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我正忙于在Dapper和DapperExtensions之上创建包装器扩展方法。目前我正在尝试向GetList<T>扩展方法添加过滤，类似于LINQ的Where<T>扩展方法。我已经看到了这个问题，但似乎我无法实现Marc Gravell所建议的，因为.NET 4.5中没有类型EqualsExpression 。这是一些演示代码，以帮助解释我的问题：

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Diagnostics;
using System.Linq.Expressions;
using DapperExtensions;

namespace Dapper.Extensions.Demo
{
    public class Program
    {
        private static readonly string ConnectionString = ConfigurationManager.ConnectionStrings["DapperDbContext"].ConnectionString;
        public static IDbConnection Connection { get { return new SqlConnection(ConnectionString); } }

        public static void Main(string[] args)
        {
            const int marketId = 2;
            var matchingPeople = Connection.Get<Person>(p => p.MarketId, marketId); // This works

            // Below is a LambdaExpression. expression.Body is, bizarrely, a UnaryExpression with a Convert
            //var matchingPeople = Connection.Get<Person>(p => p.MarketId == marketId); // Does not work

            foreach (var person in matchingPeople)
            {
                Console.WriteLine(person);
            }

            if (Debugger.IsAttached)
                Console.ReadLine();
        }
    }

    public static class SqlConnectionExtensions
    {
        public static IEnumerable<T> Get<T>(this IDbConnection connection, Expression<Func<T, object>> expression, object value = null) where T : class
        {
            using (connection)
            {
                connection.Open();

                // I want to be able to pass in: t => t.Id == id then:
                // Expression<Func<T, object>> expressionOnLeftOfFilterClause = t => t.Id;
                // string operator = "==";
                // object valueFromLambda = id;
                // and call Predicates.Field(expressionOnLeftOfFilterClause, Operator.Eq, valueFromLambda)

                var predicate = Predicates.Field(expression, Operator.Eq, value);
                var entities = connection.GetList<T>(predicate, commandTimeout: 30);
                connection.Close();
                return entities;
            }
        }
    }

    public class Person
    {
        public int Id { get; set; }

        public string FirstName { get; set; }

        public string Surname { get; set; }

        public int MarketId { get; set; }

        public override string ToString()
        {
            return string.Format("{0}: {1}, {2} - MarketId: {3}", Id, Surname, FirstName, MarketId);
        }
    }
}

特别注意我的Get<T>扩展方法：当我传入p => p.MarketId或p => p.MarketId == marketId ， expression.Body的类型为UnaryExpression 。对于后者， expression.Body实际上包含{Convert((p.MarketId == 2))} 。

尝试

var binaryExpression = expression as BinaryExpression;

返回null ，这是不幸的，因为我可以找到有用的Left和Right属性。

那么，有谁知道如何实现我想要的？我希望能够根据传入的lambda表达式选择Operator枚举。我们非常感谢任何帮助。