C# 同时获取集合的第一个和最后一个元素
我目前正在从事一个跨平台项目 我在尝试在WebDataLayer.Models和Shared.Models之间映射模型时遇到了这个问题C# 同时获取集合的第一个和最后一个元素,c#,entity-framework,mvvmcross,C#,Entity Framework,Mvvmcross,我目前正在从事一个跨平台项目 我在尝试在WebDataLayer.Models和Shared.Models之间映射模型时遇到了这个问题 namespace WebDataLayer.Models { public class Factory { public Guid Id { get; set; } public string Name { get; set; } public string Serie { get; set;
namespace WebDataLayer.Models
{
public class Factory
{
public Guid Id { get; set; }
public string Name { get; set; }
public string Serie { get; set; }
public Guid? AreaId { get; set; }
public virtual ICollection<FactoryHotline> FactoryHotlines { get; set; }
}
public class FactoryHotline
{
public Guid Id { get; set; }
public Guid FactoryId { get; set; }
[Required]
[MaxLength(256)]
public string Caption { get; set; }
[Required]
[MaxLength(256)]
public string Hotline { get; set; }
}
这是控制器中的代码,我尝试将WebDatalayer.Models.Factory
转换为Shared.Models.Factory
:
public ActionResult Edit()
{
var factories = _factoryService.All().OrderBy(p => p.Name);
List<Shared.Models.Factory> response = new List<Shared.Models.Factory>();
response = factories.Select(k => new Shared.Models.Factory
{
Id = k.Id,
Name = k.Name,
Serie = k.Serie,
Hotline1 = new Shared.Models.FactoryHotline {
Id = k.FactoryHotlines.FirstOrDefault().Id,
Caption = k.FactoryHotlines.FirstOrDefault().Caption,
Hotline = k.FactoryHotlines.FirstOrDefault().Hotline,
FactoryId = k.FactoryHotlines.FirstOrDefault().FactoryId
},
Hotline2 = new Shared.Models.FactoryHotline
{
Id = k.FactoryHotlines.LastOrDefault().Id,
Caption = k.FactoryHotlines.LastOrDefault().Caption,
Hotline = k.FactoryHotlines.LastOrDefault().Hotline,
FactoryId = k.FactoryHotlines.LastOrDefault().FactoryId
},
}).OrderBy(f => f.Name).ToList();
return View("Edit", response);
}
public ActionResult Edit()
{
var factories=\u factoryService.All().OrderBy(p=>p.Name);
列表响应=新列表();
响应=工厂。选择(k=>newshared.Models.Factory
{
Id=k.Id,
Name=k.Name,
Serie=k.Serie,
Hotline1=新的Shared.Models.FactoryHotline{
Id=k.FactoryHotlines.FirstOrDefault().Id,
Caption=k.FactoryHotlines.FirstOrDefault().Caption,
热线=k.FactoryHotlines.FirstOrDefault()热线,
FactoryId=k.FactoryHotlines.FirstOrDefault().FactoryId
},
Hotline2=新的Shared.Models.FactoryHotline
{
Id=k.FactoryHotlines.LastOrDefault().Id,
Caption=k.FactoryHotlines.LastOrDefault().Caption,
热线=k.FactoryHotlines.LastOrDefault().热线,
FactoryId=k.FactoryHotlines.LastOrDefault().FactoryId
},
}).OrderBy(f=>f.Name).ToList();
返回视图(“编辑”,响应);
}
但是linq-to-entities不识别lastordefault方法,不能使用降序
,因为我同时也获取第一个元素
需要帮助 我不确定这是否是最干净的解决方案,但您可以将链接到其中
.Where((v, i) => { return i == 0 || i == list.Count() -1; })
所以
您似乎希望返回按名称订购的所有工厂,对于每个工厂,返回第一条和最后一条热线:
var query = factories.Select(f => new Shared.Models.Factory
{
Id = f.Id,
Name = f.Name,
Serie = f.Serie,
Hotline1 = f.FactoryHotLines
.OrderBy(h => h.Id)
.Select(h => new Shared.Models.FactoryHotline
{
Id = h.Id,
Caption = h.Caption,
Hotline = h.Hotline,
FactoryId = h.FactoryId
}).FirstOrDefault(),
Hotline2 = x.FactoryHotLines
.OrderByDescending(h => h.Id)
.Select(h => new Shared.Models.FactoryHotline
{
Id = h.Id,
Caption = h.Caption,
Hotline = h.Hotline,
FactoryId = h.FactoryId
}).FirstOrDefault(),
}).OrderBy(f => f.Name)
.ToList();
这里的关键点是:在使用FirstOrDefault()
时,始终提供一个OrderBy
子句。与其依赖于FirstOrDefault()
来获取每个单独的值,不如将其与OrderBy()
一起使用以获取实体,然后使用Select()
将其缩减为所需的视图模型
上面的示例假设您需要添加它们的顺序。(标识基于身份的记录)通过这种方式,我们执行OrderBy()
以获取第一条热线,然后执行OrderByDescending()
以获取第二条热线
factories = factories.Where((v, i) => { return i == 0 || i == factories.Count() -1; })
var query = factories.Select(f => new Shared.Models.Factory
{
Id = f.Id,
Name = f.Name,
Serie = f.Serie,
Hotline1 = f.FactoryHotLines
.OrderBy(h => h.Id)
.Select(h => new Shared.Models.FactoryHotline
{
Id = h.Id,
Caption = h.Caption,
Hotline = h.Hotline,
FactoryId = h.FactoryId
}).FirstOrDefault(),
Hotline2 = x.FactoryHotLines
.OrderByDescending(h => h.Id)
.Select(h => new Shared.Models.FactoryHotline
{
Id = h.Id,
Caption = h.Caption,
Hotline = h.Hotline,
FactoryId = h.FactoryId
}).FirstOrDefault(),
}).OrderBy(f => f.Name)
.ToList();