Question

如何返回依赖于fields参数的匿名类型，其中列出了必须包含在匿名类型中的属性？任务实体拥有20多个属性，客户希望获得不同的属性组合。

public class Test
{
    public class Task
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }
        //... more 20 properties
    }

    public List<Task> Tasks = new List<Task>();

    public Test()
    {
        Tasks.Add(new Task { Id = 1, Name = "Task #1", Description = "Description task #1" });
        Tasks.Add(new Task { Id = 2, Name = "Task #2", Description = "Description task #2" });
        Tasks.Add(new Task { Id = 3, Name = "Task #3", Description = "Description task #3" });
    }

    public IEnumerable<object> GetAllTasks(string fields)
    {
        //if fields == 'Id,Name' then return anonymous type new { Id = t.Id, Name = t.Name }
        return Tasks.Select(t => new { Id = t.Id, Name = t.Name });

        //if fields == 'Id,Name,Description' then return anonymous type new { Id = t.Id, name = t.Name, Description = t.Description }
        return Tasks.Select(t => new { Id = t.Id, Name = t.Name, Description = t.Description });
    }
}

Answer 1

我希望它能帮到你

public List<Task> Tasks = new List<Task>();

public void Test()
{
    Tasks.Add(new Task { Id = 1, Name = "Task #1", Description = "Description task #1" });
    Tasks.Add(new Task { Id = 2, Name = "Task #2", Description = "Description task #2" });
    Tasks.Add(new Task { Id = 3, Name = "Task #3", Description = "Description task #3" });
}

public ActionResult Index()
{
    Test();

    return Json(GetAllTasks(), JsonRequestBehavior.AllowGet);
}

public IEnumerable<object> GetAllTasks()
{
    return Tasks.Select(GetTask);
}

private object GetTask(Task task)
{
    dynamic expandoObject = new ExpandoObject();
    //your if statment block
    if (task.Id == 1)
    {
        expandoObject.Id = task.Id;
    }

    expandoObject.Name = task.Name;
    expandoObject.Description = task.Description;

    var dictionary = expandoObject as IDictionary<string, object>;
    return dictionary.ToDictionary(item => item.Key, item => item.Value);
}

查看结果：

[
   [
      {
         "Key":"Id",
         "Value":1
      },
      {
         "Key":"Name",
         "Value":"Task #1"
      },
      {
         "Key":"Description",
         "Value":"Description task #1"
      }
   ],
   [
      {
         "Key":"Name",
         "Value":"Task #2"
      },
      {
         "Key":"Description",
         "Value":"Description task #2"
      }
   ],
   [
      {
         "Key":"Name",
         "Value":"Task #3"
      },
      {
         "Key":"Description",
         "Value":"Description task #3"
      }
   ]
]

Answer 2

您可以尝试使用ExpandoObject和System.Reflection：

public IEnumerable<object> GetAllTasks(string[] fields)
{
    List<object> response = new List<object>();
    Tasks.ForEach((a) =>
    {
        dynamic expando = new ExpandoObject();
        var p = expando as IDictionary<String, object>;
        foreach (string item in fields)
        {
            p[item] = a.GetType().GetProperty(item).GetValue(a);
        }
        response.Add(expando);
    });
    return response;
}

示例用法是：

static void Main(string[] args)
{
    var test = new Test();
    var results = test.GetAllTasks(new[] { "Id"});
    foreach (var result in results)
    {
        Console.WriteLine((result as dynamic).Id);
    }

    results = test.GetAllTasks(new[] { "Name", "Description" });
    foreach (var result in results)
    {
        var dynamicResult=result as dynamic;
        Console.WriteLine("{0} {1}", dynamicResult.Name, dynamicResult.Description);
        // The following line will throw an exception
        //Console.WriteLine((result as dynamic).Id);
    }
}

Answer 3

在这种情况下，如果Tasks是IQueryable<Task>并且我们需要从数据源（例如，从数据库）收紧，那么只有那些客户端必需的列（不要使DB服务器过载），在那里很有用是SelectDynamic方法。因此，完成的决定将在这里：

public class Test
{
    public class Task
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }
        //... more 20 properties
    }

    public IQueryable<Task> Tasks;

    public Test()
    {
        Tasks = new List<Task>
            {
                new Task {Id = 1, Name = "Task #1", Description = "Description task #1"},
                new Task {Id = 2, Name = "Task #2", Description = "Description task #2"},
                new Task {Id = 3, Name = "Task #3", Description = "Description task #3"}
            }.AsQueryable();
    }

    public IEnumerable<object> GetAllTasks(string[] fields)
    {
        var response = new List<object>();
        var customTasks = Tasks.SelectDynamic(fields).Cast<dynamic>();
        foreach (var t in customTasks.Take(100))
        {
            dynamic expando = new ExpandoObject();

            if (fields.Contains("Id")) expando.Id = t.Id;
            if (fields.Contains("Name")) expando.Name = t.Name;
            if (fields.Contains("Description")) expando.Description = t.Description;
            // ... other properties

            response.Add(expando);
        }
        return response;
    }
}

示例用法为here

如何返回自定义匿名类型？

3 个答案: