Building OrderBy Lambda Expression from Property Name in C#

骑猪看日落 2022-08-12 01:05 154阅读 0赞

原文：[http://www.codeproject.com/Tips/817372/Building-OrderBy-Lambda-Expression-from-Property-N][http_www.codeproject.com_Tips_817372_Building-OrderBy-Lambda-Expression-from-Property-N]

Fork地址：[https://dotnetfiddle.net/sEmFzq][https_dotnetfiddle.net_sEmFzq]

using System;
    using System.Collections.Generic;
    using System.Diagnostics;
    using System.Linq;
    using System.Linq.Expressions;
    using System.Text;
    
    
    public class Phone
    {
    	public double Price { get; set; }
    	public string Brand { get; set; }
    }
    
    public class Db
    {
    	public static IQueryable<Phone> Phones
    	{
    		get
    		{
    			return new List<Phone>()
    			{
    				new Phone(){ Price = 2, Brand = "A"},
    				new Phone(){ Price = 1, Brand = "B"}
    			}.AsQueryable();
    		}
    	}
    }
    
    
    public static class Utility
    {
    	//makes expression for specific prop
    	public static Expression<Func<TSource, object>> GetExpression<TSource>(string propertyName)
    	{
    		var param = Expression.Parameter(typeof(TSource), "x");
    		Expression conversion = Expression.Convert(Expression.Property(param, propertyName), typeof(object));   //important to use the Expression.Convert 
    		return Expression.Lambda<Func<TSource, object>>(conversion, param);
    	}
    
    	//makes deleget for specific prop
    	public static Func<TSource, object> GetFunc<TSource>(string propertyName)
    	{
    		return GetExpression<TSource>(propertyName).Compile();  //only need to compiled expression
    	}
    
    	//OrderBy overload
    	public static IOrderedEnumerable<TSource> OrderBy<TSource>(this IEnumerable<TSource> source, string propertyName)
    	{
    		return source.OrderBy(GetFunc<TSource>(propertyName));
    	}
    
    	//OrderBy overload
    	public static IOrderedQueryable<TSource> OrderBy<TSource>(this IQueryable<TSource> source, string propertyName) 
    	{
    		return source.OrderBy(GetExpression<TSource>(propertyName));
    	}
    }
    
    
    public class Program
    {
    	public static void Dump(IEnumerable<Phone> phones, string mesg)
    	{
    		Console.WriteLine("\n" + mesg);
    		foreach (var item in phones)
    		{
    			Console.WriteLine(String.Format("Brand = {0}, Price = {1}", item.Brand, item.Price));
    		}
    	}
    
    	public static void Main(string[] args)
    	{
    
    		List<Phone> orderedByPrice = null;
    		List<Phone> orderedByBrand = null;
    
    		/*When using lambda expression*/
    		orderedByPrice = Db.Phones.OrderBy(x => x.Price).ToList();
    		orderedByBrand = Db.Phones.OrderBy(x => x.Brand).ToList();
    		Dump(orderedByPrice, "lambda expression, Order By: Price");
    		Dump(orderedByBrand, "lambda expression, Order By: Brand");
    
    
    		/*When source is IQueryable*/
    		orderedByPrice = Db.Phones.OrderBy("Price").ToList();
    		orderedByBrand = Db.Phones.OrderBy("Brand").ToList();
    		Dump(orderedByPrice, "Source is IQueryable, Order By: Price");
    		Dump(orderedByBrand, "source is IQueryable, Order By: Brand");
    
    		/*When source is IEnumerable*/
    		orderedByPrice = Db.Phones.AsEnumerable().OrderBy("Price").ToList();
    		orderedByBrand = Db.Phones.AsEnumerable().OrderBy("Brand").ToList();
    		Dump(orderedByPrice, "Source is IEnumerable, Order By: Price");
    		Dump(orderedByBrand, "Source is IEnumerable, Order By: Brand");
    
    	}
    }

输出：

lambda expression, Order By: Price
    Brand = B, Price = 1
    Brand = A, Price = 2
    
    lambda expression, Order By: Brand
    Brand = A, Price = 2
    Brand = B, Price = 1
    
    Source is IQueryable, Order By: Price
    Brand = B, Price = 1
    Brand = A, Price = 2
    
    source is IQueryable, Order By: Brand
    Brand = A, Price = 2
    Brand = B, Price = 1
    
    Source is IEnumerable, Order By: Price
    Brand = B, Price = 1
    Brand = A, Price = 2
    
    Source is IEnumerable, Order By: Brand
    Brand = A, Price = 2
    Brand = B, Price = 1

[http_www.codeproject.com_Tips_817372_Building-OrderBy-Lambda-Expression-from-Property-N]: http://www.codeproject.com/Tips/817372/Building-OrderBy-Lambda-Expression-from-Property-N
[https_dotnetfiddle.net_sEmFzq]: https://dotnetfiddle.net/sEmFzq