如何使用 TTL 创建 MongoDB 集合？

Question

我创建了一个对象集合

public class User
{
public User(string fullname, string email)
{
Fullname = fullname;
Email = email;
}

    public string Fullname { get; }
    public string Email { get; }
}

并创建索引和一些文档

var collection = _database.GetCollection(“bar”);
collection.Indexes.CreateOne(new CreateIndexModel
(new BsonDocument(“lastModifiedDate”, 1), new CreateIndexOptions { ExpireAfter = new TimeSpan(0, 0, 30) }));

            var user = new User("Vasya", "billgates@ms.com");
            collection.InsertOne(user.ToBsonDocument());
            var user1 = new User("Petya", "Petya@ms.com");
            collection.InsertOne(user1.ToBsonDocument());
            var user2 = new User("Kolya", "Kolya@ms.com");
            collection.InsertOne(user2.ToBsonDocument());
            count = collection.CountDocuments(new BsonDocument());

但是当我看到 http://localhost:8081/db/dbtest/ 然后我看不到任何 TTL 并且文档在 30 秒后不会过期。

我做错了什么？如何使用 TTL 在其中创建集合或文档？

Answer 1

您的用户对象没有您在索引中指定的字段

public class User
{
    public User(string fullname, string email, DateTime lastModifiedDate) 
    {
        Fullname = fullname;
        Email = email;
        LastModifiedDate = lastModifiedDate;
    }

    public string Fullname { get; }
    public string Email { get; }
    public DateTime LastModifiedDate { get; }
}

此外，MongoDB C# 驱动程序中序列化的默认约定不是驼峰式大小写，因此您需要将索引更新为以下内容：

var collection = _database.GetCollection("bar");
collection.Indexes.CreateOne(new CreateIndexModel
(new BsonDocument("LastModifiedDate", 1), new CreateIndexOptions { ExpireAfter = new TimeSpan(0, 0, 30) }));

您可能还希望通过使用用户类型而不是 BsonDocument 来接受 C# 和 MongoDB 驱动程序为您提供的类型安全性。以下是如何执行此操作的示例。

using MongoDB.Driver;

var client = new MongoClient();
var database = client.GetDatabase("test");
var collection = database.GetCollection<User>("users");
await collection.Indexes.CreateOneAsync(
    Builders<User>.IndexKeys.Ascending(x => x.LastModifiedDate),
    new CreateIndexOptions { ExpireAfter = new TimeSpan(0, 0, 30) });

var user = new User("Vasya", "billgates@ms.com", DateTime.UtcNow);
collection.InsertOne(user);
var user1 = new User("Petya", "Petya@ms.com", DateTime.UtcNow);
collection.InsertOne(user1);
var user2 = new User("Kolya", "Kolya@ms.com", DateTime.UtcNow);
collection.InsertOne(user2);

for (var i = 0; i < 10; i++)
{
    var count = await collection.CountDocumentsAsync(Builders<User>.Filter.Empty);
    Console.WriteLine($"Count: {count} @ {DateTime.UtcNow}");
    await Task.Delay(10000);
}


// Count: 4 @ 02/01/2022 11:42:13
// Count: 4 @ 02/01/2022 11:42:23
// Count: 4 @ 02/01/2022 11:42:33
// Count: 4 @ 02/01/2022 11:42:43
// Count: 4 @ 02/01/2022 11:42:53
// Count: 1 @ 02/01/2022 11:43:03
// Count: 1 @ 02/01/2022 11:43:13
// Count: 1 @ 02/01/2022 11:43:23
// Count: 1 @ 02/01/2022 11:43:33
// Count: 0 @ 02/01/2022 11:43:43


public class User
{
    public User(string fullname, string email, DateTime lastModifiedDate)
    {
        Fullname = fullname;
        Email = email;
        LastModifiedDate = lastModifiedDate;
    }

    public string Fullname { get; }
    public string Email { get; }
    public DateTime LastModifiedDate { get; }
}

您可能会注意到文档不会立即被删除，而是如 MongoDB 文档中所述

删除过期文档的后台任务每 60 秒运行一次。因此，在文档到期和后台任务运行之间的时间段内，文档可能会保留在集合中。 https://docs.mongodb.com/manual/core/index-ttl/#timing-of-the-delete-operation