Solution with pre Core Class Library & .net Core 2 MVC projects - web.config connectionstring not working

Question

I have a solution containing many projects.

One of the projects is a data access layer Class Library. It uses this line for the connection string which it gets from the web.config of any other project that references it:

private string Constr = ConfigurationManager.ConnectionStrings["DefaultConn"].ConnectionString;

I've added a web.config to a .net core 2 MVC app, but I get this error:

FileNotFoundException: Could not load file or assembly 'System.Configuration.ConfigurationManager, Version=0.0.0.0, Culture=neutral, PublicKeyToken=123456'. The system cannot find the file specified.

I've also tried adding the connection string to the appsettings.json file - but it also doesn't help; the full contents of appsettings.json:

{
  "ConnectionStrings": {
    "DefaultConn": "Server=.;Database=MyDatabase;Trusted_Connection=true;"
  },

  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Warning"
    }
  }
}

I've found a few articles online dancing around it - but none that can fix this.

How to read web.config file in .Net Core app This one mentions a similar situation and a nuget package - but it doesn't solve the issue for the user.

How to include reference to assembly in ASP.NET Core project This one touches on it but applies to Hangfire only, not a Class Library using ConfigurationManager

How can I do this? Thanks.

In your asp.net core project, You should inject IConfiguration and then you can read the connection string. Read this learn.microsoft.com/en-us/aspnet/core/fundamentals/… — Shyju
– Shyju, Commented May 24, 2018 at 2:00
Thanks - I'm not quite clear. So in the core project I still need the web.config with the connectionstring section? The link is long and mentions IConfiguration a lot - an answer with the specific code required would be appreciated - thanks. — niico
– niico, Commented May 24, 2018 at 2:08
No. You keep the connection string in the appsetttings json file — Shyju
– Shyju, Commented May 24, 2018 at 2:13
Ahh OK - I have already done that too. Can you point me at the specific code to add? — niico
– niico, Commented May 24, 2018 at 2:14
Check that page i linked. Check the sample line Configuration["MyConfig"];. Replace that with connection string key( Ex : Configuration["ConnectionStrings:DefaultConn"];) — Shyju
– Shyju, Commented May 24, 2018 at 2:16

niico · Accepted Answer · 2018-05-25 12:04:05Z

0

I realise that ideally you'd use DI and appsettings.json to store a connection string in .net core MVC 2.

However, regarding my specific question - passing a connectionstring to a Class Library that's already expecting something from the web.config - and to aid in transitioning to .net core - this other question was useful: How to read web.config file in .Net Core app

But no answer answered it - a comment did from Zuhair. Basically just rename web.config app.config and it works. It works for the linked class library too.

Here is my app.config:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <connectionStrings>
    <add name="DefaultConnection" connectionString="Server=.;Database=mydb;Trusted_Connection=true;" providerName="System.Data.SqlClient" />
  </connectionStrings>
</configuration>

You also need to install this NuGet package:

System.Configuration.ConfigurationManager

edited May 25, 2018 at 12:04

answered May 25, 2018 at 11:51

niico

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