EF去除重复列DistinctBy

转载自：https://blog.csdn.net/ying456baby/article/details/81075336?utm_source=blogxgwz5
1.添加一个扩展方法

 public static class DistinctByClass
    {
        public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
        {
            HashSet<TKey> seenKeys = new HashSet<TKey>();
            foreach (TSource element in source)
            {
                if (seenKeys.Add(keySelector(element)))
                {
                    yield return element;
                }
            }
        }
	}

2.使用方法如下（针对ID，和Name进行Distinct）

var query = people.DistinctBy(p => new { p.Id, p.Name });

3.若仅仅针对ID进行distinct

var query = people.DistinctBy(p => p.Id);

例如：

var q = (from f in db.FW_Cultivate
                     join p in db.Sys_Product on f.ProdID equals p.ProdID
                     select new
                     {
                         f.ProdID,
                         f.EntID,
                         f.DisID,
                         p.ProdName
                     })
                .WhereIf(filter.EntID > 0, t => t.EntID == filter.EntID)
                .WhereIf(filter.DisID > 0, t => t.DisID == filter.DisID).DistinctBy(t=>t.ProdName);