c# - 带有 LINQ 查询的 Entity Framework

Question

change/change2 有什么区别？

using (var context = new NORTHWNDEntities())
{
    var change = context.Regions.Where(r => r.RegionDescription == "East").ToList();

    var change2 = (from r in context.Regions where r.RegionDescription == "East" select new {r.RegionID, r.RegionDescription }).ToList();

    foreach (var p in change2)
    {
        p.RegionDescription = "West";
    }
    context.SaveChanges();
}

当我尝试在 foreach 循环中更新 change2 时出现错误:

Property or indexer '......' cannot be assigned to -- it is read only

它适用于使用 lambda 的先前版本。我怎样才能让它工作？

Answer 1

 var change2 = (from r in context.Regions 
                where r.RegionDescription == "East" 
                select new {r.RegionID, r.RegionDescription }).ToList();

您返回的是匿名类型。匿名类型属性是只读的。如果要更改值，则需要返回已定义的实际类型。

您可以new 其他东西，比如new Region 或者只返回r

var change2 = (from r in context.Regions 
                where r.RegionDescription == "East" 
                select r).ToList(); 


 var change2 = (from r in context.Regions 
                where r.RegionDescription == "East" 
                select new Region {.RegionID = r.RegionID, 
                                   .RegionDescription = r.RegionDescription }).ToList();