Bug in to_pydantic_model/from_pydantic_model

[JohannesMessner]

Problem description:

The class methods to_pydantic_model() / from_pydantic_model() do not appear to be inverses of each other.

How to reproduce:

>>> Document.from_pydantic_model(Document(blob=b'hello').to_pydantic_model())
binascii.Error: Invalid base64-encoded string: number of data characters (5) cannot be 1 more than a multiple of 4

Seems like this part of the conversion (in the from_pydantic_model() method) might be based on an assumption that does not always hold:

elif f_name == 'blob':
    # here is a dirty fishy itchy trick
    # the original bytes will be encoded two times:
    # first time is real during `to_dict/to_json`, it converts into base64 string
    # second time is at `from_dict/from_json`, it is unnecessary yet inevitable, the result string get
    # converted into a binary string and encoded again.
    # consequently, we need to decode two times here!
    fields[f_name] = base64.b64decode(base64.b64decode(value))

My guess is that the blob is actually only encoded once, but it tries to decode twice, giving the error above.

Related Issue

The .dict() method of PydanticDocument does not implement any decoding of blob, but I think it should:

>>> d = Document(blob=b'hello')
>>> d.blob
b'hello'
>>> d_pyd = d.to_pydantic_model()  # encodes the blob
>>> d_pyd.blob
'aGVsbG8='
>>> d_pyd.dict()['blob']  # I think this should decode the blob and return b'hello'
'aGVsbG8='

@JoanFM I believe that if this behaviour of .dict() is fixed then the trick in the core of creating a DocumentArray becomes unnecessary.