资源库使用排序依据 [英] Repository With OrderBy

问题描述

我试图使该有权责令基于一个之类的参数结果的方法库类。我需要把它作为参数传递，因为我想是非常严谨的，我的资料库不返回IQueryable的，只有返回列表。问题是，我不知道如何使它使其符合下列要求：

I'm trying to make a repository class that has a method to order the results based upon a "sort" parameter. I need to pass it as a parameter since I'm trying to be very strict that my repository doesn't return IQueryable and only returns List. The problem is that I have no idea how to make it so that it meets the following requirements:

1. 允许多个列。


2. 强类型到的返回（无字符串列作为参数）的实体。


3. 能够设置一个特定的列递减。

这甚至可能还是没用，一个库允许与订货回来？如果存储库只是能够执行CRUD操作？也许返回IQueryable的将是最好的选择吗？

Is this even possible or is it useless that a Repository allows returning with ordering? Should the repository be just able to perform CRUD operations? Maybe returning IQueryable would be the best option?

推荐答案

也许你需要的东西是这样的：

Perhaps you need something like this:

public class Ordering<T>
{
    private readonly Func<IQueryable<T>, IOrderedQueryable<T>> transform;

    private Ordering(Func<IQueryable<T>, IOrderedQueryable<T>> transform)
    {
        this.transform = transform;
    }

    public static Ordering<T> Create<TKey>
        (Expression<Func<T, TKey>> primary)
    {
        return new Ordering<T>(query => query.OrderBy(primary));
    }

    public Ordering<T> ThenBy<TKey>(Expression<Func<T, TKey>> secondary)
    {
        return new Ordering<T>(query => transform(query).ThenBy(secondary));
    }

    // And more for the descending methods...

    internal IOrderedQueryable<T> Apply(IQueryable<T> query)
    {
        return transform(query);
    }
}

然后，客户机可以创建一个订购＆LT; T＆GT; 要传递到存储库，而repositry可以调用应用与的IQueryable＆LT; T＆GT; 。这是否有意义？

Then a client can create an Ordering<T> to be passed into the repository, and the repositry can call Apply with the IQueryable<T>. Does that make sense?

样品（略带傻气）使用方法：

Sample (slightly silly) use:

var ordering = Ordering<FileInfo>.Create(fi => fi.Length)
                                 .ThenBy(fi => fi.Name);

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