重复的LINQ to SQL实体/记录？ [英] Duplicate LINQ to SQL entity / record?

问题描述

什么会被认为是最好的做法，复制[克隆]一个LINQ to SQL的实体，从而在数据库中的新记录？

What would be considered the best practice in duplicating [cloning] a LINQ to SQL entity resulting in a new record in the database?

的背景是，我希望做一个复制功能，记录管理员的网格。网站和尝试一些事情，明显后，读取数据，更改ID = 0，更改名称，的SubmitChanges（），并创下了异常，大声笑。我想我可能会停下来问专家。

The context is that I wish to make a duplicate function for records in a grid of an admin. website and after trying a few things and the obvious, read data, alter ID=0, change name, submitChanges(), and hitting an exception, lol. I thought I might stop and ask an expert.

我要开始第一次读记录，改变以副本由prefixing的名称，然后保存为一个新的记录。

I wish to start with first reading the record, altering the name by prefixing with "Copy Of " and then saving as a new record.

推荐答案

创建一个新的实例，然后使用LINQ的映射类以及反射复制成员的值。

Create a new instance and then use the linq mapping classes together with reflection to copy member values.

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
        }
    }
}

...或者你可以使用DataContractSerializer的克隆它：

...or you can clone it using the DataContractSerializer:

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);
    }
}

这篇关于重复的LINQ to SQL实体/记录？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！