Entity Framework writes in the database while doing a read-only operation

Question

In a console application, I have a SQL Server CE database which I am accessing using Entity Framework. Why is the hash value of the .sdf database changing after a read only operation?

class Program
{
    static void Main(string[] args)
    {
        string fileName = @" C:\...\bin\Debug\exportedDb.sdf";
        Console.WriteLine("The Hash Before is -->"+ComputeHash(fileName));
        using (var context = new DbaseEntities())
        {
            Console.WriteLine(context.ANNEES.First().ANNEE_UNIVERSITAIRE);
        }
        Console.WriteLine("The Hash After is -->" + ComputeHash(fileName));
        Console.ReadLine();
    }

    public static string ComputeHash(string fileName)
    {
        var hash = "";

        using (var md5 = MD5.Create())
        {        
            using (var stream = File.OpenRead(fileName))
            {
                hash = BitConverter.ToString(md5.ComputeHash(stream));
            }                                             

            return hash;
        }
    }
}

The above code gives returns these results :

Answer 1

When the SQL CE engine does sorting and other internal operations, they can be written to temporary tables/objects in the database file.

BUT, you can prevent this from happening by changing your connection string. Add Mode = Read Only to your connection string.

Data Source=C:\data\mydb.sdf;Mode=Read Only