ConnectorLib C++ 25.1
ConnectorLib C++ SDK Programming Guide

# Implement Custom Fetch Actions

You can implement custom fetch actions in a ConnectorLib C++ connector.

Action | Description | Method to override
--- | --- | ---
`action=Fetch&FetchAction=MyAction` | Perform custom fetch actions on a repository. | ``customFetch``

First add the `custom_fetch` feature to the list of supported features returned by the `features` function on `ConnectorBase`:

           Features::feature_type MyConnector::features()
           {
              return Features::synchronize|Features::collect|Features::custom_fetch;
           }

To implement a custom fetch action, override the `customFetch` method on the `ConnectorBase` interface.

The ``customFetch`` method is passed the name of the fetch action that was called in the request. The name is always in upper case, because action names are case-insensitive. You can use the ``customFetch`` method to handle as many fetch action names as necessary, however the action names `SYNCHRONIZE`, `COLLECT`, `HOLD`, and so on, are reserved by the connector for the standard fetch actions.

The `customFetch` method is also passed a `CustomFetchTask` object. The `CustomFetchTask` object provides access to a request object which provides all of the action parameters. You can access action parameters using `task.request().getParameter(parameterName)`.

Other resources, including a collection of identifiers and an ingester, are available through the `CustomFetchTask` object. You can use these in your implementation of the custom fetch action.

The ``customFetch`` method can run many times for a single request; each time it is passed a different `CustomFetchTask` instance. The number of times that the ``customFetch`` method runs is determined as follows:

- The ``customFetch`` method runs for each distinct configuration file section name embedded in the identifiers (provided by the `identifiers` or `identifiersXML` action parameters) or included in the request (using the `configsection` or `tasksections` parameters). The `configsection` parameter accepts a single name. The `tasksections` parameter accepts a comma-separated list of names.
- If no configuration file sections are provided by identifiers or by the `configsection` or `tasksections` parameters, then the `customFetch` method runs one time for each task listed in the `[FetchTasks]` section of the configuration file.

- If no fetch tasks are configured in the connector's configuration file, the `customFetch` method does not run and the following warning is written to the connector's logs:

  `WARNING: Custom fetch action is not associated with any task configuration sections, no tasks will be executed`

Your code must use the parameters from the request to perform the action and populate the action response. Use the method `response.setValue(elementName, value)` to set the value of XML elements in the response.

You can add attributes and nested elements to the action response using XPath-like expressions with element indexes. For example:

           Response.setValue("document[0]/metadata[7]/@name", "MyField");

Your implementation of the ``customFetch`` method should return `false` only if the fetch action name is not supported. In all other cases, return `true`. If another failure occurs then throw an exception from the ``customFetch`` method, giving the reason for the failure.

The following sample code shows how a custom fetch action might be implemented for a basic connector. This example provides `action=fetch&FetchAction=count`, and counts the files below a list of paths:

          bool MyConnector::customFetch(const std::string& action, const CustomFetchTask& task)
          {
             if (action == "COUNT")
             {
                auto paths = task.taskConfig().getCollection("DirectoryPathCSVs");

                std::size_t count = 0;
                for (const std::string& path : paths)
                {
                    // Count files below path
                }
                task.response().setValue("file_count", count);

                return true;
             }

             return false;
          }

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Version 25.1 | Last updated January 2025

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Product: Knowledge Discovery ConnectorLib C++ 25.1

Topic Title: Implement Custom Fetch Actions