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API Controller Validation Guide

This guide explains how to configure validations in api-framework controllers, covering all available patterns, built-in validators, and best practices.

Overview
Validation Patterns
- Object-Based Validation
- Function-Based Validation
Validating Options (Query Parameters)
Validating Data (Request Body)
Built-in Global Validators
Method-Specific Validation Behavior
Complete Examples
Error Handling
Best Practices

Overview

The api-framework uses a pipeline-based validation system where validations run as the first processing stage:

Validation ← You are here
Input serialisation
Permissions
Query (controller execution)
Output serialisation

Validation ensures that:

Required fields are present
Values are in allowed lists
Data types are correct (IDs, emails, slugs, etc.)
Request structure is valid before processing

Validation Patterns

Pattern 1: Object-Based Validation

The most common pattern using configuration objects:

browse: {
  options: ['include', 'page', 'limit'],
  validation: {
    options: {
      include: {
        values: ['tags', 'authors'],
        required: true
      },
      page: {
        required: false
      }
    }
  },
  permissions: true,
  query(frame) {
    return models.Post.findPage(frame.options);
  }
}

When to use:

Standard field validation (required, allowed values)
Most common case for API endpoints

Pattern 2: Function-Based Validation

Complete control over validation logic:

add: {
  validation(frame) {
    const {ValidationError} = require('@tryghost/errors');

    if (!frame.data.posts || !frame.data.posts.length) {
      return Promise.reject(new ValidationError({
        message: 'No posts provided'
      }));
    }

    const post = frame.data.posts[0];

    if (!post.title || post.title.length < 3) {
      return Promise.reject(new ValidationError({
        message: 'Title must be at least 3 characters'
      }));
    }

    return Promise.resolve();
  },
  permissions: true,
  query(frame) {
    return models.Post.add(frame.data.posts[0], frame.options);
  }
}

When to use:

Complex validation logic
Cross-field validation
Conditional validation rules
Custom error messages

Validating Options (Query Parameters)

Options are URL query parameters and route params. Define allowed options in the options array and configure validation rules.

Required Fields

browse: {
  options: ['filter'],
  validation: {
    options: {
      filter: {
        required: true
      }
    }
  },
  permissions: true,
  query(frame) {
    return models.Post.findAll(frame.options);
  }
}

Allowed Values

Two equivalent syntaxes:

Object notation:

validation: {
  options: {
    include: {
      values: ['tags', 'authors', 'count.posts']
    }
  }
}

Array shorthand:

validation: {
  options: {
    include: ['tags', 'authors', 'count.posts']
  }
}

Combined Rules

validation: {
  options: {
    include: {
      values: ['tags', 'authors'],
      required: true
    },
    status: {
      values: ['draft', 'published', 'scheduled'],
      required: false
    }
  }
}

Special Behavior: Include Parameter

The include parameter has special handling - invalid values are silently filtered instead of causing an error:

// Request: ?include=tags,invalid_field,authors
// Result: frame.options.include = 'tags,authors'

This allows for graceful degradation when clients request unsupported includes.

Validating Data (Request Body)

Data validation applies to request body content. The structure differs based on the HTTP method.

For READ Operations

Data comes from query parameters:

read: {
  data: ['id', 'slug'],
  validation: {
    data: {
      slug: {
        values: ['featured', 'latest']
      }
    }
  },
  permissions: true,
  query(frame) {
    return models.Post.findOne(frame.data, frame.options);
  }
}

For ADD/EDIT Operations

Data comes from the request body with a root key:

add: {
  validation: {
    data: {
      title: {
        required: true
      },
      status: {
        required: false
      }
    }
  },
  permissions: true,
  query(frame) {
    return models.Post.add(frame.data.posts[0], frame.options);
  }
}

Request body structure:

{
  "posts": [{
    "title": "My Post",
    "status": "draft"
  }]
}

Root Key Validation

For ADD/EDIT operations, the framework automatically validates:

Root key exists (e.g., posts, users)
Root key contains an array with at least one item
Required fields exist and are not null

Built-in Global Validators

The framework automatically validates common field types using the @tryghost/validator package:

