EF first database change connection string

Hi I have server with some databases that have the same schema. I use EF6 Database/Model First code and I do not want to create deterrent DbContext for them. for example my generated DbContext is :

public partial class TEST_Rev5_FINALEntities : DbContext
{
    public TEST_Rev5_FINALEntities()
        : base("name=TEST_Rev5_FINALEntities")
    {
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        throw new UnintentionalCodeFirstException();
    }

    public virtual DbSet<Header> tbl_Headers { get; set; }
    public virtual DbSet<Output> tbl_Output { get; set; }
    public virtual DbSet<Run> tbl_Run { get; set; }
}

and I created a partial class to set the connection string

public partial class TEST_Rev5_FINALEntities : DbContext 
{
    public TEST_Rev5_FINALEntities(DbConnection dbConnection)
        : base(dbConnection, true)
    {
    }
}

And I have the following method to create the connection with deterrent connection string:

public DbConnection GetConnectionString()
{
    DbConnection conn;
    SqlConnectionStringBuilder sqlConnectionStringBuilder = new SqlConnectionStringBuilder
    {
        DataSource = DataSource,
        IntegratedSecurity = false,
        UserID = User,
        Password = Password,
        MultipleActiveResultSets = true
    };

    SqlConnectionFactory sqlConnectionFactory = new SqlConnectionFactory(sqlConnectionStringBuilder.ConnectionString);
    conn = sqlConnectionFactory.CreateConnection(DatabaseName);

    return conn;
}

Finally I try to run it like this:

using (var context = new TEST_Rev5_FINALEntities(_dal.Connector.GetConnectionString()))
{
    return context.tbl_Headers.FirstOrDefault();
}

but I get this error :

System.Data.Entity.Infrastructure.UnintentionalCodeFirstException
HResult=0x80131509 Message=The context is being used in Code First mode with code that was generated from an EDMX file for either Database First or Model First development.

How can I do it?

The behavior EF uses depends on the way your connection string looks. If it includes a metadata attribute like this:

metadata=res://*/model.csdl|res://*/model.ssdl|res://*/model.msl;

It will presume you are using Database or Model first development.

To make sure Code First is used, remove metadata part of the connection string.