How to map a property as NOT a column in EF 4.1

Question

I have a class:

public class classParty
{
    private int _arrivedCount;

    public int PartyID {get; private set;}
    public DateTime PartyDate {get; private set;}
    public int ArrivedCount
    {
        get
        {
            return _arrivedCount;
        }

        set
        {
            _arrivedCount = value;
        }
    }
}

I can map the PartyId and the PartyDate but I don't have a column for ArrivedCount (it's a moment in time count, it doesn't persist).

How do I tell EF 4.1 to stop looking for a column named "ArrivedCount"? It's not in the table. It's not going to be in the table. It's simply a property of the object and that's all.

Thanks in advance.

EDIT: Here's the Fluent API configuration for classParty.

public class PartyConfiguration : EntityTypeConfiguration<classParty>
{
    public PartyConfiguration()
        : base()
    {
        HasKey(p => p.PartyID);

        Property(p => p.PartyID)
            .HasColumnName("PartyID")
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity)
            .IsRequired();
        Property(p => p.PartyDate)
            .HasColumnName("PartyDate")
            .IsRequired();

        ToTable("Party");
    }
}

Answer 1

With data annotations:

[NotMapped]
public int ArrivedCount
//...

Or using Fluent API:

modelBuilder.Entity<classParty>()
    .Ignore(c => c.ArrivedCount);