# FilterByInclude

**Kind:** Interface

**Source:** [`packages/core/discovery/discovery-service.ts`](https://github.com/nestjs/nest/blob/master/packages/core/discovery/discovery-service.ts#L16)

**Part of:** [Core](subsystem-packages-core)

`FilterByInclude` defines an inclusion filter used by the discovery service. Its `include` field contains predicate functions that determine which discovered items should be retained during discovery processing.

## Properties

| Property | Type |
|---|---|
| `include` | `Function[]` |

## Diagram

```mermaid
graph LR
  A[Discovery Service] --> B[FilterByInclude]
  B --> C[include: Function[]]
  C --> D[Inclusion Predicate 1]
  C --> E[Inclusion Predicate 2]
  D --> F[Discovered Items]
  E --> F
  F --> G[Included Results]
```

## Usage

```ts
import type { FilterByInclude } from './discovery-service';

const filter: FilterByInclude = {
  include: [
    (item) => item.enabled === true,
    (item) => item.name.startsWith('api-'),
  ],
};

// Pass the filter to the discovery workflow.
// Only items matching the configured inclusion predicates are retained.
discoveryService.discover({
  filter,
});
```

## AI Coding Instructions

- Provide inclusion logic as functions in the `include` array; keep each predicate focused on a single filtering concern.
- Ensure predicate functions safely handle missing or optional properties on discovered items.
- Use `FilterByInclude` when configuring discovery behavior that should explicitly retain matching items.
- Avoid placing side effects in include predicates; they should only evaluate whether an item belongs in the results.

## Relationships

- IMPORTS → `CustomDecorator`
- IMPORTS → `flatten`
- IMPORTS → `Injectable`
- IMPORTS → `SetMetadata`