Field Name	Validation Rule	Example Valid Values
`id`	MongoDB ObjectId, `1`, or `me`	`507f1f77bcf86cd799439011`, `me`
`uuid`	UUID format	`550e8400-e29b-41d4-a716-446655440000`
`slug`	URL-safe slug	`my-post-title`
`email`	Email format	`user@example.com`
`page`	Numeric	`1`, `25`
`limit`	Numeric or `all`	`10`, `all`
`from`	Date format	`2024-01-15`
`to`	Date format	`2024-12-31`
`order`	Sort format	`created_at desc`, `title asc`
`columns`	Column list	`id,title,created_at`

Fields with No Validation

These fields skip validation by default:

filter
context
forUpdate
transacting
include
formats
name

Method-Specific Validation Behavior

Different HTTP methods have different validation behaviors:

BROWSE / READ

Validates frame.data against apiConfig.data
Allows empty data
Uses global validators for field types

ADD

Validates root key exists in frame.data
Checks required fields are present
Checks required fields are not null

Error examples:

"No root key ('posts') provided."
"Validation (FieldIsRequired) failed for title"
"Validation (FieldIsInvalid) failed for title" (when null)

EDIT

Performs all ADD validations
Validates ID consistency between URL and body

// URL: /posts/123
// Body: { "posts": [{ "id": "456", ... }] }
// Error: "Invalid id provided."

Special Methods

These methods use specific validation behaviors:

changePassword() - Uses ADD rules
resetPassword() - Uses ADD rules
setup() - Uses ADD rules
publish() - Uses BROWSE rules

Complete Examples

Example 1: Simple Browse with Options

module.exports = {
  docName: 'posts',

  browse: {
    options: ['include', 'page', 'limit', 'filter', 'order'],
    validation: {
      options: {
        include: ['tags', 'authors', 'count.posts'],
        page: {
          required: false
        },
        limit: {
          required: false
        }
      }
    },
    permissions: true,
    query(frame) {
      return models.Post.findPage(frame.options);
    }
  }
};

Example 2: Read with Data Validation

module.exports = {
  docName: 'posts',

  read: {
    options: ['include'],
    data: ['id', 'slug'],
    validation: {
      options: {
        include: ['tags', 'authors']
      },
      data: {
        id: {
          required: false
        },
        slug: {
          required: false
        }
      }
    },
    permissions: true,
    query(frame) {
      return models.Post.findOne(frame.data, frame.options);
    }
  }
};

Example 3: Add with Required Fields

module.exports = {
  docName: 'users',

  add: {
    validation: {
      data: {
        name: {
          required: true
        },
        email: {
          required: true
        },
        password: {
          required: true
        },
        role: {
          required: false
        }
      }
    },
    permissions: true,
    query(frame) {
      return models.User.add(frame.data.users[0], frame.options);
    }
  }
};

Example 4: Custom Validation Function

module.exports = {
  docName: 'subscriptions',

  add: {
    validation(frame) {
      const {ValidationError} = require('@tryghost/errors');
      const subscription = frame.data.subscriptions?.[0];

      if (!subscription) {
        return Promise.reject(new ValidationError({
          message: 'No subscription data provided'
        }));
      }

      // Validate email format
      if (!subscription.email || !subscription.email.includes('@')) {
        return Promise.reject(new ValidationError({
          message: 'Valid email address is required'
        }));
      }

      // Validate plan
      const validPlans = ['free', 'basic', 'premium'];
      if (!validPlans.includes(subscription.plan)) {
        return Promise.reject(new ValidationError({
          message: `Plan must be one of: ${validPlans.join(', ')}`
        }));
      }

      // Cross-field validation
      if (subscription.plan !== 'free' && !subscription.payment_method) {
        return Promise.reject(new ValidationError({
          message: 'Payment method required for paid plans'
        }));
      }

      return Promise.resolve();
    },
    permissions: true,
    query(frame) {
      return models.Subscription.add(frame.data.subscriptions[0], frame.options);
    }
  }
};

Example 5: Edit with ID Consistency

module.exports = {
  docName: 'posts',

  edit: {
    options: ['id', 'include'],
    validation: {
      options: {
        include: ['tags', 'authors']
      },
      data: {
        title: {
          required: false
        },
        status: {
          values: ['draft', 'published', 'scheduled']
        }
      }
    },
    permissions: {
      unsafeAttrs: ['status', 'author_id']
    },
    query(frame) {
      return models.Post.edit(frame.data.posts[0], frame.options);
    }
  }
};

