# Backend DB API Module

## Overview

The DB API module provides the data access layer that sits between services and Sequelize models. It encapsulates query logic, filtering, pagination, and data transformations using a declarative configuration pattern via the `GenericDBApi` base class.

**Location:** `backend/src/db/api/`

**Files:** 20 files (1 base class + 18 entity APIs + 1 utility)

| File | Class/Purpose | LOC | Extends GenericDBApi |
|------|---------------|-----|---------------------|
| `base.api.ts` | `GenericDBApi` - Base class | 726 | - |
| `users.ts` | `UsersDBApi` - User accounts | 979 | No (custom) |
| `projects.ts` | `ProjectsDBApi` - Projects | ~320 | Yes |
| `tour_pages.ts` | `Tour_pagesDBApi` - Tour pages | ~350 | Yes |
| `assets.ts` | `AssetsDBApi` - Media assets | ~92 | Yes |
| `asset_variants.ts` | `Asset_variantsDBApi` - Asset variants | 82 | Yes |
| `roles.ts` | `RolesDBApi` - RBAC roles | 71 | Yes |
| `permissions.ts` | `PermissionsDBApi` - RBAC permissions | 53 | Yes |
| `project_memberships.ts` | `Project_membershipsDBApi` - Team access | 86 | Yes |
| `element_type_defaults.ts` | `Element_type_defaultsDBApi` - Global defaults | ~409 | Yes |
| `project_element_defaults.ts` | `Project_element_defaultsDBApi` - Project defaults | ~410 | Yes |
| `project_audio_tracks.ts` | `Project_audio_tracksDBApi` - Audio tracks | ~199 | Yes |
| `project_transition_settings.ts` | `Project_transition_settingsDBApi` - Project transition settings | ~277 | Yes |
| `global_transition_defaults.ts` | `Global_transition_defaultsDBApi` - Global transition defaults | ~155 | Yes |
| `global_ui_control_defaults.ts` | `Global_ui_control_defaultsDBApi` - Global UI control defaults | ~160 | Yes |
| `project_ui_control_settings.ts` | `Project_ui_control_settingsDBApi` - Project UI control settings | ~150 | Yes |
| `publish_events.ts` | `Publish_eventsDBApi` - Publishing history | 101 | Yes |
| `pwa_caches.ts` | `Pwa_cachesDBApi` - PWA manifests | 76 | Yes |
| `access_logs.ts` | `Access_logsDBApi` - Audit trail | 88 | Yes |
| `presigned_url_requests.ts` | `Presigned_url_requestsDBApi` - S3 URL audit | 90 | Yes |
| `file.ts` | `FileDBApi` - Polymorphic file attachments | ~95 | No (custom) |
| `runtime-context.ts` | Runtime context helpers | 57 | - |

