Home > kibana-plugin-core-server > SavedObjectsClientContract
Saved Objects is Kibana's data persisentence mechanism allowing plugins to use Elasticsearch for storing plugin state.
## SavedObjectsClient errors
Since the SavedObjectsClient has its hands in everything we are a little paranoid about the way we present errors back to to application code. Ideally, all errors will be either:
- Caused by bad implementation (ie. undefined is not a function) and as such unpredictable 2. An error that has been classified and decorated appropriately by the decorators in SavedObjectsErrorHelpers
Type 1 errors are inevitable, but since all expected/handle-able errors should be Type 2 the isXYZError() helpers exposed at SavedObjectsErrorHelpers should be used to understand and manage error responses from the SavedObjectsClient.
Type 2 errors are decorated versions of the source error, so if the elasticsearch client threw an error it will be decorated based on its type. That means that rather than looking for error.body.error.type or doing substring checks on error.body.error.reason, just use the helpers to understand the meaning of the error:
```js if (SavedObjectsErrorHelpers.isNotFoundError(error)) { // handle 404 }
if (SavedObjectsErrorHelpers.isNotAuthorizedError(error)) { // 401 handling should be automatic, but in case you wanted to know }
// always rethrow the error unless you handle it throw error; ```
### 404s from missing index
From the perspective of application code and APIs the SavedObjectsClient is a black box that persists objects. One of the internal details that users have no control over is that we use an elasticsearch index for persistance and that index might be missing.
At the time of writing we are in the process of transitioning away from the operating assumption that the SavedObjects index is always available. Part of this transition is handling errors resulting from an index missing. These used to trigger a 500 error in most cases, and in others cause 404s with different error messages.
From my (Spencer) perspective, a 404 from the SavedObjectsApi is a 404; The object the request/call was targeting could not be found. This is why #14141 takes special care to ensure that 404 errors are generic and don't distinguish between index missing or document missing.
See SavedObjectsClient See SavedObjectsErrorHelpers
Signature:
export declare type SavedObjectsClientContract = Pick<SavedObjectsClient, keyof SavedObjectsClient>;