如何在 MongoDB.Driver C# 的深度嵌套數組中檢查值是否存在？

Question

如下圖，集合為Posts 。 帖子和評論的_id是已知的。

那么，如何檢查給定值d是否存在於AgreedUserIds中？

Answer 1

試試這個進行單字符搜索：

db.Posts.find(
    {
        _id: "b4d5...ff79",
        Comments: {
            $elemMatch: {
                _id: "c1ea...d45",
                AgreedUserIds: "d"
            }
        }
    }
);

這用於多字符搜索：

db.Posts.find(
    {
        _id: "b4d5...ff79",
        Comments: {
            $elemMatch: {
                _id: "c1ea...d45",
                AgreedUserIds: { $in: ["c", "d"] }
            }
        }
    }
);

Answer 2

如果你想保留它BsonDocument你可以選擇像這樣組合過濾器>

var client = new MongoClient();
var database = client.GetDatabase("test");
var collection = database.GetCollection<BsonDocument>("posts");
var postId = new BsonObjectId(new ObjectId("604b5ff389ff6887d1b91a93"));
var commentId = new BsonObjectId(new ObjectId("604b5ff389ff6887d1b91a92"));
var userId = "a";
//var userId = "e"; // not found
var postIdMatches = Builders<BsonDocument>.Filter.Eq("_id", postId);
var commentIdMatches = Builders<BsonDocument>.Filter.Eq("_id", commentId);
var userIdInside = Builders<BsonDocument>.Filter.AnyEq("AgreedUserIds", userId); // "a" in checking
var commentCheck = Builders<BsonDocument>.Filter.ElemMatch("Comments", userIdInside & commentIdMatches); // & combines filters. Also ElemMatch on any of the Comments is passing the criteria
var rows = (await collection.FindAsync<BsonDocument>(postIdMatches & commentCheck)).ToList(); 

您還可以GetCollection<Post>與 C# Post class 描述郵政業務 object，並使用。任何 Z7FB58B61118DFE38B666Z 查詢。