如何阻止实体框架继续从数据库中记录？

Question

我正在研究 ASP.NET 样板。我有一个问题，我尝试从名为Buildings 的表中获取记录并对其进行更新。我通过以下方式从数据库中获取记录：

var buildingApp = _buildingsAppService.getBuildingsById(buildingInput);

然后，我对数据进行了一些更改，如下所示：

buildingApp.streetName = Request["buildingaddress"];
buildingApp.isInHoush = Convert.ToBoolean(Request["buildingOutput.isInHoush"]);
buildingApp.houshName = Request["HoushName"];

然后将buildingApp复制到另一个具有相同属性的对象中，以便将新对象传递给update方法，如下所示：

var updateBuildingInput = new UpdateBuidlingsInput()
{
    Id = buildingApp.Id,
    buildingID = buildingApp.buildingID,
    numOfBuildingUnits = buildingApp.numOfBuildingUnits,
    numOfFloors = buildingApp.numOfFloors,
    streetName = buildingApp.streetName,
    buildingNo = buildingApp.buildingNo,
    neighborhoodID = buildingApp.neighborhoodID,
    buildingTypeID = buildingApp.buildingTypeID,
    GISMAP = buildingApp.GISMAP,
    houshProperty = buildingApp.houshProperty,
    houshName = buildingApp.houshName,
    X = buildingApp.X,
    Y = buildingApp.Y,
    buildingName = buildingApp.buildingName,
    isInHoush = buildingApp.isInHoush,
    buildingUsesID = buildingApp.buildingUsesID
};

而update方法如下：

_buildingsAppService.update(updateBuildingInput);

问题是当它执行上一行时，我得到以下错误：

System.InvalidOperationException：“附加类型为“TaawonMVC.Models.Buildings”的实体失败，因为同一类型的另一个实体已经具有相同的主键值。如果图中的任何实体具有冲突的键值，则在使用“附加”方法或将实体的状态设置为“未更改”或“已修改”时，可能会发生这种情况。这可能是因为某些实体是新实体，尚未收到数据库生成的键值。在这种情况下，使用“添加”方法或“已添加”实体状态来跟踪图形，然后将非新实体的状态设置为“未更改”或“已修改”。

我可以看到，当我手动初始化对象updateBuildingInput 时，update 方法运行没有错误。但是当它依赖于使用buildingApp从数据库中获取的对象时，就会发生错误。似乎get 方法从数据库中获取数据并继续保留数据库中的记录，当我尝试更新同一记录时，就会发生冲突。这是所有get 和update 发生的整个动作：

public ActionResult UpdateApplication (UpdateApplicationsInput model)
{
    var updateApplication = new UpdateApplicationsInput();
    updateApplication.buildingId = Convert.ToInt32(Request["buildingnumber"]);
    updateApplication.buildingUnitId = Convert.ToInt32(Request["dropDownBuildingUnitApp"]);
    //==== get building and unit related to application for update ======
    var buildingInput = new GetBuidlingsInput()
    {
        Id = updateApplication.buildingId
    };
    var buildingUnitInput = new GetBuildingUnitsInput()
    {
        Id = updateApplication.buildingUnitId
    };
    var buildingApp = _buildingsAppService.getBuildingsById(buildingInput);

    var buildingUnitApp = _buildingUnitsAppService.GetBuildingUnitsById(buildingUnitInput);
        buildingApp.streetName = Request["buildingaddress"];
        buildingApp.isInHoush = Convert.ToBoolean(Request["buildingOutput.isInHoush"]);
        buildingApp.houshName = Request["HoushName"];
        // buildingUnitApp.BuildingId = updateApplication.buildingId;
        buildingUnitApp.ResidenceStatus = Request["residentstatus"];
        // copy object getBuildingUnitInput to updateBuildingUnitInput

    var updateBuildingUnitInput = new UpdateBuildingUnitsInput()
    {
        BuildingId = buildingUnitApp.BuildingId,
        ResidentName = buildingUnitApp.ResidentName,
        ResidenceStatus = buildingUnitApp.ResidenceStatus,
        NumberOfFamilyMembers = buildingUnitApp.NumberOfFamilyMembers,
        Floor = buildingUnitApp.Floor,
        UnitContentsIds = buildingUnitApp.UnitContentsIds
    };

    //============================================
    // copy object from getBuildingOutput to updateBuildingInput
    var updateBuildingInput = new UpdateBuidlingsInput()
    {
        Id = buildingApp.Id,
        buildingID = buildingApp.buildingID,
        numOfBuildingUnits = buildingApp.numOfBuildingUnits,
        numOfFloors = buildingApp.numOfFloors,
        streetName = buildingApp.streetName,
        buildingNo = buildingApp.buildingNo,
        neighborhoodID = buildingApp.neighborhoodID,
        buildingTypeID = buildingApp.buildingTypeID,
        GISMAP = buildingApp.GISMAP,
        houshProperty = buildingApp.houshProperty,
        houshName = buildingApp.houshName,
        X = buildingApp.X,
        Y = buildingApp.Y,
        buildingName = buildingApp.buildingName,
        isInHoush = buildingApp.isInHoush,
        buildingUsesID = buildingApp.buildingUsesID
    };

    //======================================================
    updateApplication.Id = Convert.ToInt32(Request["applicationId"]);
    updateApplication.fullName = model.fullName;
    updateApplication.phoneNumber1 = model.phoneNumber1;
    updateApplication.phoneNumber2 = model.phoneNumber2;
    updateApplication.isThereFundingOrPreviousRestoration = model.isThereFundingOrPreviousRestoration;
    updateApplication.isThereInterestedRepairingEntity = model.isThereInterestedRepairingEntity;
    updateApplication.housingSince = model.housingSince;
    updateApplication.previousRestorationSource = model.previousRestorationSource;
    updateApplication.interestedRepairingEntityName = model.interestedRepairingEntityName;
    updateApplication.PropertyOwnerShipId = Convert.ToInt32(Request["PropertyOwnerShip"]);
    updateApplication.otherOwnershipType = model.otherOwnershipType;
    updateApplication.interventionTypeId = Convert.ToInt32(Request["interventionTypeName"]);
    updateApplication.otherRestorationType = model.otherRestorationType;
    updateApplication.propertyStatusDescription = model.propertyStatusDescription;
    updateApplication.requiredRestoration = model.requiredRestoration;
    updateApplication.buildingId = Convert.ToInt32(Request["buildingnumber"]);
    updateApplication.buildingUnitId = Convert.ToInt32(Request["dropDownBuildingUnitApp"]);

    // ==== get of restoration types which it is multi select drop down list ======
    var restorationTypes = Request["example-getting-started"];
    string[] restorationTypesSplited = restorationTypes.Split(',');
    byte[] restorationTypesArray = new byte[restorationTypesSplited.Length];
    for (var i = 0; i < restorationTypesArray.Length; i++)
    {
        restorationTypesArray[i] = Convert.ToByte(restorationTypesSplited[i]);
    }

    updateApplication.restorationTypeIds = restorationTypesArray;
    // ====== end of RestorationTypes
    _buildingsAppService.update(updateBuildingInput);
    _applicationsAppService.Update(updateApplication);

    // _buildingUnitsAppService.Update(updateBuildingUnitInput);

    // ==== get list of applications ==============
    var applicationsUpdate = _applicationsAppService.getAllApplications();
    var applicationsViewModel = new ApplicationsViewModel()
    {
        Applications = applicationsUpdate
    };

    return View("Applications", applicationsViewModel);
}

我使用的 ASP.NET Boilerplate 模板如何对数据库进行 CRUD 操作：

public class BuildingsManager : DomainService, IBuildingsManager
{
    private readonly IRepository<Buildings> _repositoryBuildings;

    public BuildingsManager(IRepository<Buildings> repositoryBuildings)
    {
        _repositoryBuildings = repositoryBuildings;
    }
    // create new building in table buildings .
    public async Task<Buildings> create(Buildings entity)
    {
        var building = _repositoryBuildings.FirstOrDefault(x => x.Id == entity.Id);
        if(building!=null)
        {
            throw new UserFriendlyException("Building is already exist");
        }
        else
        {
            return  await _repositoryBuildings.InsertAsync(entity);
        }
    }
    // delete a building from buildings table .
    public void delete(int id)
    {
        try
        {
            var building = _repositoryBuildings.Get(id);
            _repositoryBuildings.Delete(building);
        }
        catch (Exception)
        {
            throw new UserFriendlyException("Building is not exist");
        }
    }

    public IEnumerable<Buildings> getAllList()
    {
        return _repositoryBuildings.GetAllIncluding(b => b.BuildingType, n => n.NeighboorHood,u=>u.BuildingUses);
    }

    public Buildings getBuildingsById(int id)
    {
        return _repositoryBuildings.Get(id);
    }

    public void update(Buildings entity)
    {
        _repositoryBuildings.Update(entity);
    }
}

我该如何解决这个问题？非常感谢您的帮助。

Answer 1

通过创建一个新实体 (updateBuildingInput)，其主键与您在上下文中已读取的主键相同，当您尝试对新实体（如您所见）进行操作时，Entity 将抛出错误，因为它已经在上下文中使用该主键跟踪实体。

如果_buildingsAppService 是DbContext 并且您只需对实体进行一些更改，您可以：

1. 读取实体
2. 直接对该实体对象进行更改
3. 致电_buildingsAppService.SaveChanges()

SaveChanges() 将：

将在此上下文中所做的所有更改保存到底层数据库。

Answer 2

从 db 获取记录时可以使用.AsNoTracking()

或者如果你真的需要更新一个附加的实体，首先找到附加的副本并分离它，然后修改和更新；

public async Task<bool> UpdateAsync<T>(T entity)
        where T : class, IHasId
    {
        // check if entity is being tracked
        var local = _context.Set<T>().Local.FirstOrDefault(x => x.Id.Equals(entity.Id));

        // if entity is tracked detach it from context
        if (local != null)
            _context.Entry<T>(local).State = EntityState.Detached;

        _context.Attach(entity).State = EntityState.Modified;

        var result = await _context.SaveChangesAsync();


        // detach entity if it was not tracked, otherwise it will be kept tracking
        if(local == null)
            _context.Entry(entity).State = EntityState.Detached;

        return result > 0;
    }

顺便说一句，IHasId 是一个简单的接口，可以让泛型类型可以访问 Id 属性；

public interface IHasId {
    int Id { get; set; }
}

Answer 3

使用.AsNoTracking():

public class BuildingsManager : DomainService, IBuildingsManager
{
    public Buildings getBuildingsById(int id)
    {
        return _repositoryBuildings.GetAll().AsNoTracking().First(b => b.Id == id);
    }

    // ...
}