using System;

using System.Collections.Generic;

//using System.Linq.Dynamic;

using DynamicExpression=System.Linq.Dynamic.DynamicExpression;

using System.Linq.Expressions;

​

​

//https://stackoverflow.com/questions/48868277/how-to-get-predicatet-or-expressionfunct-bool-from-string-expressions-at-r/49403670#49403670

//Install-Package System.Linq.Dynamic -Version 1.0.7

//https://github.com/kahanu/System.Linq.Dynamic

​

public class Program

{

    static  List<Part> parts = new List<Part>();

    public static void Main()

    {

        Console.WriteLine("Dynamic Linq Predicate Demo using String Expression");

        //add sample data

        parts.Add(new Part() { PartName = "crank arm", PartId = 1234 });

        parts.Add(new Part() { PartName = "chain ring", PartId = 1334 });

        parts.Add(new Part() { PartName = "regular seat", PartId = 1434 });

        parts.Add(new Part() { PartName = "banana seat", PartId = 1444 });

        parts.Add(new Part() { PartName = "cassette", PartId = 1534 });

        parts.Add(new Part() { PartName = "shift lever", PartId = 1634 }); ;

        var p1=FindByLambda();

        var p2=FindByStringExpression();

        Console.WriteLine("P1 IsEqualto P2: {0}",p1.Equals(p2));

​

    }

    static Part FindByLambda()

    {

        Console.WriteLine("------- Find items using lambda expression ------");     

        var part= parts.Find(x => x.PartId==1444);

        Console.WriteLine("Part: Find: PartId= {0} , PartName={1}",part.PartId, part.PartName);

        return part;

    }

    static Part FindByStringExpression()

    {

        Console.WriteLine("------- Find items using string expression ------");     

        var predicate = MyDynamics.GetPredicate<Part>("PartId==1444");

        var part= parts.Find(predicate);

        Console.WriteLine("Part: Find: PartId= {0} , PartName={1}",part.PartId, part.PartName);

        return part;

    }

}   

​

​

public class Part

{

    public string PartName {get;set;}

    public int PartId {get;set;}

}

​

 public static class MyDynamics

    {   

        public static Predicate<T> GetPredicate<T>(string stringExpression)

        {        

            var exp = DynamicExpression.ParseLambda<T, bool>(stringExpression).Compile();               

            var predicate = new Predicate<T>(exp);

            return predicate;

        }

 }