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Feathers provides a powerful adapter system that allows you to connect your services to different databases using a consistent API. All adapters share common patterns and querying capabilities while supporting database-specific features.

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Available Adapters

Feathers supports multiple database adapters out of the box:

MongoDB

Native MongoDB adapter for document-based storage

Knex (SQL)

SQL adapter supporting PostgreSQL, MySQL, SQLite, and more

Memory

In-memory storage for testing and prototyping

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Common Features

All Feathers database adapters share these core capabilities:

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Standard Service Methods

Every adapter implements the standard Feathers service interface: 
interface ServiceMethods {
  find(params?: Params): Promise<Paginated<Result> | Result[]>
  get(id: Id, params?: Params): Promise<Result>
  create(data: Data | Data[], params?: Params): Promise<Result | Result[]>
  update(id: Id, data: Data, params?: Params): Promise<Result>
  patch(id: Id | null, data: PatchData, params?: Params): Promise<Result | Result[]>
  remove(id: Id | null, params?: Params): Promise<Result | Result[]>
}

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Query Syntax

All adapters support a common query syntax for filtering, sorting, and pagination: 
// Find users with age greater than 18
await app.service('users').find({
  query: {
    age: { $gt: 18 }
  }
})

// Find users with specific names
await app.service('users').find({
  query: {
    name: { $in: ['Alice', 'Bob'] }
  }
})

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Supported Query Operators

OperatorDescriptionExample
$eqEqual (implicit){ age: 25 }
$neNot equal{ status: { $ne: 'deleted' } }
$ltLess than{ age: { $lt: 30 } }
$lteLess than or equal{ age: { $lte: 30 } }
$gtGreater than{ age: { $gt: 18 } }
$gteGreater than or equal{ age: { $gte: 18 } }
$inIn array{ role: { $in: ['admin', 'user'] } }
$ninNot in array{ role: { $nin: ['guest'] } }
$orLogical OR{ $or: [{ age: { $lt: 18 } }, { age: { $gt: 65 } }] }
$andLogical AND{ $and: [{ age: { $gte: 18 } }, { verified: true }] }

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Pagination

Enable pagination in your service options: 
const service = new MongoDBService({
  Model: collection,
  paginate: {
    default: 10,  // Default page size
    max: 50       // Maximum page size
  }
})
Paginated responses include: 
interface Paginated<T> {
  total: number    // Total count of matching records
  limit: number    // Page size
  skip: number     // Number of records skipped
  data: T[]        // Array of results
}

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Adapter Options

All adapters support these common options: 
interface AdapterServiceOptions {
  id: string              // Primary key field name (default: 'id')
  events: string[]        // Custom events to emit
  paginate?: PaginationOptions  // Pagination configuration
  multi?: boolean | string[]    // Allow multi updates/deletes
  filters?: FilterSettings      // Custom query filters
  operators?: string[]          // Custom query operators
}

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Multi Operations

By default, patch and remove without an ID will throw an error. Enable multi operations: 
const service = new MongoDBService({
  Model: collection,
  multi: true  // Allow all multi operations
})

// Or enable for specific methods only
const service = new MongoDBService({
  Model: collection,
  multi: ['patch', 'remove']
})

// Now you can patch/remove multiple records
await service.patch(null, { status: 'archived' }, {
  query: { active: false }
})

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Internal Methods

Adapters provide internal _method versions that bypass hooks and validation: 
// These skip hooks and sanitization
await service._find(params)
await service._get(id, params)
await service._create(data, params)
await service._update(id, data, params)
await service._patch(id, data, params)
await service._remove(id, params)
Internal methods should only be used within hooks or when you need to bypass the normal service flow. They don’t run hooks or emit events.

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Type Safety

All adapters support full TypeScript typing: 
interface User {
  _id: ObjectId
  name: string
  email: string
  age: number
}

interface UserData {
  name: string
  email: string
  age: number
}

interface UserParams extends Params {
  user?: User
}

class UserService extends MongoDBService<User, UserData, UserParams> {
  // Fully typed service methods
}

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Next Steps

MongoDB Adapter

Learn how to use the MongoDB adapter

Knex Adapter

Connect to SQL databases with Knex

Common Patterns

Explore adapter patterns and best practices

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