asp.net-mvc - Entity Framework 不更新模型的复杂集合属性

Question

之前可能已经以多种形式提出过这个问题，但我仍然认为他们对这种情况没有明确的解决方案。

我有以下实体类。

public class Project
{
    public int ProjectId { get; set; }
    [Required(ErrorMessage="please enter name")]
    public string Name { get; set; }
    public string Url { get; set; }
    public DateTime CreatedOn { get; set; }
    public DateTime UpdatedOn { get; set; }
    public bool isFeatured { get; set; }
    public bool isDisabled { get; set; }
    public int GroupId { get; set; }
    public virtual Group Group { get; set; }
    [Required(ErrorMessage="Please select atleast one tag")]
    public virtual ICollection<Tag> Tags { get; set; }
}

public class Tag
{
    public int TagId { get; set; }
    public string Name { get; set; }
    public DateTime CreatedOn { get; set; }
    public DateTime UpdatedOn { get; set; }
    public virtual ICollection<Project> Projects { get; set; }
}

public class Group
{
    public int GroupId { get; set; }
    public string Name { get; set; }
    public DateTime CreatedOn { get; set; }
    public DateTime UpdatedOn { get; set; }
    public virtual ICollection<Project> Projects { get; set; }
}

我有项目实体的 View 模型和这个 View 模型的自定义模型绑定(bind)器。

public class NewProjectModelBinder : DefaultModelBinder
{
    public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        ProjectNewViewModel model = (ProjectNewViewModel)bindingContext.Model ??
            (ProjectNewViewModel)DependencyResolver.Current.GetService(typeof(ProjectNewViewModel));
        bool hasPrefix = bindingContext.ValueProvider.ContainsPrefix(bindingContext.ModelName);
        string searchPrefix = (hasPrefix) ? bindingContext.ModelName + ".":"";

        //since viewmodel contains custom types like project make sure project is not null and to pass key arround for value providers
        //use Project.Name even if your makrup dont have Project prefix

        model.Project  = model.Project ?? new Project();
        //populate the fields of the model
        if (GetValue(bindingContext, searchPrefix, "Project.ProjectId") !=  null)
        {
            model.Project.ProjectId = int.Parse(GetValue(bindingContext, searchPrefix, "Project.ProjectId"));
        }

        //
        model.Project.Name = GetValue(bindingContext, searchPrefix, "Project.Name");
        model.Project.Url = GetValue(bindingContext, searchPrefix, "Project.Url");
        model.Project.CreatedOn  =  DateTime.Now;
        model.Project.UpdatedOn = DateTime.Now;
        model.Project.isDisabled = GetCheckedValue(bindingContext, searchPrefix, "Project.isDisabled");
        model.Project.isFeatured = GetCheckedValue(bindingContext, searchPrefix, "Project.isFeatured");
        model.Project.GroupId = int.Parse(GetValue(bindingContext, searchPrefix, "Project.GroupId"));
        model.Project.Tags = new List<Tag>();

        foreach (var tagid in GetValue(bindingContext, searchPrefix, "Project.Tags").Split(','))
        {
            var tag = new Tag { TagId = int.Parse(tagid)};
            model.Project.Tags.Add(tag);
        }

        var total = model.Project.Tags.Count;

        return model;
    }

    private string GetValue(ModelBindingContext context, string prefix, string key)
    {
        ValueProviderResult vpr = context.ValueProvider.GetValue(prefix + key);
        return vpr == null ? null : vpr.AttemptedValue;
    }

    private bool GetCheckedValue(ModelBindingContext context, string prefix, string key)
    {
        bool result = false;
        ValueProviderResult vpr = context.ValueProvider.GetValue(prefix + key);
        if (vpr != null)
        {
            result = (bool)vpr.ConvertTo(typeof(bool));
        }

        return result;
    }
}

//My project controller edit action defined as under:
[HttpPost]
[ActionName("Edit")]
public ActionResult EditProject( ProjectNewViewModel ProjectVM)
{
   if (ModelState.IsValid) {
       projectRepository.InsertOrUpdate(ProjectVM.Project);
       projectRepository.Save();
       return RedirectToAction("Index");
   } 
   else {
    ViewBag.PossibleGroups = groupRepository.All;
        return View();
   }
}


//Group Repository
public void InsertOrUpdate(Project project)
    {
        if (project.ProjectId == default(int)) {
            // New entity
            foreach (var tag in project.Tags)
            {
                context.Entry(tag).State = EntityState.Unchanged;
            }
            context.Projects.Add(project);
        } else {               
            context.Entry(project).State = EntityState.Modified;
        }
    }

现在，当我在编辑 View 中有一个项目并为项目选择新标签并提交表单编辑操作参数时，使用模型绑定(bind)器并设置项目对象的所有属性，包括标签。但是当项目对象被传递给 grouprepository 的 insertorupdate 方法时，我们所做的所有更改都会在数据库中存储，除了 Tags 集合属性现在我对这件事感到非常沮丧。

请向我提供到目前为止已经开发出不会改变结构的解决方案。

Answer 1

你的 else 这样的东西InsertOrUpdate 中的案例(我认为 if 案例很好)可能有效:

//...
else {
    // Reload project with all tags from DB
    var projectInDb = context.Projects.Include(p => p.Tags)
        .Single(p => p.ProjectId == project.ProjectId);

    // Update scalar properties of the project
    context.Entry(projectInDb).CurrentValues.SetValues(project);

    // Check if tags have been removed, if yes: remove from loaded project tags
    foreach(var tagInDb in projectInDb.Tags.ToList())
    {
        // Check if project.Tags collection contains a tag with TagId
        // equal to tagInDb.TagId. "Any" just asks: Is there an element
        // which meets the condition, yes or no? It's like "Exists".
        if (!project.Tags.Any(t => t.TagId == tagInDb.TagId))
            projectInDb.Tags.Remove(tagInDb);
    }

    // Check if tags have been added, if yes: add to loaded project tags
    foreach(var tag in project.Tags)
    {
        // Check if projectInDb.Tags collection contains a tag with TagId
        // equal to tag.TagId. See comment above.
        if (!projectInDb.Tags.Any(t => t.TagId == tag.TagId))
        {
            // We MUST attach because tag already exists in the DB
            // but it was not assigned to the project yet. Attach tells
            // EF: "I know that it exists, don't insert a new one!!!"
            context.Tags.Attach(tag);
            // Now, we just add a new relationship between projectInDb and tag,
            // not a new tag itself
            projectInDb.Tags.Add(tag);
        }
    }
}

// context.SaveChanges() somewhere later

由于 EF 更改检测，SaveChanges 实际上将使用标记列表保存以前重新加载的项目。传入该方法的项目甚至没有附加到上下文中，只是用于更新重新加载的项目及其标签列表。

编辑
context.Tags.Attach(tag);添加到代码中，否则 SaveChanges将在数据库中创建新标签。