为什么Linq-to-SQL生成错误的代码，但是编译时没有错误

Question

I use Linq-to-SQL which will generate classes for database tables dragged to its designer. When I drag Product table to designer, Visual Studio will generate like this:

[global::System.Data.Linq.Mapping.TableAttribute(Name="dbo.Products")]
public partial class Product : INotifyPropertyChanging, INotifyPropertyChanged
{
    // ...
    partial void OnProductIDChanging(int value);
    partial void OnProductIDChanged();

    [global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_ProductID", AutoSync=AutoSync.OnInsert, DbType="Int NOT NULL IDENTITY", IsPrimaryKey=true, IsDbGenerated=true)]
    public int ProductID
    {
        get
        {
            return this._ProductID;
        }
        set
        {
            if ((this._ProductID != value))
            {
                this.OnProductIDChanging(value);
                this.SendPropertyChanging();
                this._ProductID = value;
                this.SendPropertyChanged("ProductID");
                this.OnProductIDChanged();
            }
        }
    }
     //...
}

OnProductIDChanging and OnProductIDChanged are not abstract methods and they are empty but why they don't give compiling-error. Thanks.

Answer 1

Because they're partial methods . From MSDN:

One part of the class contains the signature of the method. An optional implementation may be defined in the same part or another part. If the implementation is not supplied, then the method and all calls to the method are removed at compile time.

Answer 2

Because they are partial methods.

This article has a very good explanation of partial methods.