Example 6: Complex Browse with Multiple Validations

module.exports = {
  docName: 'analytics',

  browse: {
    options: ['from', 'to', 'interval', 'metrics', 'dimensions'],
    validation: {
      options: {
        from: {
          required: true
        },
        to: {
          required: true
        },
        interval: {
          values: ['hour', 'day', 'week', 'month'],
          required: false
        },
        metrics: {
          values: ['pageviews', 'visitors', 'sessions', 'bounce_rate'],
          required: true
        },
        dimensions: {
          values: ['page', 'source', 'country', 'device'],
          required: false
        }
      }
    },
    permissions: true,
    query(frame) {
      return analytics.query(frame.options);
    }
  }
};

Error Handling

Error Types

Validation errors use types from @tryghost/errors:

ValidationError - Field validation failed
BadRequestError - Malformed request structure

Error Message Format

// Missing required field
"Validation (FieldIsRequired) failed for title"

// Invalid value
"Validation (AllowedValues) failed for status"

// Field is null when required
"Validation (FieldIsInvalid) failed for title"

// Missing root key
"No root key ('posts') provided."

// ID mismatch
"Invalid id provided."

Custom Error Messages

When using function-based validation:

validation(frame) {
  const {ValidationError} = require('@tryghost/errors');

  if (!frame.data.email) {
    return Promise.reject(new ValidationError({
      message: 'Email address is required',
      context: 'Please provide a valid email address to continue',
      help: 'Check that the email field is included in your request'
    }));
  }

  return Promise.resolve();
}

Best Practices

1. Define All Allowed Options

Always explicitly list allowed options to prevent unexpected parameters:

// Good - explicit allowed options
options: ['include', 'page', 'limit', 'filter'],

// Bad - no options defined (might allow anything)
// options: undefined

2. Use Built-in Validators

Let the framework handle common field types:

// Good - framework validates automatically
options: ['id', 'email', 'slug']

// Unnecessary - these are validated by default
validation: {
  options: {
    id: { matches: /^[a-f\d]{24}$/ }  // Already built-in
  }
}

3. Mark Required Fields Explicitly

Be explicit about which fields are required:

validation: {
  data: {
    title: { required: true },
    slug: { required: false },
    status: { required: false }
  }
}

4. Use Array Shorthand for Simple Cases

When only validating allowed values:

// Shorter and cleaner
validation: {
  options: {
    include: ['tags', 'authors'],
    status: ['draft', 'published']
  }
}

// Equivalent verbose form
validation: {
  options: {
    include: { values: ['tags', 'authors'] },
    status: { values: ['draft', 'published'] }
  }
}

5. Combine with Permissions

Validation runs before permissions, ensuring data structure is valid:

edit: {
  validation: {
    data: {
      author_id: { required: false }
    }
  },
  permissions: {
    unsafeAttrs: ['author_id']  // Validated first, then permission-checked
  },
  query(frame) {
    return models.Post.edit(frame.data.posts[0], frame.options);
  }
}

6. Use Custom Functions for Complex Logic

When validation rules depend on multiple fields or external state:

validation(frame) {
  // Date range validation
  if (frame.options.from && frame.options.to) {
    const from = new Date(frame.options.from);
    const to = new Date(frame.options.to);

    if (from > to) {
      return Promise.reject(new ValidationError({
        message: 'From date must be before to date'
      }));
    }

    // Max 30 day range
    const diffDays = (to - from) / (1000 * 60 * 60 * 24);
    if (diffDays > 30) {
      return Promise.reject(new ValidationError({
        message: 'Date range cannot exceed 30 days'
      }));
    }
  }

  return Promise.resolve();
}

7. Provide Helpful Error Messages

Make errors actionable for API consumers:

// Good - specific and actionable
"Status must be one of: draft, published, scheduled"

// Bad - vague
"Invalid status"

Validation Flow Diagram

HTTP Request
    ↓
Frame Creation
    ↓
Frame Configuration (pick options/data)
    ↓
┌─────────────────────────────┐
│     VALIDATION STAGE        │
├─────────────────────────────┤
│ Is validation a function?   │
│ ├─ Yes → Run custom logic   │
│ └─ No → Framework validation│
│     ├─ Global validators    │
│     ├─ Required fields      │
│     ├─ Allowed values       │
│     └─ Method-specific rules│
└─────────────────────────────┘
    ↓
Input Serialisation
    ↓
Permissions
    ↓
Query Execution
    ↓
Output Serialisation
    ↓
HTTP Response

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