---

## Architecture

```
┌─────────────────────────────────────────────────────────────────────────┐
│                         DB API Layer Architecture                        │
└─────────────────────────────────────────────────────────────────────────┘

                        ┌─────────────────────┐
                        │    Service Layer    │
                        │  (services/*.js)    │
                        └──────────┬──────────┘
                                   │
                                   ▼
┌─────────────────────────────────────────────────────────────────────────┐
│                           DB API Layer                                   │
│                                                                          │
│  ┌─────────────────────────────────────────────────────────────────┐    │
│  │                      GenericDBApi (base.api.ts)                 │    │
│  │                                                                  │    │
│  │  Static Getters (Configuration):                                 │    │
│  │    • MODEL, TABLE_NAME                                           │    │
│  │    • SEARCHABLE_FIELDS, RANGE_FIELDS, ENUM_FIELDS, UUID_FIELDS  │    │
│  │    • ASSOCIATIONS, RELATION_FILTERS                              │    │
│  │    • FIND_BY_INCLUDES, FIND_ALL_INCLUDES                        │    │
│  │    • JSON_FIELDS, FIELD_DEFAULTS, FIELD_TRANSFORMERS            │    │
│  │    • CSV_FIELDS, AUTOCOMPLETE_FIELD                             │    │
│  │                                                                  │    │
│  │  Methods (CRUD + Query):                                         │    │
│  │    • create(), bulkImport(), update()                           │    │
│  │    • deleteByIds(), remove()                                    │    │
│  │    • findBy(), findAll(), findAllAutocomplete()                 │    │
│  │    • getFieldMapping(), toCSV()                                 │    │
│  └─────────────────────────────────────────────────────────────────┘    │
│                                   │                                      │
│                    ┌──────────────┼──────────────┐                      │
│                    │              │              │                      │
│                    ▼              ▼              ▼                      │
│  ┌──────────────────┐ ┌──────────────────┐ ┌──────────────────┐        │
│  │  Simple Entity   │ │ Runtime-Aware    │ │ Fully Custom     │        │
│  │     API          │ │     API          │ │     API          │        │
│  │                  │ │                  │ │                  │        │
│  │ • PermissionsDB  │ │ • Tour_pagesDB   │ │ • UsersDBApi     │        │
│  │ • RolesDBApi     │ │ • ProjectsDBApi  │ │ • FileDBApi      │        │
│  │ • AssetsDBApi    │ │ • AudioTracksDB  │ │                  │        │
│  │                  │ │                  │ │                  │        │
│  │ Override only:   │ │ Override:        │ │ Fully custom     │        │
│  │ - Static getters │ │ - Static getters │ │ implementation   │        │
│  │ - getFieldMapping│ │ - findBy()       │ │                  │        │
│  │                  │ │ - findAll()      │ │                  │        │
│  └──────────────────┘ └──────────────────┘ └──────────────────┘        │
│                                                                          │
│  ┌─────────────────────────────────────────────────────────────────┐    │
│  │                    Supporting Utilities                          │    │
│  │    runtime-context.ts - Environment/project filtering helpers    │    │
│  │    ../utils.js - UUID validation, ILIKE query building           │    │
│  └─────────────────────────────────────────────────────────────────┘    │
│                                                                          │
└─────────────────────────────────────────────────────────────────────────┘
                                   │
                                   ▼
                        ┌─────────────────────┐
                        │   Sequelize Models  │
                        │  (models/*.js)      │
                        └─────────────────────┘
```

---

## GenericDBApi Base Class

**Location:** `backend/src/db/api/base.api.ts`

The base class provides a Template Method pattern where subclasses configure behavior through static getters and optionally override methods for custom logic.

### Static Getters (Configuration)

| Getter | Type | Default | Description |
|--------|------|---------|-------------|
| `MODEL` | Model | (required) | Sequelize model reference |
| `TABLE_NAME` | string | From MODEL | Database table name |
| `SEARCHABLE_FIELDS` | string[] | `[]` | Fields for ILIKE text search |
| `RANGE_FIELDS` | string[] | `[]` | Fields for range queries (min/max) |
| `ENUM_FIELDS` | string[] | `[]` | Fields for exact match filtering |
| `UUID_FIELDS` | string[] | `[]` | UUID foreign key fields (validated before query) |
| `RELATION_FILTERS` | object[] | `[]` | Related entity filter configs |
| `ASSOCIATIONS` | object[] | `[]` | M:N or belongsTo setters |
| `FIND_BY_INCLUDES` | object[] | `[]` | Includes for findBy() |
| `FIND_ALL_INCLUDES` | object[] | `[]` | Includes for findAll() |
| `CSV_FIELDS` | string[] | `['id', 'createdAt']` | Fields for CSV export |
| `AUTOCOMPLETE_FIELD` | string | `'name'` | Field for autocomplete |
| `JSON_FIELDS` | string[] | `[]` | Fields to auto-stringify |
| `FIELD_DEFAULTS` | object | `{}` | Default values for fields |
| `FIELD_TRANSFORMERS` | object | `{}` | Custom field transformations |

### Methods

#### getFieldMapping(data)

Transforms input data for database operations using declarative configuration:

```javascript
static getFieldMapping(data) {
  if (!data) return data;
  const mapped = { ...data };

  // 1. Apply field defaults
  for (const [field, config] of Object.entries(this.FIELD_DEFAULTS)) {
    if (mapped[field] === undefined) {
      mapped[field] = config.default;
    } else if (mapped[field] === null && config.nullDefault !== undefined) {
      mapped[field] = config.nullDefault;
    }
  }

  // 2. Auto-stringify JSON fields
  for (const field of this.JSON_FIELDS) {
    if (mapped[field] !== undefined && mapped[field] !== null) {
      if (typeof mapped[field] !== 'string') {
        mapped[field] = JSON.stringify(mapped[field]);
      }
    }
  }

  // 3. Apply custom transformers
  for (const [field, transformer] of Object.entries(this.FIELD_TRANSFORMERS)) {
    if (mapped[field] !== undefined) {
      mapped[field] = transformer(mapped[field]);
    }
  }

  return mapped;
}
```

