Sequence

One-dimensional array. All the values contained in a sequence are scalars of the same type. A sequence contains a finite number of element but can also contain zero element.

Definition

To specify a sequence, you can use any of the following options:

List of values

The easiest way to define a sequence is to specify each member. This can be done using the item element one or more times.

<sequence type="text">
  <item>be</item>
  <item>fr</item>
</sequence>

Sentinel loops

Usage of a loop-sentinel element is targetting the definition of sequence containing elements developed one by one with the help of a recursive calculation. The first element is defined by the seed attribute and is always returned by the loop (meaning that a loop-sentinel has a minimum of one element). The next element of the sequence is calculated based on the seed and the addition of the step attribute. The third element will be calculated based on the second element and the step. The sequence is over when the next element is greater than the terminal attribute.

<sequence type="dateTime">
    <loop-sentinel seed="2015-01-01" terminal="2017-01-01" step="1 year"/>
</sequence>

Expl:

• A sequence having for seed the value 1, for step the value 1 and for terminal the value 5 will have 5 elements having for values 1,2,3,4,5.
• A sequence having for seed the value 1 for step the value 2, and for terminal the value 5 will have 3 elements having for values 1,3,5.
• A sequence having for seed the value 1 for step the value 3, and for terminal the value 5 will have 2 elements having for values 1 and 4.

Due to its definition, a loop-sentinel can only be used for the definition of a sequence containing a numeric type or a dateTime type.

For a numeric type, the seed, step and terminal attributes are defined as numeric scalars. In the case of a sequence containing scalar with a dateTime type, then the attributes seed and terminal are dateTime but the step is a duration.

Half-open

It’s possible to define a sentinel loop where the terminal value shouldn’t be included in the sequence. This is done by setting the xml attribute interval to the value half-open.

Expl:

• A sequence, with the interval set to half-open, having a seed of 1 and a step of 1 and a terminal of 5 will have 4 elements having for values 1,2,3 and 4.
• A sequence, with the interval set to half-open, having a seed of 1 and a step of 2 and a terminal of 5 will have 2 elements having for values 1 and 3.
• A sequence, with the interval set to half-open, having a seed of 1 and a step of 3 and a terminal of 5 will have 2 elements having for values 1 and 4.

File loops

It’s possible to define a file loop to get the name of all the files within a directory and for which the filename matches a given pattern. The elements of the sequence returned by a loop-file are composed of the filename and the extension.

<loop-file path="..\csv\" pattern="MyData*.csv"/>

Query-based definition

This solution retrieves the values from a the result of the execution of a query.

In this example, the sequence named myVar is set to the values returned by the query defined in the element query-sequence. If the query returns more than one column , the first column is considered. All the possibilities offered by the standard query element is available. For mor information on how to define a query, take a look in the result-set definition documentation.

<sequence name="myVar">
  <query-sequence connection-string="...">
    select [myColumn] from [myTable] where [myFilterColumn]=@filter;
    <parameter name="filter">myFilterValue</parameter>
  </query-sequence>
</sequence>

Custom sequence

This solution retrieves the values from an external C# assembly. This assembly must contain one or more types implementing the interface ISequenceResolver.

In this example, the sequence named myVar is set to the values returned by the type MyCustomClass of the assembly myassembly.dll when executing the method Execute() . Optionaly, you can pass some parameters to the type MyType when instantiating it. In this example, the class MyCustomClass has a constructor accepting two parameters (foo, bar).

<sequence name="myVar">
  <custom assembly="myAssembly.dll" type="MyCustomClass">
    <parameter name="bar">10</parameter>
    <parameter name="foo">@myValue</parameter>
  </custom>
</sequence>

using NBi.Core.Scalar.Resolver;
using System;

namespace NBi.Testing.Core.Scalar.Resolver.Resources
{
    public class MyCustomClass : ISequenceResolver
    {
      private int Foo { get; }
      private DateTime Bar { get; }

      public MyCustomClass(DateTime bar, int foo)
        => (Bar, Foo) = (bar, foo);

      public IList Execute() 
        => new DateTime[] { Bar.AddDays(-Foo), Bar.AddDays(Foo) }.ToList();

      object IResolver.Execute() => Execute();
    }
}

Filtering

From time to times, it’s useful to perform an additional filtering to remove a few values. Typically when using loop-file, you’ll remove files with a size less than a few bytes or updated more than 10 days ago.

To achieve this, you’ll define a filter implementing a predicate. The predicate will be applied to each of the values contained in the sequence. Each value will be hold if the predicate is successful and will be removed in case of failure to validate the predicate.

The attribute operand is containing the native transformations that will be applied to each value of the sequence. If no transformation is expected, you must specify the value value for the operand.

In the example here under, the loop-file will define all the files matching the pattern MyData.csv* in the directory ..\csv. Then a filter will be applied to only hold the files that have been updated less than 10 days ago (defined in a variable @TenDaysAgo). Keep in mind that loo-file doesn’t return the full path but just the filename with the extension so you’ll have to rebuild the full path before applying a native transformation such as file-to-update-dateTime. Note also that the predicate is of type dateTime in that case and not text. This is because the predicate will compare two dateTime and not a dateTime and a text.

<sequence name="myVar"/>
  <loop-file path="..\csv\" pattern="MyData*.csv"/>
  <filter>
    <predicate 
       operand="text-to-prefix(..\csv\) | file-to-update-dateTime"
       type="dateTime"
    >
      <more-than>@TenDaysAgo<more-than>
    </predicate>
  </filter>
</sequence>

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