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PrecedenceConstraints using Transformers

Introduction​

I am currently working with one of our partners to convert their BimlExpress framework to BimlStudio and secure their IP using Transformers. I will post detailed instructions on that subject in the next week or two. One of the things that they do in the first task in every ControlFlow is to check a repository to determine whether the package should execute. I have seen similar approaches in various frameworks out there and provide the following code as a demonstration of how you can achieve this using a single transformer. The sample project is available as TransformerPrecedenceConstraint.zip. If you are new to Transformers please refer to the BimlScript Transformers Primer.

A Simple DataFlow​

<Biml xmlns="http://schemas.varigence.com/biml.xsd">
  <Packages>
    <Package Name="DummyPackage" ConstraintMode="Parallel">
      <Tasks>
        <Dataflow Name="DFT - Dummy">
          <Annotations>
            <Annotation AnnotationType="Tag" Tag="AddExecuteCheck">AddExecuteCheck</Annotation>
          </Annotations>
        </Dataflow>
      </Tasks>
    </Package>
  </Packages>
</Biml>

Add Variables to Package​

<#@ target type="Package" mergemode="LocalMerge" #>
<Package>
  <Variables>
    <Variable Name="IsExecutable" DataType="String" Namespace="User">"N"</Variable>
  </Variables>
</Package>

Add Execute SQL Task to DataFlow​

<#@ target type="DataflowTask" mergemode="LocalReplace" #>
<#	if (TargetNode.Annotations["AddExecuteCheck"] != null) { #>
<Transformations>
  <ExecuteSQL Name="SQL - Execute Check" ForcedExecutionValueDataType="Empty" ConnectionName="AW" ResultSet="SingleRow">
    <Results>
      <Result Name="0" VariableName="User.IsExecutable" />
    </Results>
    <DirectInput>SELECT	'Y'</DirectInput>
  </ExecuteSQL>
  <#=TargetNode.GetBiml()#>
</Transformations>
<#	} #>
<#@ import namespace="System.Data"

Add PrecedenceConstraint to DataFlow​

<#@ target type="DataflowTask" mergemode="LocalMerge" #>
<#	if (TargetNode.Annotations["AddExecuteCheck"] != null) { #>
<DataFlow>
  <PrecedenceConstraints LogicalType="And">
    <Inputs>
      <Input OutputPathName="SQL - Execute Check.Output" EvaluationOperation="ExpressionAndConstraint" Expression="@IsExecutable == "Y"" />
    </Inputs>
  </PrecedenceConstraints>
</DataFlow>
<#	} #>
<#@ import namespace="System.Data" #>