Class RowSourceBase<TDerived, TOutput>

An abstract dataflow worker which repeatedly executes the OnOutputRowDemand() method when there is demand on the Output port. The library user must inherit this class and override OnOutputRowDemand() to provide custom functionality.

This class simplifies the implementation by allowing the developer to write synchronous code that operates on a single row at a time, without having to check for output demand.

The derived class can additionally override RunAsync() to add logic that runs before and after all processing of rows, in which case the base class base.RunAsync() must be called. The derived class (or its user) can also use worker callbacks to add logic.

Also see the RowSourceBase example.

Inheritance
Object
WorkerParent
WorkerBase
WorkerBase<TDerived>
RowSourceBase<TDerived, TOutput>
Implements
Inherited Members
Namespace: actionETL
Assembly: actionETL.dll
Syntax
public abstract class RowSourceBase<TDerived, TOutput> : WorkerBase<TDerived>, IDisposeOnFinished where TDerived : RowSourceBase<TDerived, TOutput> where TOutput : class
Type Parameters
Name Description
TDerived

The type of the derived worker. Class definition example:

public class MySource<TOutput>
    : RowSourceBase<MySource<TOutput>,TOutput>
    where TOutput : class, new()
{ 
    // ...
}
TOutput

The type of each Output row.

Constructors

RowSourceBase(WorkerParent, String, Func<Boolean>)

Initializes a new instance of the RowSourceBase<TDerived, TOutput> abstract dataflow worker, which repeatedly executes the OnOutputRowDemand() method when there is demand on the Output port.

Declaration
protected RowSourceBase(WorkerParent workerParent, string workerName, Func<bool> isStartableFunc)
Parameters
Type Name Description
WorkerParent workerParent

The parent worker or worker system that the new child worker will be added to. Cannot be null.
String workerName

Name of the worker.

Set to a prefix plus a trailing "/" (e.g. "MyPrefix-/") to generate a unique name from the prefix plus an increasing number starting at 1.

While less useful, set to null, whitespace or "/" to generate a unique name from the worker type plus an increasing number starting at 1.

The name cannot otherwise contain "/", and cannot start with double underscore "__".

Func<Boolean> isStartableFunc

Function to calculate the worker start constraint; it should return true for startable and false for not startable. Defaults to startable if null.
Exceptions
Type Condition
ArgumentException

workerName:

  • Workers with the same parent must have unique names.
  • Worker and worker system names cannot contain '/' or start with double underscore '__'.
ArgumentNullException

workerParent - All workers must have a parent. The top level workers have the worker system as parent.
InvalidOperationException
  • Cannot add child worker to parent which has completed. Are you adding it to the correct parent?
  • Cannot add worker to parent, since its children have been started. Are you adding it to the correct parent?

Properties

Output

Gets the output port for sending rows to the downstream worker.

Declaration
public OutputPort<TOutput> Output { get; }
Property Value
Type Description
OutputPort<TOutput>

Methods

OnOutputRowDemand()

An abstract method that gets called repeatedly when there is demand for one more row on the Output port. Override it and produce zero or one output rows per invocation.

Note that this method must not send rows by calling methods directly on the Output port.

Declaration
protected abstract ProgressStatusResult<TOutput> OnOutputRowDemand()
Returns
Type Description
ProgressStatusResult<TOutput>

In the returned ProgressStatusResult<TResult>, set Status to:

  • NotCompleted to continue to be called when there is demand for rows
  • Succeeded to finish row processing and (if not already completed) automatically call SendSucceeded() to complete the Output port
  • An error status to fail the Output port (if not already completed) and the worker
For NotCompleted and Succeeded, also set Result to either a row to be sent to the output, or null to not send a row.

RunAsync()

This method can be overridden to add custom functionality to the derived worker that runs before and after the row processing. In this case, the base class base.RunAsync() must be called for the worker to function correctly.

Typically, only OnOutputRowDemand() is overridden to add required custom logic.

Declaration
protected override async Task<OutcomeStatus> RunAsync()
Returns
Type Description
Task<OutcomeStatus>

A Task describing the success or failure of the worker. An asynchronous async implementation would e.g. return OutcomeStatus.Succeeded on success, while a synchronous implementation would return OutcomeStatus.SucceededTask.
Overrides

Implements