如何从 MongoDB MVC 列表中选择一个对象答案

【问题标题】：How do I select an object from a list MongoDB MVC如何从 MongoDB MVC 列表中选择一个对象
【发布时间】：2021-06-11 00:15:12
【问题描述】：

我有以下数据结构：

[
  {
    "id": "604ab2c4a568b9181987c9eb",
    "name": "Paul",
    "eventDate": "2021-03-12T00:16:03.672Z",
    "created": "2021-03-12T00:16:03.673Z",
    "images": [
      {
        "id": "604ab2c3a568b9181987c603",
        "name": "DSC_0",
        "url": "https://picsum.photos/300/300",
        "isSelected": true
      },
      ...
    ]
  },
  {
    "id": "604ab3889c5ac2289b450e3c",
    "name": "Paul",
    "eventDate": "2021-03-12T00:16:03.672Z",
    "created": "2021-03-12T00:16:03.673Z",
    "images": [
      {
        "id": "604ab3879c5ac2289b450a54",
        "name": "DSC_0",
        "url": "https://picsum.photos/300/300",
        "isSelected": true
      },
      ...
    ]
  },
  ...
]

我试图通过用户 ID 和图像 ID 获取图像，但由于某种原因我不能

var filter = Builders<Client>.Filter.Eq("Id", "604ab2c4a568b9181987c9eb");
filter &= Builders<Client>.Filter.ElemMatch(u => u.Images,t => t.Id == "604ab2c3a568b9181987c603");
return _client.Find(filter).FirstOrDefault();

这将返回所有 ID 为“604ab2c4a568b9181987c9eb”的文档，但我只想接收 ID 为“604ab2c3a568b9181987c603”的图像

这里是对象的模型：

public class Client
{
    [BsonId]
    [BsonRepresentation(BsonType.ObjectId)]
    public string Id { get; set; }

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

    [BsonElement("eventDate")]
    [BsonDateTimeOptions]
    public DateTime EventDate { get; set; }

    [BsonElement("created")]
    [BsonDateTimeOptions]
    public DateTime Created { get; set; }

    [BsonElement("images")]
    public List<Image> Images { get; set; }
}

public class Image
{
    [BsonId]
    [BsonRepresentation(BsonType.ObjectId)]
    public string Id { get; set; }

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

    [BsonElement("url")]
    [DataType(DataType.ImageUrl)]
    public string Url { get; set; }

    [BsonElement("isSelected")]
    public bool IsSelected { get; set; }
}

所以我想知道如何修复我的代码，让它只给我一张图片，或者来自我正在搜索的用户的多张图片。

最后但同样重要的是，我想知道我是否可以更改 isSelected 值，即使我使用相同的过滤器。

【问题讨论】：

你试过了吗？ var filter = Builders.Filter.Eq("images.Id", "604ab2c4a568b9181987c9eb");
@tyrion 这个过滤器返回 null...

标签： c# asp.net-mvc mongodb mongodb-.net-driver

【解决方案1】：

您只想使用投影来请求具有给定 ID 的特定图像。所以查询看起来像>

var client = new MongoClient();
var database = client.GetDatabase("test");
var collection = database.GetCollection<Client>("clients");
//collection.InsertOne(new Client
//{
//    Created = DateTime.Now,
//    EventDate = DateTime.Now,
//    Name = "myClient",
//    Images = new List<Image>
//    { 
//        new Image
//        {
//            Id = ObjectId.GenerateNewId(DateTime.Now).ToString(),
//            Name = "Image1",
//            IsSelected = true,
//            Url = "myUrl1"
//        }, 
//        new Image
//        {
//            Id = ObjectId.GenerateNewId(DateTime.Now).ToString(),
//            Name = "Image2",
//            IsSelected = true,
//            Url = "myUrl2"
//        }
//    }
//});
var filter = Builders<Client>.Filter.Eq("Id", "605a60a76b25fefcc3b1bc00");
var imageFilter = Builders<Image>.Filter.Eq("Id", "605a60a76b25fefcc3b1bbff");
var projection = (ProjectionDefinition<Client, Client>)Builders<Client>.Projection.ElemMatch("Images", imageFilter);
var image = collection.Find(filter).Project(projection).FirstOrDefault() // here you have the specific client with only the right Image in the Images. Other props are default.
  ?.Images?[0]; // selecting the only Image in the list.

抱歉，更新部分没那么简单。采取完全不同的方法>

var filter = Builders<Client>.Filter.Eq(x => x.Id, "605a60a76b25fefcc3b1bc00");
var update = Builders<Client>.Update.Set("images.$[f].isSelected", false);
var arrayFilters = new[]
{
    new BsonDocumentArrayFilterDefinition<BsonDocument>(
        new BsonDocument("f._id", BsonObjectId.Create("605a60a76b25fefcc3b1bbff")))
};
collection.UpdateOne(filter, update, new UpdateOptions { ArrayFilters = arrayFilters });

大部分取自https://kevsoft.net/2020/03/23/updating-arrays-in-mongodb-with-csharp.html

【讨论】：