AddIfNotExists DBSet Extension Method

gistfile1.txt

 public static class DbSetExtensions
    {
        public static void AddIfNotExists<TEntity, TProperty>(this IDbSet<TEntity> dbSet,
                                                              Expression<Func<TEntity, TProperty>> selector,
                                                              params TEntity[] toAdd) where TEntity : class
        {

            var compiled = selector.Compile();
            foreach (var entity in toAdd)
            {
                var key = compiled(entity);
                var predicate = BuildPredicate(selector, key);
                if (!dbSet.Any(predicate))
                {
                    dbSet.Add(entity);
                }
            }
        }

        private static Expression<Func<TEntity, bool>> BuildPredicate<TEntity, TProperty>(
            Expression<Func<TEntity, TProperty>> selector, TProperty comparer)
        {
            var body = selector.Body;
            var newBody = Expression.Equal(body, Expression.Constant(comparer));
            return Expression.Lambda<Func<TEntity, bool>>(newBody, selector.Parameters[0])'
        }
    }