#### create(options)

Creates a new record with associations:

```javascript
static async create({ data, currentUser = { id: null }, transaction, runtimeContext }) {

  const mappedData = this.getFieldMapping(data);

  const record = await this.MODEL.create(
    {
      ...mappedData,
      importHash: data.importHash || null,
      createdById: currentUser.id,
      updatedById: currentUser.id,
    },
    { transaction },
  );

  // Handle M:N and belongsTo associations
  for (const assoc of this.ASSOCIATIONS) {
    if (data[assoc.field] !== undefined) {
      const setter = record[assoc.setter];
      await setter.call(
        record,
        data[assoc.field] || (assoc.isArray ? [] : null),
        { transaction },
      );
    }
  }

  return record;
}
```

#### update({ id, data, currentUser, transaction, runtimeContext })

Updates a record with partial data:

```javascript
static async update({ id, data, currentUser = { id: null }, transaction }) {

  const record = await this.MODEL.findByPk(id, { transaction });

  if (!record) {
    throw { status: 404, message: `${this.TABLE_NAME} not found` };
  }

  const updatePayload = { updatedById: currentUser.id };
  const mappedData = this.getFieldMapping(data);

  // Only update defined fields
  for (const [key, value] of Object.entries(mappedData)) {
    if (value !== undefined) {
      updatePayload[key] = value;
    }
  }

  await record.update(updatePayload, { transaction });

  // Update associations
  for (const assoc of this.ASSOCIATIONS) {
    if (data[assoc.field] !== undefined) {
      const setter = record[assoc.setter];
      await setter.call(record, data[assoc.field], { transaction });
    }
  }

  return record;
}
```

#### findAll(filter, options)

Full-featured query with filtering, pagination, and sorting:

```javascript
static async findAll(filter = {}, options = {}) {
  const limit = filter.limit || 0;
  const currentPage = +filter.page || 0;
  const offset = currentPage * limit;

  let where = {};
  let include = [...this.FIND_ALL_INCLUDES];

  // ID exact match (with UUID validation)
  if (filter.id) {
    if (!Utils.isValidUuid(filter.id)) {
      return { rows: [], count: 0 };
    }
    where.id = filter.id;
  }

  // Text search (ILIKE)
  for (const field of this.SEARCHABLE_FIELDS) {
    if (filter[field]) {
      where[Op.and] = Utils.ilike(this.TABLE_NAME, field, filter[field]);
    }
  }

  // Range queries (fieldRange: [min, max])
  for (const field of this.RANGE_FIELDS) {
    const rangeKey = `${field}Range`;
    if (filter[rangeKey]) {
      const [start, end] = filter[rangeKey];
      if (start) where[field] = { ...where[field], [Op.gte]: start };
      if (end) where[field] = { ...where[field], [Op.lte]: end };
    }
  }

  // Enum exact match
  for (const field of this.ENUM_FIELDS) {
    if (filter[field] !== undefined) {
      where[field] = filter[field];
    }
  }

  // Relation filters (search by related entity ID or name)
  for (const rel of this.RELATION_FILTERS) {
    if (filter[rel.filterKey]) {
      // ... adds required include with where clause
    }
  }

  // createdAt date range
  if (filter.createdAtRange) {
    // ... applies date range
  }

  const queryOptions = {
    where,
    include,
    distinct: true,
    order: filter.field && filter.sort
      ? [[filter.field, filter.sort]]
      : [['createdAt', 'desc']],
    transaction: options.transaction,
  };

  if (!options.countOnly) {
    queryOptions.limit = limit ? Number(limit) : undefined;
    queryOptions.offset = offset ? Number(offset) : undefined;
  }

  const { rows, count } = await this.MODEL.findAndCountAll(queryOptions);
  return { rows: options.countOnly ? [] : rows, count };
}
```

#### Other Methods

| Method | Description |
|--------|-------------|
| `bulkImport(data, options)` | Bulk create with timestamps offset |
| `deleteByIds({ ids, currentUser, transaction, runtimeContext })` | Soft delete multiple records |
| `remove({ id, currentUser, transaction, runtimeContext })` | Soft delete single record |
| `findBy(where, options)` | Find single record by criteria |
| `findAllAutocomplete({ query, limit, offset }, options)` | Autocomplete search |
| `toCSV(rows)` | Convert rows to CSV string |

