Class ChainTransformer<TSource, TIntermediate, TDestination>

Namespace: Wolfgang.Etl.Transformers

Assembly: Wolfgang.Etl.Transformers.dll

Combines two transformers into a single transformer: items flow through the first, then through the second, with the intermediate type erased from the chain's public signature.

public sealed class ChainTransformer<TSource, TIntermediate, TDestination> : ITransformAsync<TSource, TDestination> where TSource : notnull where TIntermediate : notnull where TDestination : notnull

Type Parameters

TSource: The input type of the chain (the input type of the first transformer). Must be non-null.
TIntermediate: The output type of the first transformer and input type of the second. Must be non-null.
TDestination: The output type of the chain (the output type of the second transformer). Must be non-null.

Inheritance: object

ChainTransformer<TSource, TIntermediate, TDestination>

Implements: ITransformAsync<TSource, TDestination>

Inherited Members: object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.ReferenceEquals(object, object)

object.ToString()

Extension Methods: TransformerExtensions.Then<TSource, TIntermediate, TDestination>(ITransformAsync<TSource, TIntermediate>, ITransformAsync<TIntermediate, TDestination>)

Remarks

ChainTransformer<TSource, TIntermediate, TDestination> is the building block for composing multi-stage transformer pipelines as a single Wolfgang.Etl.Abstractions.ITransformAsync<TSource, TDestination> that can be passed to a loader, registered in DI, or otherwise treated as a unit.

For chains longer than two stages, prefer the Then<TSource, TIntermediate, TDestination>(ITransformAsync<TSource, TIntermediate>, ITransformAsync<TIntermediate, TDestination>) extension method, which nests ChainTransformer<TSource, TIntermediate, TDestination> instances and lets the C# compiler infer all type parameters:

// 5-stage pipeline, all intermediate types inferred
var pipeline = parseRaw
    .Then(normalize)
    .Then(lookupCustomer)
    .Then(validate)
    .Then(formatForLoad);

Implements only Wolfgang.Etl.Abstractions.ITransformAsync<TSource, TDestination> - matching the lightweight pattern of the rest of the library. The chain itself adds no per-item state-machine wrapping; it returns the inner transformers' enumerables composed directly.

Formerly known internally as MultiStepTransformer.

Constructors

ChainTransformer(ITransformAsync<TSource, TIntermediate>, ITransformAsync<TIntermediate, TDestination>)

Initializes a new instance with the two transformers that make up the chain.

public ChainTransformer(ITransformAsync<TSource, TIntermediate> first, ITransformAsync<TIntermediate, TDestination> second)

Parameters

first ITransformAsync<TSource, TIntermediate>: The first transformer; consumes TSource items and produces TIntermediate items.
second ITransformAsync<TIntermediate, TDestination>: The second transformer; consumes TIntermediate items and produces TDestination items.

Exceptions

ArgumentNullException: first or second is null.

Methods

TransformAsync(IAsyncEnumerable<TSource>)

Asynchronously yields each item from items after passing it through the first transformer and then the second.

public IAsyncEnumerable<TDestination> TransformAsync(IAsyncEnumerable<TSource> items)

Parameters

items IAsyncEnumerable<TSource>: The asynchronous source sequence.

Returns

IAsyncEnumerable<TDestination>: An asynchronous sequence of the items produced by the second transformer.

Exceptions

ArgumentNullException: items is null.