Entity framework throwing invalid operation exception - Connection string in app.config not found

Question

I added a new ADO.NET data model from the database, and everything generated fine.

Then I try to make a call to get one of the tables:

public Sensor[] GetAllRegisteredSensors()
        {
            using (var context = new ClientSensorLocationEntities())
            {
                try
                {
                    return context.Sensors.ToArray();

                }
                catch (Exception ex)
                {
                    throw;
                }
            }
        }

and I get an exception:

No connection string named 'ClientSensorLocationEntities' could be found in the application config file.

Pretty self-explanatory and then I went to my app.config file which looks like this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <connectionStrings>
    <add name="ClientSensorLocationEntities" connectionString="metadata=res://*/ClientSensorLocationModel.csdl|res://*/ClientSensorLocationModel.ssdl|res://*/ClientSensorLocationModel.msl;
               provider=System.Data.SqlClient;provider connection string=&quot;data source=MYUSER\SQLEXPRESS;initial catalog=ClientSensorLocation;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework&quot;"
               providerName="System.Data.EntityClient" />
              </connectionStrings>
              <startup>
                <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6" />
          </startup>
        </configuration>

So the connection string with that name exists. What seems to be the problem then?

Answer 1

If you are using DbContext from referencing Projects, you also need to register the connection string on the project configuration file.

For example, if you are using the DbContext on a web project, check if the connection string is on the web.config.