---

## Query Filter Patterns

### SEARCHABLE_FIELDS - Text Search

Case-insensitive partial match using ILIKE:

```javascript
// Configuration
static get SEARCHABLE_FIELDS() {
  return ['name', 'description', 'email'];
}

// Usage
GET /api/users?name=john
// Generates: WHERE LOWER(users.name) LIKE '%john%'
```

### RANGE_FIELDS - Range Queries

Min/max range filtering:

```javascript
// Configuration
static get RANGE_FIELDS() {
  return ['sort_order', 'price', 'created_at'];
}

// Usage
GET /api/assets?sort_orderRange=[0,10]
// Generates: WHERE sort_order >= 0 AND sort_order <= 10

GET /api/users?createdAtRange=[2024-01-01,2024-12-31]
// Generates: WHERE createdAt >= '2024-01-01' AND createdAt <= '2024-12-31'
```

### ENUM_FIELDS - Exact Match

Direct equality filtering:

```javascript
// Configuration
static get ENUM_FIELDS() {
  return ['environment', 'status', 'asset_type'];
}

// Usage
GET /api/tour_pages?environment=production
// Generates: WHERE environment = 'production'
```

### RELATION_FILTERS - Related Entity Search

Filter by related entity ID or searchable field:

```javascript
// Configuration
static get RELATION_FILTERS() {
  return [
    {
      filterKey: 'project',      // Query param name
      model: db.projects,        // Related model
      as: 'project',             // Association alias
      searchField: 'name',       // Field for text search
    },
  ];
}

// Usage
GET /api/assets?project=abc123
// Filters by project ID: abc123

GET /api/assets?project=my-tour
// Filters by project name containing "my-tour"

GET /api/assets?project=abc123|my-tour
// Pipe-separated: matches either
```

---

## API Categories

### 1. Simple Entity APIs

Extend `GenericDBApi` with minimal configuration. Only override static getters and `getFieldMapping()`.

**Example: PermissionsDBApi**

```typescript
class PermissionsDBApi extends GenericDBApi {
  static override get MODEL(): unknown { return db.permissions; }
  static override get TABLE_NAME(): string { return 'permissions'; }
  static override get SEARCHABLE_FIELDS(): string[] { return ['name']; }
  static override get CSV_FIELDS(): string[] { return ['id', 'name', 'createdAt']; }
  static override get AUTOCOMPLETE_FIELD(): string { return 'name'; }

  static override getFieldMapping(data: PermissionData): PermissionFieldMapping {
    return {
      id: data.id || undefined,
      name: data.name || null,
    };
  }
}
```

**Entities using this pattern:**
- `PermissionsDBApi`
- `AssetsDBApi`
- `Asset_variantsDBApi`
- `Publish_eventsDBApi`
- `Pwa_cachesDBApi`
- `Access_logsDBApi`
- `Presigned_url_requestsDBApi`

### 2. Runtime-Aware APIs

Override `findBy()` and `findAll()` to apply runtime environment/project filters for public presentation access.

**Example: Tour_pagesDBApi**

```javascript
class Tour_pagesDBApi extends GenericDBApi {
  // ... configuration getters ...

  static async findBy(where, options = {}) {
    const queryWhere = applyRuntimeEnvironment({ ...where }, options);
    const projectInclude = applyRuntimeProjectFilter(
      { model: db.projects, as: 'project' },
      options,
    );

    const record = await this.MODEL.findOne({
      where: queryWhere,
      include: [projectInclude],
    });

    return record ? record.get({ plain: true }) : null;
  }

  static async findAll(filter = {}, options = {}) {
    // ... standard filtering logic ...

    // Apply runtime environment filter
    where = applyRuntimeEnvironment(where, options);

    // Apply project slug filter to include
    include[0] = applyRuntimeProjectFilter(include[0], options);

    // ... execute query ...
  }
}
```

**Example: ProjectsDBApi**

`ProjectsDBApi` uses runtime slug filtering but with two unique behaviors:

