LINQ

$project

The $project aggregation stage returns a document containing only the specified fields.

Select the Method Syntax or Query Syntax tab to see how to generate a $project stage using LINQ:

var query = queryableCollection
    .Select(r => new { r.Name, r.Address });

var query = from r in queryableCollection
    select new { r.Name, r.Address };

The result of the preceding example contains the following document:

{ "name" : "The Movable Feast", "address" : { "building" : "284", "coord" : [-73.982923900000003, 40.6580753], "street" : "Prospect Park West", "zipcode" : "11215" } }

$match

The $match aggregation stage returns the documents that match a specified criteria.

Select the Method Syntax or Query Syntax tab to see how to generate a $match stage using LINQ:

var query = queryableCollection
    .Where(r => r.Name == "The Movable Feast");

var query = from r in queryableCollection
    where r.Name == "The Movable Feast"
    select r;

The result of the preceding example contains the following document:

// Results Truncated
{ "_id" : ObjectId(...), "name" : "The Movable Feast", "restaurant_id" : "40361606", "cuisine" : "American", "address" : {...}, "borough" : "Brooklyn", "grades" : [...] }

$limit

The $limit aggregation stage limits the number of documents returned by the query. The following example shows how to generate a $limit stage using LINQ:

var query = queryableCollection
    .Where(r => r.Cuisine == "Italian")
    .Select(r => new {r.Name, r.Cuisine})
    .Take(5);

The result of the preceding example contains the following documents:

{ "name" : "Philadelhia Grille Express", "cuisine" : "Italian" }
{ "name" : "Isle Of Capri Resturant", "cuisine" : "Italian" }
{ "name" : "Marchis Restaurant", "cuisine" : "Italian" }
{ "name" : "Crystal Room", "cuisine" : "Italian" }
{ "name" : "Forlinis Restaurant", "cuisine" : "Italian" }

$skip

The $skip aggregation stage skips over a specified number of documents returned by a query, then returns the rest of the results. The following example shows how to generate a $skip stage using LINQ:

var query = queryableCollection
    .Where(r => r.Cuisine == "Italian")
    .Select(r => new {r.Name, r.Cuisine})
    .Skip(2);

The preceding example skips the first two restaurants that match the criteria, and returns the rest. The result contains the following documents:

// Results Truncated
{ "name" : "Marchis Restaurant", "cuisine" : "Italian" }
{ "name" : "Crystal Room", "cuisine" : "Italian" }
{ "name" : "Forlinis Restaurant", "cuisine" : "Italian" }
...

$unwind

The $unwind aggregation stage deconstructs a specified array field and returns a document for each element in that array.

Select the Method Syntax or Query Syntax tab to see how to generate an $unwind stage using LINQ:

var query = queryableCollection
    .Where(r => r.Name == "The Movable Feast")
    .SelectMany(r => r.Grades);

var query = from r in queryableCollection
    where r.Name == "The Movable Feast"
    from grade in r.Grades
    select grade;

The query in the preceding example finds the document where the Name field has the value "The Movable Feast." Then, for each element in this document's Grades array, the query returns a new document. The result contains the following documents:

{ "date" : ISODate("2014-11-19T00:00:00Z"), "grade" : "A", "score" : 11 }
{ "date" : ISODate("2013-11-14T00:00:00Z"), "grade" : "A", "score" : 2 }
{ "date" : ISODate("2012-12-05T00:00:00Z"), "grade" : "A", "score" : 13 }
{ "date" : ISODate("2012-05-17T00:00:00Z"), "grade" : "A", "score" : 11 }

$group

The $group aggregation stage separates documents into groups according to the criteria you specify.

