动态Lambda进阶一

直接上代码：

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

namespace ConsoleApplication1
{
    public static class Extensions
    {
        public static Predicate<T> ToPredicate<T>(this Func<T, bool> source)
        {
            Predicate<T> result = new Predicate<T>(source);
            return result;
        }
    }

    public class LambdaExtention<T>
    {
        /// <summary>
        /// 表达式集合
        /// </summary>
        private List<Expression> m_lstExpression = null;

        /// <summary>
        /// 参数
        /// </summary>
        private ParameterExpression m_Parameter = null;

        /// <summary>
        /// 构造函数
        /// </summary>
        public LambdaExtention()
        {
            m_lstExpression = new List<Expression>();
            m_Parameter = Expression.Parameter(typeof(T), "x");
        }

        /// <summary>
        /// 字符串Contains筛选
        /// </summary>
        /// <param name="expProperty">表达式属性</param>
        /// <param name="objValue">值</param>
        public void Contains(Expression<Func<T, object>> expProperty, object objValue)
        {
            Expression expRes = Expression.Call(GetMemberExpression(expProperty), typeof(string).GetMethod("Contains"),
                                Expression.Constant(objValue));

            m_lstExpression.Add(expRes);
        }

        /// <summary>
        /// 等于
        /// </summary>
        /// <param name="expProperty">表达式属性</param>
        /// <param name="objValue">值</param>
        public void Equal(Expression<Func<T, object>> expProperty, object objValue)
        {
            var member = GetMemberExpression(expProperty);
            Expression expRes = Expression.Equal(member, Expression.Constant(objValue, member.Type));
            m_lstExpression.Add(expRes);
        }

        /// <summary>
        /// 等于
        /// </summary>
        /// <param name="expProperty">表达式属性</param>
        /// <param name="objValue">值</param>
        public void Equal(string strProperty, object objValue)
        {
            var member = GetMemberExpression(strProperty);
            Expression expRes = Expression.Equal(member, Expression.Constant(objValue, member.Type));
            m_lstExpression.Add(expRes);
        }

        /// <summary>
        /// 小于
        /// </summary>
        /// <param name="expProperty">表达式属性</param>
        /// <param name="objValue">值</param>
        public void LessThan(Expression<Func<T, object>> expProperty, object objValue)
        {
            var member = GetMemberExpression(expProperty);
            Expression expRes = Expression.LessThan(member, Expression.Constant(objValue, member.Type));
            m_lstExpression.Add(expRes);
        }

        /// <summary>
        /// 小于等于
        /// </summary>
        /// <param name="expProperty">表达式属性</param>
        /// <param name="objValue">值</param>
        public void LessThanOrEqual(Expression<Func<T, object>> expProperty, object objValue)
        {
            var member = GetMemberExpression(expProperty);
            Expression expRes = Expression.LessThanOrEqual(member, Expression.Constant(objValue, member.Type));
            m_lstExpression.Add(expRes);
        }

        /// <summary>
        /// 大于
        /// </summary>
        /// <param name="expProperty">表达式属性</param>
        /// <param name="objValue">值</param>
        public void GreaterThan(Expression<Func<T, object>> expProperty, object objValue)
        {
            var member = GetMemberExpression(expProperty);
            Expression expRes = Expression.GreaterThan(member, Expression.Constant(objValue, member.Type));
            m_lstExpression.Add(expRes);
        }

        /// <summary>
        ///  大于等于
        /// </summary>
        /// <param name="expProperty">表达式属性</param>
        /// <param name="objValue">值</param>
        public void GreaterThanOrEqual(Expression<Func<T, object>> expProperty, object objValue)
        {
            var member = GetMemberExpression(expProperty);
            Expression expRes = Expression.GreaterThanOrEqual(member, Expression.Constant(objValue, member.Type));
            m_lstExpression.Add(expRes);
        }

