Lambda动态创建

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Linq.Expressions;

namespace ExpressionToSql
{
    public class LambdaHelper
    {
        /// <summary>
        /// Id等于
        /// </summary>
        /// <param name="Id"></param>
        /// <returns></returns>
        public Func<Model, bool> CreateFilterID(int Id)
        {
            ParameterExpression obj = Expression.Parameter(typeof(Model), "obj");

            ConstantExpression constant = Expression.Constant(Id);

            MemberExpression member = Expression.PropertyOrField(obj, "Id");


            BinaryExpression query = Expression.Equal(member, constant);


            var lambda = Expression.Lambda<Func<Model, bool>>(query, obj);

            var func = lambda.Compile();
            return func;
        }

        /// <summary>
        /// Model等于
        /// </summary>
        /// <param name="model"></param>
        /// <returns></returns>
        public Func<Model, bool> CreateFilterModel(Model model)
        {
            ParameterExpression obj = Expression.Parameter(typeof(Model), "obj");

            ConstantExpression constant = Expression.Constant(model.Id);

            MemberExpression member = Expression.PropertyOrField(obj, "Id");


            BinaryExpression query = Expression.Equal(member, constant);


            var lambda = Expression.Lambda<Func<Model, bool>>(query, obj);

            var func = lambda.Compile();
            return func;
        }

        /// <summary>
        /// Object 等于（1参数）
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="model"></param>
        /// <returns></returns>
        public Func<T, bool> CreateFilterObject<T>(T model) where T : class,new()
        {
            ParameterExpression obj = Expression.Parameter(typeof(T), "obj");

            var constVal = Convert.ToInt32(GetPropertyValue(model, "Id"));
            ConstantExpression constant = Expression.Constant(constVal);

            MemberExpression member = Expression.PropertyOrField(obj, "Id");


            BinaryExpression query = Expression.Equal(member, constant);


            var lambda = Expression.Lambda<Func<T, bool>>(query, obj);

            var func = lambda.Compile();
            return func;
        }

        /// <summary>
        /// Model等于（2参数)
        /// </summary>
        /// <returns></returns>
        public Func<Model, Model, bool> CreateModelEqual()
        {
            ParameterExpression obj = Expression.Parameter(typeof(Model), "obj");


            ParameterExpression obj1 = Expression.Parameter(typeof(Model), "obj1");

            MemberExpression member = Expression.PropertyOrField(obj, "Id");

            MemberExpression member1 = Expression.PropertyOrField(obj1, "Id");

            BinaryExpression query = Expression.Equal(member, member1);


            var lambda = Expression.Lambda<Func<Model, Model, bool>>(query, obj, obj1);

            var func = lambda.Compile();
            return func;
        }

        /// <summary>
        /// Int 等于
        /// </summary>
        /// <returns></returns>
        public Func<int, int, bool> CreateIntEqual()
        {
            ParameterExpression member = Expression.Parameter(typeof(int), "id");

            ParameterExpression val = Expression.Parameter(typeof(int), "val");

            BinaryExpression bin = Expression.Equal(member, val);

            var lambda = Expression.Lambda<Func<int, int, bool>>(bin, member, val);

            var func = lambda.Compile();
            return func;
        }

        #region Extend

        private object GetPropertyValue<T>(T model, string proertyName)
            where T : class
        {
            return model.GetType().GetProperty(proertyName).GetValue(model);
        }
        #endregion

    }


    public class Model
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }
}

static void TestLambda()
        {

            LambdaHelper helper = new LambdaHelper();

            Model test1 = new Model() { Id = 1, Name = "lcc1" };
            Model test2 = new Model() { Id = 2, Name = "lcc2" };
            Model test3 = new Model() { Id = 3, Name = "lcc3" };


            List<Model> list = new List<Model>() { test1, test2, test3 };

            //CreateFilterID
            Console.WriteLine("-----------------CreateFilterID--------------------------");
            var filterFunc = helper.CreateFilterID(1);

            Console.WriteLine("test1中的Id 等于1:" + filterFunc(test1));
            Console.WriteLine("test2中的Id 等于1:" + filterFunc(test1));

            //CreateFilterModel
            Console.WriteLine("--------------------CreateFilterModel---------------------");
            var filterModelFunc = helper.CreateFilterModel(test1);
            Console.WriteLine("test1中的等于test1:" + filterModelFunc(test1));
            Console.WriteLine("test1中的等于test2:" + filterModelFunc(test2));
            Console.WriteLine("list中的等于test1的数量:" + list.Where(filterModelFunc).Count());

            //CreateFilterObject
            Console.WriteLine("----------------------CreateFilterObject--------------------");
            var filterObjectlFunc = helper.CreateFilterObject(test2);
            Console.WriteLine("test2中的等于test1:" + filterObjectlFunc(test1));
            Console.WriteLine("test2中的等于test2:" + filterObjectlFunc(test2));

            Console.WriteLine("list中的等于test2的数量:" + list.Where(filterObjectlFunc).Count());


            //CreateModelEqual
            Console.WriteLine("-------------------CreateModelEqual--------------------------");
            var modelEqualFunc = helper.CreateModelEqual();

            Console.WriteLine("test1,test2是否相等:" + modelEqualFunc(test1, test2));
            Console.WriteLine("test1,test1是否相等:" + modelEqualFunc(test1, test2));

            //CreateIntEqual
            Console.WriteLine("-----------------CreateIntEqual------------------------------");
            var intEqualFunc = helper.CreateIntEqual();
            Console.WriteLine("1,2是否相等:" + intEqualFunc(1, 2));
            Console.WriteLine("1,1是否相等:" + intEqualFunc(1, 1));

            Console.Read();


        }