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I am getting an error while adding 'AddSession' in ASP.Net Core 1.1 using VS2017.

'IServiceCollection' does not contain a definition for 'AddSession'
and no extension method 'AddSession' accepting a first argument of
type 'IServiceCollection' could be found (are you missing a using
directive or an assembly reference?)

.csproj

<Project Sdk="Microsoft.NET.Sdk.Web">

<PropertyGroup>
<TargetFramework>netcoreapp1.1</TargetFramework>
</PropertyGroup>

<PropertyGroup>
<PackageTargetFallback>$(PackageTargetFallback);portable-net45+win8+wp8+wpa81;</PackageTargetFallback>
</PropertyGroup>
 <ItemGroup>
 <PackageReference Include="Microsoft.ApplicationInsights.AspNetCore" Version="2.0.0" />
 <PackageReference Include="Microsoft.AspNetCore" Version="1.1.1" />
<PackageReference Include="Microsoft.AspNetCore.Mvc" Version="1.1.2" />
<PackageReference Include="Microsoft.AspNetCore.Session" Version="1.1.2" />
<PackageReference Include="Microsoft.AspNetCore.StaticFiles" Version="1.1.1" />
<PackageReference Include="Microsoft.Extensions.Logging.Debug" Version="1.1.1" />
<PackageReference Include="Microsoft.VisualStudio.Web.BrowserLink" Version="1.1.0" />
 </ItemGroup>
 <ItemGroup>
 <DotNetCliToolReference 
 Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="1.0.0" />
</ItemGroup>

 </Project>

Error :

You need to include following Nuget package

AutoMapper.Extensions.Microsoft.Dependencyinjection

I know this is a bit late, but did you try to install the Microsoft.AspNetCore.Session package from nuget?

https://www.nuget.org/packages/Microsoft.AspNetCore.Session/

In Visual Studio:
Install-Package Microsoft.AspNetCore.Session -Version 1.1.2(in my case)

It worked for me!

The following way I fixed the Issue.

1. Clean and Rebuild the solution.


2. Restart Visual Studio 2017.

Thanks @HenkMollema

The versions of the dependencies seem to be out of sync. Use Nuget to update all your packages to be the same version and that should solve the issue. This applies to most if not all Microsoft.* packages.

Also you need the following using statements:

using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.DependencyInjection;
using System;

Make sure you have

<PackageReference Include="Microsoft.AspNetCore.Session" Vesion="1.1.1" />

(or more up-to-date version) within your .csproj file

In my case AutoMapper.Extensions.Microsoft.DependencyInjection (v1 was installed). Uninstalled and installed AutoMapper.Extensions.Microsoft.DependencyInjection v5.0.1