Class RowsSourceBase<TDerived, TOutput>

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

This class allows the developer to write synchronous or asynchronous code as needed, without having to check for output demand (which simplifies the implementation), as long as no more than RowsPerBuffer rows are sent on each invocation (or demand is checked for explicitly).

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.

Use RowsSourceBase<TDerived, TOutput, TError> instead if an ErrorOutput port is needed. Also see the RowsSourceBase example.

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

The type of the derived worker. Class definition example:

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

The type of each Output row.

Constructors

RowsSourceBase(WorkerParent, String, Func<Boolean>)

Initializes a new instance of the RowsSourceBase<TDerived, TOutput, TError> abstract dataflow worker, which repeatedly executes the OnOutputRowsDemandAsync method when there is RowsPerBuffer demand on the Output port.

Declaration
protected RowsSourceBase(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

OnOutputRowsDemandAsync()

An abstract method that gets called repeatedly when there is RowsPerBuffer demand for more rows on the Output port. Override it and call methods on the Output port and ErrorOutput port (if present) to pass rows to the downstream workers.

On each invocation of this method there is a demand of at least RowsPerBuffer rows; the method is not allowed to send more than this without checking for additional demand with e.g. TrySendRow(TOutput). Alternatively you can check for demand with HasBufferDemand, but then it is normally easier to send no more than RowsPerBuffer rows and return, to get called again.

Declaration
protected abstract Task<ProgressStatus> OnOutputRowsDemandAsync()
Returns
Type Description
Task<ProgressStatus>
  • 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
  • Error to fail the Output port (if not already completed) and the worker

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 OnOutputRowsDemandAsync() 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