Entity Framework底层操作封装V2版本号（3）

如今是附加的，组合查询须要的扩展类。大家知道lanmda表达式的组合条件比較麻烦，所以就加了一样一个类，方便进行组合查询：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;
namespace JFrame.AccessCommon
{
    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;
        }
        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.Cast<Expression>());
            return Expression.Lambda<Func<T, bool>>(Expression.Or(expression1.Body, invokedExpression), expression1.Parameters);
        }
        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.Cast<Expression>());
            return Expression.Lambda<Func<T, bool>>(Expression.And(expression1.Body, invokedExpression), expression1.Parameters);
        }
    }
}