MSBuild Metadata on joined item groups

Question

I have two item groups that I wish to join:

  <ItemGroup>
<ServerTypeA Include="ServerA;ServerB;">
  <MetaDataA>A</MetaDataA>
</ServerTypeA>
</ItemGroup>

  <ItemGroup>
<ServerTypeB Include="ServerB;ServerC;">
  <MetaDataB>B</MetaDataB>
</ServerTypeB>
</ItemGroup>

Using the regular join will give me a collection with 4 items:

ServerA with Metadata A;
ServerB with Metadata A;
ServerB with Metadata B;
ServerC with Metadata B;

How can I create the following collection:

ServerA with Metadata A
ServerB with Metadata A & B
ServerC with Metadata B

Answer 1

It's possible. You have to can manually perform the join.

Here's an example of how to do it (msbuild 3.5 or greater required):

<ItemGroup>
  <ServerTypeA Include="ServerA;ServerB;">
    <MetaDataA>A</MetaDataA>
  </ServerTypeA>

  <ServerTypeB Include="ServerB;ServerC;">
    <MetaDataB>B</MetaDataB>
  </ServerTypeB>
</ItemGroup>

<Target Name="JoinServers" DependsOnTargets="ProcessServerTypeA;ProcessServerTypeB">
  <Message Text="%(Joined.Identity) Metadata: %(Joined.MetaDataA)%(Joined.MetaDataB)"/>
</Target>

<!--Create -->
<Target Name="ProcessServerTypeA">
  <ItemGroup>
    <Joined Include="%(ServerTypeA.Identity)">
      <MetaDataA>%(ServerTypeA.MetaDataA)</MetaDataA>
    </Joined>
  </ItemGroup>
</Target>

<!--Need to batch at the target level for this to work-->
<Target Name="ProcessServerTypeB" Inputs="@(ServerTypeB)" Outputs="%(ServerTypeB.Identity)'">

  <PropertyGroup>
    <!--Create Temporary Properties for the Item Metadata-->
    <TempItemName>%(ServerTypeB.Identity)</TempItemName>
    <TempMetaDataB>%(ServerTypeB.MetaDataB)</TempMetaDataB>
    <!--Does the current item already exist?-->
    <TempIsDuplicate Condition="'%(Joined.Identity)' == '$(TempItemName)'">True</TempIsDuplicate>
  </PropertyGroup>

  <ItemGroup>
    <!--Update the existing item's metadata if this is a duplicate-->
    <!--Don't provide the include attribute.  This will allow you to update existing items metadata-->
    <!--Have to reference %(Joined.Identity) in the condtion to ensure we only update the correct item-->
    <!--You cannot directly reference metadata from ServerTypeB here.  Hence the need for the temp Properties-->
    <Joined Condition="'%(Joined.Identity)' == '$(TempItemName)'">
      <MetaDataB>$(TempMetaDataB)</MetaDataB>
    </Joined>

    <!--Create a new item if current item is not a duplicate-->
    <Joined Include="$(TempItemName)" Condition="'$(TempIsDuplicate)' != 'True'">
      <MetaDataB>$(TempMetaDataB)</MetaDataB>
    </Joined>
  </ItemGroup>
</Target>

Running the JoinServers target will produce the following output:

ServerA Metadata: A
ServerB Metadata: AB
ServerC Metadata: B

Update with a better answer

This question pointed me to a much simpler solution.

Basically you use Transform modifiers with %(Identity) to perform the join.

You can replace all 3 targets from above with the following to obtain the same output.

<Target Name="JoinServers">
  <ItemGroup>
    <Joined Include="%(Identity)">
      <MetaDataA>@(ServerTypeA->'%(MetaDataA)')</MetaDataA>
      <MetaDataB>@(ServerTypeB->'%(MetaDataB)')</MetaDataB>
    </Joined>
  </ItemGroup>

  <Message Text="%(Joined.Identity) Metadata: %(Joined.MetaDataA)%(Joined.MetaDataB)"/>
</Target>