Entity Framework: The context is being used in Code First mode with code that was generated from an EDMX file

My mistake was using standard connection string in constructor

(Server = test\test; Database = DB; User Id = test_user;Password = test),

but Entity Framework needs different format

(metadata=res://*/DBModel.csdl|res://*/DBModel.ssdl|res://*/DBModel.msl;provider=System.Data.SqlClient;provider connection string="data source=test\test;initial catalog=DB;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework""" providerName = ""System.Data.EntityClient)

Edit: Changed code to be formatted as code so it’s easier to read.