Question

MongoDB比我想象的更难！我尝试了各种版本的if-exists-replace-else-insert以及各种功能和选项。它应该很容易，不应该吗？

我个人认为以下内容应该有效。

var collection = storageClient.GetCollection<Observer>("observers");
await collection.Indexes.CreateOneAsync(Builders<Observer>.IndexKeys.Ascending(_ => _.MyId), new CreateIndexOptions { Unique = true });

foreach (var observer in _observers)
{
     observer.Timestamp = DateTime.Now;

     var res = await collection.FindAsync(o => o.MyId == observer.MyId);
     if (res==null ||res.Current == null) {
         await collection.InsertOneAsync(observer); //Part 1, fails 2nd time solved with res.MoveNextAsync()
     } 
     else
     {
            observer.ID = res.Current.Single().ID;
            var res2 = await collection.ReplaceOneAsync(o=>o.MyId==observer.MyId, observer);

            var res3 = await collection.FindAsync(o => o.MyId == observer.MyId);
            await res3.MoveNextAsync();
            Debug.Assert(res3.Current.Single().Timestamp == observer.Timestamp); //Part 2, Assert fails.
     }
}

观察者看起来大致如下：

public class Observer : IObserver
{
    [BsonId]
    public Guid ID { get; set; }

    public int MyId { get; set; }

    public DateTime Timestamp { get; set; }
}

我第二次用完全相同的集合运行它，我意外得到：

E11000 duplicate key error index: db.observers.$MyId_1  dup key: { : 14040 }

编辑：

添加原始第二部分代码：替换。

编辑2：

现在我的代码看起来像这样。仍然失败。

var collection = storageClient.GetCollection<Observer>("gavagai_mentions");
    await collection.Indexes.CreateOneAsync(Builders<Observer>.IndexKeys.Ascending(_ => _.MyID), new CreateIndexOptions { Unique = true });
    foreach (var observer in _observers)
    {
    observer.Timestamp = DateTime.Now;

    // Create a BsonDocument version of the POCO that we can manipulate
    // and then remove the _id field so it can be used in a $set.
    var bsonObserver = observer.ToBsonDocument();
    bsonObserver.Remove("_id");

    // Create an update object that sets all fields on an insert, and everthing
    // but the immutable _id on an update.
    var update = new BsonDocument("$set", bsonObserver);
    update.Add(new BsonDocument("$setOnInsert", new BsonDocument("_id", observer.ID)));

    // Enable the upsert option to create the doc if it's not found.
    var options = new UpdateOptions { IsUpsert = true };
    var res = await collection.UpdateOneAsync(o => o.MyID == observer.MyID,
                          update, options);


    var res2 = await collection.FindAsync(o => o.MyID == observer.MyID);
    await res2.MoveNextAsync();
    Debug.Assert(res2.Current.Single().Timestamp == observer.Timestamp); //Assert fails, but only because MongoDB stores dates as UTC, or so I deduce. It works!!
    }

Answer 1

如果文档尚不存在，可以使用IsUpsert选项创建文档，然后使用UpdateOneAsync以原子方式执行此操作。

foreach (var observer in _observers)
{
    // Create a BsonDocument version of the POCO that we can manipulate
    // and then remove the _id field so it can be used in a $set.
    var bsonObserver = observer.ToBsonDocument();
    bsonObserver.Remove("_id");

    // Create an update object that sets all fields on an insert, and everthing
    // but the immutable _id on an update.
    var update = new BsonDocument("$set", bsonObserver);
    update.Add(new BsonDocument("$setOnInsert", new BsonDocument("_id", observer.ID)));

    // Enable the upsert option to create the doc if it's not found.
    var options = new UpdateOptions { IsUpsert = true };    
    var res = await collection.UpdateOneAsync(o => o.MyId == observer.MyId,
                                              update, options);
}

Answer 2

好吧，自从我使用游标以来，已经很长时间了。

if's

帮助。

这个东西对谷歌来说并不难，但事实是，我失败了，所以我要提出这个问题。

如果您对第二部分https://stackoverflow.com/questions/32586064/replace-poco-with-mongodb-net-driver-2有答案，那么我真的很想在此发布，那么我很高兴两个人编辑问题。

正如评论中指出的那样，信息实际上可以在文档http://mongodb.github.io/mongo-csharp-driver/2.0/reference/driver/crud/reading/#finding-documents中找到。

使用MongoDB .Net驱动程序查找POCO

2 个答案: