Question: how to install npgsql visual studio 2015?
Answer: Npgsql. First you'll need to install Npgsql. Download the latest release from the link below and install it. ... 
Ddex Package. Now you'll need to install the Ddex package to connect your VS 2015/2017 with PostgreSQL. You can obtain the latest version on the link below. ... 
Copy Npgsql. dll to PrivateAssemblies.