EF Core：保留Request及RequestAnswers跟踪，禁用关联Question实体跟踪

模型定义 #

public class Request
{
    public Guid Id { get; set; }
    public int StatusId { get; set; }

    public List<RequestAnswer> RequestAnswers { get; set; } = [];
}

public class RequestAnswer
{
    public int Id { get; set; }
    public string? Answer { get; set; }
    public Guid RequestId { get; set; }
    public int QuestionId { get; set; }

    public Question Question { get; set; }
    public Request Request { get; set; }
}

public class Question
{
    public int Id { get; set; }
    public string Prompt { get; set; }

    public List<RequestAnswer> RequestAnswers { get; set; } = [];
}

DbContext配置 #

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    // Request与RequestAnswer的关联配置
    modelBuilder.Entity<Request>()
       .HasMany(e => e.RequestAnswers)
       .WithOne(e => e.Request)
       .HasForeignKey(e => e.RequestId)
       .HasPrincipalKey(e => e.Id);

    // Question与RequestAnswer的关联配置
    modelBuilder.Entity<Question>()
       .HasMany(e => e.RequestAnswers)
       .WithOne(e => e.Question)
       .HasForeignKey(e => e.QuestionId)
       .HasPrincipalKey(e => e.Id);
}

当前问题场景 #

查询包含关联RequestAnswers和Question的Request：

var request = _db.Requests
                 .Where(r => r.Id == id)
                 .Include(r => r.RequestAnswers)
                 .ThenInclude(a => a.Question)
                 .FirstOrDefault();

更新Request状态并保存：

request.StatusId = 2;
_db.Requests.Update(request);
_db.SaveChanges();

执行时，EF Core会尝试更新Request、所有关联的RequestAnswers（可接受），但还会尝试更新关联的Question记录（无字段变更）。由于操作用户仅对Question表拥有SELECT权限，导致更新失败。

需要实现：跟踪Request和RequestAnswers以便更新，但不跟踪Question实体。

解决方案 #

方法1：查询后手动分离Question实体 #

查询完成后，将所有关联的Question实体从跟踪上下文分离，EF Core后续不会尝试更新它们：

var request = _db.Requests
                 .Where(r => r.Id == id)
                 .Include(r => r.RequestAnswers)
                 .ThenInclude(a => a.Question)
                 .FirstOrDefault();

if (request != null)
{
    // 取消所有Question实体的跟踪状态
    foreach (var answer in request.RequestAnswers)
    {
        _db.Entry(answer.Question).State = EntityState.Detached;
    }

    // 执行更新
    request.StatusId = 2;
    _db.Requests.Update(request);
    _db.SaveChanges();
}

优点：代码改动极小，逻辑简单直接，适合快速适配现有代码。

方法2：投影查询加载无跟踪Question #

通过投影构造实体，明确让EF Core跟踪Request和RequestAnswers，同时以无跟踪方式加载Question：

var request = _db.Requests
    .Where(r => r.Id == id)
    .Select(r => new Request
    {
        Id = r.Id,
        StatusId = r.StatusId,
        RequestAnswers = r.RequestAnswers.Select(a => new RequestAnswer
        {
            Id = a.Id,
            Answer = a.Answer,
            RequestId = a.RequestId,
            QuestionId = a.QuestionId,
            Request = r, // 关联回Request以保持跟踪
            Question = _db.Questions.AsNoTracking().First(q => q.Id == a.QuestionId)
        }).ToList()
    })
    .FirstOrDefault();

if (request != null)
{
    request.StatusId = 2;
    _db.Requests.Update(request);
    _db.SaveChanges();
}

优点：从查询阶段就控制跟踪范围，避免后续手动操作；缺点：实体属性较多时，手动映射会比较繁琐。

方法3：利用EF Core 8的TrackNodes精细控制跟踪 #

EF Core 8新增TrackNodes API，可精确指定需要跟踪的实体节点：

var request = _db.Requests
    .Where(r => r.Id == id)
    .Include(r => r.RequestAnswers)
    .ThenInclude(a => a.Question)
    .TrackNodes(nodes => nodes
        .Include(r => r.RequestAnswers) // 跟踪Request和RequestAnswers
        .Exclude(r => r.RequestAnswers.Select(a => a.Question))) // 排除Question的跟踪
    .FirstOrDefault();

if (request != null)
{
    request.StatusId = 2;
    _db.Requests.Update(request);
    _db.SaveChanges();
}

优点：API原生支持，代码优雅；缺点：依赖EF Core 8特性，版本较低时无法使用。

内容的提问来源于stack exchange，提问作者Maxime