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# Exists
<a name="dp-object-exists"></a>

 Checks whether a data node object exists. 

**Note**  
We recommend that you use system-managed preconditions instead. For more information, see [Preconditions](dp-concepts-preconditions.md).

## Example
<a name="exists-example"></a>

The following is an example of this object type. The `InputData` object references this object, `Ready`, plus another object that you'd define in the same pipeline definition file. `CopyPeriod` is a `Schedule` object.

```
{
  "id" : "InputData",
  "type" : "S3DataNode",
  "schedule" : { "ref" : "CopyPeriod" },
  "filePath" : "s3://amzn-s3-demo-bucket/InputData/#{@scheduledStartTime.format('YYYY-MM-dd-hh:mm')}.csv",
  "precondition" : { "ref" : "Ready" }
},
{
  "id" : "Ready",
  "type" : "Exists"
}
```

## Syntax
<a name="exists-syntax"></a>


****  

| Optional Fields | Description | Slot Type | 
| --- | --- | --- | 
| attemptStatus | Most recently reported status from the remote activity. | String | 
| attemptTimeout | Timeout for remote work completion. If set then a remote activity that does not complete within the set time of starting may be retried. | Period | 
| failureAndRerunMode | Describes consumer node behavior when dependencies fail or are rerun. | Enumeration | 
| lateAfterTimeout | The elapsed time after pipeline start within which the object must complete. It is triggered only when the schedule type is not set to ondemand. | Period | 
| maximumRetries | Maximum number attempt retries on failure | Integer | 
| onFail | An action to run when current object fails. | Reference Object, e.g. "onFail":\$1"ref":"myActionId"\$1 | 
| onLateAction | Actions that should be triggered if an object has not yet been scheduled or still not completed. | Reference Object, e.g. "onLateAction":\$1"ref":"myActionId"\$1 | 
| onSuccess | An action to run when current object succeeds. | Reference Object, e.g. "onSuccess":\$1"ref":"myActionId"\$1 | 
| parent | Parent of the current object from which slots will be inherited. | Reference Object, e.g. "parent":\$1"ref":"myBaseObjectId"\$1 | 
| preconditionTimeout | The period from start after which precondition is marked as failed if still not satisfied | Period | 
| reportProgressTimeout | Timeout for remote work successive calls to reportProgress. If set, then remote activities that do not report progress for the specified period may be considered stalled and so retried. | Period | 
| retryDelay | The timeout duration between two retry attempts. | Period | 

 


****  

| Runtime Fields | Description | Slot Type | 
| --- | --- | --- | 
| @activeInstances | List of the currently scheduled active instance objects. | Reference Object, e.g. "activeInstances":\$1"ref":"myRunnableObjectId"\$1 | 
| @actualEndTime | Time when the execution of this object finished. | DateTime | 
| @actualStartTime | Time when the execution of this object started. | DateTime | 
| cancellationReason | The cancellationReason if this object was cancelled. | String | 
| @cascadeFailedOn | Description of the dependency chain the object failed on. | Reference Object, e.g. "cascadeFailedOn":\$1"ref":"myRunnableObjectId"\$1 | 
| emrStepLog | EMR step logs available only on EMR activity attempts | String | 
| errorId | The errorId if this object failed. | String | 
| errorMessage | The errorMessage if this object failed. | String | 
| errorStackTrace | The error stack trace if this object failed. | String | 
| hadoopJobLog | Hadoop job logs available on attempts for EMR-based activities. | String | 
| hostname | The host name of client that picked up the task attempt. | String | 
| node | The node for which this precondition is being performed. | Reference Object, e.g. "node":\$1"ref":"myRunnableObjectId"\$1 | 
| reportProgressTime | Most recent time that remote activity reported progress. | DateTime | 
| @scheduledEndTime | Schedule end time for object. | DateTime | 
| @scheduledStartTime | Schedule start time for object. | DateTime | 
| @status | The status of this object. | String | 
| @version | Pipeline version the object was created with. | String | 
| @waitingOn | Description of list of dependencies this object is waiting on. | Reference Object, e.g. "waitingOn":\$1"ref":"myRunnableObjectId"\$1 | 

 


****  

| System Fields | Description | Slot Type | 
| --- | --- | --- | 
| @error | Error describing the ill-formed object. | String | 
| @pipelineId | Id of the pipeline to which this object belongs to. | String | 
| @sphere | The sphere of an object denotes its place in the lifecycle: Component Objects give rise to Instance Objects which execute Attempt Objects. | String | 

## See Also
<a name="exists-seealso"></a>
+ [ShellCommandPrecondition](dp-object-shellcommandprecondition.md)