asp.net-mvc – 调用SaveChanges()时从更新中排除属性

myDbContext.Dogs.Attach(dog);
myDbContext.Entry(dog).State = EntityState.Modified;

var objectContext = ((IObjectContextAdapter) myDbContext).ObjectContext;
foreach (var entry in objectContext.ObjectStateManager.GetObjectStateEntries(EntityState.Modified).Where(entity => entity.Entity.GetType() == typeof(Dogs)))
{
    // You need to give Foreign Key Property name
    // instead of Navigation Property name
    entry.RejectPropertyChanges("OwnerID"); 

}

myDbContext.SaveChanges();

如果您想在一行中执行此操作,请使用以下扩展方法：

public static void DontUpdateProperty<TEntity>(this DbContext context,string propertyName)
{
    var objectContext = ((IObjectContextAdapter) context).ObjectContext;
    foreach (var entry in objectContext.ObjectStateManager.GetObjectStateEntries(EntityState.Modified).Where(entity => entity.Entity.GetType() == typeof(TEntity)))
    {
        entry.RejectPropertyChanges(propertyName); 
    }
}

并像这样使用它

// After you modify some POCOs
myDbContext.DontUpdateProperty<Dogs>("OwnerID");
myDbContext.SaveChanges();

如您所见,您可以修改此解决方案以满足您的需求,例如：使用string []属性而不是字符串propertyName作为参数.

建议的方法

更好的解决方案是使用您建议的属性([NeverUpdate]).要使其工作,您需要使用SavingChanges事件(检查我的blog)：

void ObjectContext_SavingChanges(object sender,System.Data.Objects.SavingChangesEventArgs e)
{
    ObjectContext context = sender as ObjectContext;
    if(context != null)
    {
        foreach(ObjectStateEntry entry in context.ObjectStateManager.GetObjectStateEntries(EntityState.Modified))
        {
            var type = typeof(entry.Entity);
            var properties = type.GetProperties();
            foreach( var property in properties )
            {
                var attributes = property.GetCustomAttributes(typeof(NeverUpdateAttribute),false);
                if(attributes.Length > 0)
                    entry.RejectPropertyChanges(property.Name);
            }
        }
    }
}
// Check Microsoft documentation on how to create custom attributes:
// http://msdn.microsoft.com/en-us/library/sw480ze8(v=vs.80).aspx
public class NeverUpdateAttribute: SystemAttribute
{

}

//In your POCO
public class Dogs
{
    [NeverUpdate]
    public int OwnerID { get; set; }
}

警告：我没有编译此代码.我不在家 ：/

警告2：我刚刚阅读了MSDN documentation,它说：

ObjectStateEntry.RejectPropertyChanges Method

Rejects any changes made to the property with the given name since the
property was last loaded,attached,saved,or changes were accepted.
The orginal value of the property is stored and the property will no
longer be marked as modified.

我不确定在附加修改后的实体时它的行为是什么.我明天会试试.

警告3：我现在已经尝试过了.此解决方案有效.使用RejectPropertyChanges()方法拒绝的属性不会在持久性单元(数据库)中更新.

但是,如果通过调用Attach()附加更新的实体,则在SaveChanges()之后当前上下文仍然是脏的.假设数据库中存在以下行：

Dogs
ID: 1
Name: Max
OwnerID: 1

请考虑以下代码：

var myDog = new Dogs();
myDog.ID = 1;
myDog.Name = Achilles;
myDog.OwnerID = 2;

myDbContext.Dogs.Attach(myDog);
myDbContext.Entry(myDog).State = EntityState.Modified;
myDbContext.SaveChanges();

SaveChanges()之后的数据库的当前状态：

Dogs:
ID: 1
Name: Achilles
OwnerID: 1

SaveChanges()之后的myDbContext的当前状态：

var ownerId = myDog.OwnerID;  // it is 2
var status = myDbContext.Entry(myDog).State; // it is Unchanged

那么你应该怎么做？在SaveChanges()之后分离它：

Dogs myDog = new Dogs();
//Set properties
...
myDbContext.Dogs.Attach(myDog);
myDbContext.Entry(myDog).State = EntityState.Modified;
myDbContext.SaveChanges();
myDbContext.Entry(myDog).State = EntityState.Detached;