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var result = from
a in
model
join
b in
orderDetailModel on
a.FoodMenuID equals
b.FoodMenuID into
g
from
b in
g.DefaultIfEmpty()
select
new Model.WebApiModel.WMFoodMenu
{
BarginPrice = a.BarginPrice,
Credits = a.Credits,
FoodMenuCategoryID = a.FoodMenuCategoryID,
FoodMenuID = a.FoodMenuID,
RestaurantID = a.RestaurantID,
FoodMenuName = a.FoodMenuName,
SaleCount = b != null
? b.FoodMenuSaleCount : 0,
ImgUrl100 = a.ImgUrl100,
ImgUrl150 = a.ImgUrl150,
IsRecommend = a.IsRecommend,
Price = a.Price
};
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这里，必须要注意一点是：SaleCount = b != null ? b.FoodMenuSaleCount : 0，这里如果SaleCount字段不允许为空，必须先判定。
如果写成 SaleCount = b.FoodMenuSaleCount，当右边数据为空时，将出现未将对象引用设置对实例的错误