GUIDs

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Overview

GUIDs in MongoDB
Serializing GUIDs
Configure with Attributes
Configure in Code
Serializing Objects
Additional Information

Overview

In this guide, you can learn how to serialize globally unique identifiers (GUIDs), also known as universally unique identifiers (UUIDs).

Tip

ObjectId

In MongoDB applications, you can use the ObjectId type as a unique identifier for a document. Consider using ObjectId instances in place of GUIDs in MongoDB applications where possible.

GUIDs in MongoDB

A GUID is a 16-byte integer that you can use as a unique ID for a MongoDB document. The following code block shows an example GUID:

00112233-4455-6677-8899-aabbccddeeff

Originally, MongoDB represented GUIDs as BsonBinaryData values of subtype 3. Because subtype 3 didn't standardize the byte order of GUIDs during encoding, different MongoDB drivers encoded GUIDs with different byte orders.

The following tabs show different driver encodings of the preceding GUID to BsonBinaryData subtype 3:

33221100-5544-7766-8899-aabbccddeeff

00112233-4455-6677-8899-aabbccddeeff

77665544-3322-1100-ffee-ddccbbaa9988

To standardize GUID byte order across applications, we added BsonBinaryData subtype 4, which all MongoDB drivers encode in the same way. If your application uses GUIDs, we recommend using BsonBinaryData subtype 4 to store them.

For a list of all BsonBinaryData subtypes, see the API documentation for the BsonBinarySubType enum.

Serializing GUIDs

Although we recommend using subtype 4 for all new BsonBinaryData GUIDs, some older MongoDB collections might contain some GUID fields that use subtype 3 and others that use subtype 4. To account for these differences, the .NET/C# Driver handles GUID serialization at the level of individual properties.

The .NET/C# Driver uses the GuidRepresentation enum to represent the different BsonBinaryData subtypes. The following table shows the GuidRepresentation enum members and the corresponding BsonBinaryData subtypes:

GuidRepresentation Member	BsonBinaryData Subtype
`Standard`	4
`CSharpLegacy`	3
`JavaLegacy`	3
`PythonLegacy`	3
`Unspecified`	N/A

Note

The CSharpLegacy, JavaLegacy, and PythonLegacy GUID representations are all equivalent to BsonBinaryData subtype 3, but use different byte orders.

The following sections describe the ways in which you can configure GUID representation in your application.

Configure with Attributes

If you're using the .NET/C# Driver to automap your C# classes to document schemas, you can add the BsonGuidRepresentation attribute to a GUID property to specify its representation. This attribute accepts a value from the GuidRepresentation enum.

The following code example specifies the Standard GUID representation for the G property:

public class Widget
{
    public int Id { get; set; }
   [BsonGuidRepresentation(GuidRepresentation.Standard)]
   public Guid G { get; set; }
}

Configure in Code

If you're writing your own serialization code, you can use the GuidSerializer class to serialize and deserialize individual GUID values to and from BSON fields. To ensure that the driver handles GUIDs correctly, use the GuidRepresentation parameter when you construct a GuidSerializer.

The following code sample creates an instance of the GuidSerializer class for serializing properties that use BsonBinaryData subtype 4:

var guidSerializer = new GuidSerializer(GuidRepresentation.Standard);

If most of your GUIDs use the same representation, you can register a GuidSerializer globally. To create and register a GuidSerializer, run the following code early in your application, such as during the bootstrapping phase:

BsonSerializer.RegisterSerializer(new GuidSerializer(GuidRepresentation.Standard));

Tip

When you're working with two BsonBinaryData subtypes, you can combine a global serializer with the BsonGuidRepresentation property attribute. For example, you can register a global serializer for the most commonly used GUID subtype, then use the BsonGuidRepresentation attribute to denote any GUID properties of another subtype.

Important

If you don't globally register a serializer, you must apply the BsonGuidRepresentation attribute to every serializable GUID property. Otherwise, the driver throws an exception when it tries to serialize the property.

Serializing Objects

You can use an ObjectSerializer to serialize hierarchical objects to subdocuments. To ensure that GUIDs in these objects are serialized and deserialized correctly, select the correct GUID representation when constructing your ObjectSerializer.

The following code sample shows how to create an ObjectSerializer for a GUID representation of subtype 4:

var objectDiscriminatorConvention = BsonSerializer.LookupDiscriminatorConvention(typeof(object));
var objectSerializer = new ObjectSerializer(objectDiscriminatorConvention, GuidRepresentation.Standard);

If your application relies on an ObjectSerializer to serialize any GUIDs, you must also register the serializer early in your application, such as during the bootstrapping phase. The serializer that you register will be used globally whenever an object serializer is needed and has not been otherwise specified.

To register your ObjectSerializer, pass it to the BsonSerializer.RegisterSerializer() method:

var objectDiscriminatorConvention = BsonSerializer.LookupDiscriminatorConvention(typeof(object));
var objectSerializer = new ObjectSerializer(objectDiscriminatorConvention, GuidRepresentation.Standard);
BsonSerializer.RegisterSerializer(objectSerializer);

Additional Information

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

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