在LINQ查询中调用自定义方法 [英] Calling a custom method in LINQ query

问题描述

我有一个这样的查询：

 var q = 
        from u in db.User
        select new
        {
            userId = u.UserId,
            userName = o.Name,
            userAvatar = o.AvatarCode
        };

然后，我必须将 AvatarCode 转换为 AvatarPath 使用自定义静态方法 Image.GetPath 。

Then, I have to transform AvatarCode to AvatarPath using custom static method Image.GetPath.

可以通过以下方式进行设置：

It's possible to make this in the following way:

 var q = 
        (from u in db.User
        select new
        {
            userId = u.UserId,
            userName = o.Name,
            userAvatar = o.AvatarCode
        })
        .AsEnumerable()
        .Select(new
        {
            userId = u.UserId,
            userName = o.Name,
            userAvatar = Image.GetPath(o.AvatarCode)
        };

但是如果对象字段的数量很大，那么在第二个选择中复制所有字段是一个过分。

But if the number of object fields is large then it's an overkill to duplicate all fields in the second Select.

有没有其他选择？

例如，一些方法来标记应该执行的方法查询执行离子：

For example, some approach to mark methods that should be executed after query execution:

 var q = 
        from u in db.User
        select new
        {
            userId = u.UserId,
            userName = o.Name,
            userAvatar = Linq.ExecuteLater(Image.GetPath(o.AvatarCode))
        };

推荐答案

没有任何这样的方法，但如果问题是只能在第二次选择中再次指定的字段数量可以这样做：

There is not any such method but if the problem is only number of fields which must be specified again in the second select you can do something like this:

var q = 
    (from u in db.User
    select new
    {
        userId = u.UserId,
        userName = u.Name,
        userAvatar = u.AvatarCode
    })
    .AsEnumerable()
    .Select(u => new
    {
        User = u,
        Path = Image.GetPath(u.AvatarCode)
    });

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