更新验证失败后重新显示带有 .Include(related-entity) 的原始模型答案

【问题标题】：Redisplay original Model with .Include( related-entity ) after update validation fails更新验证失败后重新显示带有 .Include(related-entity) 的原始模型
【发布时间】：2018-08-01 22:11:33
【问题描述】：

当用户发送 GET 请求以编辑记录时，我正在使用 .Include() 加载发送给视图的模型以及相关实体，如下所示：

 var client = await _context.Client
                             .Include(c => c.Office)
                             .Where(c => c.client_id == id)
                             .AsNoTracking()
                             .SingleOrDefaultAsync();
 return View(client);

当用户 POST 回编辑表单并且缺少必填字段ModelState.IsValid == false 时，不会执行更新，并且未保存更改的模型将被发送回视图。

public async Task<IActionResult> Edit(Client client_edited )
{
    if (!ModelState.IsValid)
    {
            return View(client_edited); // .Include(c => c.Office) is missing
    }
}

如何返回发布的视图模型（用户等待更改）并重新附加所需的 .Include()？

当我重新查询模型（客户端）记录时，挂起的更改会丢失。

我正在尝试做一些事情，比如重新查询带有包含的客户端，然后在顶部复制带有挂起更改的客户端。比如……

var client = await _context.Client
                             .Include(c => c.Office)
                             .Where(c => c.client_id == id)
                             .AsNoTracking()
                             .SingleOrDefaultAsync();

 // need to copy pending client_edited changes to the client 
 // but does not work because it overwrites the .Include(c => c.Office)
 client = client_edited 

 return View(client_edited);

【问题讨论】：

标签： c# asp.net-core entity-framework-core

【解决方案1】：

回答我自己的问题，以防它帮助别人......

基于blog post by Lori Peterson Entity Framework cloning, 请参阅EF 复制当前值，我可以通过几行代码解决问题，示例如下：

public async Task<IActionResult> Edit(Client client_posted)
{
  if (!ModelState.IsValid)
  {

    ModelState.AddModelError("", "Record is missing required values");

    // requery the client entity from our db to get related child entities
    var client_current = await _context.Client
                                        .Include(c => c.Office)
                                        // include 4 or 5 more entities here
                                        .Where(c => c.client_id == client_posted.client_id)
                                        .AsNoTracking()
                                        .SingleOrDefaultAsync();

    // now replace client_current values with client_posted values by

    // 1 - add entity to your db context (we are not saving it)
    _myDbContext.Client.Add(client_posted);

    // 2 - use the db context to extract current values from the client entity posted
    var client_posted_values =_myDbContext.Entry(client_posted).CurrentValues;

    // 3 - copy the extracted values to the client_current we re-queried from db
    _myDbContext.Entry(client_current).CurrentValues.SetValues(client_posted_values);

    // 4 return the view passing client with original values and the attached office entity(ies)
    return View(client_current);
  }
  // otherwise ModelState is valid, do the update here
  ...
  ...
}

【讨论】：