動態的LINQ/LAMBDA過濾

Question

我havea方法，返回式被用於基於客戶需求記錄的動態過濾，我在做的一個問題，我想是這樣的

 public Expression<T> FilterCreator<T>(FilterCondition condition, string columnName, object value) 
    { 

     Expression<Func<Customer, bool>> query; 

     // FilterCondition is an enum flag for conditions 
     if(condition.Condition == ConditionFlags.EQUALS) 
     { 
      // here is the problem, 
      // i want the emailAddress to be dynamic based on the passed columName parameter of the client 
      // and be able to cast its type of the value that was passed 
      query = p => p.EmailAddress == (typeof(p.EmailAddress))value; 

      //i want something like this 
      // query = p => p.(columnName)=> (typeOf(p.(columnName)))value; 

     } 
     else if(condition.Condition == ConditionFlags.CONTAINS) 
     { 
      ..... 
     } 

     return query; 

    } 

任何意見球員？在此先感謝

Answer 1

你需要建立一個表達式樹：

var param = Expression.Parameter<Customer>(); 
p = Expression.LambdaFunc<Customer, bool>(
    Expression.Call(typeof(object), "Equals", null, //non-generic 
        Expression.Property(param, columnName), 
        Expresssion.Constant(value) 
    ) 
);