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Mongodb – Copy a field for all documents in a collection

I want to be able copy one field to another in a UpdateMany statement.

Something like this:

var updateDef = MongoDB.Driver.Builders<UserStory>
    .Update
    .Set(x => x.SemanticId, x => x.Id);

But the current API doesn’t support that.

How can I do something similar with the Csharp driver, i.e., copy a field to another for all documents in the collection? I also need to get an ObjectId generated in a new field.

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2

Answers


  1. Chosen as BEST ANSWER
    0

    Can't be done with the correct collection type, from what I've found..

    Must use BsonDocument:

    var collection = _mongo.GetCollection<BsonDocument>("SomCollection");
var updateDefinition = Builders<BsonDocument>.Update.Set("someField", "$otherField");
var result = collection.UpdateMany(FilterDefinition<BsonDocument>.Empty, updateDefinition);

  2. 0

    Close to what @jgauffin provided above, but a bit more good looking:

            var client = new MongoClient();
        var db = client.GetDatabase("db");
        var collection = db.GetCollection<Entity>("coll");
        collection.InsertOne(new Entity() { SomeField = "sf", otherFields = "of"});
        var pipeline = new EmptyPipelineDefinition<Entity>()
            .AppendStage<Entity, Entity, Entity>(
                new BsonDocument
                {
                    { "$set", new BsonDocument(nameof(Entity.SomeField), $"${nameof(Entity.OtherFields)}") }
                });
        var rendered = pipeline.Render(BsonSerializer.SerializerRegistry.GetSerializer<Entity>(), BsonSerializer.SerializerRegistry);
        var updated = collection.UpdateMany(FilterDefinition<Entity>.Empty, pipeline);
        var result = collection.Find("{}").ToList();
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