MongoDB run command with json return

Question

My overall goal is to run a query that shows all the collections with the amount of data / counts and so on.

I found the following command/query and try to run it like this:

MongoClient client = new MongoClient(server);
var db = client.GetDatabase(database);
 
const string mongoQueryA = "var collectionNames = db.getCollectionNames(), stats = []; " +
"collectionNames.forEach(function(n) { stats.push(db[n].stats()); }); " +
"stats = stats.sort(function(a, b) { return b['size'] - a['size']; }); ";
var command = new JsonCommand<BsonDocument>(mongoQueryA);
var test = db.RunCommand<BsonDocument>(command);

And the code fails here. Exceptions:

JSON reader was expecting a value but found 'var'.

My understanding is that this shoul be run as command?

Running the query in Robot T works as expected. Bonus the plan was to return the data in the following format ( Based on Json from running query manualy in Robot T)

 class MongoCollectionInfo
    {
        public string ns { get; set; }

        public long size { get; set; }

        public long count { get; set; }

        public long avgObjSize { get; set; }

        public long storageSize { get; set; }

        public long nindexes { get; set; }

        public long totalIndexSize { get; set; }
    }

Im aware, the question is how do i run this command / Query with the offical MongoDB C# driver. Im clearly lacking some MongoDB knowlage, so im hoping to figure out where i went wrong. — EKS
– EKS, Commented Aug 10, 2020 at 7:55
As it seems, you only need to get collections via C# driver (look around mongodb.github.io/mongo-csharp-driver/2.10/apidocs/html/…) and do anything else in C#. As for the deserialization to MongoCollectionInfo use nuget.org/packages/Newtonsoft.Json — JeffRSon
– JeffRSon, Commented Aug 10, 2020 at 8:12
Im sure i could do: IMongoDatabase.ListCollectionsAsync and then run stats on eatch collection. But that would generate 80 queries instead of 1, im hoping to avoid that. — EKS
– EKS, Commented Aug 10, 2020 at 8:30
You might use db.Eval - however I would do it from C# as it is more maintainable. Do you expect real performance hits? How often do you need it be called? — JeffRSon
– JeffRSon, Commented Aug 10, 2020 at 9:42

Kevin Smith · Accepted Answer · 2020-08-13 18:02:28Z

What you're trying to achieve can be done purely in C# as it looks like what you've attempted to do is send javascript to the server to be executed which is not how commands work.

To start off with we'll need to get a list of all the collections within a database inside the MongoDB instance.

var client = new MongoClient();

var db = client.GetDatabase("test");

var collectionNames = await (await db.ListCollectionNamesAsync()).ToListAsync();

once we've got the collection names (collectionNames) we can then go ask the database for the stats on that collection by issue a command.

var allCollStats = new List<BsonDocument>(collectionNames.Count);
foreach (var name in collectionNames)
{
    var collStatsResult = await db.RunCommandAsync(new BsonDocumentCommand<BsonDocument>(new BsonDocument("collStats", name)));

    allCollStats.Add(collStatsResult);
}

The allCollStats then will hold all the stats for the collections and we can then use it as we see fit

foreach (var collStats in allCollStats)
{
    Console.WriteLine($"ns: {collStats["ns"]}, size: {collStats["size"]}");
}

// ns: test.test, size: 117
// ns: test.people, size: 5092

Also, if you wanted to use a typed result instead of a BsonDocument you can pass this in as the generic agrument to the command.

var collStatsResult = await db.RunCommandAsync(new BsonDocumentCommand<MongoCollectionInfo>(new BsonDocument("collStats", name)));

Console.WriteLine($"ns: {collStatsResult .ns}, size: {collStatsResult .size}");

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