Adding a property that copies another property from the same document

[Stephan_Steiner]

I have an object like this:

public class MigrationObject: IIdItem
{
    public string Id { get; set; }

    public string Name { get; set; }
}

Now I’m adding a property Fqdn which should be a copy of the Name property:

public class MigrationObject: IIdItem
{
    public string Id { get; set; }

    public string Name { get; set; }

    public string Fqdn { get; set; }

}

Now I could either iterate through all documents, and calling collection.UpdateOne on each,

    foreach (var item in col.FindSync(filter).ToList())
    {
        var update = Builders<MigrationObject>.Update.Set(c => c.Fqdn, item.Name);
        col.UpdateOne(Builders<MigrationObject>.Filter.Eq(c => c.Id, item.Id), update);
    }

but that’s not a good approach since apparently there’s a way without having to load all the documents. I tried it with this

    var updatePipeline = "{{ '$set': {{ 'Fqdn': {{ '$Name' }} }} }}";
    var updateDoc = BsonDocument.Parse(updatePipeline);
    var res = col.UpdateMany(filter, updateDoc);

but this cannot be parsed. Any idea where I’m going wrong?

[Stephan_Steiner]

Found the solution after some additional searching

   var filter = Builders<MigrationObject>.Filter.Empty;
    var col = db.GetCollection<MigrationObject>(collectionName);
    var pipeline = new EmptyPipelineDefinition<MigrationObject>()
        .AppendStage<MigrationObject, MigrationObject, MigrationObject>("{ $set: { Fqdn: '$Name' } }");
    var update = Builders<MigrationObject>.Update.Pipeline(pipeline);
    var res = col.UpdateMany(filter, update);

[steevej (Steeve Juneau)]

Thanks for sharing the solution you found. You may mark your post as the solution.

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