MSBuild Metadata on joined item groups - collections

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>