# @DependsOn

`@DependsOn([...])` names beans that must be created before this one and destroyed after it.

## Why

The container already orders beans by their injected dependencies: if `A` takes `B` in its constructor, `B` is created first and destroyed last. You do not need `@DependsOn` for that.

Use it only for a dependency the container cannot see: a bean that relies on another bean's side effect without injecting it. Examples: a schema that another bean creates in the database, a global value that another bean sets up, a file that another bean writes.

Every name must exist. `refresh()` checks that before any bean is created.

## Example

```dart
import 'package:spring_core_dart/spring_core_dart.dart';

// Creates the database tables when it starts.
@Component('schema')
class Schema {
  @PostConstruct()
  void create() {
    // CREATE TABLE ...
  }
}

// Reads the tables, but never calls Schema. Without @DependsOn the
// container could create it first.
@Component()
@DependsOn(['schema'])
class Migrations {
  @PostConstruct()
  void run() {
    // runs after the `schema` bean was created and initialized
  }
}
```

## Parameters

| Name | Type | Default | Meaning |
|---|---|---|---|
| `value` (positional) | `List<String>` | required | Names of the beans created before this one. |

## In Spring (Java)

```java
@Component
@DependsOn("schema")
class Migrations { ... }
```

Differences that matter: Spring takes a single name or an array; here it is always a list. A missing name fails `refresh()` before any bean is created.

## See also

- [@PostConstruct](post-construct.md), [@PreDestroy](pre-destroy.md)
- [@Bean](bean.md)
- [BeanRegistrar](bean-registrar.md) (`dependsOn`)