1. **Auto-snapshot on create**: Copies global element defaults to new projects
2. **Slug filter skipped for ID lookups**: Prevents stale `X-Runtime-Project-Slug` headers from breaking ID-based queries

```javascript
class ProjectsDBApi extends GenericDBApi {
  // ... configuration getters ...

  static async findBy(where, options = {}) {
    const runtimeProjectSlug = getRuntimeProjectSlug(options);
    const queryWhere = { ...where };

    // Runtime access: filter by project slug
    // Skip if finding by ID (unambiguous lookup)
    if (runtimeProjectSlug && !where.id) {
      queryWhere.slug = runtimeProjectSlug;
    }

    const record = await this.MODEL.findOne({
      where: queryWhere,
      include: options.include ?? this.DEFAULT_INCLUDES,
    });

    return record ? record.get({ plain: true }) : null;
  }

  static async create(options) {
    const { transaction } = options;
    // Create the project using parent's create
    const project = await super.create(options);

    // Auto-snapshot global element defaults to the new project
    await Project_element_defaultsDBApi.snapshotGlobalDefaults(project.id, {
      ...options,
      transaction,
    });

    return project;
  }

  static async findAll(filter = {}, options = {}) {
    // ... standard filtering logic ...

    // Runtime access: filter by project slug (no ID bypass needed for list)
    const runtimeProjectSlug = getRuntimeProjectSlug(options);
    if (runtimeProjectSlug) {
      where.slug = runtimeProjectSlug;
    }

    // ... execute query ...
  }
}
```

**Entities using this pattern:**
- `Tour_pagesDBApi` - Environment filtering via `applyRuntimeEnvironment()`
- `ProjectsDBApi` - Slug filtering with ID bypass and auto-snapshot on create
- `Project_audio_tracksDBApi` - Environment filtering

### 3. APIs with Custom Methods

Extend base functionality with domain-specific methods.

**Example: Element_type_defaultsDBApi**

```javascript
class Element_type_defaultsDBApi extends GenericDBApi {
  // ... configuration ...

  // Self-initialization pattern
  static async ensureInitialized() {
    if (!this.initializationPromise) {
      this.initializationPromise = (async () => {
        const count = await this.MODEL.count();
        if (count > 0) return;

        // Seed default rows
        await this.MODEL.bulkCreate(
          this.DEFAULT_ROWS.map((item) => this.getFieldMapping(item)),
        );
      })();
    }
    await this.initializationPromise;
  }

  // Override all methods to ensure initialization
  static async create(options) {
    await this.ensureInitialized();
    return super.create(options);
  }

  // ... similar overrides for other methods ...

  // Default data configuration
  static get DEFAULT_ROWS() {
    return [
      { element_type: 'navigation_next', name: 'Navigation Forward Button', ... },
      { element_type: 'tooltip', name: 'Tooltip', ... },
      // ... 11 default element types
    ];
  }
}
```

**Example: Project_element_defaultsDBApi**

```javascript
class Project_element_defaultsDBApi extends GenericDBApi {
  // ... configuration ...

  // Snapshot global defaults to a project
  static async snapshotGlobalDefaults(projectId, options = {}) {
    const globalDefaults = await Element_type_defaultsDBApi.findAll({});

    return this.MODEL.bulkCreate(
      globalDefaults.rows.map((global) => ({
        projectId,
        element_type: global.element_type,
        settings_json: global.default_settings_json,
        source_element_id: global.id,
        snapshot_version: 1,
      })),
      { transaction: options.transaction },
    );
  }

  // Reset project default to current global
  static async resetToGlobal(id, options = {}) {
    const projectDefault = await this.MODEL.findByPk(id);
    const globalDefault = await Element_type_defaultsDBApi.MODEL.findOne({
      where: { element_type: projectDefault.element_type },
    });

    await projectDefault.update({
      settings_json: globalDefault.default_settings_json,
      snapshot_version: projectDefault.snapshot_version + 1,
    });

    return projectDefault.reload();
  }

  // Compare project default with global
  static async getDiffFromGlobal(id) {
    // ... returns diff object
  }
}
```

### 4. Fully Custom APIs

Don't extend `GenericDBApi` due to significantly different requirements.

