EF Core报错：无法跟踪实体实例，同ID实例已被跟踪

错误信息 #

无法跟踪该实体类型的实例，因为已存在另一个具有相同键（id = "2"）的同类型实例正在被跟踪。

问题描述 #

我在更新FeatureDisa实体时遇到上述错误，不清楚原因。另外我不能使用AsNoTracking()，因为需要记录日志。

相关代码 #

查询与更新逻辑 #

var updateFeatureDisas = await _featureDisaRepository.
                GetAll()
                 .Where(a => featureDisaIdInsert.Contains(a.DisadvantageId) &&
                 featureIdInsert.Contains(a.FeatureId)
                 && featureParentIdInsert.Contains(a.ParentFeatureId)).ToListAsync();
    
var sqInsertFeatureDisa = insertTagDisa.Where(a => updateFeatureDisas.All(d => d.Id != a.Id)).ToList();

if (updateFeatureDisas.Any())
{
    var sqUpdateFeatureDisa = insertTagDisa.Where(a => updateFeatureDisas.
        All(d => d.Id.Equals(a.Id, StringComparison.Ordinal))).ToList();
    var updateFeatureDisa = _mapper.Map<List<FeatureDisa>>(sqUpdateFeatureDisa);
    _featureDisaRepository.UpdateRangeWithOutSaveChangeAsync(updateFeatureDisa);
}

仓储更新方法 #

public void UpdateWithOutSaveChangeAsync(TEntity entity)
{
    DbContext.Update(entity);
}

原因与解决方案 #

错误原因 #

你从数据库查询出的updateFeatureDisas集合已经被EF上下文跟踪，之后通过AutoMapper生成了新的updateFeatureDisa实例（这些实例与已跟踪实体的ID完全相同）。调用DbContext.Update()时，EF检测到同一个ID的实体已在跟踪列表中，因此抛出冲突错误。

解决方案（二选一） #

方案1：直接修改已跟踪实体（推荐）

无需创建新实例，直接将新值映射到已被EF跟踪的实体上，EF会自动识别变更并标记为修改状态：

if (updateFeatureDisas.Any())
{
    // 修正原条件逻辑错误：用Any匹配存在相同ID的项，而非All
    var sqUpdateFeatureDisa = insertTagDisa.Where(a => updateFeatureDisas.Any(d => d.Id.Equals(a.Id, StringComparison.Ordinal))).ToList();
    
    foreach (var trackedEntity in updateFeatureDisas)
    {
        var updateModel = sqUpdateFeatureDisa.First(u => u.Id == trackedEntity.Id);
        // 将新值映射到已跟踪的实体
        _mapper.Map(updateModel, trackedEntity);
        // 无需调用Update，EF自动跟踪变更
    }
    // 后续执行SaveChangesAsync即可保存更新
}

方案2：解除旧实体跟踪后更新新实例

如果必须使用AutoMapper生成的新实例，先解除旧实体的跟踪状态，再添加新实例的跟踪：

if (updateFeatureDisas.Any())
{
    var sqUpdateFeatureDisa = insertTagDisa.Where(a => updateFeatureDisas.Any(d => d.Id.Equals(a.Id, StringComparison.Ordinal))).ToList();
    var updateFeatureDisa = _mapper.Map<List<FeatureDisa>>(sqUpdateFeatureDisa);
    
    foreach (var newEntity in updateFeatureDisa)
    {
        var oldEntity = updateFeatureDisas.First(e => e.Id == newEntity.Id);
        // 解除旧实体的跟踪状态
        _featureDisaRepository.DbContext.Entry(oldEntity).State = EntityState.Detached;
        // 现在可以安全更新新实例
        _featureDisaRepository.DbContext.Update(newEntity);
    }
}

额外建议 #

你的仓储方法UpdateWithOutSaveChangeAsync是同步方法但命名带Async，容易造成误解，建议改名为UpdateRangeWithoutSaveChanges以符合命名规范。

内容的提问来源于stack exchange，提问作者Masoud H