$ プロジェクト （集計ステージ）

db.movies.aggregate( [
   { $match: { title: "The Great Train Robbery" } },
   { $project : { "rated": 0 } },
   { $limit: 1 }
] )

var pipeline = new EmptyPipelineDefinition<Movie> ()
    .Project(
        Builders<Movie>.Projection
            .Include(m => m.Title)
            .Include(m => m.Plot)
    );
var result = movieCollection.Aggregate(pipeline).FirstOrDefault();

var pipeline = new EmptyPipelineDefinition<Movie>()
    .Project(
        Builders<Movie>.Projection
            .Exclude(m => m.Type)
    );
var result = movieCollection.Aggregate(pipeline).FirstOrDefault();

var pipeline = new EmptyPipelineDefinition<Movie> ()
    .Project(
        Builders<Movie>.Projection
            .Exclude(m => m.Id)
            .Include(m => m.Title)
            .Include(m => m.Plot)
    );
var result = movieCollection.Aggregate(pipeline).FirstOrDefault();

var pipeline = new EmptyPipelineDefinition<Movie> ()
    .Project(
        Builders<Movie>.Projection
            .Exclude("Imdb.id")
            .Exclude(m => m.Type)
    );
var result = movieCollection.Aggregate(pipeline).FirstOrDefault();

var stage = new BsonDocument
{
    { "title", 1 },
    { "imdb.id", 1 },
    { "imdb.rating", 1 },
    {
        "imdb.votes", new BsonDocument("$cond", new BsonDocument
        {
            { "if", new BsonDocument("$eq", new BsonArray { "", "$imdb.votes" }) },
            { "then", "$$REMOVE" },
            { "else", "$imdb.votes" }
        })
    }
};
var pipeline = new EmptyPipelineDefinition<Movie>()
    .Project(stage)
    .Sample(1);
var result = movieCollection.Aggregate(pipeline).FirstOrDefault();

public class ProjectedMovie
{
    public ObjectId Id { get; set; }
    public string Title { get; set; }
    
    public string LeadActor { get; set; }
    
    public List<string> Crew { get; set; }
}

var pipeline = new EmptyPipelineDefinition<Movie>()
    .Project(
        Builders<Movie>
            .Projection
            .Expression(m => new ProjectedMovie
            {
                Id = m.Id,
                Title = m.Title,
                LeadActor = m.Cast[0],
            })
    );
var result = movieCollection.Aggregate(pipeline).FirstOrDefault();

public class ProjectedMovie
{
    public ObjectId Id { get; set; }
    public string Title { get; set; }
    
    public string LeadActor { get; set; }
    
    public List<string> Crew { get; set; }
}

var pipeline = new EmptyPipelineDefinition<Movie> ()
    .Project(
        Builders<Movie>
            .Projection
            .Expression(m => new ProjectedMovie
                {
                    Id = m.Id,
                    Title = m.Title,
                    LeadActor = m.Cast[0],
                    Crew = m.Directors.Concat(m.Writers).ToList()
                }
            )
    )
    .Sample(1);
var result = movieCollection.Aggregate(pipeline).FirstOrDefault();

var stage = new BsonDocument
{
    { "crew", new BsonArray { "$directors", "$writers", "$makeupArtists" } }
};
var pipeline = new EmptyPipelineDefinition<Movie>()
    .Project(stage)
    .Sample(1);
var result = movieCollection.Aggregate(pipeline).FirstOrDefault();

const pipeline = [
  {
    $project: {
      title: 1, 
      plot: 1
    }
  }
];
const cursor = collection.aggregate(pipeline);
return cursor;

const pipeline = [
  {
    $project: {
      type: 0
    }
  }
];
const cursor = collection.aggregate(pipeline);
return cursor;

const pipeline = [
  {
    $project: {
      _id: 0, 
      title: 1,
      plot: 1 
    }
  }
];
const cursor = collection.aggregate(pipeline);
return cursor;

const pipeline = [
  {
    $project: {
      "imdb.id": 0, 
      type: 0
    }
  }
];
const cursor = collection.aggregate(pipeline);
return cursor;

const pipeline = [
  {
    $project: {
      title: 1,
      "imdb.id": 1, 
      "imdb.rating": 1,
      "imdb.votes": {
        $cond: {
          if: { $eq: ["$imdb.votes", ""] },
          then: "$REMOVE",
          else: "$imdb.votes"
        }
      }
    }
  }
];
const cursor = collection.aggregate(pipeline);
return cursor;

const pipeline = [
  {
    $project: {
      _id: "$_id",
      title: "$title",
      leadActor: { $arrayElemAt: ["$cast", 0] }
    }
  }
];
const cursor = collection.aggregate(pipeline);
return cursor;

const pipeline = [
  {
    $project: {
      _id: "$_id",
      title: "$title",
      leadActor: { $arrayElemAt: ["$cast", 0] },
      crew: { $concatArrays: ["$directors", "$writers"] }
    }
  }
];
const cursor = collection.aggregate(pipeline);
return cursor;

const pipeline = [
  {
    $project: {
      crew: ["$directors", "$writers", "$makeupArtists"]
    }
  }
];
const cursor = collection.aggregate(pipeline);
return cursor;