How to call a stored JavaScript in MongoDb from C#

Question

I'm evaluating the porting of SQL Server database to MongoDb.

The problem is moving stored procedures, I read about MongoDb stored JavaScript and I would like make some test in in .Net. I've installed MongoDb driver 2.4.0 and created this function on MongoDb named test_function:

function (x) 
{
  return x;
}

This is the code I use to try to invoke that function:

MongoClient oMongoClient = new MongoClient(Properties.Settings.Default.MongoCN);
IMongoDatabase oMongoDatabase = oMongoClient.GetDatabase("test_db");
var result = oMongoDatabase.RunCommand<BsonDocument>("test_function(3)");

I get this error:

An unhandled exception of type 'System.FormatException' occurred in MongoDB.Bson.dll Additional information: JSON reader was expecting a value but found 'test_function'.

Community · Accepted Answer · 2017-05-23 11:54:28Z

3

The exact same question was here: MongoDB db.runCommand() from C#

My first answer was there, but I think, it's better to do here.

I think you could call with this code:

var doc = new BsonDocument(new Dictionary<string, string> { { "test_function", "3" }});
var command = new BsonDocumentCommand<int>(doc);
var result = db.RunCommand(command );

But, as you could see here, it is really not recommended to use stored procedures this way.

I have found another solution here:

https://gist.github.com/jamesikanos/b5897b1693b5c3dd1f87

With this snippet, you could call your function this way:

db.EvalAsync("test_function(2)").Result

edited May 23, 2017 at 11:54

CommunityBot

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answered Dec 7, 2016 at 14:19

Maksim Simkin

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3 Comments

FDB Over a year ago

thanks, it still throws exception: An unhandled exception of type 'MongoDB.Driver.MongoCommandException' occurred in MongoDB.Driver.Core.dll Additional information: Command test_function failed: no such cmd: test_function.

Maksim Simkin Over a year ago

got the same exception. Sorry, i have found another way of doing it, see update of the answer.

FDB Over a year ago

eval and EvalAsync has been removed in 2.4.0 driver. I Think it is impossible to call a stored js from the client. Also there's no way to migrate sql server storted procedures to Mongo. My evaluation is ended, i realized it is impossible.

shA.t · Accepted Answer · 2016-12-19 12:53:20Z

0

I think you can use this way to run a stored script:

var cmd = new JsonCommand<BsonDocument>("{ eval: \"test_function(2)\" }");
var result = db.RunCommand(cmd);

But result is in BsonDocument to get the correct result you can use this methods:

var intResult = result["retval"].ToInt32();

answered Dec 19, 2016 at 12:53

shA.t

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2 Comments

FDB Over a year ago

when the function return a number it works fine. Now i want to try to return a document's list. i changed test_function to this: function (x,y) { return db.MyDB.find({_id:1}); } running into mongo shell it return one document. but from dotnet it does not work.

shA.t Over a year ago

@FDB AFAIK you can't get results of database commands in this way in C#, please ask another question for that and I hope someone answers it ;).

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