Exporting JSON

The .NET BSON library supports writing JSON documents with the JsonWriter class.

The program below will export all documents from a collection to a file with one document per line.

Given the collection’s contents:

> db.mydata.find()
{ "_id" : ObjectId("5513306a2dfd32ffd580e323"), "x" : 1.0 }
{ "_id" : ObjectId("5513306c2dfd32ffd580e324"), "x" : 2.0 }
{ "_id" : ObjectId("5513306e2dfd32ffd580e325"), "x" : 3.0 }
{ "_id" : ObjectId("551330712dfd32ffd580e326"), "x" : 4.0 }

And the program:

using MongoDB.Bson;
using MongoDB.Bson.IO;
using MongoDB.Bson.Serialization;
using MongoDB.Driver;

// ...

string outputFileName; // initialize to the output file
IMongoCollection<BsonDocument> collection; // initialize to the collection to read from

using (var streamWriter = new StreamWriter(outputFileName))
{
    await collection.Find(new BsonDocument())
        .ForEachAsync(async (document) =>
        {
            using (var stringWriter = new StringWriter())
            using (var jsonWriter = new JsonWriter(stringWriter))
            {
                var context = BsonSerializationContext.CreateRoot(jsonWriter);
                collection.DocumentSerializer.Serialize(context, document);
                var line = stringWriter.ToString();
                await streamWriter.WriteLineAsync(line);
            }
        });
}

The output file should look this:

{ "_id" : ObjectId("5513306a2dfd32ffd580e323"), "x" : 1.0 }
{ "_id" : ObjectId("5513306c2dfd32ffd580e324"), "x" : 2.0 }
{ "_id" : ObjectId("5513306e2dfd32ffd580e325"), "x" : 3.0 }
{ "_id" : ObjectId("551330712dfd32ffd580e326"), "x" : 4.0 }