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Sorting

For ETL.NET streams can have specific characteristics. These characteristics are sometimes required by some operators. There are some operator to issue streams with there characteristics.

SortedStream​

A SortedStream is a stream that issues payloads in a specific order. The stream hosts the sorting criteria and its type for the operators that uses it can operate properly with input payloads.

There are two ways to make a SortedStream.

From a Stream that issues payloads that are not sorted:

var sortedStream = stream.Sort("Sort values", i => i.OutputId);

To sort on different criterias, and with different direction:

var sortedStream = stream.Sort("Sort values", i => new { i.OutputId, i.Label });

To sort with different directions:

// Sort Label descending, and then by OutputId
var sortedStream = stream.Sort("Sort values", i => new { i.OutputId, i.Label }, new { Label = -1, OutputId = 2});

It can happen that the develop knows that, as a matter of a fact, a Stream is actually sorted, for example when values come from a query from a database engine. In this situation, the point is just to check if the stream is actually sorted:

var sortedStream = stream.EnsureSorted("Ensure sorted", i => i.OutputId);

EnsureSorted operator work in the same way that Sort.

danger

If a payload doesn't obey the sorting criteria, the EnsureSorted operator will issue an exception, causing the process to fail.

KeyedStream​

A KeyedStream is a specific SortedStream. It has the same characteristics than a SortedStream except that there are no duplicates on the sorting key.

To make a KeyedStream out of a stream that is not sorted, first sort it, then ensure it is keyed:

var keyedStream1 = stream
    .Sort("Sort values1", i => i.OutputId)
    .EnsureKeyed("Ensure values are keyed1", i => i.OutputId);

var keyedStream2 = stream
    .Sort("Sort values2", i => new { i.OutputId, i.Label })
    .EnsureKeyed("Ensure values are keyed2", i => new { i.OutputId, i.Label });

var keyedStream3 = stream
    .Sort("Sort values3", i => new { i.OutputId, i.Label }, new { Label = -1, OutputId = 2})
    .EnsureKeyed("Ensure values are keyed3", i => new { i.OutputId, i.Label }, new { Label = -1, OutputId = 2});

Like for SortedStream the develop may know that a regular stream is, as a matter of a fact keyed. Then just use EnsureKeyed for this purpose.

danger

Like EnsureSorted operator, EnsureKeyed will issue an exception, causing the process to fail, if the stream is not actually keyed.

SingleStream​

A SingleStream is a specific KeyedStream that has the payload it self a the key criteria. What characterizes it is that not more and not less than one event will be emitted in this stream.

EnsureSingle is the way to get a SingleStream and checks if the streams is actually a one event stream.

var singleStream = stream.EnsureSingle("Ensure only one event is emitted");
danger

EnsureSingle will issue an exception, causing the process to fail, if the input stream completes without having emitted a payload previously, or if a payload is emitted whereas another one was issued before.