Does Visual Studio 2015 include .edmx support?
I have a project that includes an .edmx data model and double-clicking it in VS2015 just opens the XML editor.
The
During setup of VS2015, go to the advanced options and select Web or Database Development tools. Now the Installers install the EF tools (Designer + templates). If you have VS already installed, to the Programs & features in control panel and modify the currently installed VS2015.
You have to select the Microsoft SQL Server Data Tools in the VS2015 setup to get this editor back.
NOTE: You can modify the current installation via Program And Features as magicandre1981 has already suggested.
see how this is done here