asp.net mvc – connectionStrings in web.config is missing?
Entity Framework is all about conventions. If you dont provide it with a connection string (name), it will determine one by convention.
This is explained in MSDN: Entity Framework Connections and Models:
If you have not done any other configuration in your application, then calling the parameterless constructor on DbContext will cause DbContext to run in Code First mode with a database connection created by convention.
In this example DbContext uses the namespace qualified name of your derived context class—Demo.EF.BloggingContext—as the database name and creates a connection string for this database using either SQL Express or LocalDb. If both are installed, SQL Express will be used.