Linq表达式拓展类（Or条件，排除重复等）

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

namespace OSS.ETS.OMS.Common
{
    /// <summary>
    /// 构造函数使用True时：单个AND有效，多个AND有效；单个OR无效，多个OR无效；混合时写在AND后的OR有效
    /// 构造函数使用False时：单个AND无效，多个AND无效；单个OR有效，多个OR有效；混合时写在OR后面的AND有效
    /// </summary>
    /// 创建者：王宇
    /// 创建日期：9/1/2014 10:38 AM
    /// 修改者：
    /// 修改时间：
    /// ------------------------------------
    public static class PredicateExtensions
    {
        public static Expression<Func<T, bool>> True<T>() { return f => true; }

        public static Expression<Func<T, bool>> False<T>() { return f => false; }

        /// <summary>
        /// lambda表达式Or
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="expression1">The expression1.</param>
        /// <param name="expression2">The expression2.</param>
        /// <returns></returns>
        /// 创建者：王宇
        /// 创建日期：9/1/2014 10:32 AM
        /// 修改者：
        /// 修改时间：
        /// ------------------------------------
        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)
        {
            var invokedExpression = Expression.Invoke(expression2, expression1.Parameters);

            return Expression.Lambda<Func<T, bool>>(Expression.Or(expression1.Body, invokedExpression), expression1.Parameters);
        }


        /// <summary>
        /// lambda表达式And
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="expression1">The expression1.</param>
        /// <param name="expression2">The expression2.</param>
        /// <returns></returns>
        /// 创建者：王宇
        /// 创建日期：9/1/2014 10:30 AM
        /// 修改者：
        /// 修改时间：
        /// ------------------------------------
        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)
        {
            var invokedExpression = Expression.Invoke(expression2, expression1.Parameters);

            return Expression.Lambda<Func<T, bool>>(Expression.And(expression1.Body, invokedExpression), expression1.Parameters);
        }

        /// <summary>
        /// 排除重复数据.
        /// </summary>
        /// <typeparam name="TSource"></typeparam>
        /// <typeparam name="TKey"></typeparam>
        /// <param name="source">集合.</param>
        /// <param name="keySelector">排重表达式.</param>
        /// <returns></returns>
        /// 创建者：王宇
        /// 创建日期：9/1/2014 10:28 AM
        /// 修改者：
        /// 修改时间：
        /// ------------------------------------
        public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
        {
            var seenKeys = new HashSet<TKey>();
            return source.Where(element => seenKeys.Add(keySelector(element)));
        }
    }
}