[英]How to declare the return Type of a grouping Linq query
以下查詢返回的類型是什么:
var photos = job.Photos.GroupBy(x => x.Location)
.Select(group =>
new
{
Name = group.Key,
Photos = group.OrderByDescending(x => x.DateAdded)
})
.OrderBy(group => group.Name)
.ToList();
根據調試器,其類型為:
'System.Collections.Generic.List<<anonymous type: string Name, System.Linq.IOrderedEnumerable<Project.Models.Photo> Photos>>'
但是我不知道如何聲明這種類型。
我試過了
public List<string, IOrderedEnumerable<Photo>> Photos {get; set;)
但是列表只能包含一個元素
如果您不想創建其他類,則可以使用Dictionary將字符串鍵和照片列表作為值保存,僅保留此信息。
IDictionary<string, List<Photo>> photos = job.Photos.GroupBy(x => x.Location)
.Select(group =>
new
{
Name = group.Key,
Photos = group.OrderByDescending(x => x.DateAdded)
})
.OrderBy(group => group.Name)
.ToDictionary(kv=>kv.Name, kv=>kv.Photos.ToList());
您有幾種選擇:
Dictionary<TKey, TValue>
,將Value
IOrderedEnumerable<T>
var photos = job.Photos
.GroupBy(x => x.Location)
.ToDictionary(group => group.Key,
group => group.OrderByDescending(x => x.DateAdded));
我將在OrderByDescending
之后添加一個額外的ToList
調用,以防止項目被解析和排序一次。
就像調試器所說的那樣,它是一個匿名類型 。 這意味着您不能寫它的名字,因為它沒有名字。 您可以做的是創建一個新類,並在查詢中使用它:
List<PhotosGroup> photos = job.Photos.GroupBy(x => x.Location)
.Select(group =>
new PhotosGroup
{
Name = group.Key,
Photos = group.OrderByDescending(x => x.DateAdded)
})
.OrderBy(group => group.Name)
.ToList();
或者,您可以使用Tuple
類型:
List<Tuple<string, IOrderedEnumerable<Photo>> photos = job.Photos.GroupBy(x => x.Location)
.Select(group =>
Tuple.Create(
group.Key,
group.OrderByDescending(x => x.DateAdded)))
.OrderBy(group => group.Item1)
.ToList();
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