Examples

These examples use the generated Message type. Generate it with pixi run generate if tests/generated/Message.mojo is missing. Run a file with pixi run mojo run -I src -I tests/generated.

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Encode and decode a struct

examples/encode_message.mojo:

from bson import decode, encode
from Message import Message

def main() raises:
    var msg = Message()
    msg.f_bool = True
    msg.f_int32 = 150
    msg.f_string = "hi"
    var raw = encode(msg)
    var back = decode[Message](Span(raw))
    print(back.f_int32, back.f_string)

encode asks the struct for its byte count, allocates that many bytes, and writes once. decode reads one document and rejects trailing bytes.

A document without a schema

from runtime.extjson import decode_extjson, encode_extjson
from runtime.value import encode_document

def main() raises:
    var doc = decode_extjson("{\"a\":{\"$numberInt\":\"1\"}}")
    var raw = encode_document(doc)
    print(encode_extjson(doc, True))
    print(len(raw))

decode_extjson accepts canonical or relaxed Extended JSON. encode_extjson with True writes canonical Extended JSON. The bytes from encode_document are the BSON document.

Skip an unknown field

A generated decoder compares each name with the schema. A name that is not a field is skipped by its type byte. The next field is still read. Missing fields keep the value from __init__.