LINQ
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Overview
In this guide you can learn how to use LINQ with the MongoDB .NET/C# Driver. LINQ allows you to construct queries against strongly typed collections of objects by using language keywords and operators. The .NET/C# Driver automatically translates LINQ queries into aggregation operations.
Important
LINQ3 is the only LINQ provider available in the MongoDB .NET/C# Driver. If you have manually configured your project to use LINQ2, it will not compile.
The examples in this guide use the restaurants
collection
in the sample_restaurants
database provided in the Atlas sample datasets.
To learn how to create a free MongoDB Atlas cluster and load the sample datasets,
see the Quick Start.
The following Restaurant
, Address
and GradeEntry
classes model the
documents in this collection:
public class Restaurant { public ObjectId Id { get; set; } public string Name { get; set; } [ ] public string RestaurantId { get; set; } public string Cuisine { get; set; } public Address Address { get; set; } public string Borough { get; set; } public List<GradeEntry> Grades { get; set; } }
public class Address { public string Building { get; set; } [ ] public double[] Coordinates { get; set; } public string Street { get; set; } [ ] public string ZipCode { get; set; } }
public class GradeEntry { public DateTime Date { get; set; } public string Grade { get; set; } public float Score { get; set; } }
Note
The documents in the restaurants
collection use the snake-case naming
convention. The examples in this guide use a ConventionPack
to deserialize the fields in the collection into Pascal case and map them to
the properties in the Restaurant
class.
To learn more about custom serialization, see Custom Serialization.
Make A Collection Queryable
To use LINQ to query your collection, you must first create an
an IQueryable
object that links to the collection. To create the object, use the AsQueryable()
method
as follows:
var restaurantsDatabase = client.GetDatabase("sample_restaurants"); var restaurantsCollection = restaurantsDatabase.GetCollection<Restaurant>("restaurants"); var queryableCollection = restaurantsCollection.AsQueryable();
Once you have the queryable object, you can compose a query using method syntax. Some pipeline stages also support query comprehension syntax, which resembles SQL query syntax.
Select the Method Syntax or Query Syntax tab to see how to compose a query using LINQ:
var query = queryableCollection .Where(r => r.Name == "The Movable Feast") .Select(r => new { r.Name, r.Address });
var query = from r in queryableCollection where r.Name == "The Movable Feast" select new { r.Name, r.Address };
You can print the results of the preceding example as follows:
foreach (var restaurant in query) { Console.WriteLine(restaurant.ToJson()); }
{ "name" : "The Movable Feast", "address" : { "building" : "284", "coord" : [-73.982923900000003, 40.6580753], "street" : "Prospect Park West", "zipcode" : "11215" } }
Tip
Accessing Query Results
You can also access the results of your query by using the ToList()
or
ToCursor()
methods:
var results = query.ToList();
var results = query.ToCursor();
Supported Aggregation Stages
You can use LINQ to create an aggregation pipeline. The .NET/C# Driver automatically translates each LINQ statement into the corresponding aggregation pipeline stages. In this section you can learn which aggregation pipeline stages are supported.
To learn more about the aggregation pipeline stages, see the Aggregation Stages page in the server manual.
$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" } }
Note
Excluding the _id Field
If you don't include the _id
field in your LINQ projection, the .NET/C# Driver
automatically excludes it from the results.
$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 } ...
Note
Result Order
The preceding queries don't always return results in the same order. Running this example may return the results in a different order than shown above.
$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.
Note
To perform a lookup, you must make both collections queryable by using the
AsQueryable()
method.
To learn how to make a collection queryable, see Make A Collection Queryable.
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; } [ ] public string RestaurantName { get; set; } public string Reviewer { get; set; } [ ] public string ReviewText { get; set; } }
Select the Method Syntax or Query Syntax tab to see how
to generate a $lookup
stage by 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 shows 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" } ] }
$vectorSearch
The $vectorSearch
aggregation stage performs an approximate nearest neighbor search
on a vector in the specified field. Your collection must have a
defined Atlas Vector Search index before you can perform a vector search on your data.
