在C＃中使用动态或表达式 [英] Using Dynamic Or Expressions in C#

问题描述

  public static IQueryable< T> MyFilter< T>（此IQueryable< T>可查询）其中T：class，IModel 
 {
 var someIds = new int [] {1,2,3,4,5}; 
 var userId = 2; 
 
表达式< Func< T，bool>>> predicate1 = e => someIds.Contains（e.Id）; 
表达式< Func< T，bool>>> predicate2 = e => e.UserId ==用户id; 
表达式< Func< T，bool>>>谓词3 = e => e.CreatedDate！= null; 
 
 var pred1 = Expression.Lambda< Func< T，bool>>（System.Linq.Expressions.Expression.Or（predicate1，predicate2））; 
 var pred2 = Expression.Lambda< Func< T，bool>>（System.Linq.Expressions.Expression.Or（pred1，predicate3））; 
 
 
 var result = queryable 
 .Where（pred2）; 
 
返回结果; 
} 
  

IModel 像这样：

 公共界面IModel {
 int Id {get;组; } 
 int UserId {get;组; } 
 DateTime？ CreatedDate {get;组; } 
} 
  

但是我收到这个错误：

二进制运算符或未定义为类型'System.Func 2 [AnyClass，System.Boolean]'和'System.Func 2 [AnyClass，System.Boolean]'。

在这一行：

  var pred1 = Expression.Lambda&FunC< T，bool>>（System.Linq.Expressions.Expression.Or（predicate1，predicate2））; 
  

如何解决这个问题？

预先感谢任何帮助

解决方案

您可以创建一个没有Expression.Or的谓词：

  public static IQueryable< T> MyFilter< T>（此IQueryable< T可查询）其中T：class，IModel 
 {
 var someIds = new int [] {1,2,3,4,5}; 
 var userId = 2; 
 
 var result = queryable 
 .Where（e => someIds.Contains（e.Id）|| e.UserId == userId || e.CreatedDate！= null）; 
 
返回结果; 
} 
  

I use the dynamic filter in my program like following solution:

public static IQueryable<T> MyFilter<T>(this IQueryable<T> queryable) where T : class ,IModel
{
        var someIds = new int[]{1,2,3,4,5};
        var userId = 2;

        Expression<Func<T, bool>> predicate1 = e => someIds.Contains(e.Id);
        Expression<Func<T, bool>> predicate2 = e => e.UserId==userId;
        Expression<Func<T, bool>> predicate3 = e => e.CreatedDate != null;

        var pred1 = Expression.Lambda<Func<T, bool>>(System.Linq.Expressions.Expression.Or(predicate1, predicate2));
        var pred2 = Expression.Lambda<Func<T, bool>>(System.Linq.Expressions.Expression.Or(pred1, predicate3));


        var result = queryable
            .Where(pred2);

        return result;
    }

The IModel is like this:

Public interface IModel{
   int Id { get; set; }
   int UserId { get; set; }
   DateTime? CreatedDate { get; set; }
}

but, I get this error:

The binary operator Or is not defined for the types 'System.Func2[AnyClass,System.Boolean]' and 'System.Func2[AnyClass,System.Boolean]'.

at this line:

var pred1 = Expression.Lambda<Func<T, bool>>(System.Linq.Expressions.Expression.Or(predicate1, predicate2));

How can I solve this problem?

beforehand appreciate any help

解决方案

You can create one predicate without Expression.Or:

public static IQueryable<T> MyFilter<T>(this IQueryable<T> queryable) where T : class ,IModel
    {
        var someIds = new int[] { 1, 2, 3, 4, 5 };
        var userId = 2;

        var result = queryable
            .Where(e => someIds.Contains(e.Id) || e.UserId == userId || e.CreatedDate != null);

        return result;
    }

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