**Example: UsersDBApi**

Complex user management with:
- Password hashing (bcrypt)
- File avatar handling
- Token generation for email verification and password reset
- OAuth authentication support

```typescript
class UsersDBApi {
  static async create(options: UserCreateOptions): Promise<UserRecord> {
    const { data, currentUser = { id: null }, transaction } = options;
    const users = await db.users.create({
      firstName: data.firstName || null,
      lastName: data.lastName || null,
      email: data.email || null,
      password: data.password || null,  // Already hashed by service
      // ...
    }, { transaction });

    // Auto-assign default role
    if (!data.app_role) {
      const role = await db.roles.findOne({ where: { name: 'User' } });
      await users.setApp_role(role, { transaction });
    }

    // Handle avatar file
    await FileDBApi.replaceRelationFiles(
      { belongsTo: 'users', belongsToColumn: 'avatar', belongsToId: users.id },
      data.data.avatar,
      options,
    );

    return users;
  }

  static async update({ id, data, currentUser, transaction, runtimeContext }) {
    const users = await db.users.findByPk(id, { transaction });

    // Hash password if changed
    if (data.password) {
      data.password = bcrypt.hashSync(data.password, config.bcrypt.saltRounds);
    } else {
      data.password = users.password;
    }

    // ... update fields ...
  }

  // Token generation
  static async generateEmailVerificationToken(email, options) {
    return this._generateToken(
      ['emailVerificationToken', 'emailVerificationTokenExpiresAt'],
      email,
      options,
    );
  }

  static async _generateToken(keyNames, email, options) {
    const users = await db.users.findOne({ where: { email: email.toLowerCase() } });
    const token = crypto.randomBytes(20).toString('hex');
    const tokenExpiresAt = Date.now() + (24 * 60 * 60 * 1000); // 24 hours

    await users.update({
      [keyNames[0]]: token,
      [keyNames[1]]: tokenExpiresAt,
    });

    return token;
  }

  // Token lookup
  static async findByPasswordResetToken(token, options) {
    return db.users.findOne({
      where: {
        passwordResetToken: token,
        passwordResetTokenExpiresAt: { [Op.gt]: Date.now() },
      },
    });
  }
};
```

**Example: FileDBApi**

Polymorphic file attachment handling:

```typescript
export default class FileDBApi {
  static async replaceRelationFiles(relation, rawFiles, options = {}) {
    assert(relation.belongsTo);
    assert(relation.belongsToColumn);
    assert(relation.belongsToId);

    const files = Array.isArray(rawFiles) ? rawFiles : rawFiles ? [rawFiles] : [];

    await this._removeLegacyFiles(relation, files, options);
    await this._addFiles(relation, files, options);
  }

  static async _addFiles(relation, files, options) {
    const inexistentFiles = files.filter((file) => !!file.new);

    for (const file of inexistentFiles) {
      await db.file.create({
        belongsTo: relation.belongsTo,
        belongsToColumn: relation.belongsToColumn,
        belongsToId: relation.belongsToId,
        name: file.name,
        publicUrl: file.publicUrl,
        privateUrl: file.privateUrl,
      }, { transaction: options.transaction });
    }
  }

  static async _removeLegacyFiles(relation, files, options) {
    const filesToDelete = await db.file.findAll({
      where: {
        belongsTo: relation.belongsTo,
        belongsToId: relation.belongsToId,
        belongsToColumn: relation.belongsToColumn,
        id: { [Op.notIn]: files.filter((f) => !f.new).map((f) => f.id) },
      },
    });

    for (const file of filesToDelete) {
      await services.deleteFile(file.privateUrl);
      await file.destroy({ transaction: options.transaction });
    }
  }
};
```

---

## Runtime Context Helpers

**Location:** `backend/src/db/api/runtime-context.ts`

Utilities for filtering queries based on runtime presentation context (public tour access).

```javascript
// Get runtime environment from options.runtimeContext
function getRuntimeEnvironment(options = {}) {
  const runtimeContext = options.runtimeContext || null;
  if (!runtimeContext) return null;

  // SECURITY: Only allow 'production' and 'stage' from header
  if (runtimeContext.headerEnvironment === 'production') return 'production';
  if (runtimeContext.headerEnvironment === 'stage') return 'stage';
  return null;
}

// Get project slug from runtime context
function getRuntimeProjectSlug(options = {}) {
  const runtimeContext = options.runtimeContext || null;
  return runtimeContext?.headerProjectSlug || null;
}

// Apply environment filter to where clause
function applyRuntimeEnvironment(where = {}, options = {}) {
  const environment = getRuntimeEnvironment(options);
  if (!environment) return where;

  return { ...where, environment };
}

// Apply project slug filter to include
function applyRuntimeProjectFilter(projectInclude = {}, options = {}) {
  const projectSlug = getRuntimeProjectSlug(options);
  if (!projectSlug) return projectInclude;

  return {
    ...projectInclude,
    required: true,
    where: { ...(projectInclude.where || {}), slug: projectSlug },
  };
}
```

