c# - 如何在 EF 中获取实体更改增量？

Question

我只需要获取已更改字段的列表，数据存储是 ssce，因此没有可用的触发器

EF 是否支持获取列表或构建通用组件？

Answer 1

根据上下文的类型和生成的实体，您可以通过几种不同的方式来完成。对于从 Entity 或 POCO 继承的对象，您可以使用 ObjectStateManager如果是 self 跟踪实体，您可以使用实体本身的跟踪器。

请提供更多关于您如何生成上下文以及如何进行更改的详细信息

编辑(2):您可以像这样查询 ObjectStateManager 更改的条目:

 var changed = ctx.ObjectStateManager.GetObjectStateEntries().Where(e=>e.State != EntityState.Unchanged);

编辑(1):

以下例子来自MSDN演示如何查询更改:

int orderId = 43680;

using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
var order = (from o in context.SalesOrderHeaders
             where o.SalesOrderID == orderId
             select o).First();

// Get ObjectStateEntry from EntityKey.
ObjectStateEntry stateEntry =
    context.ObjectStateManager
    .GetObjectStateEntry(((IEntityWithKey)order).EntityKey);

//Get the current value of SalesOrderHeader.PurchaseOrderNumber.
CurrentValueRecord rec1 = stateEntry.CurrentValues;
string oldPurchaseOrderNumber =
    (string)rec1.GetValue(rec1.GetOrdinal("PurchaseOrderNumber"));

//Change the value.
order.PurchaseOrderNumber = "12345";
string newPurchaseOrderNumber =
    (string)rec1.GetValue(rec1.GetOrdinal("PurchaseOrderNumber"));

// Get the modified properties.
IEnumerable<string> modifiedFields = stateEntry.GetModifiedProperties();
foreach (string s in modifiedFields)
    Console.WriteLine("Modified field name: {0}\n Old Value: {1}\n New Value: {2}",
        s, oldPurchaseOrderNumber, newPurchaseOrderNumber);

// Get the Entity that is associated with this ObjectStateEntry.
SalesOrderHeader associatedEnity = (SalesOrderHeader)stateEntry.Entity;
Console.WriteLine("Associated Enity's ID: {0}", associatedEnity.SalesOrderID);
}