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Retrieve Data

Overview

In this guide, you can learn how to use the MongoDB .NET/C# Driver to retrieve data from a MongoDB collection by using read operations. You can call the Find() method to retrieve documents that match a set of criteria.

Tip

Interactive Lab

This page includes a short interactive lab that demonstrates how to retrieve data by using the Find() method. You can complete this lab directly in your browser window without installing MongoDB or a code editor.

To start the lab, click the Open Interactive Tutorial button at the top of the page. To expand the lab to a full-screen format, click the full-screen button (⛶) in the top-right corner of the lab pane.

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 Get Started with the .NET/C# Driver.

The examples on this page use the following Restaurant, Address, and GradeEntry classes as models:

public class Restaurant
{
    public ObjectId Id { get; set; }
    public string Name { get; set; }
    [BsonElement("restaurant_id")]
    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; }
    [BsonElement("coord")]
    public double[] Coordinates { get; set; }
    public string Street { get; set; }
    [BsonElement("zipcode")]
    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.

Find Documents

Use the Find() method to retrieve documents from a collection. The Find() method takes a query filter and returns all matching documents. A query filter is an object that specifies the documents you want to retrieve in your query.

To learn more about query filters, see Create a Query Filter.

Find One Document

To find a single document in a collection, pass a query filter that specifies the criteria of the document you want to find, then chain the FirstOrDefault() or FirstOrDefaultAsync() method. If more than one document matches the query filter, these methods return the first matching document from the retrieved results. If no documents match the query filter the methods return null.

var restaurants = _restaurantsCollection.Find(filter).FirstOrDefault();

var restaurants = await _restaurantsCollection.Find(filter).FirstOrDefaultAsync();

Tip

First Document

The FirstOrDefault() method returns the first document in natural order on disk if no sort criteria is specified.

To see a full example of using the Find() method to find a single document, see Additional Information.

Find Multiple Documents

To find multiple documents in a collection, pass a query filter to the Find() method that specifies the criteria of the documents you want to retrieve.

You can use a cursor to iterate over the documents returned by the Find() method. A cursor is a mechanism that allows an application to iterate over database results while holding only a subset of them in memory at a given time. Cursors are useful when your Find() method returns a large amount of documents.

To use a cursor to iterate over the documents, pass a query filter to the Find() method that specifies the criteria of the documents you want to find, then chain the ToCursor() or ToCursorAsync() method. To view a synchronous or asynchronous example, select the corresponding tab.

var restaurants = _restaurantsCollection.Find(filter).ToCursor();

var restaurants = await _restaurantsCollection.Find(filter).ToCursorAsync();

If you are returning a small number of documents, or need your results returned as a List object, use the ToList() or ToListAsync() methods.

To find multiple documents in a collection and hold them in memory as a list, pass a query filter to the Find() method that specifies the criteria of the documents you want to find, then chain the ToList() or ToListAsync() method. To view a synchronous or asynchronous example, select the corresponding tab.

var restaurants = _restaurantsCollection.Find(filter).ToList();

var restaurants = await _restaurantsCollection.Find(filter).ToListAsync();

To see a full example of using the Find() method to find multiple documents, see Additional Information.

Note

Find All Documents

To find all documents in a collection, pass an empty filter to the Find() method.

var filter = Builders<Restaurant>.Filter.Empty;
var allRestaurants = _restaurantsCollection.Find(filter);

To see a fully runnable example of using the Find() method to find all documents, see Additional Information.

Modify Find Behavior

You can modify the behavior of the Find() method by passing a FindOptions object.

You can configure the commonly used options with the following methods:

Method	Description
`BatchSize`	Gets or sets the maximum number of documents within each batch returned in a query result. If `batchSize` is not set, the `Find()` method has an initial batch size of `101` documents and a maximum size of 16 mebibytes (MiB) for each subsequent batch. This option can enforce a smaller limit than 16 MiB, but not a larger one. If you set `batchSize` to a limit that results in batches larger than 16 MiB, this option has no effect and the `Find()` method uses the default batch size.
`Collation`	Sets the collation options. See the Collation section of this page for more information.
`Comment`	Sets the comment to the query to make looking in the profiler logs easier.
`Hint`	Sets the hint for which index to use.
`MaxTime`	Sets the maximum execution time on the server for this operation.

