ConnectorLib .NET 25.2
ConnectorLib .NET SDK Programming Guide

# Implement Custom Fetch Actions

You can implement custom fetch actions in a ConnectorLib .NET connector.

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

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 an `ICustomFetchTask` object. To obtain a request object that provides the action parameters included in the request, access the property `Request` on this object.

Other resources, including a collection of identifiers and an ingester, are available through the `ICustomFetchTask` 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 `I` `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.

To obtain the response object, access the property `Response` on the `ICustomFetchTask` object. Set the value of XML elements in the response by calling the method `SetValue` on the response object. The arguments for this method are the name to use for the new element, and a value.

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=echo`. The action writes a message to the connector's `customfetch` log. The response to the action returns the action parameters that were set in the request, and the reference of each document that was processed. Your users can retrieve the response for an asynchronous action such as `Fetch` through the `QueueInfo` action.

          override public bool CustomFetch(String action, ICustomFetchTask task)
          {
             if (action != "ECHO")
                return false;

             task.Log.WriteLine(LogLevel.Always, "Custom Fetch action " + action + " called");
             task.Response.SetValue("token", task.Response.Token);
             foreach (String param in task.Request.Parameters)
             {
                task.Response.SetValue("parameters/" + param, task.Request[param]);
             }

             int refIndex = 0;
             foreach (IDocInfo docInfo in task.Docs)
             {
                task.Response.SetValue("documents/reference[" + (refIndex++) + "]", docInfo.Identifier.Reference);
             }

             return true;
          }

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Version 25.2 | Last updated April 2025

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Product: Knowledge Discovery ConnectorLib .NET 25.2

Topic Title: Implement Custom Fetch Actions