How to deserialize a BsonDocument object back to class

Question

How do I deserialize a BsonDocument object back to the class after getting it from the server?

QueryDocument _document = new QueryDocument("key", "value"); MongoCursor<BsonDocument> _documentsReturned = _collection.FindAs<BsonDocument>(_document);  foreach (BsonDocument _document1 in _documentsReturned) {     //deserialize _document1     //? } 

Do I deserialize using a BsonReader?

Answer 1

There are three ways actually:

1.Specify type you want to load directly in FindAs<>

var docs = _collection.FindAs<MyType>(_document); 

2.Deserialize document via BsonSerializer:

BsonSerializer.Deserialize<MyType>(doc); 

3.Map bson document manually to your class:

var myClass = new Mytype(); myClass.Name = bsonDoc["name"].AsString; 

For most cases you are okay with first approach. But sometimes, when your documents is unstructured, you may need third approach.

Answer 2

For big applications and which has some structured data, it's recommended to use your custom model while creating and getting the data instead of using BsonDocument.

Creating a model is an important step for deserialization.

Helpful annotations to remember while creating your model:

• add id property in model. Try to use [BsonId] attribute for good practice:
• Create a property with annotation as [BsonExtraElements] this will be used to hold any extra elements found during deserialization.
• you can use [BsonElement] to specify the elementName.
• [BsonIgnoreIfDefault] - Initializes a new instance of the BsonIgnoreIfDefaultAttribute class

Sample Model structure, where I tried to cover maximum cases. I have created a base class for _id property just for better architecture, but you can use directly in MyModel class as well.

    public abstract class BaseEntity     {         // if you'd like to delegate another property to map onto _id then you can decorate it with the BsonIdAttribute, like this         [BsonId]         public string id { get; set; }     }      public class MyModel: BaseEntity     {         [BsonElement("PopulationAsOn")]         public DateTime? PopulationAsOn { get; set; }              [BsonRepresentation(BsonType.String)]         [BsonElement("CountryId")]         public int CountryId { get; set; }          [Required(AllowEmptyStrings = false)]         [StringLength(5)]         [BsonIgnoreIfDefault]         public virtual string CountryCode { get; set; }          [BsonIgnoreIfDefault]         public IList<States> States { get; set; }          [BsonExtraElements]         public BsonDocument ExtraElements { get; set; }     } 

Now to Deserialise, directly use your model while calling FindAsync like this:

cursor = await _collection.FindAsync(filter,  new FindOptions<MyModel, MyModel>()  { BatchSize = 1000, Sort = sort }, ct);