Work with POCOs

Overview

In this guide, you can learn about how you can use "Plain Old CLR/Class Objects", or POCOs, with the .NET/C# Driver for your operations and queries. POCOs are simple class objects that do not inherit features from any framework-specific base classes or interfaces. We recommend using POCOs in your C# code to adhere to idiomatic driver usage and achieve the best performance.

You should read this guide if you want to learn more about how to use POCOs with the .NET/C# Driver or if you need to adjust the driver's default field mapping behavior.

Create a POCO

You can create a POCO by defining a simple class that does not implement interfaces or extend classes from a framework. When you execute an operation such as a read or write using a POCO, the driver internally serializes, or converts, the POCO to BSON.

Select the POCO or BSON tab to see how the driver serializes a sample POCO to BSON:

You can define a POCO with any object structure that suits your needs, including nested objects, arrays, lists, and any data types.

Custom Serialization

If the default field mapping behavior does not meet your needs, you can specify custom behavior using serialization-related attributes. These attributes change the way that the driver serializes each property of your POCO. This section describes some of the common serialization-related attributes.

public class House
{
    public ObjectId Id { get; set; }
    [BsonElement("year_built")]
    public int YearBuilt { get; set; }
}

var camelCaseConvention = new ConventionPack { new CamelCaseElementNameConvention() };
ConventionRegistry.Register("CamelCase", camelCaseConvention, type => true);

public class House
{
    public ObjectId Id { get; set; }
    [BsonRepresentation(BsonType.Int32)]
    public char YearBuilt { get; set; }
}

public class House
{
    public ObjectId Id { get; set; }
    [BsonElement(Order = 2)]
    public int YearBuilt { get; set; }
    [BsonElement(Order = 1)]
    public string Style { get; set; }
}

public class House
{
    [BsonId]
    public string Identifier { get; set; }
}

public class House
{
    public ObjectId Id { get; set; }
    [BsonIgnore]
    public int YearBuilt { get; set; }
    public string Style { get; set; }
}

Example

The following example shows how to insert a Clothing document with custom field mapping specifications into MongoDB.

The following code defines the Clothing class with these serialization-related attributes:

• [BsonElement()], which specifies custom field names in the camel case naming convention

• [BsonRepresentation()], which specifies serialization of the Price field as a BSON Double type

public class Clothing
{
    public ObjectId Id { get; set; }
    [BsonElement("name")]
    public string Name { get; set; }
    [BsonElement("inStock")]
    public bool InStock { get; set; }
    [BsonElement("price")]
    [BsonRepresentation(BsonType.Decimal128)]
    public decimal Price { get; set; }
    [BsonElement("colorSelection")]
    public List<string> ColorSelection { get; set; }
}

The following code instantiates a Clothing object and inserts the document into a collection:

var doc = new Clothing
{
    Name = "Denim Jacket",
    InStock = false,
    Price = 32.99m,
    ColorSelection = new List<string> { "dark wash", "light wash" }
};
_myColl.InsertOne(doc);

The BSON representation of the inserted document looks like this:

{
  "_id": ObjectId("..."),
  "name": "Denim Jacket",
  "inStock": false,
  "price": 32.99,
  "colorSelection": [ "dark wash", "light wash" ]
}

Additional Information

For a full list of serialization-related attributes, see the Serialization.Attributes API documentation.

For additional read and write operation examples using POCOs, see the Usage Examples or the CRUD Fundamentals Pages.

To learn more about how the driver maps BSON documents to POCOs, see Class Mapping.