重复 LINQ to SQL 实体/记录?

Duplicate LINQ to SQL entity / record?(重复 LINQ to SQL 实体/记录?)

问题描述

复制 [克隆] LINQ to SQL 实体从而在数据库中生成新记录的最佳实践是什么?

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

上下文是我希望为管理员网格中的记录创建一个重复的函数.网站并在尝试了一些显而易见的事情后，读取数据，更改 ID=0，更改名称，submitChanges()，然后遇到异常，哈哈.我想我可能会停下来问问专家.

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.

我希望首先读取记录，通过添加前缀Copy Of"更改名称，然后另存为新记录.

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

创建一个新实例，然后使用 linq 映射类和反射来复制成员值.

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
        }
    }
}

...或者您可以使用 DataContractSerializer 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);
    }
}

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