EF6 DBContext Dynamic Connection String

Question

public partial class ProcessContext : DbContext
{
    static ProcessContext()
    {
        Database.SetInitializer<ProcessContext>(null);
    }

    public ProcessContext()
        : base("Name=ProcessCS") //Comes from Config File
    {
    }

    --DBSets 
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
       --Code
    }
}

This is a Multi Tenent DB where we have 3 Different DB's. Centralized DB is in common location and would not be changed. This is where rest of the DB details will be stored. I need to create the Connection string @ runtime where the details will be coming from this centralized DB. Can some one please let me know how to go about it?

I tried with the following code, but it is not working. This Method will be called here

public ProcessContext()
    : base(nameOrConnectionString: ConnectionString())
{
}

private static string ConnectionString()
{
    SqlConnectionStringBuilder sqlBuilder = new SqlConnectionStringBuilder();
    sqlBuilder.DataSource = "XXX";
    sqlBuilder.InitialCatalog = "YYY";
    sqlBuilder.PersistSecurityInfo = true;
    sqlBuilder.IntegratedSecurity = true;
    sqlBuilder.MultipleActiveResultSets = true;

    EntityConnectionStringBuilder entityBuilder = new EntityConnectionStringBuilder();
    entityBuilder.ProviderConnectionString = sqlBuilder.ToString();
    entityBuilder.Metadata = "res://*/";
    entityBuilder.Provider = "System.Data.SqlClient";

    return entityBuilder.ToString();
}

Answer 1

For SQL Server connection, override the entity container class: (works in EF6, SQL server 2012 express, VS2013)

public partial class PxxxxEntities
{
    private PxxxxEntities(string connectionString)
        : base(connectionString)
    {
    }

    public static PxxxxEntities ConnectToSqlServer(string host, string catalog, string user, string pass, bool winAuth)
    {
        SqlConnectionStringBuilder sqlBuilder = new SqlConnectionStringBuilder
        {
            DataSource = host,
            InitialCatalog = catalog,
            PersistSecurityInfo = true,
            IntegratedSecurity = winAuth,
            MultipleActiveResultSets = true,

            UserID = user,
            Password = pass,
        };

        // assumes a connectionString name in .config of MyDbEntities
        var entityConnectionStringBuilder = new EntityConnectionStringBuilder
        {
            Provider = "System.Data.SqlClient",
            ProviderConnectionString = sqlBuilder.ConnectionString,
            Metadata = "res://*/DbModel.csdl|res://*/DbModel.ssdl|res://*/DbModel.msl",
        };

        return new PxxxxEntities(entityConnectionStringBuilder.ConnectionString);
    }
}