Add support for annotations

This guide explains how to add support for [annotations]({{< relref "../../dashboards/annotations.md" >}}) to an existing data source plugin.

This guide assumes that you're already familiar with how to [Build a data source plugin]({{< relref "../../../../../tutorials/build-a-data-source-plugin.md" >}}).

Data sources in Grafana can support [Annotations]({{< relref "../../dashboards/annotations.md" >}}) by handling annotation queries.

Handling annotation queries is similar to how you'd handle a metrics query. The difference is that instead of returning [data frames]({{< relref "data-frames.md" >}}), an annotation query returns annotation events.

Add annotations support to your data source

To add logs support to an existing data source, you need to:

Enable annotations support
Override the annotationQuery method
Construct annotation events

Enable annotations support

Tell Grafana that your data source plugin can return annotations events by adding "annotations": true to the [plugin.json]({{< relref "metadata.md" >}}) file.

{
  "annotations": true
}

Override the `annotationQuery` method

In DataSource.ts, override the annotationQuery method from DataSourceApi.

async annotationQuery(options: AnnotationQueryRequest<MyQuery>): Promise<AnnotationEvent[]> {
  return [];
}

Construct annotation events

Return an array of [AnnotationEvent]({{< relref "../../packages_api/data/annotationevent.md" >}}).

async annotationQuery(options: AnnotationQueryRequest<MyQuery>): Promise<AnnotationEvent[]> {
  const events: AnnotationEvent[] = [];

  const date = new Date();

  const event: AnnotationEvent = {
    time: date.valueOf(),
    text: 'foo',
    tags: ['bar'],
  };

  events.push(event);

  return events;
}

Region annotations

[Region annotations]({{< relref "../../dashboards/annotations.md#adding-regions-events" >}}) have a start and end time. This can for example be used to annotate maintenance windows or downtime.

To return a region annotation, set the timeEnd, and isRegion properties.

const regionEvent: AnnotationEvent = {
  time: startDate.valueOf(),
  timeEnd: endDate.valueOf(),
  isRegion: true,
  text: 'foo',
  tags: ['bar'],
};

Build a annotation query editor

Let users write custom annotation queries to only display the annotation events they care about, by adding a query editor.

Note: Annotation query editors have yet to receive support for React. The instructions here are given for Angular. Fortunately, you can run Angular even in a plugin otherwise written using React. This section will be updated once React support for annotation queries editors is available.

Create a file called AnnotationQueryEditor.ts in the src directory, with the following content.

export class AnnotationQueryEditor {
  static templateUrl = 'partials/annotations.editor.html';

  annotation: any;

  constructor() {
    this.annotation.queryText = this.annotation.queryText || '';
  }
}

Create a directory called partials in the src directory.

Create a file called annotations.editor.html in the partials directory you just created, with the following content.

<div class="gf-form-group">
  <div class="gf-form-inline">
    <div class="gf-form gf-form--grow">
      <input
       class="gf-form-input"
       placeholder="query expression"
       ng-model="ctrl.annotation.queryText"
       ></input>
    </div>
  </div>
</div>

In your data source query—the one that extends [DataQuery]({{< relref "../../packages_api/data/dataquery.md" >}})—add the queryText property. The name of the property needs to correspond to the text in ng-model, e.g. ctrl.annotation.<propertyName>.
```
export interface MyQuery extends DataQuery {
  // ...
  queryText?: string;
}
```

In module.ts, add the annotation query editor to the plugin.

import { AnnotationQueryEditor } from './AnnotationQueryEditor';

export const plugin = new DataSourcePlugin<DataSource, MyQuery, MyDataSourceOptions>(DataSource)
  .setConfigEditor(ConfigEditor)
  .setQueryEditor(QueryEditor)
  .setAnnotationQueryCtrl(AnnotationQueryEditor);

The queryText property is now available on the options object in the annotationQuery method:

async annotationQuery(options: AnnotationQueryRequest<MyQuery>): Promise<AnnotationEvent[]> {
  const expression = options.annotation.queryText;

  // ...
}

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