C# 实体框架 ORDER BY 问题

Entity Framework ORDER BY issue

提问by Dakine83

I'm attempting to build my first MVC 4 application using the entity framework. All I'm looking for is to create a drop down list with the value and text of each option set to the same value.

我正在尝试使用实体框架构建我的第一个 MVC 4 应用程序。我正在寻找的是创建一个下拉列表，其中每个选项的值和文本都设置为相同的值。

This works, right up until I throw in the GroupBy().

这有效，直到我将GroupBy().

Create.cshtml

创建.cshtml

@Html.DropDownList("CustomerName",(SelectList)ViewData["companies"]);

ticketController.cs

票务控制器.cs

ViewBag.companies = new SelectList(oc_db.company.Where(c => c.status == "ACTIVE")
                                                 .OrderBy(c => c.name_1)
                                                  .GroupBy(c=>c.name_1)
                                   , "name_1", "name_1");

Here is the Error I'm receiving:

这是我收到的错误：

DataBinding: 'System.Data.Objects.ELinq.InitializerMetadata+Grouping`2[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[OpsTicketing.Models.company, OpsTicketing, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]' does not contain a property with the name 'name_1'.

数据绑定：'System.Data.Objects.ELinq.InitializerMetadata+Grouping`2[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[OpsTicketing.Models.company, OpsTicketing= 1.0.0.0, Culture=neutral, PublicKeyToken=null]]' 不包含名为 'name_1' 的属性。

If I don't use the GroupBythe query works, albeit with duplicates.

如果我不使用GroupBy查询工作，尽管有重复。

采纳答案by D Stanley

GroupBydoesn't give you an enumeration of the underlying type. It gives you an enumeration of IGroupingobjects with a Keyfield that gives you the key value for that group and an IEnumerableinterface that lets you iterate the members of that group.

GroupBy不会为您提供基础类型的枚举。它为您提供了一个IGrouping对象枚举，其中一个Key字段为您提供该组的键值，以及一个IEnumerable让您迭代该组成员的界面。

If all you want is a unique list of name_1values in order, just select that field and do a Distinctfollowed by an OrderBy:

如果您想要的name_1只是按顺序排列的唯一值列表，只需选择该字段并执行 aDistinct后跟OrderBy：

ViewBag.companies = new SelectList(oc_db.company.Where(c => c.status == "ACTIVE")
                                                .Select(c=> new {c.name_1})
                                                .Distinct()
                                                .OrderBy(c => c.name_1)
                                   , "name_1", "name_1");

Note that you coulddo it without the .Select(), but you'd have to define "equality" for your companyclass, which is more trouble than it's worth for this exercise. That's why the Distinctdidn't work before - because you didn't define what makes two companies distinct.

请注意，您可以在没有 的情况下执行此操作.Select()，但是您必须为您的company班级定义“平等” ，这比本练习的价值要麻烦。这就是为什么Distinct以前不起作用的原因-因为您没有定义使两家公司不同的原因。

回答by mattytommo

You'll have to resolve the query before performing the GroupBy, which you can do by calling .ToList()

您必须在执行 GroupBy 之前解决查询，您可以通过调用 .ToList()

回答by Scott Isaacs

Are you using the grouping just to make the list distinct? If so, try:

您是否使用分组只是为了使列表不同？如果是这样，请尝试：

.Where(c => c.status == "ACTIVE")
.OrderBy(c => c.name_1)
.Distinct()

回答by Chen

How about using .Distinct()? http://msdn.microsoft.com/en-us/library/bb348436.aspx

使用 .Distinct() 怎么样？ http://msdn.microsoft.com/en-us/library/bb348436.aspx

Should work if this is all you need.

如果这就是你所需要的，应该可以工作。