Use BsonReader & BsonWriter

[zigzago]

Hello,

Trying to implement a first version of org.bson.codecs.Codec ( Litote/kmongo@8b03c13#diff-43a261a5b319c5b393c2428d036ce9f4R39 ), I hit a first issue.

encode & decode methods of Codec use BsonWriter & BsonReader but kbson takes BsonDocumentWriter & BsonDocument

Is it doable to change Encoder and Decoder input type?

Thank you

[jershell]

Hello,
I will check and try to change it

[jershell]

Hello. I finished.
I added BsonDecoder(with BsonReader) and related method the load()
I changed type in encoder on BsonWriter
The method parse() continue to use BsonDocumentDecoder(i renamed to avoid confuse)
The BsonDecoder required strict order of a fields

[jershell]

Litote/kmongo#104

[zigzago]

@jershell The strict order of fields during deserialization is quite problematic :(

For example, this class does not deserialize well:

@Serializable
data class Friend(
    var name: String?,
    val address: String?,
    @NonEncodeNull
    @ContextualSerialization
    val _id: ObjectId? = null)

because in the bson coming from Mongo, the _id comes always first.

But this one is ok (of course):

data class Friend2(
    @NonEncodeNull
    @ContextualSerialization
    val _id: ObjectId? = null,
    var name: String?,
    val address: String?)

For the other fields, Mongo returns the fields in the insertion order, so it works. But imagine you insert a document using the shell in a different field order... The deserialization then is also broken.

I would suggest a mechanism similar to the class of the mongo java driver org.bson.codecs.pojo.PojoCodecImpl:

• Calculate at startup the set of properties to deserialize for the class

• For each deserialization, use a temporary map where you store the field values

• When you read a property during deserialization:

  1. If the property is in the set of properties to deserialize? If not: skip completely the value (perf improvement)
  2. if yes, set the value in the map

• At the end of deserialization, create the instance with the map

[jershell]

@zigzago
I changed BsonDocumentDecoder on work with BsonReader too. It can work with another an order of fields

[zigzago]

Thank you! It works fine as you can see: https://github.com/Litote/kmongo/compare/serialization?expand=1

I hit several other issues: #3 #4 #5, the polymorphic one is the biggest - if you fix #3, I think I will be able to release a first version :)