c# Expression 扩展

一、简介

当查询比较复杂时，需要很多判断或者跨方法传递参数时使用

二、扩展类

 
 public static class DynamicLinqExpressions
    {
        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>> 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);
        }
    }

三、如何使用

1.关于引用

using System.Linq;
using System.Linq.Expressions;

2.使用示例

     Expression<Func<User, bool>> pre;
            pre = s => s.NickName.Contains("李");
            pre = pre.Or(s => s.NickName.Contains("陈"));
            pre = pre.And(s => s.CompanyId == "");

            var data = _userRepository.GetAll().AsExpandable().Where(pre);