Specify a Query

Overview

In this guide, you can learn how to specify a query using the MongoDB .NET/C# Driver.

You can narrow the set of matched documents returned by your query by creating a query filter. A query filter is an expression that specifies the documents you want to match in a read, update, or delete operation.

The examples in this guide use the following documents in a collection called guitars:

{ "_id": 1, "make": "Fender", "models": ["Stratocaster", "Telecaster"], "establishedYear": 1946, "rating": 9 }
{ "_id": 2, "make": "Gibson", "models": ["Les Paul", "SG", "Explorer"], "establishedYear": 1902, "rating": 8 }
{ "_id": 3, "make": "PRS", "models": ["Silver Sky", "SE", "Custom"], "establishedYear": 1985, "rating": 9 }
{ "_id": 4, "make": "Kiesel", "models": ["Ares", "Vader", "Solo"], "establishedYear": 2015 }
{ "_id": 5, "make": "Ibanez", "models": ["RG", "AZ"], "establishedYear": 1957, "rating": 7 }
{ "_id": 6, "make": "Strandberg", "models": ["Boden", "Salen"], "establishedYear": 1982 }

The following Guitar class models the documents in this collection.

public class Guitar
{
    public int Id { get; set; }
    public string Make { get; set; }
    public List<string> Models { get; set; }
    public int EstablishedYear { get; set; }
    public int? Rating { get; set; }
}

To learn more about class mapping, see Class Mapping.

The following code instantiates the _guitarsCollection object using the Guitar class as a type parameter. This type parameter causes the driver to automatically serialize and deserialize the documents it sends to and receives from MongoDB to instances of the Guitar class:

private static IMongoCollection<Guitar> _guitarsCollection;

Literal Values

Literal value queries return documents with an exact match to your query filter.

The following example specifies a query filter as a parameter to the Find() method. The query matches all documents where the make field equals "Fender".

var results = _guitarsCollection.Find(g => g.Make == "Fender").ToList();
foreach (var doc in results)
{
    Console.WriteLine(doc.ToBsonDocument());
}

{ "_id" : 1, "make" : "Fender", "models" : ["Stratocaster", "Telecaster"], "establishedYear" : 1946, "rating" : 9 }

The following example uses builders to create a query filter that matches the same documents as the preceding example:

var filter = Builders<Guitar>.Filter.Eq(g => g.Make, "Fender");
var result = _guitarsCollection.Find(filter).ToList();
foreach (var doc in result)
{
    Console.WriteLine(doc.ToBsonDocument());
}

{ "_id" : 1, "make" : "Fender", "models" : ["Stratocaster", "Telecaster"], "establishedYear" : 1946, "rating" : 9 }

var result = _guitarsCollection.Find(Builders<Guitar>.Filter.Empty).ToList();

To learn more about using builders, see Operations with Builders.

Comparison Operators

Comparison operators analyze the value in a document against the specified value in your query filter. Common comparison operators include:

For a full list of comparison operators, see the Comparison Query Operators page.

The following example specifies a query filter as a parameter to the Find() method. The query matches all documents where the establishedYear field is greater than 1985.

var results = _guitarsCollection.Find(g => g.EstablishedYear > 1985).ToList();
foreach (var doc in results)
{
    Console.WriteLine(doc.ToBsonDocument());
}

{ "_id" : 4, "make" : "Kiesel", "models" : ["Ares", "Vader", "Solo"], "establishedYear" : 2015, "rating" : null }

The following example uses builders to create a query filter that matches the same documents as the preceding example:

var filter = Builders<Guitar>.Filter.Gt(g => g.EstablishedYear, 1985);
var result = _guitarsCollection.Find(filter).ToList();
foreach (var doc in result)
{
    Console.WriteLine(doc.ToBsonDocument());
}

{ "_id" : 4, "make" : "Kiesel", "models" : ["Ares", "Vader", "Solo"], "establishedYear" : 2015, "rating" : null }

To learn more about using builders, see Operations with Builders.

Logical Operators

Logical operators match documents using logic applied to the results of two or more sets of expressions. The following is a list of some logical operators:

For a full list of logical operators, see the Logical Query Operators page.

