如何使用字符串通过表达式创建EF顺序？

Question

我试图实现这种转换

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

我能够找到一种通过表达式使用反射生成订单的方法,但它不适用于复杂排序,Address.Street因为它适用于单个属性级别.

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

Answer 1

创建表达式并不难,但是当你不知道属性的类型(因此是选择器表达式结果的类型)时,如何将它绑定到相应的OrderBy(Descending)/ ThenBy(Descendig)方法是棘手的.

以下是自定义扩展方法中封装的所有内容:

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);
    }