linq查询匿名类型无法转换为POCO对象

Question

我有以下 linq 查询...

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>();
}

我有以下 View 对象，我正在尝试填充......

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 条消息。我的目标是将 UserProject 对象列表传递到我的 MVC View ，每个 UserProject 对象可以有一个消息集合。我得到的错误如下

Error 1 Instance argument: cannot convert from 'System.Linq.IQueryable<AnonymousType#1>' to 'System.Collections.Generic.IEnumerable<Riebro.Services.UserProject>'

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

目前消息实体没有项目的导航属性...它应该...我稍后会添加该更改...但目前我只需要继续工作。

编辑

现在 linq 查询看起来像这样......

    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>();

View 类看起来像这样......

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;
}

我现在收到以下错误...

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?)

Answer 1

您应该在 select 语句中创建一个 UserProject 实例而不是匿名对象。

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