如何使用字符串通过表达式创建 EF 订单? [英] How to use a string to create a EF order by expression?

问题描述

我正在努力实现这种转换

I'm trying to achive this conversion

"Address.Street" => (p) => p.Address.Street
"Name" => (p) => p.Name

我能够找到一种使用反射通过表达式生成订单的方法，但它不适用于像 Address.Street 这样的复杂排序，因为它适用于单个属性级别.

I was able to find a method to generate an order by expression using reflection but it won't work for complex sort as Address.Street since works for a single property level.

有没有办法做到这一点?我已经看到我编译了 lambda 表达式，但我无法理解如何使它适用于这种情况.

Is there a way to do this? I've seen that I compile lambda expressions but I couldn't understand how to make it work for this case.

推荐答案

创建一个表达式并不难，但棘手的部分是如何将它绑定到相应的OrderBy(Descending)/ThenBy(Descendig) 方法，当您不知道属性的类型(因此不知道选择器表达式结果的类型)时.

Creating an expression is not hard, but the tricky part is how to bind it to the corresponding OrderBy(Descending) / ThenBy(Descendig) methods when you don't know the type of the property (hence the type of the selector expression result).

以下是封装在自定义扩展方法中的所有内容:

Here is all that encapsulated in a custom extension method:

public static partial class QueryableExtensions
{
    public static IOrderedQueryable<T> OrderByMember<T>(this IQueryable<T> source, string memberPath)
    {
        return source.OrderByMemberUsing(memberPath, "OrderBy");
    }
    public static IOrderedQueryable<T> OrderByMemberDescending<T>(this IQueryable<T> source, string memberPath)
    {
        return source.OrderByMemberUsing(memberPath, "OrderByDescending");
    }
    public static IOrderedQueryable<T> ThenByMember<T>(this IOrderedQueryable<T> source, string memberPath)
    {
        return source.OrderByMemberUsing(memberPath, "ThenBy");
    }
    public static IOrderedQueryable<T> ThenByMemberDescending<T>(this IOrderedQueryable<T> source, string memberPath)
    {
        return source.OrderByMemberUsing(memberPath, "ThenByDescending");
    }
    private static IOrderedQueryable<T> OrderByMemberUsing<T>(this IQueryable<T> source, string memberPath, string method)
    {
        var parameter = Expression.Parameter(typeof(T), "item");
        var member = memberPath.Split('.')
            .Aggregate((Expression)parameter, Expression.PropertyOrField);
        var keySelector = Expression.Lambda(member, parameter);
        var methodCall = Expression.Call(
            typeof(Queryable), method, new[] { parameter.Type, member.Type },
            source.Expression, Expression.Quote(keySelector));
        return (IOrderedQueryable<T>)source.Provider.CreateQuery(methodCall);
    }

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