Tip
To obtain the sample dataset used in the following example, see Quick Start. To create the sample Atlas Vector Search index used in the following example, see Create an Atlas Vector Search Index in the Atlas manual.
Consider the embedded_movies
collection in the sample_mflix
database. You
can use a $vectorSearch
stage to perform a semantic search on the plot_embedding
field of the documents in the collection.
The following EmbeddedMovie
class models the documents in the embedded_movies
collection:
[ ]public class EmbeddedMovie { [ ] public string Title { get; set; } public string Plot { get; set; } [ ] public double[] Embedding { get; set; } }
The following example shows how to generate a $vectorSearch
stage to search
the plot_embedding
field using vector embeddings for the string "time travel"
:
// Defines vector embeddings for the string "time travel" var vector = new[] 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// Specifies that the vector search will consider the 150 nearest neighbors // in the specified index var options = new VectorSearchOptions<EmbeddedMovie>() { IndexName = "vector_index", NumberOfCandidates = 150 }; // Builds aggregation pipeline and specifies that the $vectorSearch stage // returns 10 results var results = queryableCollection .VectorSearch(m => m.Embedding, vector, 10, options) .Select(m => new { m.Title, m.Plot });
The results of the preceding example contain the following documents:
{ "_id" : ObjectId("573a13a0f29313caabd04a4f"), "plot" : "A reporter, learning of time travelers visiting 20th century disasters, tries to change the history they know by averting upcoming disasters.", "title" : "Thrill Seekers" } { "_id" : ObjectId("573a13d8f29313caabda6557"), "plot" : "At the age of 21, Tim discovers he can travel in time and change what happens and has happened in his own life. His decision to make his world a better place by getting a girlfriend turns out not to be as easy as you might think.", "title" : "About Time" } { "_id" : ObjectId("573a13a5f29313caabd13b4b"), "plot" : "Hoping to alter the events of the past, a 19th century inventor instead travels 800,000 years into the future, where he finds humankind divided into two warring races.", "title" : "The Time Machine" } { "_id" : ObjectId("573a13aef29313caabd2e2d7"), "plot" : "After using his mother's newly built time machine, Dolf gets stuck involuntary in the year 1212. He ends up in a children's crusade where he confronts his new friends with modern techniques...", "title" : "Crusade in Jeans" } { "_id" : ObjectId("573a1399f29313caabceec0e"), "plot" : "An officer for a security agency that regulates time travel, must fend for his life against a shady politician who has a tie to his past.", "title" : "Timecop" } { "_id" : ObjectId("573a1399f29313caabcee36f"), "plot" : "A time-travel experiment in which a robot probe is sent from the year 2073 to the year 1973 goes terribly wrong thrusting one of the project scientists, a man named Nicholas Sinclair into a...", "title" : "A.P.E.X." } { "_id" : ObjectId("573a13c6f29313caabd715d3"), "plot" : "Agent J travels in time to M.I.B.'s early days in 1969 to stop an alien from assassinating his friend Agent K and changing history.", "title" : "Men in Black 3" } { "_id" : ObjectId("573a13d4f29313caabd98c13"), "plot" : "Bound by a shared destiny, a teen bursting with scientific curiosity and a former boy-genius inventor embark on a mission to unearth the secrets of a place somewhere in time and space that exists in their collective memory.", "title" : "Tomorrowland" } { "_id" : ObjectId("573a13b6f29313caabd477fa"), "plot" : "With the help of his uncle, a man travels to the future to try and bring his girlfriend back to life.", "title" : "Love Story 2050" } { "_id" : ObjectId("573a13e5f29313caabdc40c9"), "plot" : "A dimension-traveling wizard gets stuck in the 21st century because cell-phone radiation interferes with his magic. With his home world on the brink of war, he seeks help from a jaded ...", "title" : "The Portal" }
For more information about Atlas Vector Search, Atlas Vector Search indexes, and how to incorporate them into your application, see Atlas Vector Search Overview in the Atlas manual. For more examples about running Atlas Vector Search queries using the .NET/C# Driver, see Run Vector Search Queries in the Atlas manual and select C# from the language dropdown.
