Migrating Configuration
=======================

By `Steve Smith`_ and `Scott Addie`_

In the previous article, we began :doc:`migrating an ASP.NET MVC project to ASP.NET Core MVC <mvc>`. In this article, we migrate configuration.

.. contents:: Sections:
  :local:
  :depth: 1
  
`View or download sample code <https://github.com/aspnet/Docs/tree/master/aspnet/migration/configuration/samples>`__

Setup Configuration
-------------------

ASP.NET Core no longer uses the *Global.asax* and *web.config* files that previous versions of ASP.NET utilized. In earlier versions of ASP.NET, application startup logic was placed in an ``Application_StartUp`` method within *Global.asax*. Later, in ASP.NET MVC, a *Startup.cs* file was included in the root of the project; and, it was called when the application started. ASP.NET Core has adopted this approach completely placing all startup logic in the *Startup.cs* file.

The *web.config* file has also been replaced in ASP.NET Core. Configuration itself can now be configured, as part of the application startup procedure described in *Startup.cs*. Configuration can still utilize XML files, but typically ASP.NET Core projects will place configuration values in a JSON-formatted file, such as *appsettings.json*. ASP.NET Core's configuration system can also easily access environment variables, which can provide a more secure and robust location for environment-specific values. This is especially true for secrets like connection strings and API keys that should not be checked into source control. See :doc:`/fundamentals/configuration` to learn more about configuration in ASP.NET Core.

For this article, we are starting with the partially-migrated ASP.NET Core project from :doc:`the previous article <mvc>`. To setup configuration add the following constructor and property to the *Startup.cs* class located in the root of the project:

.. literalinclude:: configuration/samples/WebApp1/src/WebApp1/Startup.cs
  :language: c#
  :linenos:
  :lines: 15-24
  :dedent: 8
  
Note that at this point the *Startup.cs* file will not compile, as we still need to add the following ``using`` statement:

.. code-block:: c#

  using Microsoft.Extensions.Configuration;

Add an *appsettings.json* file to the root of the project using the appropriate item template:

.. image:: configuration/_static/add-appsettings-json.png
    :width: 955px

Migrate Configuration Settings from web.config
----------------------------------------------

Our ASP.NET MVC project included the required database connection string in *web.config*, in the ``<connectionStrings>`` element. In our ASP.NET Core project, we are going to store this information in the *appsettings.json* file. Open *appsettings.json*, and note that it already includes the following:

.. literalinclude:: configuration/samples/WebApp1/src/WebApp1/appsettings.json
  :language: json
  :emphasize-lines: 4
  :linenos:

In the highlighted line depicted above, change the name of the database from **_CHANGE_ME** to the name of your database.

Summary
-------

ASP.NET Core places all startup logic for the application in a single file, in which the necessary services and dependencies can be defined and configured. It replaces the *web.config* file with a flexible configuration feature that can leverage a variety of file formats, such as JSON, as well as environment variables.