字符串如何转成LINQ表达式呢？麻类有经验的大牛指点一下

2014-10-25 10:58:44 308 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

FA 新增资产API Demo DECLARE l_trans_rec fa_api_types.trans_rec_type; l_dist_trans_rec fa_api_types.trans_rec_type; l_asset_hdr_rec fa_api_types.asset_hdr_rec_type; l_asset_desc_rec fa_a 阅读详情



string a="user=>u.name==txtName";

db.user.where(a);想把字符串转成到这里面来要如何写呢？

...全文

保姆级教程：用Python仿真OFDM系统（附抗多径干扰优化方案）本文提供了一份详细的Python仿真OFDM通信系统教程。通过NumPy和Matplotlib，从二进制比特流开始，逐步构建完整的OFDM系统模型，涵盖IFFT、循环前缀等核心概念。重点探讨了如何对抗多径干扰，并提供了优化方案，通过误码率曲线直观对比性能，适合通信工程学习和物理层开发实践。阅读详情

禁用F3

C# 111,128 成员 642,536 内容

+ 关注 + 加入社区

切换为时间正序

Magni2012 2017-02-23

打赏
举报

@楼主 notax的方法应该可以满足你的需求吧 -->在4.0框架上没有System.Linq.Dynamic.DynamicExpression http://dynamiclinq.codeplex.com -->PS，需要把字符串转表达式变量g的声明改为Expression<Func<User, bool>>试下

smthgdin_020 2014-10-27

打赏
举报

自己写一个转换器，或者上网找。 lambdaparse（string xxx）

禁用F3 2014-10-27

打赏
举报

引用 4 楼 duanzi_peng 的回复:

好麻烦。你的a是手动拼接的，为什么要搞成字符串？在也有错误，user=>u.name==txtName 不是user=> ，是u=>。看看下面的
Func<User, bool> filterFunc = u=>u.name==txtName;
db.user.where(filterFunc);

是的，一楼是写错了，我目的就是想把字符串改为LINQ表达式

郑州高新区WPF小王子 2014-10-27

打赏
举报

好麻烦。你的a是手动拼接的，为什么要搞成字符串？在也有错误，user=>u.name==txtName 不是user=> ，是u=>。看看下面的


Func<User, bool> filterFunc = u=>u.name==txtName;
db.user.where(filterFunc);

禁用F3 2014-10-27

打赏
举报

引用 2 楼 notax 的回复:


using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;

namespace StringToExpressionTreeTest
{
    class Program
    {
        public class User
        {
            public string Name { get; set; }
            public string Phone { get; set; }
        }

        static void Main(string[] args)
        {
            var exp = @"user => user.Name == txtName";
            //var exp = @"user => user.Name != txtName"; //for testing 
            //var exp = @"user => user.Name.Contains(txtName)"; ////for testing 
            var txtName = "abc";

            var users = new List<User>() 
            { 
                 new User { Name = "abc", Phone = "a123"},
                 new User { Name = "xyz", Phone = "x123"},
            };

            var e = BuildExpression(exp);
            Predicate<User> g = user => (bool)e.Compile().DynamicInvoke(user, txtName);
            //var query = users.Where(user => g(user));
            var query = users.FindAll(g);

            
            //Expression<Func<User, string, object>> g = (obj, s)  => e.Compile().DynamicInvoke(obj, s); //for db
            //Func<User, string, bool> g = (obj, s) => (bool)e.Compile().DynamicInvoke(obj, s); // for objets
            //var query = users.Where(user => g(user, txtName));

          
            foreach (var each in query)
                Console.WriteLine("{0} {1}", each.Name, each.Phone);


            Console.ReadKey();
        }

        private static LambdaExpression BuildExpression(string expression)
        {
            var exp = expression.Split(new string[] { "=>" }, StringSplitOptions.None)[1];
            var p1 = Expression.Parameter(typeof(User), "user");
            var p2 = Expression.Parameter(typeof(string), "txtName");

            var e = System.Linq.Dynamic.DynamicExpression.ParseLambda(
                new[] { 
                    p1, 
                    p2 
                },
                null,
                exp);
            return e;
        }
    }
}

在4.0框架上没有System.Linq.Dynamic.DynamicExpression PS，需要把字符串转表达式

notax 2014-10-26

打赏
举报


using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;

namespace StringToExpressionTreeTest
{
    class Program
    {
        public class User
        {
            public string Name { get; set; }
            public string Phone { get; set; }
        }

        static void Main(string[] args)
        {
            var exp = @"user => user.Name == txtName";
            //var exp = @"user => user.Name != txtName"; //for testing 
            //var exp = @"user => user.Name.Contains(txtName)"; ////for testing 
            var txtName = "abc";

            var users = new List<User>() 
            { 
                 new User { Name = "abc", Phone = "a123"},
                 new User { Name = "xyz", Phone = "x123"},
            };

            var e = BuildExpression(exp);
            Predicate<User> g = user => (bool)e.Compile().DynamicInvoke(user, txtName);
            //var query = users.Where(user => g(user));
            var query = users.FindAll(g);

            
            //Expression<Func<User, string, object>> g = (obj, s)  => e.Compile().DynamicInvoke(obj, s); //for db
            //Func<User, string, bool> g = (obj, s) => (bool)e.Compile().DynamicInvoke(obj, s); // for objets
            //var query = users.Where(user => g(user, txtName));

          
            foreach (var each in query)
                Console.WriteLine("{0} {1}", each.Name, each.Phone);


            Console.ReadKey();
        }

        private static LambdaExpression BuildExpression(string expression)
        {
            var exp = expression.Split(new string[] { "=>" }, StringSplitOptions.None)[1];
            var p1 = Expression.Parameter(typeof(User), "user");
            var p2 = Expression.Parameter(typeof(string), "txtName");

            var e = System.Linq.Dynamic.DynamicExpression.ParseLambda(
                new[] { 
                    p1, 
                    p2 
                },
                null,
                exp);
            return e;
        }
    }
}

devmiao 2014-10-25

打赏
举报

可以用dynamic linq这个库。如果不涉及表达式解析，也可以构造表达式树，参考 http://bbs.csdn.net/topics/390914025

字符串如何转成LINQ表达式呢？麻类有经验的大牛指点一下

相关推荐