Bitwise Operators
This section describes the bitwise operators supported by the .NET/C# Driver that you can use in an aggregation pipeline. You can use multiple bitwise operators in the same stage. The following guidelines apply when using bitwise operators:
All operands must be of type
int
orlong
.$bitAnd
,$bitOr
, and$bitXor
take two or more operands.$bitNot
takes one operand.Bitwise operations are evaluated from left to right.
The examples in this section use the following documents in a collection called
ingredients
:
{ "_id" : 1, "name" : "watermelon", "is_available" : 1, "is_cheap" : 1 }, { "_id" : 2, "name" : "onions", "is_available" : 1, "is_cheap" : 0 }, { "_id" : 3, "name" : "eggs", "is_available" : 0, "is_cheap" : 0 }, { "_id" : 4, "name" : "potatoes", "is_available" : 1, "is_cheap" : 1 }, { "_id" : 5, "name" : "pasta", "is_available" : 0, "is_cheap" : 1 }, { "_id" : 6, "name" : "cheese", "is_available" : 1 }
The "is_available"
field represents if an ingredient is available. If this
field has a value of 0
, the ingredient is not available. If it has a value
of 1
, the ingredient is available.
The "is_cheap"
field represents if an ingredient is cheap. If this field has
a value of 0
, the ingredient is not cheap. If it has a value of 1
, the
ingredient is cheap.
The following Ingredient
class models the documents in the ingredients
collection:
public class Ingredient { public int Id { get; set; } public string Name { get; set; } [ ] public int? IsAvailable { get; set; } [ ] public int? IsCheap { get; set; } }
Note
Missing or Undefined Operands
If the operands you pass to any bitwise operator are of type nullable
int
or long
and contain a missing or undefined value, the entire expression
evaluates to null
. If the operands are of type non-nullable int
or
long
and contain a missing or undefined value, the .NET/C# Driver will
throw an error.
$bitAnd
The $bitAnd
aggregation operator performs a bitwise AND operation on the given
arguments. You can use the $bitAnd
operator by connecting two or more
clauses with a &
character.
The following example shows how to create a $bitAnd
stage by using LINQ. The
code retrieves the document in which the Name
field has the
value "watermelon"
. It then performs a bitwise AND operation on the values of the
IsAvailable
and IsCheap
fields in this document.
var query = queryableCollection .Where(i => i.Name == "watermelon") .Select(i => i.IsAvailable & i.IsCheap);
The preceding code returns 1
, the result of the AND operation on the values
of the IsAvailable
field (1
) and the IsCheap
field (1
).
The following example performs the same bitwise AND operation on all documents in the collection:
var query = queryableCollection .Select(i => i.IsAvailable & i.IsCheap);
1 0 0 1 0 null
The null
result comes from the document where the Name
field
has the value of "cheese"
. This document is missing an IsCheap
field, so
the expression evaluates to null
.
$bitOr
The $bitOr
aggregation operator performs a bitwise OR operation on the given
arguments. You can use the $bitOr
operator by connecting two or more
clauses with a |
character.
The following example shows how to create a $bitOr
stage by using LINQ. The
code retrieves the document in which the Name
field has the
value "onions"
. It then performs a bitwise OR operation on the values of the
IsAvailable
and IsCheap
fields in this document.
var query = queryableCollection .Where(i => i.Name == "onions") .Select(i => i.IsAvailable | i.IsCheap);
The preceding code returns 1
, the result of the OR operation on the values
of the IsAvailable
field (1
) and the IsCheap
field (0
).
$bitNot
The $bitNot
aggregation operator performs a bitwise NOT operation on the given
argument. You can use the $bitNot
operator by preceding an
operand with a ~
character. $bitNot
only takes one argument. The
following example shows how to create a $bitNot
stage by using LINQ:
var query = queryableCollection .Select(i => ~i.IsCheap);
-2 -1 -1 -2 -2 null
$bitXor
The $bitXor
aggregation operator performs a bitwise XOR operation on the given
arguments. You can use the $bitXor
operator by connecting two or more
clauses with a ^
character.
