Specify Fields To Return

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Overview

Sample Data
Projection Types
Specify Fields to Include
Exclude the _id Field
Specify Fields to Exclude
Additional Information
API Documentation

Overview

In this guide, you can learn how to specify which fields to return from a read operation by using a projection. A projection is a document that specifies which fields MongoDB returns from a query.

Sample Data

The examples in this guide use the sample_restaurants.restaurants collection from the Atlas sample datasets. To learn how to create a free MongoDB Atlas cluster and load the sample datasets, see the Quick Start.

Projection Types

You can use a projection to specify which fields to include in a return document, or to specify which fields to exclude.

When specifying certain fields to include in a projection, all other fields are implicitly excluded (except the _id field, which is included by default). You cannot combine inclusion and exclusion statements in a single projection, unless you are excluding the _id field.

To remove the _id field from the returned document, you must explicitly exclude it.

Specify Fields to Include

To specify the fields to include from the result, chain the Project() method to the Find() method. When calling the Project() method, you must pass in the projection definition as a parameter. You can construct a projection definition by using the Builders<T>.Projection.Include() method and passing in the field name to include as a parameter. This method can be chained to include multiple fields in the projection.

The following example uses the Find() method to find all restaurants in which the name field value is "Emerald Pub". Then, the code calls the Project() method to instruct the find operation to include the name and cuisine fields in the result:

var filter = Builders<BsonDocument>.Filter.Eq("name", "Emerald Pub");
var projection = Builders<BsonDocument>.Projection
    .Include("name")
    .Include("cuisine");
var results = collection.Find(filter).Project(projection).ToList();
foreach (var result in results)
{
    Console.WriteLine(result.ToJson());
}

{ "_id" : ObjectId("..."), "cuisine" : "American", "name" : "Emerald Pub" }
{ "_id" : ObjectId("..."), "cuisine" : "American", "name" : "Emerald Pub" }

Exclude the `_id` Field

When specifying fields to include, you can also exclude the _id field from the returned document.

The following example runs the same query as the preceding example, but excludes the _id field from the projection:

var filter = Builders<BsonDocument>.Filter.Eq("name", "Emerald Pub");
var projection = Builders<BsonDocument>.Projection
    .Include("name")
    .Include("cuisine")
    .Exclude("_id");
var results = collection.Find(filter).Project(projection).ToList();
foreach (var result in results)
{
    Console.WriteLine(result.ToJson());
}

{ "cuisine" : "American", "name" : "Emerald Pub" }
{ "cuisine" : "American", "name" : "Emerald Pub" }

Specify Fields to Exclude

To specify the fields to exclude from the result, chain the Project() method to the Find() method. You can exclude fields in your projection by using the Builders<T>.Projection.Exclude() method and passing in the field name to exclude as a parameter. This method can be chained to exclude multiple fields in the projection.

The following example uses the Find() method to find all restaurants in which the name field value is "Emerald Pub". It then uses a projection to exclude the cuisine field from the returned documents:

var filter = Builders<BsonDocument>.Filter.Eq("name", "Emerald Pub");
var projection = Builders<BsonDocument>.Projection
    .Exclude("cuisine");
var results = collection.Find(filter).Project(projection).ToList();
foreach (var result in results)
{
    Console.WriteLine(result.ToJson());
}

{ "_id" : ObjectId("..."), "address" : { "building" : "308", "coord" : [-74.008493599999994, 40.725807199999998], "street" : "Spring Street", "zipcode" : "10013" }, "borough" : "Manhattan", "grades" : [{ "date" : ISODate("2014-02-24T00:00:00Z"), "grade" : "A", "score" : 5 }, { "date" : ISODate("2013-08-26T00:00:00Z"), "grade" : "A", "score" : 13 }, { "date" : ISODate("2013-03-04T00:00:00Z"), "grade" : "A", "score" : 12 }, { "date" : ISODate("2012-06-25T00:00:00Z"), "grade" : "A", "score" : 10 }, { "date" : ISODate("2011-12-23T00:00:00Z"), "grade" : "A", "score" : 10 }, { "date" : ISODate("2011-07-26T00:00:00Z"), "grade" : "C", "score" : 32 }], "name" : "Emerald Pub", "restaurant_id" : "40367329" }
{ "_id" : ObjectId("..."), "address" : { "building" : "18301", "coord" : [-73.791184999999999, 40.740119999999997], "street" : "Horace Harding Expressway", "zipcode" : "11365" }, "borough" : "Queens", "grades" : [{ "date" : ISODate("2014-05-07T00:00:00Z"), "grade" : "A", "score" : 12 }, { "date" : ISODate("2013-04-30T00:00:00Z"), "grade" : "A", "score" : 9 }, { "date" : ISODate("2012-03-01T00:00:00Z"), "grade" : "A", "score" : 13 }], "name" : "Emerald Pub", "restaurant_id" : "40668598" }

Additional Information

To learn more about projections, see the Project Fields guide in the MongoDB Server manual.

API Documentation

To learn more about any of the functions or types discussed in this guide, see the following API Documentation:

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