**Usage:**

```javascript
// In runtime-aware API
static async findAll(filter = {}, options = {}) {
  let where = { /* ... */ };
  let include = [{ model: db.projects, as: 'project' }];

  // Apply runtime filters
  where = applyRuntimeEnvironment(where, options);
  include[0] = applyRuntimeProjectFilter(include[0], options);

  // ... execute query
}
```

---

## DB Utils

**Location:** `backend/src/db/utils.js`

Utility functions for UUID validation and query building:

```javascript
const validator = require('validator');
const { v4: uuidv4 } = require('uuid');

module.exports = class Utils {
  // Check if value is a valid UUID
  static isValidUuid(value) {
    return Boolean(value && validator.isUUID(String(value)));
  }

  // Generate a new UUID v4
  static generateUuid() {
    return uuidv4();
  }

  // Filter array to only valid UUIDs
  static filterValidUuids(values) {
    return values.filter((v) => this.isValidUuid(v));
  }

  // Case-insensitive LIKE query
  static ilike(model, column, value) {
    return Sequelize.where(
      Sequelize.fn('lower', Sequelize.col(`${model}.${column}`)),
      { [Sequelize.Op.like]: `%${value}%`.toLowerCase() },
    );
  }
};
```

**UUID Utility Functions:**

| Function | Purpose | Returns |
|----------|---------|---------|
| `isValidUuid(value)` | Check if valid UUID | `boolean` |
| `generateUuid()` | Create new UUID v4 | `string` |
| `filterValidUuids(values)` | Filter array to valid UUIDs only | `string[]` |
| `ilike(model, column, value)` | Case-insensitive search | Sequelize where clause |

**UUID Validation Behavior:**
- Invalid single ID filter (`?id=xxx`) → returns `{ rows: [], count: 0 }` immediately
- Invalid UUID in relation filter (`?project=uuid|name`) → filters out invalid UUIDs for ID search, keeps all terms for text search
- Invalid UUID field filter (`?projectId=xxx`) → returns `{ rows: [], count: 0 }` immediately

---

## Declarative Configuration Examples

### Simple Entity

```javascript
class AssetsDBApi extends GenericDBApi {
  static get MODEL() { return db.assets; }
  static get TABLE_NAME() { return 'assets'; }

  static get SEARCHABLE_FIELDS() {
    return ['name', 'cdn_url', 'storage_key', 'mime_type', 'checksum'];
  }

  static get RANGE_FIELDS() {
    return ['size_mb', 'width_px', 'height_px', 'duration_sec'];
  }

  static get ENUM_FIELDS() {
    return ['asset_type', 'type', 'is_public'];
  }

  // UUID foreign key fields - validated before querying
  static get UUID_FIELDS() {
    return ['projectId'];
  }

  static get ASSOCIATIONS() {
    return [{ field: 'project', setter: 'setProject', isArray: false }];
  }

  static get FIND_BY_INCLUDES() {
    return [
      { association: 'asset_variants_asset' },
      { association: 'project' },
    ];
  }

  static get RELATION_FILTERS() {
    return [
      { filterKey: 'project', model: db.projects, as: 'project', searchField: 'name' },
    ];
  }

  static getFieldMapping(data) {
    return {
      name: data.name || null,
      asset_type: data.asset_type || null,
      type: data.type || 'general',
      cdn_url: data.cdn_url || null,
      storage_key: data.storage_key || null,
      mime_type: data.mime_type || null,
      size_mb: data.size_mb || null,
      width_px: data.width_px || null,
      height_px: data.height_px || null,
      duration_sec: data.duration_sec || null,
      checksum: data.checksum || null,
      is_public: data.is_public || false,
    };
  }
}
```

### Foreign Key Fields in getFieldMapping

**Important:** Foreign key fields (like `assetId`, `projectId`) must be included in `getFieldMapping()` if they are passed directly to `create()` or `update()`. Without this, the foreign key value is silently dropped and the record is created without the relationship.

