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c# - 通过消息传递服务传输实体对象，对其进行更改并将其附加回来

问题描述

我通过 MassTransit 传输实体对象，更改一些属性并将其返回。这当然涉及后台的序列化/反序列化，由 MassTransit 使用 RabbitMQ 自动完成。

当我尝试附加或更新实体时

_machinesContext.Machines.Update((Machine)machine);

它引发了密钥丢失的期望。

ex = {"Value cannot be null. (Parameter 'key')"}

at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)\r\n   at System.Collections.Generic.Dictionary`2.FindEntry(TKey key)\r\n   at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)\r\n   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityReferenceMap.TryGet(Object entity, IEntityType entityType, InternalEntityEntry& entry, Boolean throwOnNonUniqueness)\r\n   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.TryGetEntry(Object entity, IEntityType entityType, Boolean throwOnTypeMismatch)\r\n   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.InitialFixup(InternalEntityEntry entry, Boolean fromQuery)\r\n   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.StateChanged(InternalEntityEntry entry, EntityState oldState, Boolean fromQuery)\r\n   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntryNotifier.StateChanged(InternalEntityEntry entry, EntityState oldState, Boolean fromQuery)\r\n   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.FireStateChanged(EntityState oldState)\r\n   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState oldState, EntityState newState, Boolean acceptChanges, Boolean modifyProperties)\r\n   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState entityState, Boolean acceptChanges, Boolean modifyProperties, Nullable`1 forceStateWhenUnknownKey)\r\n   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityGraphAttacher.PaintAction(EntityEntryGraphNode`1 node)\r\n   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityEntryGraphIterator.TraverseGraph[TState](EntityEntryGraphNode`1 node, Func`2 handleNode)\r\n   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityEntryGraphIterator.TraverseGraph[TState](EntityEntryGraphNode`1 node, Func`2 handleNode)\r\n   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityGraphAttacher.AttachGraph(InternalEntityEntry rootEntry, EntityState targetState, EntityState storeGeneratedWithKeySetTargetState, Boolean forceStateWhenUnknownKey)\r\n   at Microsoft.EntityFrameworkCore.DbContext.SetEntityState(InternalEntityEntry entry, EntityState entityState)\r\n   at Microsoft.EntityFrameworkCore.DbContext.SetEntityState[TEntity](TEntity entity, EntityState entityState)\r\n   at Microsoft.EntityFrameworkCore.DbContext.Update[TEntity](TEntity entity)\r\n   at Microsoft.EntityFrameworkCore.Internal.InternalDbSet`1.Update(TEntity entity)\r\n

只是提到调用的主键.MachineId不为空，它有一个int值。

我发现更新对象以通过 再次从上下文中获取它的唯一方法.Find，然后.CurrentValues.SetValues(transferedObject)像这样使用：

var existingMachine = await _machinesContext.Machines.FindAsync(machine.MachineId);
_machinesContext.Entry(existingMachine).CurrentValues.SetValues((Machine)machine);
await _machinesContext.SaveChangesAsync();

有没有更好的方法来附加和更新实体？

标签： c#entity-frameworkentity-framework-coremasstransit

解决方案

update 方法 它将所有属性放在查询中，即使没有对它们进行任何更改。在后台，对象集的状态已修改。您可以通过反射搜索所有属性，并且只修改已更改的属性。

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