LINQ to SQL实体/记录重复？

Question

什么被认为是复制[克隆] LINQ to SQL实体导致数据库中新记录的最佳实践？

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.网站和尝试了一些事情和明显的,读取数据后,改变ID = 0,更改名称submitChanges(),并点击异常,大声笑.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以复制成员值.

例如

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();