Set Entity Framework Connection String in context

You can use DbContext constructor and send name of connectionString.

namespace Dersanem
{
    using System;    
    using System.Data.Entity;
    using System.Data.Entity.Infrastructure;

    public partial class DERSANEM_MASTEREntities : DbContext
    {
        public DERSANEM_MASTEREntities()
            : base("MyDbConnection")
        {
        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            throw new UnintentionalCodeFirstException();
        }    
        public DbSet<sysdiagrams> sysdiagrams { get; set; }
        public DbSet<T_HATA_LOG> T_HATA_LOG { get; set; }
        public DbSet<T_MUSTERILER> T_MUSTERILER { get; set; }
    }
}

More info:

//
// Summary:
//     Constructs a new context instance using the given string as the name or connection
//     string for the database to which a connection will be made. See the class remarks
//     for how this is used to create a connection.
//
// Parameters:
//   nameOrConnectionString:
//     Either the database name or a connection string.
[SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope")]
public DbContext(string nameOrConnectionString);

thank you for Answers

I Solved this problem

public partial class DERSANEM_MASTEREntities : DbContext
{
    public DERSANEM_MASTEREntities()            
    {
        this.Database.Connection.ConnectionString = CS_Sifreleme.Decrypt("TcF8EGfKWDbCdqgS.........");
    }

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

    public DbSet<sysdiagrams> sysdiagrams { get; set; }
    public DbSet<T_HATA_LOG> T_HATA_LOG { get; set; }
    public DbSet<T_MUSTERILER> T_MUSTERILER { get; set; }
}