EntityExtensionMethods.cs

using System.Linq;
using System.Reflection;

namespace System.Data.Linq
{
    /// <summary>
    /// LINQ-to-SQL extension methods
    /// </summary>
    public static class EntityExtensionMethods
    {
        /// <summary>
        /// Performs database UPSERT operation.
        /// </summary>
        public static void InsertOrUpdateOnSubmit<TEntity>(this Table<TEntity> table, TEntity entity, TEntity original = null)
            where TEntity : class, new()
        {
            // if entity does not exist by primary keys then insert
            if (!table.Contains(entity))
            {
                table.InsertOnSubmit(entity);
            }
            else // update without pulling data
            {
                table.UpdateOnSubmit(entity, original);
            }
        }

        public static void UpdateOnSubmit<TEntity>(this Table<TEntity> table, TEntity entity, TEntity original = null)
            where TEntity : class, new()
        {
            if (original == null)
            {
                // Create original object with only primary keys set
                original = new TEntity();
                var entityType = typeof(TEntity);
                var dataMembers = table.Context.Mapping.GetMetaType(entityType).DataMembers;
                foreach (var member in dataMembers.Where(m => m.IsPrimaryKey))
                {
                    var propValue = entityType.GetProperty(member.Name).GetValue(entity, null);
                    entityType.InvokeMember(member.Name, BindingFlags.SetProperty, Type.DefaultBinder,
                        original, new[] { propValue });
                }
            }

            // This will update all columns that are not set in 'original' object. For
            // this to work, entity has to have UpdateCheck=Never for all properties except
            // for primary keys. This will update the record without querying it first.
            table.Attach(entity, original);
        }

        public static void InsertOnSubmitIfNotExists<TEntity>(this Table<TEntity> table, TEntity entity)
            where TEntity : class
        {
            if (!table.Contains(entity))
            {
                table.InsertOnSubmit(entity);
            }
        }

    }
}