using string for mongodb _id

Question

I have a json document that I entered into my mongo db using the mongoimport command. I set it's _id to "MyDocId", looking at it in mongo, the _id is correctly set. in my C# code, I want to read this document using this _id:

ObjectId id = ObjectId.Parse("MyDocId");

I am getting an exception in the above code

There is a convention which you can try to use I post it in this thread stackoverflow.com/a/65621787/4319938 — SzymonB
– SzymonB, Commented Jan 8, 2021 at 8:17

Community · Accepted Answer · 2017-05-23 11:46:09Z

15

You may need to use a Bson attribute on your property like so.

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

There is quite a good explanation of these attributes in this answered question

BsonId vs BsonRepresentation

edited May 23, 2017 at 11:46

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answered Oct 17, 2016 at 21:59

pieperu

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1 Comment

Gopinath Over a year ago

How does it work with filter query builders? //Not fetching any documents collection.FindAsync(Builders<MyObj>.Filter.Where(x=>x.Id == "stringvalue")) //Gives syntax error (can't company ObjectId & string) collection.FindAsync(Builders<MyObj>.Filter.Where(x=>x.Id == ObjectId.Parse("stringvalue")))

SzymonB · Accepted Answer · 2021-01-08 00:20:11Z

7

Since version 2.9 of MongoDB.Driver you can also use built-in convention StringIdStoredAsObjectIdConvention

        var pack = new ConventionPack
        {
            new StringIdStoredAsObjectIdConvention()
        };

        ConventionRegistry.Register("Custom Convention", pack, t => true);

answered Jan 8, 2021 at 0:20

SzymonB

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Comments

andresk · Accepted Answer · 2016-10-17 20:52:43Z

2

ObjectId parse will only parse strings that have a valid format. In your case, if the document's _id is a string, you don't need to parse it as an ObjectId, just use the string value in your query.

answered Oct 17, 2016 at 20:52

andresk

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2 Comments

Pacman Over a year ago

I create a filter like so: Builders<PropertyHelperLookup>.Filter.Eq("_id", this._docId) and I am getting an exception

andresk Over a year ago

What is the exception?

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