c# Expression 擴展

一、簡介

當查詢比較復雜時，需要很多判斷或者跨方法傳遞參數時使用

二、擴展類

 
            
           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.關於引用

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("陳"));
            pre = pre.And(s => s.CompanyId == "1");

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