C# MongoDb - Using ElemMatch to check if array contains item

Question

I have a DTO that contains a string array field AccountIds. I want to check if a given string AccountId is contained within this array.

I tried using the ElemMatch filter to achieve this like so:

var accountId = "04935ec9ecf94eb5b57ac9b2957bfb9a";
var filter = Builders<MapDto>.Filter.ElemMatch(x => x.AccountIds, accountId);
var result = await _collection.Find(filter).ToListAsync();

This is how my document looks like:

{
    "_id" : ObjectId("62c1628a39094e414593c8c7"),
    "AccountIds" : [ 
        "04935ec9ecf94eb5b57ac9b2957bfb9a"
    ]
}

However, the following exception is thrown, and I'm not sure why.

System.FormatException: Invalid JSON number '04'.
   at MongoDB.Bson.IO.JsonScanner.GetNumberToken(JsonBuffer buffer, Int32 firstChar)
   at MongoDB.Bson.IO.JsonScanner.GetNextToken(JsonBuffer buffer)
   at MongoDB.Bson.IO.JsonReader.PopToken()
   at MongoDB.Bson.IO.JsonReader.ReadBsonType()
   at MongoDB.Bson.IO.BsonReader.GetCurrentBsonType()
   at MongoDB.Bson.Serialization.Serializers.SerializerBase`1.EnsureBsonTypeEquals(IBsonReader reader, BsonType bsonType)
   at MongoDB.Bson.Serialization.Serializers.BsonValueSerializerBase`1.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
   at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer`1 serializer, BsonDeserializationContext context)
   at MongoDB.Bson.BsonDocument.Parse(String json)
   at MongoDB.Driver.JsonFilterDefinition`1.Render(IBsonSerializer`1 documentSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.ElementMatchFilterDefinition`2.Render(IBsonSerializer`1 documentSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.AndFilterDefinition`1.Render(IBsonSerializer`1 documentSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.MongoCollectionImpl`1.CreateFindOperation[TProjection](FilterDefinition`1 filter, FindOptions`2 options)
   at MongoDB.Driver.MongoCollectionImpl`1.FindAsync[TProjection](IClientSessionHandle session, FilterDefinition`1 filter, FindOptions`2 options, CancellationToken cancellationToken)
   at MongoDB.Driver.MongoCollectionImpl`1.<>c__DisplayClass47_0`1.<FindAsync>b__0(IClientSessionHandle session)
   at MongoDB.Driver.MongoCollectionImpl`1.UsingImplicitSessionAsync[TResult](Func`2 funcAsync, CancellationToken cancellationToken)
   at MongoDB.Driver.IAsyncCursorSourceExtensions.ToListAsync[TDocument](IAsyncCursorSource`1 source, CancellationToken cancellationToken)

score 0 · Answer 1 · answered Jul 03 '22 at 13:09

0

You dont need to use elemMatch when you search for single entry in array , you can do easily via:

   db.collection.find({"AccountIds":"04935ec9ecf94eb5b57ac9b2957bfb9a"})

or in C#:

  Builders<MapDto>.Filter.Eq(x => x.AccountIds, accountId)

answered Jul 03 '22 at 13:09

R2D2

9,410
2
12
28

Thank you, however, is the `ElemMatch` not valid in this case? Also, using `Eq` gives me the following error: `Cannot convert lambda expression to type 'FieldDefinition' because it is not a delegate type` – Jul 03 '22 at 13:22
maybe check here: https://stackoverflow.com/questions/9549358/cannot-convert-lambda-expression-to-type-system-delegate – R2D2 Jul 03 '22 at 15:47

score 0 · Answer 2 · answered Mar 06 '23 at 07:04

0

Try this instead.

var accountId = "04935ec9ecf94eb5b57ac9b2957bfb9a";
var filter = Builders<MapDto>.Filter.AnyEq(x => x.AccountIds, accountId);
var result = await _collection.Find(filter).ToListAsync();

answered Mar 06 '23 at 07:04

Proshonul Haq Rafa

1

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Mar 10 '23 at 17:25

C# MongoDb - Using ElemMatch to check if array contains item

2 Answers2