实体框架:连接不同类型的实体，并按日期排序

Question

我读过一些听起来类似的文章，但我不太能理解其中讨论的内容。我使用的是c#实体框架代码和MVC 4。以下是一些模型的层次结构。

 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，并在同一列表中显示最新到最老的任何这些事件。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，让你知道如何处理这个问题。我基本上是从列表中读取(在您的例子中，您是从数据库表中读取)。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。表示代码由您决定，但我将向您展示如何根据对象类型打印到控制台。

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; }
}