**Two ways to handle foreign keys:**

1. **Direct field mapping** (preferred for programmatic use):
```javascript
// In getFieldMapping()
static getFieldMapping(data) {
  return {
    assetId: data.assetId || null,  // Include FK field directly
    variant_type: data.variant_type || null,
    // ...
  };
}

// In service
await Asset_variantsDBApi.create({ assetId: asset.id, ... });
```

2. **Via ASSOCIATIONS setter** (used by frontend forms):
```javascript
// ASSOCIATIONS config uses 'asset' (relation name)
static get ASSOCIATIONS() {
  return [{ field: 'asset', setter: 'setAsset', isArray: false }];
}

// Service passes 'asset' instead of 'assetId'
await Asset_variantsDBApi.create({ asset: asset.id, ... });
// GenericDBApi.create() calls record.setAsset(asset.id) with record as `this`
```

**Common mistake:** Passing `assetId` when only `asset` association is configured (or vice versa) results in orphaned records with NULL foreign keys.

**Implementation detail:** Sequelize association mixins rely on the model
instance as `this`. `GenericDBApi` must call association setters as bound
record methods (`setter.call(record, ...)`) rather than detached functions;
otherwise belongsTo setters such as `setProject`/`setAsset` receive an
undefined source instance and fail before the foreign key can be saved.

### Entity with M:N Relations

```typescript
class RolesDBApi extends GenericDBApi {
  static override get MODEL(): unknown { return db.roles; }

  static override get ASSOCIATIONS(): RoleAssociationConfig[] {
    return [{ field: 'permissions', setter: 'setPermissions', isArray: true }];
  }

  static override get FIND_BY_INCLUDES(): unknown[] {
    return [
      { association: 'users_app_role' },
      { association: 'permissions' },
    ];
  }

  static override get FIND_ALL_INCLUDES(): unknown[] {
    return [
      { model: db.permissions, as: 'permissions', required: false },
    ];
  }

  static get RELATION_FILTERS() {
    return [
      { filterKey: 'permissions', model: db.permissions, as: 'permissions_filter', searchField: 'name' },
    ];
  }
}
```

### Entity with JSON Fields and Defaults

```javascript
class Element_type_defaultsDBApi extends GenericDBApi {
  // Auto-stringify JSON fields
  static get JSON_FIELDS() {
    return ['default_settings_json'];
  }

  // Field defaults
  static get FIELD_DEFAULTS() {
    return {
      element_type: { default: null },
      name: { default: null },
      sort_order: { default: 0 },
    };
  }

  static getFieldMapping(data) {
    // Apply base class transformations first
    const mapped = super.getFieldMapping(data);

    return {
      id: mapped.id || undefined,
      element_type: mapped.element_type,
      name: mapped.name,
      sort_order: mapped.sort_order,
      default_settings_json: mapped.default_settings_json,
    };
  }
}
```

---

## API Summary Table

| API | Pattern | Getters | Custom Methods | Notes |
|-----|---------|---------|----------------|-------|
| `PermissionsDBApi` | Simple | 6 | 0 | Minimal config |
| `AssetsDBApi` | Simple | 9 | 0 | With associations |
| `RolesDBApi` | Simple | 10 | 0 | M:N permissions |
| `ProjectsDBApi` | Runtime-aware | 10 | 3 | Auto-snapshot on create, slug filter skipped for ID lookups |
| `Tour_pagesDBApi` | Runtime-aware | 9 | 0 | Environment filtering |
| `Project_audio_tracksDBApi` | Runtime-aware | 8 | 0 | Environment filtering |
| `Element_type_defaultsDBApi` | Self-init | 9 | 1 | Default seeding |
| `Project_element_defaultsDBApi` | Extended | 10 | 4 | Snapshot, reset, diff |
| `UsersDBApi` | Fully custom | - | 12 | Auth, tokens, files |
| `FileDBApi` | Fully custom | - | 3 | Polymorphic files |

---

## Best Practices

### When to Extend GenericDBApi

- Standard CRUD operations needed
- Filtering by searchable/range/enum fields
- Pagination and sorting
- CSV export
- Autocomplete

### When to Override Methods

- Custom runtime environment filtering
- Special business logic during create/update
- Complex association handling
- Self-initialization patterns

### When to Use Fully Custom API

- Complex authentication logic (password hashing, tokens)
- Polymorphic associations (FileDBApi)
- Significantly different query patterns
- Multiple specialized methods

---

## Related Documentation

- [DB Models Module](./db-models.md) - Sequelize model definitions
- [Factories Module](./factories.md) - Service/router factories that use APIs
- [Services Module](./services.md) - Business logic layer
- [Middleware Module](./middleware.md) - Runtime context middleware