen: chaotisch, erfordert ein Backfill
UPDATE products
SET attributes = attributes || '{"weight_kg": null}'
WHERE NOT (attributes ? 'weight_kg');
-- Plus Anwendungscode aktualisieren, um fehlendes weight_kg zu handhaben
-- Plus Validierungslogik aktualisieren
-- Plus jede API-Response aktualisieren, die Attribute enthält

-- SICHER: Nur Metadaten, sofort (PostgreSQL 11+)
ALTER TABLE users ADD COLUMN bio TEXT;
ALTER TABLE users ADD COLUMN is_premium BOOLEAN NOT NULL DEFAULT false;
 
-- GEFÄHRLICH: Schreibt die gesamte Tabelle um, volle Tabellensperre
ALTER TABLE users ALTER COLUMN email TYPE VARCHAR(500);
ALTER TABLE users ADD COLUMN score INTEGER NOT NULL DEFAULT compute_score();
 
-- GEFÄHRLICH: Scannt die gesamte Tabelle zur Validierung
ALTER TABLE orders ADD CONSTRAINT check_total CHECK (total_cents >= 0);

-- Das sperrt die Tabelle und schreibt sie um. Mach das nicht auf einer großen Tabelle.
ALTER TABLE users ADD COLUMN avatar_url TEXT NOT NULL DEFAULT 'https://example.com/default.png';

-- Migration 1: Die nullable Spalte hinzufügen
ALTER TABLE users ADD COLUMN normalized_email TEXT;

-- Migration 2: In Batches backfillen (mach das nicht in einem Statement für große Tabellen)
UPDATE users SET normalized_email = LOWER(TRIM(email))
WHERE normalized_email IS NULL
LIMIT 10000;
-- Wiederholen, bis alle Zeilen backgefüllt sind

-- Migration 3: Constraint hinzufügen (NOT VALID verwenden, um Full Table Scan zu vermeiden, dann separat validieren)
ALTER TABLE users ADD CONSTRAINT users_normalized_email_not_null
    CHECK (normalized_email IS NOT NULL) NOT VALID;
 
-- Migration 4: Die Constraint validieren (nimmt ein ShareUpdateExclusiveLock, kein AccessExclusiveLock)
ALTER TABLE users VALIDATE CONSTRAINT users_normalized_email_not_null;

-- BLOCKIERT SCHREIBVORGÄNGE: mach das nicht auf einer Live-Tabelle
CREATE INDEX idx_users_email ON users (email);
 
-- NICHT-BLOCKIEREND: verwende stattdessen das
CREATE INDEX CONCURRENTLY idx_users_email ON users (email);

-- So fragt man kommagetrennte Werte ab. Mach das nicht.
SELECT * FROM posts WHERE tags LIKE '%react%';
-- Das matcht auch "react-native" und "preact"
 
-- Was ich hätte tun sollen:
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);
 
-- Saubere Abfragen
SELECT * FROM posts WHERE 'react' = ANY(tags);
SELECT * FROM posts WHERE tags @> ARRAY['react', 'nextjs'];

-- Schien damals in Ordnung
CREATE TABLE notifications (
    id      BIGSERIAL PRIMARY KEY,
    type    TEXT NOT NULL,  -- "email", "sms", "push"
    -- ...
);
 
-- Dann versuchst du es in buchstäblich jedem ORM abzufragen:
-- notification.type  ← kollidiert mit dem Typsystem jeder Sprache
-- "type" ist ein reserviertes Wort in den meisten SQL-Dialekten
-- Du musst es überall quoten: SELECT "type" FROM notifications

-- Extensions
CREATE EXTENSION IF NOT EXISTS "pgcrypto";  -- für gen_random_uuid()
 
-- Updated_at Trigger-Funktion (wiederverwendbar)
CREATE OR REPLACE FUNCTION update_updated_at_column()
RETURNS TRIGGER AS $$
BEGIN
    NEW.updated_at = NOW();
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;
 
-- Mandanten
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();
 
-- Nutzer
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 aktivieren
ALTER TABLE users ENABLE ROW LEVEL SECURITY;
CREATE POLICY tenant_isolation ON users
    USING (tenant_id = current_setting('app.current_tenant_id')::UUID);
 
-- Projekte
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);
 
-- Aufgaben
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);
 
-- Aufgabenkommentare
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 (kein RLS — Admin-only Tabelle)
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);