The following example specifies a query filter as a parameter to the Find() method. The query matches all documents where the establishedYear field is greater than or equal to 1985, and the make field is not equal to "Kiesel".

var results = _guitarsCollection.Find(g => g.EstablishedYear >= 1985 && r.Make != "Kiesel").ToList();
foreach (var doc in results)
{
    Console.WriteLine(doc.ToBsonDocument());
}

{ "_id" : 3, "make" : "PRS", "models" : ["Silver Sky", "SE", "Custom"], "establishedYear" : 1985, "rating" : 9 }

The following example uses builders to create a query filter that matches the same documents as the preceding example:

var builder = Builders<Guitar>.Filter;
var filter = builder.And(builder.Gte(g => g.EstablishedYear, 1985), builder.Ne(r => r.Make, "Kiesel"));
var result = _guitarsCollection.Find(filter).ToList();
foreach (var doc in result)
{
    Console.WriteLine(doc.ToBsonDocument());
}

{ "_id" : 3, "make" : "PRS", "models" : ["Silver Sky", "SE", "Custom"], "establishedYear" : 1985, "rating" : 9 }

To learn more about using builders, see Operations with Builders.

Array Operators

Array operators match documents based on the value or quantity of elements in an array field. The following is a list of builder methods that use array operators:

For more information on the array operators, see the Array Query Operators page.

The following example uses builders to create a query filter that matches all documents that have 3 elements in the models field:

var filter = Builders<Guitar>.Filter.Size(g => g.Models, 3);
var result = _guitarsCollection.Find(filter).ToList();
foreach (var doc in result)
{
    Console.WriteLine(doc.ToBsonDocument());
}

{ "_id" : 2, "make" : "Gibson", "models" : ["Les Paul", "SG", "Explorer"], "establishedYear" : 1902, "rating" : 8 }
{ "_id" : 3, "make" : "PRS", "models" : ["Silver Sky", "SE", "Custom"], "establishedYear" : 1985, "rating" : 9 }
{ "_id" : 4, "make" : "Kiesel", "models" : ["Ares", "Vader", "Solo"], "establishedYear" : 2015, "rating" : null }

To learn more about using builders, see Operations with Builders.

Element Operators

Element operators query data based on the presence or type of a field.

For a full list of element operators, see the Element Query Operators page.

The following example uses builders to create a query filter that matches all documents that have a rating field:

var filter = Builders<Guitar>.Filter.Exists(g => g.Rating);
var result = _guitarsCollection.Find(filter).ToList();
foreach (var doc in result)
{
    Console.WriteLine(doc.ToBsonDocument());
}

{ "_id" : 1, "make" : "Fender", "models" : ["Stratocaster", "Telecaster"], "establishedYear" : 1946, "rating" : 9 }
{ "_id" : 2, "make" : "Gibson", "models" : ["Les Paul", "SG", "Explorer"], "establishedYear" : 1902, "rating" : 8 }
{ "_id" : 3, "make" : "PRS", "models" : ["Silver Sky", "SE", "Custom"], "establishedYear" : 1985, "rating" : 9 }
{ "_id" : 5, "make" : "Ibanez", "models" : ["RG", "AZ"], "establishedYear" : 1957, "rating" : 7 }

To learn more about using builders, see Operations with Builders.

Evaluation Operators

Evaluation operators analyze data on individual fields, or on the entire collection's documents. Some builder methods that use evaluation operators include Regex() and Text().

For a full list of evaluation operators, see the Evaluation Query Operators page.

The following example uses builders to create a query filter that matches all documents that have a value in the make field that starts with the letter "G":

var filter = Builders<Guitar>.Filter.Regex(g => g.Make, "^G");
var result = _guitarsCollection.Find(filter).ToList();
foreach (var doc in result)
{
    Console.WriteLine(doc.ToBsonDocument());
}

{ "_id" : 2, "make" : "Gibson", "models" : ["Les Paul", "SG", "Explorer"], "establishedYear" : 1902, "rating" : 8 }

To learn more about using builders, see Operations with Builders.

Additional Information

For more information about the operators mentioned in this guide, see the following Server Manual Entries:

• Comparison Query Operators

• Logical Query Operators

• Array Query Operators

• Element Query Operators

• Evaluation Query Operators

To learn more about using Builders, see Operations with Builders.

To learn how to specify queries using LINQ, see LINQ.