LINQ动态查询类--[DynamicLinqExpressions]

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

namespace Test
{
    /// <summary>
    /// 一個老外寫的擴充Expression方法的靜態類別,可以解決上面冗長的程式碼
    /// </summary>
    public static class DynamicLinqExpressions//注意static靜態型別
    {
        public static Expression<Func<T, bool>> True<T>() { return f => true; }
        public static Expression<Func<T, bool>> False<T>() { return f => false; }

        //注意this
        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1,
                                                            Expression<Func<T, bool>> expr2)
        {
            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
            return Expression.Lambda<Func<T, bool>>
                  (Expression.Or(expr1.Body, invokedExpr), expr1.Parameters);
        }

        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1,
                                                             Expression<Func<T, bool>> expr2)
        {
            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
            return Expression.Lambda<Func<T, bool>>
                  (Expression.And(expr1.Body, invokedExpr), expr1.Parameters);
        }
    }
}

使用示例：

SchoolContainer school = new SchoolContainer();
            var eps = DynamicLinqExpressions.True<Teacher>();
            eps.And(T=>T.Name.Contains("1"));
            var ss = school.Teacher.Where(T => T.Name.Contains("PM")).Where(eps);
            foreach (var item in ss)
            {
                Console.WriteLine(item.Name);
            }