Entity Framework 6: Provider Error

Question

I am using EF6 Code First. While performing "Update-Database" the database is normally created. But when entering the data the following error is launched:

No Entity Framework Provider found for the ADO.NET Provider with invariant name 'System.Data.Sqlclient'. Make sure the Provider is Registered in the 'entityFramework' Section of the application config file.

On Web.config I put the Connection string with the Provider:

<connectionStrings>
    <add name="StringSqlServerConnection" connectionString="Data Source=NOTE-RAPHAEL\SQLEXPRESS;Initial Catalog=ProjetoTesteDb;Integrated Security=True" providerName="System.Data.SqlClient" />
</connectionStrings>

I put this setting below that I saw in a tutorial from Microsoft, but with it the program didn’t even open:

<configSections> 
    <section name="entityFramework" 
        type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=4.3.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" /> 
</configSections> 

Connection class:

public class AppContext : DbContext
{
    public AppContext()
        : base("StringSqlServerConnection")
    { }

    ...
}

I have other projects that are with this same configuration and had no problem.

Answer 1

This is due to the fact that although you are using a reference in the project, the reference is never used, and the Linker removes all references you think are not used at the time of execution of Seed.

This line forces an assignment, and therefore prevents the Linker to remove the reference by default.

Place your class you inherit from DBContext thus:

public class AppContext : DbContext
{
    public AppContext()
        : base("StringSqlServerConnection")
    { var chamada = System.Data.Entity.SqlServer.SqlProviderServices.Instance;  }
    ...
}

Answer 2

The project where it is mapped in webconfig the Connection string must be set as main and use providerName="System.Data.SqlClient" or do with ConfigurationManager.ConnectionStrings["teste"].ConnectionString the times I’ve been through this problem I’ve solved it this way

   public class Conexao : DbContext
        {
            public Conexao()
                : base(ConfigurationManager.ConnectionStrings["teste"].ConnectionString)
            {

            }     

        }