To see a full list of available options, see FindOptions Properties.

Collation

To configure collation for your operation, create an instance of the Collation class.

The following table describes the parameters that the Collation constructor accepts. It also lists the corresponding class property that you can use to read each setting's value.

Parameter	Description	Class Property
`locale`	Specifies the International Components for Unicode (ICU) locale. For a list of supported locales, see Collation Locales and Default Parameters in the MongoDB Server Manual. If you want to use simple binary comparison, use the `Collation.Simple` static property to return a `Collation` object with the `locale` set to `"simple"`. Data Type: `string`	`Locale`
`caseLevel`	(Optional) Specifies whether to include case comparison. When this argument is `true`, the driver's behavior depends on the value of the `strength` argument: - If `strength` is `CollationStrength.Primary`, the driver compares base characters and case. - If `strength` is `CollationStrength.Secondary`, the driver compares base characters, diacritics, other secondary differences, and case. - If `strength` is any other value, this argument is ignored. When this argument is `false`, the driver doesn't include case comparison at strength level `Primary` or `Secondary`. Data Type: `boolean` Default: `false`	`CaseLevel`
`caseFirst`	(Optional) Specifies the sort order of case differences during tertiary level comparisons. Data Type: CollationCaseFirst Default: `CollationCaseFirst.Off`	`CaseFirst`
`strength`	(Optional) Specifies the level of comparison to perform, as defined in the ICU documentation. Data Type: CollationStrength Default: `CollationStrength.Tertiary`	`Strength`
`numericOrdering`	(Optional) Specifies whether the driver compares numeric strings as numbers. If this argument is `true`, the driver compares numeric strings as numbers. For example, when comparing the strings "10" and "2", the driver treats the values as 10 and 2, and finds 10 to be greater. If this argument is `false` or excluded, the driver compares numeric strings as strings. For example, when comparing the strings "10" and "2", the driver compares one character at a time. Because "1" is less than "2", the driver finds "10" to be less than "2". For more information, see Collation Restrictions in the MongoDB Server manual. Data Type: `boolean` Default: `false`	`NumericOrdering`
`alternate`	(Optional) Specifies whether the driver considers whitespace and punctuation as base characters for purposes of comparison. Data Type: CollationAlternate Default: `CollationAlternate.NonIgnorable` (spaces and punctuation are considered base characters)	`Alternate`
`maxVariable`	(Optional) Specifies which characters the driver considers ignorable when the `alternate` argument is `CollationAlternate.Shifted`. Data Type: CollationMaxVariable Default: `CollationMaxVariable.Punctuation` (the driver ignores punctuation and spaces)	`MaxVariable`
`normalization`	(Optional) Specifies whether the driver normalizes text as needed. Most text doesn't require normalization. For more information about normalization, see the ICU documentation. Data Type: `boolean` Default: `false`	`Normalization`
`backwards`	(Optional) Specifies whether strings containing diacritics sort from the back of the string to the front. Data Type: `boolean` Default: `false`	`Backwards`

For more information about collation, see the Collation page in the MongoDB Server manual.

Example

This example performs the following actions:

Finds all documents with "Pizza" in the cuisine field
Sets the BatchSize to 3
Stores the results in a cursor
Prints the documents referenced by the cursor

var filter = Builders<Restaurant>.Filter.Eq("cuisine", "Pizza");
var findOptions = new FindOptions { BatchSize = 3 };
using (var cursor = _restaurantsCollection.Find(filter, findOptions).ToCursor())
{
   foreach (var r in cursor.ToEnumerable())
   {
      WriteLine(r.Name);
   }
}

Pizza Town
Victoria Pizza
...

Tip

Clean Up

Create a cursor with a using statement to automatically invoke the Dispose() method once the cursor is no longer in use.

Additional Information

To learn more about query filters, see Create a Query Filter.

To learn how to specify queries using LINQ, see LINQ Syntax for Aggregation Operations.

For runnable examples of the find operations, see the following usage examples:

API Documentation

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

Back

Specify a Query

Specify Documents to Return