# DataLoader

`<DataLoader />` works similarly to, and uses, `<DataSource />` but additionally
exposes various common states based on the status of the loading of the data.
These states are exposed as slots to enable you to easily render different
elements based on the state of the data.


Use the `@dataSource` decorator in your repositories to define URI to async
method mapping.

```javascript
class SomethingRepository extends Service {
  @dataSource('/:partition/:nspace/:dc/services')
  async youCouldCallItAnythingTodoWithGettingServices(params) {
    console.log(params);
    // {partition: "partition", nspace: "nspace", dc: "dc"}
    return getTheThing(params);
  }
}
```

```hbs preview-template
<DataLoader
  @src="/partition/nspace/dc/services"
as |loader|>
  <BlockSlot @name="loading">
    Loading...
  </BlockSlot>
  <BlockSlot @name="error">
    Error {{loader.error.status}}
  </BlockSlot>
  <BlockSlot @name="disconnected">
    Whilst we could load the initial data, something happened subsequently that
    meant we could load longer load updates to the data.
  </BlockSlot>
  <BlockSlot @name="loaded">
    {{#each loader.data as |service|}}
    {{service.Name}}<br />
    {{/each}}
  </BlockSlot>
</DataLoader>
```

## Attributes

| Argument | Type | Default | Description |
| --- | --- | --- | --- |
| `src` | `String` | | The source to subscribe to updates to, this should map to a string based URI |

## Exported API

| Name | Type | Description |
| --- | --- | --- |
| `data`  | `object` | The loaded dataset once any data has been loaded successfully |
| `error` | `Error` |The error thrown if an error is encountered whilst loading data |
| `invalidate` | `function` | Invalidate the data represented by the DataLoader, therefore forcing a re-request of data for the DataLoader |

## Slots

| Name           | Description |
| ---            | --- |
| `loading`      | Rendered whilst waiting for the initial data to load. |
| `error`        | If there is an error only whilst waiting for the initial data to load, this slot is rendered. |
| `disconnected` | Rendered when the initial data has already loaded, but a subsequent set of loaded data causes an error to be thrown.|
| `loaded`       | Rendered once the initial data is loaded and on subsequent successful loads of data. |

## See

- [DataSource](../data-source/README.mdx)
- [Component Source Code](./index.js)
- [Template Source Code](./index.hbs)

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