Web API CORE：POST 请求 SQLite 期间出现“外键约束失败”错误

Question

我正在使用 .Net Web API 核心和 Entity Framework Core 为产品商店构建 API。我的产品实体如下所示

public class Product
{
    [Key]
    public long ID { get; set; }

    [Required]
    [MaxLength(80)]
    public string Name { get; set; } 
    ............
}

我有订单实体是

public class Order
{
    [Key]
    public long ID { get; set; }
    public List<OrderItem> OrderItems { get; set; }
    ..........
}

我有 OrderItem 实体，它是在用户将产品添加到卡片时创建的，但尚未创建订单时：

 public class OrderItem
{
    [Key]
    public long ID { get; set; }

    public string UID { get; set; }

    public long OrderID { get; set; }
    public Order Order { get; set; }

    [Required]
    public long ProductID { get; set; }
    public Product Product { get; set; }

    public int Quantity { get; set; }
}

它告诉用户已将具有此数量的 ProductID(FK) 的产品添加到他的卡中。但是还没有创建订单（所以 OrderID FK 还为空）。

当我发出将带有 ProductID、Quantity 和 UID 的 OrderItem 添加到我的数据库的发布请求时，如下所示：

[HttpPost]
    public IActionResult Post([FromBody]JObject newItem)
    {
        OrderItem oItem = newItem.ToObject<OrderItem>();

        context.OrderItems.Add(oItem);
        context.SaveChanges();
        return StatusCode(200);
    }

在我调用 SaveChanges() 的行上抛出一个带有文本“FOREIGN KEY Constraint failed”的异常。我正在添加一个具有有效 ProductID 的对象，JObject 被正常投射。我尝试使用 SQLIte 浏览器添加相同的对象手动，它没有给出任何错误。关于我还没有给出值的 OrderID，外键可以为空，不是吗？

请帮助我，我无法理解导致此问题的原因。 附言我在 Mac OS 上使用 Visual Studio 2017。

UPD。

这是输出（我安慰 JObject 看我是否正确）：

    Application started. Press Ctrl+C to shut down.
Jobject received is:{
  "ProductID": 2,
  "UID": "6c523a76-dd6e-7782-2bc9-9b8baba36e5d",
  "Quantity": "1"
}
OrderItem casted is: ProductID=2; UID=6c523a76-dd6e-7782-2bc9-9b8baba36e5d
fail: Microsoft.EntityFrameworkCore.DbContext[1]
      An exception occurred in the database while saving changes.
      Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while updating the entries. See the inner exception for details. ---> Microsoft.Data.Sqlite.SqliteException: SQLite Error 19: 'FOREIGN KEY constraint failed'.
         at Microsoft.Data.Sqlite.Interop.MarshalEx.ThrowExceptionForRC(Int32 rc, Sqlite3Handle db)
         at Microsoft.Data.Sqlite.SqliteCommand.ExecuteReader(CommandBehavior behavior)
         at Microsoft.EntityFrameworkCore.Storage.Internal.RelationalCommand.Execute(IRelationalConnection connection, String executeMethod, IReadOnlyDictionary`2 parameterValues, Boolean closeConnection)
         at Microsoft.EntityFrameworkCore.Storage.Internal.RelationalCommand.ExecuteReader(IRelationalConnection connection, IReadOnlyDictionary`2 parameterValues)
         at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.Execute(IRelationalConnection connection)
         --- End of inner exception stack trace ---
         at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.Execute(IRelationalConnection connection)
         at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.Execute(Tuple`2 parameters)
         at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(IReadOnlyList`1 entriesToSave)
         at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(Boolean acceptAllChangesOnSuccess)
         at Microsoft.EntityFrameworkCore.DbContext.SaveChanges(Boolean acceptAllChangesOnSuccess)
Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while updating the entries. See the inner exception for details. ---> Microsoft.Data.Sqlite.SqliteException: SQLite Error 19: 'FOREIGN KEY constraint failed'.
   at Microsoft.Data.Sqlite.Interop.MarshalEx.ThrowExceptionForRC(Int32 rc, Sqlite3Handle db)
   at Microsoft.Data.Sqlite.SqliteCommand.ExecuteReader(CommandBehavior behavior)
   at Microsoft.EntityFrameworkCore.Storage.Internal.RelationalCommand.Execute(IRelationalConnection connection, String executeMethod, IReadOnlyDictionary`2 parameterValues, Boolean closeConnection)
   at Microsoft.EntityFrameworkCore.Storage.Internal.RelationalCommand.ExecuteReader(IRelationalConnection connection, IReadOnlyDictionary`2 parameterValues)
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.Execute(IRelationalConnection connection)
   --- End of inner exception stack trace ---
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.Execute(IRelationalConnection connection)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.Execute(Tuple`2 parameters)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(IReadOnlyList`1 entriesToSave)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(Boolean acceptAllChangesOnSuccess)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChanges(Boolean acceptAllChangesOnSuccess)

Answer 1

我会尝试将“long OrderID”更改为“long?OrderID”