How to build .Net Core project with TFS vNext build

So, we created a wonderful .Net Core solution, it looking forward to build it with VSTS or TFS on-premises. And of course we want to use vNext build system :)

First of all - the Hosted agent in Azure CAN NOT build .Net Core projects yet. We will therefore need to use on-premises agent. If you need to know how to configure a vNext build agent - check this manual. Also Martin has a very detailed step-by-step post here.

After build agent is on, make sure you have Visual Studio 2015 Update 2 (ot upgrade to it) and install  .Net Core SDK from here. Now we are all set!

If you just go on the easiest way and do - get the code, build:

it will not work. Reason is that package management is all different in .Net Core, and nuget restore doesn't know how to deal with your .Net Core project packages. So you get:
The dependency Ix-Async >= 1.2.5 could not be resolved.
The dependency Microsoft.AspNetCore.Antiforgery >= 1.0.0-rc2-final could not be resolved.
The dependency Microsoft.AspNetCore.Authorization >= 1.0.0-rc2-final could not be resolved.
... 
and so on. Packages are listet in your project.json file. So unless you restore them with .Net CLI tool prior to build, it ain't work.

Therefore create a packagesRestore.ps1 powershell script like this:
Get-ChildItem -Path $PSScriptRoot\MyWebApp.NetCore -Filter project.json -Recurse | ForEach-Object { & dotnet restore $_.FullName 2>1 }
and save it next next to your .sln file. Check in. 
Pay attention that my project name is MyWebApp.NetCore - so the project.json file is under corresponding directory. 

Now, in you vNext build definition add a new execute powershell before Build solution:

and that's it! Now we can build .Net Core app with VSTS on our on-premises Build agent :)