Using the mongo C# driver, how to serialize an array of custom object in order to store it?

Question

I have a product document that contains an array of documents. For example

{
 id: 1,
 name: "J-E-L-L-O",
 store:[{id: 1,
    name: "Store X"},
    {id: 2,
    name: "Store Y"}]
}

I would like to change the name of "Store Y" to Store Z", for instance. At the time, I don't know the index of the object. So, I pull the entire array, find the object to update, change the name, and then attempt to set the value of "store" with the updated array.

productCollection.Update(query, Update.Set("store", storeList.ToBsonDocument()));

However, I am getting an error: "An Array value cannot be written to the root level of a BSON document."

I think I just need to know how to serialize the array of custom objects to an array of BsonDocuments.

Thanks in advance for your help.

JustinN · Accepted Answer · 2012-08-22 15:24:25Z

9

Unfortunately I had the same problem and ended up making an extension method to help me get around it.

    public static BsonArray ToBsonDocumentArray(this IEnumerable list)
    {
        var array = new BsonArray();
        foreach (var item in list)
        {
            array.Add(item.ToBson());
        }
        return array;
    }

so you should be able to do:

productCollection.Update(query, Update.Set("store", storeList.ToBsonDocumentArray()));

answered Aug 22, 2012 at 15:24

JustinN

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3 Comments

Dheeraj Palagiri Over a year ago

When I use the extension method that u mentioned i get the below error like: A String value cannot be written to the root level of a BSON document. Any Ideas?

Sunny Sharma Over a year ago

I guess this strictly applies to BsonArray type

JustinN Over a year ago

@SunnySharma 6 years ago when I wrote that reply, it was quite specifically to the BsonArray type, yes. However I cannot answer for what the state of affairs with MongoDb may be today.

Gates VP · Accepted Answer · 2012-04-03 00:39:55Z

2

The exception says that you cannot convert an array/list into a BsonDocument. I think that you are looking to convert storeList to a [BsonArray][1].

If storeList is already an array of BsonDocument or some IEnumerable<T> where to can be converted to a BsonDocument, the you should not need to cast the storeList variable at all.

answered Apr 3, 2012 at 0:39

Gates VP

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1 Comment

JalapenoHottie Over a year ago

It's a Generic List of custom objects, so List<T>. Do I have to convert each element to a BsonDocument then put it in an array?

jack-london · Accepted Answer · 2013-11-13 08:21:18Z

1

you should use

BsonDocument.Parse(storeList);

instead of

storeList.ToBsonDocument()

answered Nov 13, 2013 at 8:21

jack-london

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1 Comment

Christopher Bonitz Over a year ago

No, you cant use Parse since it is used on strings, not lists or other objects.

Dheeraj Palagiri · Accepted Answer · 2014-06-19 08:40:59Z

1

Little edit for the accepted answer function:

public static BsonArray ToBsonDocumentArray(this IEnumerable list)
    {
        var array = new BsonArray();
        foreach (var item in list)
        {
            array.Add(item);
        }
        return array;
    }

we don't need to convert item.ToBson(). There is already an implicit conversion from string to bson.Thats the reason i was getting an error message "A String value cannot be written to the root level of a BSON document."

answered Jun 19, 2014 at 8:40

Dheeraj Palagiri

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1 Comment

Sunny Sharma Over a year ago

for me it says - "cannot convert from "object" to "MongoDB.Bson.BsonValue" at line #6 (array.Add(item))!

Aditya Gupta · Accepted Answer · 2024-08-22 12:27:15Z

One way to do this creating the class structure:

public class StoreBrand
{
    [BsonId]
    public int StoreCollectionId {get;set;} // 1
    public string Name {get;set;} // J-E-L-L-O
    public IEnumerable<Store> Stores {get;set;}
}

public class Store
{
    public int StoreId {get;set;} // 1, 2
    public string Name {get;set;} //Store X, Store Y
}


//generic way to insert into MongoDb
public class MongoDBService
{
    IMongoDatabase _database;
    public class MongoDBService(IMongoDatabase database)
    {
        _database = database;
    }
    public class Insert<T>(T entry)
    {
        //Change the collection name as needed
        string collectionName = typeof(T).Name;
        _database.GetCollection<T>(collectionName).InsertOne(entry);
    }    
}

public class Main //Your desired entry point
{
    var store = new Store(); //Create your list of stores
    var storeBrandObject = new StoreBrand(); //Insert list into Store Brand.

    var db = new MongoDbService(/*Inject your IMongoDatabase*/);
    db.Insert<StoreBrand>(storeBrandObject); //This will transform the data
}

Adjust as needed.

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