MSBuild Join Items Task

JoinItems.tasks.targets

  <UsingTask
    TaskName="JoinItems"
    TaskFactory="CodeTaskFactory"
    AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.v4.0.dll" >
      <ParameterGroup>
          <OuterItems ParameterType="Microsoft.Build.Framework.ITaskItem[]" Required="true" />
          <OuterProperty Required="false" ParameterType="System.String" />
          <InnerItems ParameterType="Microsoft.Build.Framework.ITaskItem[]" Required="true" />
          <InnerProperty Required="false" ParameterType="System.String" />
          <IgnoreCase Required="false" ParameterType="System.String" />
          <CopyMetadata Required="false" ParameterType="System.String" />
          <LeftOuterJoin Required="false" ParameterType="System.String" />
          <NewTaskItems Required="false" ParameterType="System.String" />
          <Items ParameterType="Microsoft.Build.Framework.ITaskItem[]" Output="true" />
      </ParameterGroup>
      <Task>
         <Using Namespace="System"/>
         <Using Namespace="System.Linq"/>
         <Using Namespace="System.Collections.Generic"/>
         <Using Namespace="Microsoft.Build.Framework"/>

          <Code Type="Fragment" Language="cs">
            <![CDATA[
              var xComparand = String.IsNullOrWhiteSpace(OuterProperty) ? "Identity" : OuterProperty;
              var yComparand = String.IsNullOrWhiteSpace(InnerProperty) ? "Identity" : InnerProperty;
              var comparer = Boolean.Parse( (IgnoreCase ?? "true") ) ? StringComparer.OrdinalIgnoreCase : StringComparer.Ordinal;
              var shouldCopyMetadata = Boolean.Parse( (CopyMetadata ?? "true") );
              var performLeftOuterJoin = Boolean.Parse( (LeftOuterJoin ?? "false") );
              var createNewTaskItems = Boolean.Parse( (NewTaskItems ?? "false") );

              var qryInnerJoin = OuterItems.Join(
                InnerItems, 
                x => x.GetMetadata(xComparand), 
                x => x.GetMetadata(yComparand), 
                (x, y) => new { Outer=x, Inner=y }, 
                comparer);

              var qryLeftOuterJoin = OuterItems.GroupJoin(
                  InnerItems, 
                  x => x.GetMetadata(xComparand),
                  x => x.GetMetadata(yComparand),
                  (x, y) => new { Outer=x, Inner=y }, 
                  comparer)
                .SelectMany(
                  x => x.Inner.DefaultIfEmpty(),
                  (x,y) => new { Outer=x.Outer, Inner=y });

              var output = new List<ITaskItem>(Math.Max(OuterItems.Length, InnerItems.Length));

              foreach (var joinedItem in (performLeftOuterJoin ? qryLeftOuterJoin : qryInnerJoin))
              {
                var newItem = (createNewTaskItems) ? (ITaskItem) new TaskItem(joinedItem.Outer.ItemSpec) : joinedItem.Outer;

                if (shouldCopyMetadata && createNewTaskItems)
                {
                  joinedItem.Outer.CopyMetadataTo(newItem);
                }

                if (shouldCopyMetadata && joinedItem.Inner != null) 
                {
                  joinedItem.Inner.CopyMetadataTo(newItem);
                }

                output.Add(newItem);
              }

              Items = output.ToArray();
            ]]>
          </Code>
      </Task>
  </UsingTask>