linq查询匿名类型不能转换为POCO对象 [英] linq query anonymous type cannot be converted to POCO object

问题描述

我有以下linq查询...

I have the following linq query ...

public List<UserProject> GetProjectsByUser(int userid)
{
    //var query =
    return (
               from p in this.Entities.Projects
               join c in this.Entities.Categories 
                   on p.CategoryId equals c.CategoryId
               join u in this.Entities.Users 
                   on p.UserId equals u.UserId
               where p.UserId == 11
               select
                   new
                       {
                           p.ProjectId,
                           u.UserName,
                           p.UserId,
                           ProjectName = p.Name,
                           ProjectDescription = p.Description,
                           CategoryName = c.Name
                       }
               into pcup
               join m in this.Entities.Messages
                   on
                   pcup.ProjectId equals m.ProjectId
                   into pm
               select
                   new {
                       pcup.ProjectId, 
                       pcup.UserId, 
                       pcup.ProjectName, 
                       pcup.ProjectDescription, 
                       Messages = pm
                   }
           ).ToList<UserProject>();
}

，并且我有以下试图填充的视图对象....

and I have the following view object that I am trying to populate ....

public class UserProject
{
    UserProject()
    {
        Messages = new EnumerableQuery<Message>();
    }

    public int ProjectId;
    public int UserId;
    public string ProjectName;
    public string ProjectDescription;
    public IEnumerable<Message> Messages;
    //public string UserName;
    //public string CategoryName;
    //public int CategoryId;
}

一个项目上可能有0或消息.我的目标是将UserProject对象的列表传递到我的MVC视图，每个UserProject对象可以具有消息的集合.我得到的错误如下

A project may have 0 or messages on it. My goal here is to pass a list of UserProject objects to my MVC view , each UserProject object can have a collection of messages. The error I get is as follows

错误1实例参数:无法从'System.Linq.IQueryable<AnonymousType#1>'转换为'System.Collections.Generic.IEnumerable<Riebro.Services.UserProject>'

错误2'System.Linq.IQueryable<AnonymousType#1>'不包含'ToList'的定义，最佳扩展方法重载'System.Linq.Enumerable.ToList<TSource>(System.Collections.Generic.IEnumerable<TSource>)'具有一些无效的参数

Error 2 'System.Linq.IQueryable<AnonymousType#1>' does not contain a definition for 'ToList' and the best extension method overload 'System.Linq.Enumerable.ToList<TSource>(System.Collections.Generic.IEnumerable<TSource>)' has some invalid arguments

当前message实体不具有Projects的导航属性……应该……以后再添加该更改……但此刻我只需要继续工作即可.

Currently the messages entity does not have a navigation property to Projects ... it should ... I will add that change later ... but at the moment I just need to keep on working.

现在，linq查询看起来像这样...

As it stands now the linq query looks like this ...

    return (
               from p in this.Entities.Projects
               join c in this.Entities.Categories 
                   on p.CategoryId equals c.CategoryId
               join u in this.Entities.Users 
                   on p.UserId equals u.UserId
               where p.UserId == userid
               select
                   new 
                       {
                           p.ProjectId,
                           u.UserName,
                           p.UserId,
                           p.Name,
                           p.Description,
                           //CategoryName = c.Name
                       }
                   into pcup
                   join m in this.Entities.Messages
                       on
                       pcup.ProjectId equals m.ProjectId
                       into pm
                   select
                       new UserProject { 
                           ProjectId = pcup.ProjectId, 
                           UserId = pcup.UserId,  
                           ProjectName = pcup.Name, 
                           ProjectDescription = pcup.Description, 
                           Messages = pm 
                       }
           ).ToList<UserProject>();

视图类如下所示

public class UserProject
{
    public UserProject()
    {
        Messages = new List<Message>();
    }

    public int ProjectId;
    public string UserName;
    public int UserId;
    public string ProjectName;
    public string ProjectDescription;
    public List<Message> Messages;
    //public string CategoryName;
    //public int CategoryId;
}

我现在遇到以下错误...

and I am now getting the following error ...

错误1无法将类型'System.Collections.Generic.IEnumerable<Riebro.Message>'隐式转换为'System.Collections.Generic.List<Riebro.Message>'.存在显式转换(您是否缺少演员表?)

Error 1 Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<Riebro.Message>' to 'System.Collections.Generic.List<Riebro.Message>'. An explicit conversion exists (are you missing a cast?)

推荐答案

您应在select语句中创建UserProject实例而不是匿名对象.

You should create a UserProject instance instead of an anonymous object in your select statement.

 select new UserProject 
            {
                ProjectId = pcup.ProjectId,
                UserID = pcup.UserId,
                ProjectName = pcup.ProjectName,
                ProjectDescription = pcup.ProjectDescription, 
                Messages = pm
            }

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