Question

I have only started experimenting with NHibernate and couldn’t get my head around the following scenario, hope someone can shed some light on it. Thank you.

I want to refactor existing Data Access Layer from Subsonic to NHibernate. The existing database is using BINARY(16) as primary key. In Subsonic, it has no problem dealing with byte[] as primary key. In NHibernate if I attempt to map a property that has byte[] datatype, I’ll come across the following exception messages:

{"Illegal use of an array as an identifier (arrays don't reimplement equals)."}

Example of my entity and mapping (with FluentNHibernate) as following:

    public class Product
    {
        public virtual byte[] Id { get; set; }
        public virtual string Name { get; set; }
        public virtual string Description { get; set; }
    }

.

    public ProductMapping()
    {
        Table("tblProduct");
        Id(p => p.Id).Column("prdProductGuid");
        Map(p => p.Name).Column("prdName");
        Map(p => p.Description).Column("prdDescription");
    }

Is there a way to workaround this issue? Thank you.

Currently working with .NET 4.0, NHibernate 3.3.1 and MySQL 5.1.52.

Answer 1

I had a look of Hibernate community and found a hint on utilizing IUserType.

I’ve created a custom class Bytes that’s essentially a serialized wrapper for bytes array:

[Serializable]
public class Bytes
{
    private byte[] _value;
    public byte[] Value { get { return _value; } }

    public Bytes(byte[] bytesValue)
    {
        _value = bytesValue;
    }

    public override bool Equals(object obj) {...}
    public override int GetHashCode() {...}
    public override string ToString() {...}
}

BytesUserType:

public class BytesUserType : IUserType
{
    private static readonly NHibernate.SqlTypes.SqlType[] _sqlTypes = { NHibernateUtil.Binary.SqlType };
    public NHibernate.SqlTypes.SqlType[] SqlTypes { get { return _sqlTypes; } }
    public Type ReturnedType { get { return typeof(Bytes); } }
    public bool IsMutable { get { return false; } }

    public object NullSafeGet(IDataReader dr, string[] names, object owner)
    {
        object obj = NHibernateUtil.Binary.NullSafeGet(dr, names[0]);
        if (obj == null)
            return null;
        var value = (byte[])obj;
        return new Bytes(value);
    }

    public void NullSafeSet(IDbCommand cmd, object obj, int index)
    {
        if (obj == null)
            ((IDataParameter)cmd.Parameters[index]).Value = DBNull.Value;
        else
        {
            Bytes a = (Bytes)obj;
            byte[] valueBytes = a.Value;
            ((IDataParameter)cmd.Parameters[index]).Value = valueBytes;
        }
    }

    public new bool Equals(object x, object y) {...}
    public object DeepCopy(object value) {...}
    public int GetHashCode(object x) {...}
    public object Replace(object original, object target, object owner) {...}
    public object Assemble(object cached, object owner) {...}
    public object Disassemble(object value) {...}
}

Updated my entity and mappings:

public class Product
{
    public virtual Bytes Id { get; set; }
    public virtual string Name { get; set; }
    public virtual string Description { get; set; }
}

.

public ProductMapping()
{
    Table("tblProduct");
    Id(p => p.Id).Column("prdProductGuid").CustomType<BytesUserType>();
    Map(p => p.Name).Column("prdName");
    Map(p => p.Description).Column("prdDescription");
}

And that does the trick!