Deserialize nested & unstructured BsonDocument (mongodb c# driver)

Question

Let's say this is a collection of 2 Bson documents

{
    "_id": "...",
    "name": "Test1",
    "sub": {
        "street": "134 Fake Street",
        "city": "NoWhere"
    }
},
{
    "_id": "...",
    "name": "Test2",
    "sub": {
        "height": "10",
        "width": "20",
        "sub2": {
            "type": "something"
        }
    }
}

where the first level is a structured class but sub-levels can be completely unstructured and can have further nested documents several levels deep.

How can I deserialize this document to a C# class? All samples I have seen assume some structure in nested documents.

The following class gives an error:

public class Report
{
    [BsonId]
    public ObjectId _id { get; set; }

    public string name { get; set; }

    public BsonDocument sub { get; set; }
}

Type 'MongoDB.Bson.BsonString' with data contract name '...' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.

EDIT

What I'm trying to do might be complete non-sense. Is it a better idea to just use one BsonDocument and handle everything manually without a structured class?

try using a dynamic keyword.This way your unstructured data will be mapped to a complementing c# object at run time.msdn.microsoft.com/en-us/library/dd264736.aspx — Akshat Jiwan Sharma
– Akshat Jiwan Sharma, Commented Oct 9, 2012 at 11:18
I don't think dynamic is properly supported by the official driver yet. I've battled this problem myself too, but I came to the conclusion that my documents weren't as ad-hoc as I thought. Can you describe what schema variances you have? Or is it simply that your documents are uneven. The difference being that schema variances would mean a totally different structure (different types) whereas uneven might just mean there are sparse documents. Is it possible for instance to describe the uber-document that is a superset of all variants? I also use Dictionary<,> a lot for completely variable objs — cirrus
– cirrus, Commented Oct 9, 2012 at 12:38
The problem is I can only define the first level structure, but none of the nested objects. Reason is that each user can define their own document structure and will have a collection of several "document-templates". So strongly typed objects are definitely out. I'm new to C#, but it seems to me Dictionary is also out because it's still structured. — Benjamin E.
– Benjamin E., Commented Oct 10, 2012 at 3:35
Anyway, I feel I'm asking the wrong question. Maybe I should not even try to map anything, but just use a BsonDocument or JsonSerializer. What I have to do with the Json structure is 1. consolidate/split json objects from different mongodb collections 2. CRUD via http-api 3. Different scheduled processes that run queries on the mongodb — Benjamin E.
– Benjamin E., Commented Oct 10, 2012 at 3:37

Yusuf Arapoglu · Accepted Answer · 2023-04-10 18:34:37Z

3

I don't think the error message you are getting is from the C# driver. Can you please provide a stack trace?

I've tried to reproduce your issue but it works fine with my test program.

The document inserted by the above test program looks like this:

> db.test.find()
{ "_id" : ObjectId("5075fc6ee447ad1354c1f018"), "name" : "John Doe", "sub" : { "x" : 1, "y" : 2 } }
>

edited Apr 10, 2023 at 18:34

Yusuf Arapoglu

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answered Oct 10, 2012 at 22:55

Robert Stam

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2 Comments

Benjamin E. Over a year ago

Thanks Robert! You are right, the problem was not the de-serialization to the class, which works fine, but probably the content negotiation of WebAPI. If I change my controller to return a string instead of the class, it works. I suppose the api cannot handle content negotiation with the type BsonDocument. My new problem is that without content negotiation I get a "double-processed" json string which looks like this: "{ \"_id\" : ObjectId(\"50768abb1934070e98030647\"), \"

Benjamin E. Over a year ago

Will start a new question, I think you answered it so far

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