How to parse ObjectId of dynamic type in .NET MongoDb Driver

Question

Here's my code. DbContext.Resources is IMongoCollection<dynamic> because it's highly unstructured.

var resource = await DbContext.Resources.Find(
  Builders<dynamic>.Filter.Eq("_id", ObjectId.Parse(id))
).SingleAsync();

And the resulting resource object is

[{
  "_id": {
    "timestamp":1487967980,
    "machine":614561,
    "pid":30862,
    "increment":16022269,
    "creationTime":"2017-02-24T20:26:20Z"
  },
  ...
}]

What is the best practice for parsing this _id?

Can i ask this ? are you using BSON library that goes with the c# driver to handle all the ser/deser for you. nuget.org/packages/MongoDB.Bson ? — s7vr
– s7vr, Commented May 22, 2017 at 16:04
The only problem is I have nothing to annotate. The type is dynamic. There is no class. — Matthew James Davis
– Matthew James Davis, Commented May 22, 2017 at 17:16
What is the reason to parse that id? Do you want to use it as primary key for application logic? Don't objects in that collection has own unique keys? — Yura
– Yura, Commented May 23, 2017 at 9:27
for simplicity, why return { _id: { $oid: 'guid' } } when i can just return { _id: 'guid' }. Will there ever be anything else in the object? Why make a complicated api that is obnoxious for developers to use? — Matthew James Davis
– Matthew James Davis, Commented May 23, 2017 at 9:55

Preview · Accepted Answer · 2017-05-24 06:55:48Z

2

+200

There is multiples ways to represent and construct an ObjectId. The object returned from your IMongoCollection corresponds to the actual _id value you're seeing in your database encoded using the constructor that can be seen here and composed of the following fields:

timestamp (int)
machine hash (int)
pid (short)
increment (int)

An ObjectId should implement a ToString method, allowing you to convert the object into its string representation, but if for some reason you can't use it due to your dynamic typing, you can either create a new one with the constructor, or leverage the ObjectId.Pack method, which would allow you to convert back the timestamp, machine, pid and increment into a byte array which can also be used for the ObjectId creation.

answered May 24, 2017 at 6:55

Preview

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2 Comments

Matthew James Davis Over a year ago

Is there a best way for handling this in a query with numerous results. I'm concerned that there will be a significant performance problem if I call .ToString() on 1000 records individually.

Preview Over a year ago

After looking at multiple resources, I would say the recommended way would be to use annotations. Since that's not something possible in your case, I would do a little wrapping function in charge of iterating over your collection and doing ToString on every item. 1000 items is way below the point performance would be an issue.

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