How to read data from Mongodb that have a duplicate element name in C #

Question

I use MongoDB.DriversC # MVC in my application to communicate with the Mongodb database.

C # code

            var client = new MongoClient("mongodb://localhost:27012");
            var db = client.GetDatabase("Test_DB");
            var collection = db.GetCollection<BsonDocument>("TestTable");
            var tData = await collection.FindAsync(new BsonDocument(true)); // I used - new BsonDocument(true)  to specify allow duplicate element name while read data.

MongoDB Data File

In the above image, you can see that I have several columns under the name DuplicateColwith different values. When I tried to read this data in c#using MongoDB.Driver, I got the following error:InvalidOperationException: Duplicate element name 'DuplicateCol'.

By inserting a duplicate element name, I used an AllowDuplicateNames=trueobject BsonDocumentas shown below. (It inserts the name of the repeating element without errors.)

BsonDocument obj = new BsonDocument();
obj.AllowDuplicateNames = true;
obj.Add("DuplicateCol", "Value_One");
obj.Add("propone", "newVal");
obj.Add("DuplicateCol", "Value_Two");
.... // other properties with value 
await collection.InsertOneAsync(obj);

Note: This scheme is required. I can’t change it.

Please provide me suggestions for fixing this problem. Any help would be greatly appreciated.

Thank.

Answer 1

, , , , . :

class AlwaysAllowDuplicateNamesBsonDocumentSerializer : BsonDocumentSerializer {
    protected override BsonDocument DeserializeValue(BsonDeserializationContext context, BsonDeserializationArgs args) {
        if (!context.AllowDuplicateElementNames)
            context = context.With(c => c.AllowDuplicateElementNames = true);
        return base.DeserializeValue(context, args);
    }

    public override BsonDocument Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args) {
        if (!context.AllowDuplicateElementNames)
            context = context.With(c => c.AllowDuplicateElementNames = true);
        return base.Deserialize(context, args);
    }
}

BsonDocument, AllowDuplicateElementNames . , BsonDocument ( BsonDocumentSerializer.Instance ):

// get __instance field, which is backing field for Instance property
var instanceField = typeof(BsonDocumentSerializer).GetField("__instance", BindingFlags.Static | BindingFlags.NonPublic);
// overwrite with our custom serializer
instanceField.SetValue(null, new AlwaysAllowDuplicateNamesBsonDocumentSerializer());

- , .

:

static void Main(string[] args) {
    var instanceField = typeof(BsonDocumentSerializer).GetField("__instance", BindingFlags.Static | BindingFlags.NonPublic);
    instanceField.SetValue(null, new AlwaysAllowDuplicateNamesBsonDocumentSerializer());
    TestMongoQuery();
    Console.ReadKey();
}

static async void TestMongoQuery() {
    var client = new MongoClient();
    var db = client.GetDatabase("Test_DB");            
    var collection = db.GetCollection<BsonDocument>("TestTable");
    using (var allDocs = await collection.FindAsync(FilterDefinition<BsonDocument>.Empty)) {
        while (allDocs.MoveNext()) {
            foreach (var doc in allDocs.Current) {
                var duplicateElements = doc.Elements.Where(c => c.Name == "DuplicateCol");
                foreach (var el in duplicateElements) {
                    Console.WriteLine(el.Name + ":" + el.Value);
                }
            }
        }
    }
}

Answer 2

,

InvalidOperationException: Duplicate element name 'DuplicateCol'

CodeFuller, MongoDB . , , , MongoDB ... , . , , :

AllowDuplicateNames=true

, , .

, . :

{
    "_id" : ObjectId("xxx"),
    "propTest" : 0,
    ...
    "duplicateCol": [ "Value_Two", "Value_One" ]
}

(duplicateCol), , .