C# Linq to Entity Lamda方式分組并求和求平均值

1、單字段分組并求和：

var list = data.GroupBy(g => g.GoodsId).Select(e => new { GoodsId = e.Key, Qty = e.Sum(q => q.Qty) });      

2、多字段分組求和：

var list = data.GroupBy(g => new { g.StorageId,g.GoodsId }).Select(e => new { GoodsId = e.Key, Qty = e.Sum(q => q.Qty) });      

求平均值直接把Sum更換成：Average即可。

3、具有導航屬性的類求和及分組：

var list = data.GroupBy(g => new { g.StorageId,g.GoodsId }).Select(e => new {
                    StorageName = e.Select(i => i.Storage.Name).FirstOrDefault(),
                    GoodsName = e.Select(i => i.Goods.Name).FirstOrDefault(),                   
                    CategoryName = e.Select(i => i.Goods.CategoryName).FirstOrDefault(),
                    Qty = e.Average(q => q.Qty) });      

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