实体框架：加入不同类型的实体并按日期排序

Question

我读过一些听起来很相似的文章，但我不太能理解所讨论的内容。我使用的是 C# Entity Framework Code First 和 MVC 4。这是一些分层模型的大纲。

 Project
      ProjectImage
      ProjectDoc
           Comment
                CommentVote
                CommentReply
                     CommentReplyVote

所有这些模型都有一个 DateCreated 字段。我想运行一个查询，我可以按日期排序，并在同一个列表中显示所有这些事件中最新到最旧的事件。我想以不同的方式处理（显示）每一个。我不知道从哪里开始，也不知道在 Stackoverflow 上使用什么搜索词来找到答案。

Answer 1

这是我承诺的代码...

它不是最先进的，但它是一个简单的控制台应用程序，可让您了解如何处理此问题。我基本上是从列表中读取的（在您的情况下，您将从数据库表中读取）。然后我将DateCreated 和对象本身添加到一个自定义类中，该类允许通过DateCreated 字段对所有对象进行排序。演示代码由您决定，但我会根据对象类型向您展示如何打印到控制台。

class Program
{
    static void Main(string[] args)
    {
        var projects = new List<Project>{
        new Project() {  ProjectId = 1, ProjectName = "My Secret Project", DateCreated = DateTime.Today.AddHours(-1) },
        new Project() {  ProjectId = 2, ProjectName = "My Big Project", DateCreated = DateTime.Today.AddHours(-2) }};

        var projectImages = new List<ProjectImage> {
        new ProjectImage() {  ProjectImageId = 1, ProjectImageSize = 17.17, DateCreated = DateTime.Today.AddHours(-3) },
        new ProjectImage() {  ProjectImageId = 2, ProjectImageSize = 10.17, DateCreated = DateTime.Today.AddHours(-4) }};

        var objects = new List<MyCustomClass>();

        foreach (var project in projects)
        {
            objects .Add(
                new MyCustomClass() { DateCreated = project.DateCreated, Object = project });
        }

        foreach (var projectImage in projectImages)
        {
            objects.Add(
                new MyCustomClass() { DateCreated = projectImage.DateCreated, Object = projectImage });
        }

        // Objects ordered by Date, Newest first...
        var objectsByDateCreated = objects.OrderByDescending(o => o.DateCreated);

        foreach (var @object in objectsByDateCreated)
        {
            Console.WriteLine(string.Format("{0} => {1}", @object.Object.GetType().Name, @object.DateCreated));
        }

        // Displaying objects according to type
        foreach (var @object in objectsByDateCreated)
        {
            if (@object.Object is Project)
            {
                var project = @object.Object as Project;

                Console.WriteLine(project.ProjectName);
            }
            else if (@object.Object is ProjectImage)
            {
                var projectImage = @object.Object as ProjectImage;

                Console.WriteLine(projectImage.ProjectImageSize);
            }
        }
    }
}

public class MyCustomClass
{
    public DateTime DateCreated { get; set; }
    public object Object { get; set; }
}

public class Project
{
    public int ProjectId { get; set; }
    public string ProjectName { get; set; }
    public DateTime DateCreated { get; set; }
}

public class ProjectImage
{
    public int ProjectImageId { get; set; }
    public double ProjectImageSize { get; set; }
    public DateTime DateCreated { get; set; }
}