services.AddDbContext<AppDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"))); code example

Example: services.AddDbContext(options => options.UseSqlServer(Configuration.GetConnectionString("ProjetADONet")));

services.AddDbContext<Projet_AdoNetContext>(options => options.UseSqlServer(Configuration.GetConnectionString("ProjetADONet")));