C＃中的LINQ-SQL：存储库模式的UpdateByID方法 [英] C# Linq-SQL: An UpdateByID method for the Repository Pattern

问题描述

我已经实现了一种库类，它有具有 GetByID ， DeleteByID 等方法，但我有实施 UpdateByID 方法的麻烦。

I have implemented a sort of Repository class and it has has GetByID, DeleteByID methods and so on, but I'm having trouble implementing the UpdateByID method.

我做了这样的事情：

public virtual void UpdateByID(int id, T entity)
{
        var dbcontext = DB;
        var item = GetByID(dbcontext, id);
        item = entity; 
        dbcontext.SubmitChanges();
}

protected MusicRepo_DBDataContext DB
{
    get
    {
        return new MusicRepo_DBDataContext();
    }
}

但它没有更新传递的实体。

But it's not updating the passed entity.

有没有人实现这样的方法？

Has anyone implemented such a method ?

---

的作为参考，这里是 GetByID 法的

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[更新]

正如马克正确的建议，我只是改变了局部变量的值。那么你认为我应该如何去了解这种方法吗？使用反射和属性从实体复制到项目？

As Marc correctly suggested, I am merely changing the values of the local variable. So how do you think I should go about this method? Use reflection and copy the properties from entity to item ?

推荐答案

您已经更新了所有的是一个局部变量;对于工作，你就必须给的成员值的从实体复制到项目 - 。不是那么简单

All you have updated is a local variable; for that to work you would have to copy the member values from entity to item - not quite so simple.

---

类似下面;我使用的唯一原因 TKEY的是我的Northwind.Customer测试，其中有一个字符串键;-p

Something like below; the only reason I used TKey was that I tested on Northwind.Customer, which has a string key ;-p

使用元模型的优势在于，它即使您正在使用POCO类（和基于XML的映射），并且它不尝试更新任何无关的样板工程。

The advantage of using the meta-model is that it works even if you are using POCO classes (and the xml-based mapping), and it doesn't try to update anything unrelated to the model.

有关这个例子的目的，我已经通过了在数据方面，你需要在某个时候加入的SubmitChanges ，但。剩下的应该是直接的可比性。

For the purposes of the example, I have passed in the data-context, and you need to add a SubmitChanges at some point, but the rest should be directly comparable.

顺便说一句 - 如果你很高兴从传入的对象采取的ID，这将是一件容易的事 - 然后你可以支持复合身份。表

BTW - if you are happy to take the ID from the passed in object, that would be easy too - and then you could support composite identity tables.

    static void Update<TEntity>(DataContext dataContext, int id, TEntity obj)
        where TEntity : class
    {
        Update<TEntity, int>(dataContext, id, obj);
    }
    static void Update<TEntity, TKey>(DataContext dataContext, TKey id, TEntity obj)
        where TEntity : class
    {
        // get the row from the database using the meta-model
        MetaType meta = dataContext.Mapping.GetTable(typeof(TEntity)).RowType;
        if(meta.IdentityMembers.Count != 1) throw new InvalidOperationException("Composite identity not supported");
        string idName = meta.IdentityMembers[0].Member.Name;

        var param = Expression.Parameter(typeof(TEntity), "row");
        var lambda = Expression.Lambda<Func<TEntity,bool>>(
            Expression.Equal(
                Expression.PropertyOrField(param, idName),
                Expression.Constant(id, typeof(TKey))), param);

        object dbRow = dataContext.GetTable<TEntity>().Single(lambda);

        foreach (MetaDataMember member in meta.DataMembers)
        {
            // don't copy ID
            if (member.IsPrimaryKey) continue; // removed: || member.IsVersion
            // (perhaps exclude associations and timestamp/rowversion? too)

            // if you get problems, try using StorageAccessor instead -
            // this will typically skip validation, etc
            member.MemberAccessor.SetBoxedValue(
                ref dbRow, member.MemberAccessor.GetBoxedValue(obj));
        }
        // submit changes here?
    }

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