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# Once Input Adapter

## Overview

The TIBCO StreamBase® Once Input Adapter is an embedded adapter that starts up and sends one tuple as output. It does nothing else during the lifetime of its container unless the adapter instance is restarted. Its purpose is to ensure that something happens once and only once when the container for an application starts in StreamBase Server. This adapter is designed to trigger the portion of the application that performs the initialization of an input stream, and it is useful for sequencing start and restart activities for an application.

The output schema has a single timestamp field.

It is possible for the output tuple from another input adapter to occur before the output of the Once input adapter.

## Ports

An instance of the Once adapter has a single output port.

## Properties

### General Tab

Name: Use this required field to specify or change the component's name, which must be unique in the current module. The name must contain only alphabetic characters, numbers, and underscores, and no hyphens or other special characters. The first character must be alphabetic or an underscore.

Adapter: A read-only field that shows the formal name of the adapter.

Class name: Shows the fully qualified class name that implements the functionality of this adapter. If you need to reference this class name elsewhere in your application, you can right-click this field and select Copy from the context menu to place the full class name in the system clipboard.

Start with application: If this field is set to Yes (default) or to a module parameter that evaluates to `true`, this instance of this adapter starts as part of the JVM engine that runs this EventFlow fragment. If this field is set to No or to a module parameter that evaluates to `false`, the adapter instance is loaded with the engine, but does not start until you send an epadmin container resume command (or its sbadmin equivalent), or until you start the component with StreamBase Manager.

Enable Error Output Port: Select this check box to add an Error Port to this component. In the EventFlow canvas, the Error Port shows as a red output port, always the last port for the component. See Using Error Ports to learn about Error Ports.

Description: Optionally enter text to briefly describe the component's purpose and function. In the EventFlow canvas, you can see the description by pressing Ctrl while the component's tooltip is displayed.

### Adapter Settings Tab

The Once Adapter has a single setting, which is the output field name. By default, the field name is `time`.

This setting is a string name of the one field that makes up the schema of the output tuple. The field is of type timestamp, and contains an absolute timestamp value. The field specifies the system time when the adapter sends the tuple.

### Concurrency Tab

Use the Concurrency tab to specify parallel regions for this instance of this component, or multiplicity options, or both. The Concurrency tab settings are described in Concurrency Options, and dispatch styles are described in Dispatch Styles.

### Caution

Concurrency settings are not suitable for every application, and using these settings requires a thorough analysis of your application. For details, see Execution Order and Concurrency, which includes important guidelines for using the concurrency options.

## Typechecking and Error Handling

Typechecking detects a value for the output that is null or unspecified.

## Related Topics

- Using Embedded Adapters

- Once Input Adapter Sample

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