[#5202] feat(client-python): Support Column and its default value part2 - type serializer

[tsungchih]

What changes were proposed in this pull request?

This is the second part (totally 4 planned) of implementation to the following classes from Java to support Column and its default value, including:

• JsonUtils
• TypeSerializer

The TypeSerializer will be used in the incoming ColumnDTO implementation to serialize data_type field.

Why are the changes needed?

We need to support Column and its default value in python client.

#5202

Does this PR introduce any user-facing change?

No

How was this patch tested?

Unit tests

[unknowntpo]

@tsungchih Could you explain why you need to implement a json_serdes util ? See what MetalakeDTO did, simply inherit fromDataClassJsonMixin in dataclasses_json library.

from dataclasses_json import DataClassJsonMixin, config

...
@dataclass
class MetalakeDTO(Metalake, DataClassJsonMixin):
     ...

Reference:

• Docs from dataclasses-json

[tsungchih]

@tsungchih Could you explain why you need to implement a json_serdes util ? See what MetalakeDTO did, simply inherit fromDataClassJsonMixin in dataclasses_json library.

from dataclasses_json import DataClassJsonMixin, config

...
@dataclass
class MetalakeDTO(Metalake, DataClassJsonMixin):
     ...

Reference:

• Docs from dataclasses-json

@unknowntpo Thanks for your comments.

That is because all of the current Gravitino Type defined in gravitino.api.types.types.Types, such as NullType, BooleanType, etc., do not support dataclass-json. Namely they do not inherit from DataClassJsonMixin in dataclasses_json library.

IMHO, here comes with two solutions to serialize/deserialize Type listed as follows.

1. make all of the Types support for dataclass-json; (this will be a significant change to the interface and I'm not sure if it is acceptable)
2. remain Types unchanged and define serializer/deserializer for them (this is the current PR)

I'm going to elaborate more by taking ShortType as an example. The current class definition is

class Types:
    class ShortType(IntegralType):
        _instance: Types.ShortType = None
        _unsigned_instance: Types.ShortType = None
        ...

We may have it to support for dataclass_json listed as follows.

class Types:
    @dataclass
    class ShortType(IntegralType, DataClassJsonMixin):
        _instance: Types.ShortType = None
        _unsigned_instance: Types.ShortType = None
        ...

Note that, however, the ShortType has two forms, signed and unsigned. We need to choose different serialize/deserialize methods for the instance of ShortType based on which form it is. I haven't figured out how to fulfill this case by simply inherit fromDataClassJsonMixin in dataclasses_json library from the documents.

Regards