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. |
|
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
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 customFetch
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
method can run many times for a single request; each time it is passed a different customFetch
CustomFetchTask
instance. The number of times that the
method runs is determined as follows:customFetch
- The
method runs for each distinct configuration file section name embedded in the identifiers (provided by thecustomFetch
identifiers
oridentifiersXML
action parameters) or included in the request (using theconfigsection
ortasksections
parameters). Theconfigsection
parameter accepts a single name. Thetasksections
parameter accepts a comma-separated list of names. - If no configuration file sections are provided by identifiers or by the
configsection
ortasksections
parameters, then thecustomFetch
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. 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
method should return customFetch
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
method, giving the reason for the failure.customFetch
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; }