Question

将LINQ to SQL实体复制[克隆]导致数据库中出现新记录的最佳做法是什么？

上下文是我希望为管理员的网格中的记录创建重复的功能。网站，并尝试了一些事情和明显的，读取数据，改变ID = 0，更改名称，submitChanges()，并命中一个例外，哈哈。我想我可能会停下来问一位专家。

我希望首先阅读记录，通过在“Copy Of”前面添加名称然后另存为新记录来更改名称。

Answer 1

创建一个新实例，然后将linq映射类与反射一起使用来复制成员值。

E.g。

public static void CopyDataMembers(this DataContext dc,
                                   object sourceEntity,
                                   object targetEntity)
{
    //get entity members
    IEnumerable<MetaDataMember> dataMembers = 
         from mem in dc.Mapping.GetTable(sourceEntity.GetType())
                                 .RowType.DataMembers
         where mem.IsAssociation == false
         select mem;

    //go through the list of members and compare values
    foreach (MetaDataMember mem in dataMembers)
    {
       object originalValue = mem.StorageAccessor.GetBoxedValue(targetEntity);
       object newValue = mem.StorageAccessor.GetBoxedValue(sourceEntity);

        //check if the value has changed
        if (newValue == null && originalValue != null 
            || newValue != null && !newValue.Equals(originalValue))
        {
            //use reflection to update the target
            System.Reflection.PropertyInfo propInfo = 
                targetEntity.GetType().GetProperty(mem.Name);

            propInfo.SetValue(targetEntity, 
                              propInfo.GetValue(sourceEntity, null), 
                              null);

            // setboxedvalue bypasses change tracking - otherwise 
            // mem.StorageAccessor.SetBoxedValue(ref targetEntity, newValue);
            // could be used instead of reflection
        }
    }
}

...或者您可以使用DataContractSerializer克隆它：

internal static T CloneEntity<T>(T originalEntity) where T : someentitybaseclass
{
    Type entityType = typeof(T);

    DataContractSerializer ser =
        new DataContractSerializer(entityType);

    using (MemoryStream ms = new MemoryStream())
    {
        ser.WriteObject(ms, originalEntity);
        ms.Position = 0;
        return (T)ser.ReadObject(ms);
    }
}

Answer 2

如果从DataContext将实体从ObjectTrackingEnabled加载为false，则可以在另一个DataContext中将此实体作为new插入

DataContext db1 = new DataContext();
DataContext db2 = new DataContext();

db2.ObjectTrackingEnabled = false;

MyEntity entToClone = db2.Single(e => e.Id == id);

// ... change some data if it is needed

db1.MyEntities.InsertOnSubmit(entToClone);
db1.SubmitChanges();

Answer 3

我遇到了同样的问题，Kristofer的代码完美无缺，非常感谢！

如果有人感兴趣，我稍微修改了他的代码，这样它就不会接受目标实体作为参数，而是创建一个新对象并返回它。另外，我将sourceEntity参数设为通用：

 public static T CloneEntity<T>(this DataContext dc, T sourceEntity) where T:class, new()
 {
     var targetEntity = new T();
     //... original method code...
     return targetEntity;
 }

然后我可以做以下事情：

dataContext.MyEntities.Attach(dataContext.CloneEntity(theEntity));

Answer 4

这是与Peter K.相同的解决方案，用于VB.Net中的Linq-to-Sql Entity Clone。

    Dim DC As New DataContext
    Dim DCI As New DataContext
    DC.ObjectTrackingEnabled = False

        Dim RGF As sf_RuleGroup = (From G In DC.sf_RuleGroups _
                                  Where G.RuleGroupID = CInt(e.CommandArgument) _
                                  Select G).First()
        DCI.sf_RuleGroups.InsertOnSubmit(RGF)
        DCI.SubmitChanges()

Answer 5

在实体框架6中，您可以执行此操作

Dim WorkoutNew As New Workout 'create a record
ff7db.Workouts.Add(WorkoutNew) 'add it to the table (workout)
ff7db.Entry(WorkoutNew).CurrentValues.SetValues(WorkoutsPost) ' update its values with a class with the same properties

LINQ to SQL实体/记录重复？

5 个答案: