Question

I have a scenario where I am synchronizing data between multiple VERY dissimilar systems. (The data itself is similar but the tables on the different systems have quite different formats.) To assist with this synchronization, I have a database table which stores object hashes from each of the systems along with item keys and other relevant information. When the hash of an object from either system changes, I update the other.

My database table looks something like this.

CREATE TABLE [dbo].[SyncHashes](
    [SyncHashId] [int] IDENTITY(1,1) NOT NULL,
    [ObjectName] [nvarchar](50) NULL,
    [MappingTypeValue] [nvarchar](25) NULL,
    [MappingDirectionValue] [nvarchar](25) NULL,
    [SourceSystem] [nvarchar](50) NULL,
    [SourceKey] [nvarchar](200) NULL,
    [SourceHash] [nvarchar](50) NULL,
    [TargetSystem] [nvarchar](50) NULL,
    [TargetKey] [nvarchar](200) NULL,
    [TargetHash] [nvarchar](50) NULL,
    [UpdateNeededValue] [nvarchar](max) NULL,
    [CreatedOn] [datetime] NULL,
    [ModifiedOn] [datetime] NULL,
    [Version] [timestamp] NOT NULL, 
    [IsActive] [bit] NOT NULL,
PRIMARY KEY CLUSTERED 
(
    [SyncHashId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

So far so good. But…

In order to effectively compute a hash (such as an MD5 hash (which is what i am using)) for an object, you need to be able to convert it to a byte array.

And…

It seems that in order to convert an object to a byte array, it must be serializable. (At least that’s what I have read, and the errors I am getting from .NET seem to indicate that is true.)

For one of the systems, I have the ability to make all of my database objects serializable so that’s great. Hashes get generated, everything gets synchronized, and the world is beautiful!

For another system, things are not so great. I am passed a database context from entity framework 4 (code first) model and the entities are NOT serialized.

When I attempt to cast as byte using something like the following, .NET complains and throws a minor tantrum–all the while refusing to give me the nice little byte array I so politely asked for.

foreach(var dataItem in context.TableName)
{
    var byteArray = (byte[]) dataItem;
}

Ok. No problem.

I have myself a nice little extension method which I thought might do the trick.

public static byte[] ObjectToByteArray<T>(this T obj)
{
    if (obj == null)
        return null;
    BinaryFormatter bf = new BinaryFormatter();
    MemoryStream ms = new MemoryStream();

    bf.Serialize(ms, obj);
    return ms.ToArray();
}

But oh no! If the object (the Entity) is not serializable, this routine throws me another nice little (and totally expected) exception.

So… I modify the routine and add a where clause to the method definition like so.

public static byte[] ObjectToByteArray<T>(this T obj) where T : ISerializable
{
    if (obj == null)
        return null;
    BinaryFormatter bf = new BinaryFormatter();
    MemoryStream ms = new MemoryStream();

    bf.Serialize(ms, obj);
    return ms.ToArray();
}

The only problem is that now I am back to square one where all of my objects need to be serializable to get a byte array.

Hmmm. Not good.

So I put together a hack to iterate through all of the object’s properties and generate a string representation from which I could build a byte array. It was UGLY and INEFFICIENT but it kind of sort of did the trick.

public static string ComputeMD5Hash<T>(this T input)
{
    StringBuilder sb = new StringBuilder();

    Type t = input.GetType();
    PropertyInfo[] properties = t.GetProperties();

    foreach (var property in properties)
    {
        sb.Append(property.Name);
        sb.Append("|");
        object value = property.GetValue(input, null);
        if (value != null)
        {
            sb.Append(value);
        }
        sb.Append("|");
    }

    return MD5HashGenerator.GenerateKey(sb.ToString());
}

But…

After all that, what I still really would like to be able to is efficiently and properly to create a byte array from an object whose class is not marked as serializable. What is the best way to accomplish this?

Thank you in advance!

Answer 1

create a byte array from an object whose class is not marked as serializable

You can use protobuf-net v2 to accomplish this. Download the zip then reference the protobuf-net assembly.

Consider this simple class definition we want to serialize:

public class Person
{
    public string Firstname { get; set; }
    public string Surname { get; set; }
    public int Age { get; set; }
}

You can then serialize this as a byte array:

var person = new Person {Firstname = "John", Surname = "Smith", Age = 30};
var model = ProtoBuf.Meta.TypeModel.Create();
//add all properties you want to serialize. 
//in this case we just loop over all the public properties of the class
//Order by name so the properties are in a predictable order
var properties = typeof (Person).GetProperties().Select(p => p.Name).OrderBy(name => name).ToArray();
model.Add(typeof(Person), true).Add(properties);

byte[] bytes;

using (var memoryStream = new MemoryStream())
{
    model.Serialize(memoryStream, person);
    bytes = memoryStream.GetBuffer();
}

The protobuf-net serializer will serialize much faster and produce a smaller byte[] array than BinaryFormatter

caveat 1 This will only (in its current form) serialize the public properties of your class, which looks ok for your usage.
caveat 2 This is considered brittle because adding a new property to Person may mean you are unable to deserialize a Person object that was serialized with the prior TypeModel.