Select the Method Syntax or Query Syntax tab to see how to generate an $group stage using LINQ:

var query = queryableCollection
    .GroupBy(r => r.Cuisine)
    .Select(g => new { Cuisine = g.Key, Count = g.Count() });

var query = from r in queryableCollection
    group r by r.Cuisine into g
    select new {Cuisine = g.Key, Count = g.Count()};

The preceding example groups each document by the value in its Cuisine field, then counts how many documents have each Cuisine value. The result contains the following documents:

// Results Truncated
{ "cuisine" : "Caribbean", "count" : 657 }
{ "cuisine" : "Café/Coffee/Tea", "count" : 1214 }
{ "cuisine" : "Iranian", "count" : 2 }
{ "cuisine" : "Nuts/Confectionary", "count" : 6 }
{ "cuisine" : "Middle Eastern", "count" : 168 }
...

$sort

The $sort aggregation stage returns the results of your query in the order that you specify.

Select the Method Syntax or Query Syntax tab to see how to generate an $sort stage using LINQ:

var query = queryableCollection
    .OrderBy(r => r.Name)
    .ThenByDescending(r => r.RestaurantId);

var query = from r in queryableCollection
    orderby r.Name, r.RestaurantId descending
    select r;

The preceding example returns the query results sorted alphabetically by the Name field, with a secondary descending sort on the RestaurantId field. The following is a subset of the documents contained in the returned results:

// Results Truncated
...
{ "_id" : ObjectId(...), "name" : "Aba Turkish Restaurant", "restaurant_id" : "41548686", "cuisine" : "Turkish", "address" : {...}, "borough" : "Manhattan", "grades" : [...] }
{ "_id" : ObjectId(...), "name" : "Abace Sushi", "restaurant_id" : "50006214", "cuisine" : "Japanese", "address" : { ... }, "borough" : "Manhattan", "grades" : [...] }
{ "_id" : ObjectId(...), "name" : "Abacky Potluck", "restaurant_id" : "50011222", "cuisine" : "Asian", "address" : { ... }, "borough" : "Manhattan", "grades" : [...] }
{ "_id" : ObjectId(...), "name" : "Abaleh", "restaurant_id" : "50009096", "cuisine" : "Mediterranean", "address" : { ... }, "borough" : "Manhattan", "grades" : [...] }
...

$lookup

The $lookup aggregation stage joins documents from one collection to documents from another collection in the same database. The $lookup stage adds a new array field to each input document. The new array field contains the matching documents from the "joined" collection.

Consider a second collection in the sample_restaurants database called reviews that has restaurant reviews. You can join documents from that collection to documents with the same name value in the restaurants collection using the $lookup stage.

The following Review class models the documents in the reviews collection:

public class Review
{
    public ObjectId Id { get; set; }
    [BsonElement("restaurant_name")]
    public string RestaurantName { get; set; }
    public string Reviewer { get; set; }
    [BsonElement("review_text")]
    public string ReviewText { get; set; }
}

Select the Method Syntax or Query Syntax tab to see how to generate a $lookup stage using LINQ:

var query = queryableCollection
    .GroupJoin(reviewCollection,
        restaurant => restaurant.Name,
        review => review.RestaurantName,
        (restaurant, reviews) =>
            new { Restaurant = restaurant, Reviews = reviews }
    );

var query = from restaurant in queryableCollection
    join rv in reviewCollection on restaurant.Name equals rv.RestaurantName into reviews
    select new { restaurant, reviews };

The preceding example returns all documents from the restaurants collection. Each restaurant document has an added field called reviews, which contains all reviews for that restaurant. A review matches a restaurant if the value of the name field in the review document matches the name field of the restaurant document.

The following is a subset of the returned results:

// Results Truncated
{ "restaurant" : {
   "_id" : ObjectId("..."),
   "name" : "The Movable Feast",
   "restaurant_id" : "40361606",
   "cuisine" : "American",
   "address" : {...},
   "borough" : "Brooklyn",
   "grades" : [...] },
   "reviews" : [
     { "_id" : ObjectId(...), "restaurant_name" : "The Movable Feast", "reviewer" : "Lazlo Cravensworth", "review_text" : "Great restaurant! 12/10 stars!" },
     { "_id" : ObjectId("..."), "restaurant_name" : "The Movable Feast", "reviewer" : "Michael Scarn", "review_text" : "It really was a feast" }
    ]
 }