        /// <summary>
        /// 为真方法
        /// </summary>
        /// <param name="expProperty">表达式属性</param>
        /// <param name="objValue">值</param>
        /// <param name="typeName">类名名称</param>
        /// <param name="methodName">方法名称</param>
        public void IsTureMethod(Expression<Func<T, object>> expProperty, object objValue, string typeName, string methodName)
        {
            Expression expRes = Expression.IsTrue(GetMemberExpression(expProperty), Type.GetType(typeName).GetMethod(methodName)
                             );

            m_lstExpression.Add(expRes);
        }

        /// <summary>
        /// 获得Lambda
        /// </summary>
        /// <returns>返回Lambda</returns>
        private LambdaExpression GetLambda()
        {
            Expression whereExpr = null;

            foreach (var expr in this.m_lstExpression)
            {
                if (whereExpr == null)
                {
                    whereExpr = expr;
                }
                else
                {
                    whereExpr = Expression.And(whereExpr, expr);
                }
            }

            if (whereExpr == null)
            {
                return null;
            }

            return Expression.Lambda(whereExpr, m_Parameter);
        }

        /// <summary>
        /// 获得谓词
        /// </summary>
        /// <returns>返回谓词</returns>
        public Predicate<T> GetPredicate()
        {
            Func<T, bool> match = (Func<T, bool>)GetLambda().Compile();

            return match.ToPredicate();
        }

        /// <summary>
        /// 获得方法
        /// </summary>
        /// <returns>返回方法</returns>
        public Func<T, bool> GetFunc()
        {
            Func<T, bool> match = (Func<T, bool>)GetLambda().Compile();

            return match;
        }

        /// <summary>
        /// 获得MemberExpression
        /// </summary>
        /// <param name="exp">表达式属性</param>
        /// <returns>返回MemberExpression</returns>
        private MemberExpression GetMemberExpression(Expression<Func<T, object>> exp)
        {
            var arrSplit = exp.Body.ToString().Split("(.)".ToCharArray(), StringSplitOptions.RemoveEmptyEntries);

            var strProperty = string.Join(".", arrSplit, 1, arrSplit.Length - 1);
            MemberExpression member = GetMemberExpression(strProperty);
            return member;
        }

        /// <summary>
        /// 获得MemberExpression
        /// </summary>
        /// <param name="strProperty">表达式属性</param>
        /// <returns>返回MemberExpression</returns>
        private MemberExpression GetMemberExpression(string strProperty)
        {
            MemberExpression member;

            if (strProperty.Contains('.'))
            {
                string[] aryProperty = strProperty.Split('.');

                member = Expression.Property(m_Parameter, aryProperty[0]);

                for (int i = 1; i < aryProperty.Length; i++)
                {
                    member = Expression.Property(member, member.Type, aryProperty[i]);
                }
            }
            else
            {
                member = Expression.Property(m_Parameter, strProperty);
            }

            return member;
        }
    }
}

调用示例：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            List<Student> lstStu = new List<Student>();
            lstStu.Add(new Student() { No = "001", Name = "zhangsan", Classes = new Classes() { ClassID = "002" } });
            lstStu.Add(new Student() { No = "002", Name = "lisi", Classes = new Classes() { ClassID = "003" } });
            lstStu.Add(new Student() { No = "003", Name = "wangwu", Classes = new Classes() { ClassID = "004" } });
            lstStu.Add(new Student() { No = "004", Name = "maliu", Classes = new Classes() { ClassID = "005" } });

            var le = new LambdaExtention<Student>();

            ////自定义方法
            le.IsTureMethod(x => x.Classes.ClassID, "0", "ConsoleApplication1.Test", "Show");

            ////两种写法
            le.Equal(x => x.Classes.ClassID, "002");
            le.Equal("Classes.ClassID", "002");

            List<Student> stu = lstStu.FindAll(le.GetPredicate());

            foreach (var item in stu)
            {
                Console.WriteLine(item.No);
            }

            Console.Read();
        }
    }

    static class Test
    {
        public static bool Show(string str)
        {
            return false;
        }
    }
}

文章引用自：http://blog.jobbole.com/99431/