The following example shows how to create a $bitXor
stage by using LINQ. The
code retrieves the documents in which the Name
field has
the value "watermelon"
or "onions"
. It then performs a bitwise XOR
operation on the values of the IsAvailable
and IsCheap
fields in these
documents.
var query = queryableCollection .Where(i => i.Name == "watermelon" || i.Name == "onions") .Select(i => i.IsAvailable ^ i.IsCheap);
The result contains the following values:
0 1
Unsupported Aggregation Stages
The MongoDB .NET/C# Driver implementation of LINQ does not support the following aggregation stages:
$redact
$geoNear
$out
To learn how to create an aggregation pipeline with the $out
stage by using Builders, see
the Write Pipeline Results to a Collection section.
Supported Methods
The following are some of the methods supported by the MongoDB .NET/C# Driver implementation of LINQ:
Method Name | Description |
---|---|
Any | Determines if any documents match the specified criteria |
Average | Calculates the average of the specified fields |
Count | Returns an Int32 that represents the number of documents that match the specified criteria |
LongCount | Returns an Int64 that represents the number of documents that match the specified criteria |
Distinct | Returns distinct documents that match the specified criteria |
First | Returns the first matching document, and throws an exception if none are found |
FirstOrDefault | Returns the first matching document, or null if none are found |
GroupBy | Groups documents based on specified criteria |
GroupJoin | Performs a left outer join to another collection in the same database |
Max | Returns the document with the maximum specified value |
OfType | Returns documents that match the specified type |
OrderBy , OrderByDescending | Returns results in a specified sort order |
ThenBy , ThenByDescending | Allows a secondary sort to be specified |
Select | Selects documents based on specified criteria |
SelectMany | Projects each element of a sequence and combines the resulting sequences into one document |
Single | Returns the only matching document, and throws an exception if there is not exactly one document |
SingleOrDefault | Returns a single matching document or null if no documents match |
Skip | Skips over a specified number of documents and returns the rest of the results |
Sum | Returns the sum of the values in a specified field |
Take | Specifies the number of results to return |
Where | Returns all documents that match your specified criteria |
View Translated Queries
When you run a LINQ query, the .NET/C# Driver automatically translates your
query into an aggregation pipeline written with the MongoDB Query API. You can view
the translated query by using the ToString()
method or the
LoggedStages
property.
To see the translated query for non-scalar operations, use the ToString()
method. Non-scalar operations are operations that return a query object, such
as:
Where
Select
SelectMany
GroupJoin
The following example calls the ToString()
method on a LINQ query and prints
the translated query:
var queryableCollection = _restaurantsCollection.AsQueryable(); var query = queryableCollection .Where(r => r.Name == "The Movable Feast"); var queryTranslated = query.ToString(); Console.WriteLine(queryTranslated);
sample_restaurants.restaurants.Aggregate([{ "$match" : { "name" : "The Movable Feast" } }])
To get the translated query for scalar operations use the LoggedStages
property. Scalar operations are operations that return a scalar result rather than a
query object, such as:
First
Sum
Count
Min
Max
To get a translated query with the LoggedStages
property, you must save
the translated query directly after it is executed, and before executing any
other queries with the same queryable object.
The following example uses the LoggedStages
property on a LINQ query that
uses a scalar operation, then prints the translated query:
var queryableCollection = _restaurantsCollection.AsQueryable(); var query = queryableCollection .Where(r => r.Name == "The Movable Feast"); var result = query.FirstOrDefault(); var queryTranslated = query.LoggedStages; Console.WriteLine(queryTranslated.ToJson());
[{ "$match" : { "name" : "The Movable Feast" } }, { "$limit" : NumberLong(1) }]
Important
LoggedStages
is not thread-safe. Executing a query and accessing the
associated LoggedStages
property from multiple threads might have
non-deterministic results.