使用带连接的 linq 查询查询嵌套对象

Question

我从 api 获得以下 json 结构：

    {
    "event_instance": [
        {
            "id": 55551244,
            "event_id": 11112,
            "name": "Brown Belt Karate Class",
            "staff_members": [
                {
                    "id": 12345,
                    "name": "John Smith"
                }

            ],

            "people": [
                {
                    "id": 111,
                    "name": "Jane Doe"
                },
                {
                    "id": 222,
                    "name": "Josh Smith"

                },
                {
                    "id": 333,
                    "name": "Ben Johnson"
                }

            ],
            "visits": [
                {
                    "id": 1234578,
                    "person_id": 111,
                    "state": "completed",
                    "status": "complete"
                },
                {
                    "id": 1239865,
                    "person_id": 222,
                    "state": "completed",
                    "status": "complete"
                },
                {
                    "id": 1239865,
                    "person_id": 333,
                    "state": "canceled",
                    "status": "cancel"
                }
            ]
        }
    ]
}

我正在使用 JSON.NET 将其反序列化为以下 .net 对象：

    [JsonObjectAttribute("event_instance")]
    public class EventInstance
    {
        [JsonPropertyAttribute("id")]
        public int Id { get; set; }

        [JsonPropertyAttribute("event_id")]
        public int EventId { get; set; }

        [JsonPropertyAttribute("name")]
        public string Name { get; set; }

        [JsonPropertyAttribute("staff_members")]
        public List<StaffMember> StaffMembers { get; set; }

        [JsonPropertyAttribute("visits")]
        public List<Visit> Visits { get; set; }

        [JsonPropertyAttribute("people")]
        public List<Student> Students { get; set; }
    } 

    [JsonObjectAttribute("staff_members")]
    public class StaffMember
    {
        [JsonPropertyAttribute("id")]
        public int Id { get; set; }
        [JsonPropertyAttribute("name")]
        public string Name { get; set; }
    }

    [JsonObjectAttribute("people")]
    public class People
    {
        [JsonPropertyAttribute("id")]
        public int Id { get; set; }
        [JsonPropertyAttribute("name")]
        public string Name { get; set; }
    }

    [JsonObjectAttribute("visits")]
    public class Visits
    {
        [JsonPropertyAttribute("id")]
        public int Id { get; set; }
        [JsonPropertyAttribute("person_id")]
        public int PersonId { get; set; }
        [JsonPropertyAttribute("state")]
        public string State { get; set; }
        [JsonPropertyAttribute("status")]
        public string Status { get; set; }
    }

我正在使用以下代码反序列化：

var event = (EventInstance)JsonConvert.DeserializeObject(json, typeof(EventInstance));

以上工作正常，并为我提供了上述 json 结构的准确对象表示。现在我正在尝试将此事件对象查询到 filter/project 到一个新结构，然后我可以将该结构序列化回 json 并向下发送到浏览器。我需要 return 状态为 "completed" 且状态为 "complete" 的学生列表。如您所见，people 数组与 visits 数组相关联（具有 id 和 person_id）。我想生成以下简单输出：

11112，棕带空手道 Class，John Smith，111，Jane Doe
11112，空手道棕带 Class，约翰·史密斯，222，约什·史密斯

我试过这样的事情：

var studentList =   from theClass in event
                    from staff in theClass.StaffMembers
                    from student in theClass.People
                    from visits in theClass.Visits
                    where visits.Status == "complete" 
                    && visits.State == "completed"
                           select new
                           {
                               event_id = theClass.EventId
                               class_name = theClass.Name,
                               instructor_name = staff.Name,
                               student_id = student.Id,
                               student_name = student.Name
                           };



string _data = JsonConvert.SerializeObject(studentList);

这自然会产生重复的学生姓名。我是 linq 的新手。基本上我需要 join/tie people 和 visits 数组，所以我只取回该 ID 的单个学生，以及该事件的根数据。也非常感谢任何关于更好的方法的建议！

Answer 1

诀窍是将学生和访问加入到一个集合中，该集合包含以下两者的数据：

from ei in eventInstances
from sm in ei.StaffMembers
from x in
(from vi in ei.Visits
 join st in ei.Students on vi.PersonId equals st.Id
 select new { vi, st }) // Here you get students and visits side-by-side
select new
{
    ei.EventId,
    Event = ei.Name,
    StaffMemeber = sm.Name,
    PersonId = x.st.Id,
    Student = x.st.Name
}

使用带连接的 linq 查询查询嵌套对象

Querying nested objects using linq query with join

c#

json.net

linq-to-objects