c# - EF Core - 为什么实体应该是外键关系时被保存为新的数据库实体?
问题描述
我们的上下文不再使用 EF6 DB 优先模型 - 我正在构建一个 ASP Core API,该 API 将 EF Core Code First 模型用于数据库上下文。要在滚动更新中执行此操作,我的上下文必须存在于当前数据库架构中,因此我使用 EF Fluent API 为不反映当前数据库架构的 Code First 模型构建我的实体映射。
在插入操作期间,我遇到了实体上的导航属性问题。使用标准 .Include(x => x.OtherEntity) 格式从数据库中获取主要实体的数据效果很好,将主要实体保存回数据库是问题所在。
使用 Fluent API 映射实体对我来说是新事物,因此学习曲线很可能是我的问题所在。我曾尝试使用 OwnsOne 与 HasOne,但 MS 文档表明 HasOne() 是进行此映射的正确方法。
我有问题的主要实体具有外键字段的影子属性,当我在流畅映射中使用 .HasOne() 时键链接的外键字段(在下面的代码中)
异常消息在这种情况下没有用,因为它们不反映映射问题,它们建议当导航属性的表具有标识列时无法插入数据(IE 无法插入具有显式ID)-> 这很奇怪,因为我没有尝试通过这些导航属性插入数据,我只是尝试使用外键将我的主要实体链接到该次要实体。
实体映射:
// WorkOrder Entity Mapping:
modelBuilder.Entity<WorkOrder>().ToTable("WorkOrder");
modelBuilder.Entity<WorkOrder>().Property(x => x.Id).HasColumnName("IDWorkOrder");
modelBuilder.Entity<WorkOrder>().Property(x => x.CreatedBy).HasColumnName("IDUserCreated");
modelBuilder.Entity<WorkOrder>().Property(x => x.UpdatedBy).HasColumnName("IDUserUpdated");
modelBuilder.Entity<WorkOrder>().Property<int?>("IDWOCategory");
modelBuilder.Entity<WorkOrder>().Property<int?>("IDProblem");
modelBuilder.Entity<WorkOrder>().Property<int?>("IDWOCostCenter");
modelBuilder.Entity<WorkOrder>().Property<int?>("IDWOLocation");
modelBuilder.Entity<WorkOrder>().Property<int?>("IDWOPriority");
modelBuilder.Entity<WorkOrder>().Property<int?>("IDWOStatus");
modelBuilder.Entity<WorkOrder>().Property<int?>("IDWOTrade");
modelBuilder.Entity<WorkOrder>().Property<Guid?>("IDUserCompleted");
modelBuilder.Entity<WorkOrder>().Property<Guid?>("IDParentWO");
// WO Navigation Properties:
modelBuilder.Entity<WorkOrder>().HasOne(x => x.Category).WithOne().HasForeignKey<WorkOrder>("IDWOCategory").HasPrincipalKey<Category>(c => c.Id);
modelBuilder.Entity<WorkOrder>().HasOne(x => x.Problem).WithOne().HasForeignKey<WorkOrder>("IDProblem").HasPrincipalKey<Problem>(c => c.Id);
modelBuilder.Entity<WorkOrder>().HasOne(x => x.CostCenter).WithOne().HasForeignKey<WorkOrder>("IDWOCostCenter").HasPrincipalKey<CostCenter>(c => c.Id);
modelBuilder.Entity<WorkOrder>().HasOne(x => x.Location).WithOne().HasForeignKey<WorkOrder>("IDWOLocation").HasPrincipalKey<Location>(c => c.Id);
modelBuilder.Entity<WorkOrder>().HasOne(x => x.Priority).WithOne().HasForeignKey<WorkOrder>("IDWOPriority").HasPrincipalKey<Priority>(c => c.Id);
modelBuilder.Entity<WorkOrder>().HasOne(x => x.Status).WithOne().HasForeignKey<WorkOrder>("IDWOStatus").HasPrincipalKey<Status>(c => c.Id);
modelBuilder.Entity<WorkOrder>().HasOne(x => x.Trade).WithOne().HasForeignKey<WorkOrder>("IDWOTrade").HasPrincipalKey<Trade>(c => c.Id);
modelBuilder.Entity<WorkOrder>().HasOne(x => x.Requester).WithOne().HasForeignKey<WorkOrder>("IDRequester").HasPrincipalKey<Requester>(c => c.Id);
modelBuilder.Entity<WorkOrder>().HasOne(x => x.UserCompleted).WithOne().HasForeignKey<WorkOrder>("IDUserCompleted").HasPrincipalKey<User>(c => c.Id);
modelBuilder.Entity<WorkOrder>().HasOne(x => x.ParentWorkOrder).WithOne().HasForeignKey<WorkOrder>("IDParentWO").HasPrincipalKey<WorkOrder>(c => c.Id);
在控制器中获取数据:(就像一个魅力!)
[HttpGet("{Id}")]
public async Task<ActionResult<List<WorkOrder>>> GetWorkOrders(Guid Id)
{
var result = await WorkOrdersContext.WorkOrders
.Include(x => x.Problem)
.Include(x => x.Status)
.Include(x => x.Requester)
.Include(x => x.ParentWorkOrder)
.Include(x => x.Category)
.Include(x => x.Trade)
.Include(x => x.Location)
.Include(x => x.CostCenter)
.Include(x => x.Priority)
.Where(x => x.Id == Id)
.ToListAsync();
return Ok(result);
}
在控制器中保存新数据:(它发生故障的地方!)
[HttpPost]
public async Task<ActionResult<WorkOrder>> CreateWorkOrderFromPending([FromBody]WorkOrder call)
{
// Insert the Work Order to the DB:
DbContext.WorkOrders.Add(call);
var saveResult = await DbContext.SaveChangesAsync();
// Check if any oddities occurred during the save:
if (saveResult == 0) return BadRequest("An Error occurred during saving and the Call was not saved, please try again.");
// Return the Inserted Work Order:
return Ok(call);
}
在这里,当它尝试保存新的工单时,由于映射类型(实体映射代码片段中的问题、类别、成本中心等)而引发异常它试图将数据保存为新实体而不是构建 FK与现有实体的关系。我认为这就是我缺少 Fluent API 的一些逻辑的地方!
任何帮助将不胜感激,因为很难将这个问题用谷歌搜索的几句话来表达!
解决方案
感谢@DavidBrowne-Microsoft,我得到了答案,试图让我们过去的 DB First 东西与 .NET Core 共存并非易事,并且来自 Code First 背景,其中 .Add() 是有效的路径,很难看出 .Attach() 是如何做到的。
[HttpPost]
public async Task<ActionResult<WorkOrder>> CreateWorkOrderFromPending([FromBody]WorkOrder call)
{
// Insert the Work Order to the DB:
// DbContext.WorkOrders.Add(call);
var entity = DbContext.WorkOrders.Attach(call);
entity.State = EntityState.Added;
var saveResult = await DbContext.SaveChangesAsync();
// Check if any oddities occurred during the save:
if (saveResult == 0) return BadRequest("An Error occurred during saving and the Call was not saved, please try again.");
// Return the Inserted Work Order:
return Ok(call);
}
使用 .Attach() 而不是 .Add() 就可以了,将实体放入并将 FK 映射到我的 Fluent 映射中它们各自的阴影属性!
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