How to set default value to a dataclass field?

[barenko]

I want to set a None value in Optional dataclass fields. But I was unable to find how to do it in documentation. This is possible?

I have a table like:

create table t(
   id serial primary key, 
   name varchar not null, 
   description text null
)

running sqlc generate I got:

@dataclasses.dataclass()
class T:
   id: int
   name: str
   description: Optional[str]

But what I really wants is a default None value in description, like:

@dataclasses.dataclass()
class T:
   id: int
   name: str
   description: Optional[str] = None

I'm using sqlc v1.27.0 (by docker) and generating python code for postgres with the config:

version: '2'
plugins:
- name: py
  wasm:
    url: https://downloads.sqlc.dev/plugin/sqlc-gen-python_1.2.0.wasm
    sha256: a6c5d174c407007c3717eea36ff0882744346e6ba991f92f71d6ab2895204c0e
sql:
- schema: "schema.sql"
  queries: "queries.sql"
  engine: postgresql
  codegen:
  - out: ./model
    plugin: py
    options:
      package: model
      emit_sync_querier: true
      emit_async_querier: true
      emit_empty_slices: true

[barenko]

I made a working around to continue to use the sqlc on python:

• After run sqlc generate, execute a sed on the generated file to add default values:

    sed -i '/^[[:space:]]*[a-zA-Z0-9_]*:[[:space:]]*Optional/ s/\(Optional\[\([^]]*\)\]\)/\1 = None/' models.py

• With the defaults, we need to re-sort all fields to put the fields with default as the lasts:

import re
import logging
import sys

logging.basicConfig(level=logging.DEBUG, format='%(asctime)s - %(levelname)s - %(message)s')

def main(filename: str):
    with open(filename, "r") as file:
        contents = file.read().split("\n")

    dataclass_line=-1
    class_line=-1
    inner_class_indent=''
    field_map={}
    for idx, line in enumerate(contents):
        if re.match(r"\@dataclasses.dataclass\(\)", line):
            dataclass_line = idx
            logging.debug(f"Found dataclass line: {dataclass_line}")
            continue
        if dataclass_line >= 0:
            if re.match(r"class ", line):
                class_line = idx
                logging.debug(f"Found class line: {class_line}")
                continue
        if class_line >= 0:
            if inner_class_indent == '':
                inner_class_indent = re.match(r"^(\s+)", line).group(1)
            if re.match("^"+inner_class_indent+r"[\S|\n]", line):
                if re.match(r"\s+[a-z]+[a-z_0-9]*\s*:\s*", line):
                    logging.debug(f"Found field line: {line}")
                    field_map[idx] = line
            else:
                if field_map.keys():
                    resort_fields(class_line, idx, contents, field_map)
                class_line = -1
                dataclass_line = -1
                inner_class_indent = ''
                field_map = {}

    with open(filename, 'w') as file:
        file.write("\n".join(contents))

def resort_fields(class_line, end_line, contents, field_map):
    logging.info(f"Resorting fields from: {contents[class_line]}")
    def sort(kv):
        k = kv[1]
        if "Optional" in k and " = " in k:
            return "Z"+k
        if " = " in k:
            return "Y"+k
        if " = None" in k:
            return "X"+k
        else:
            return "W"+k
        
    sorted_fields = sorted(field_map.items(), key=sort)

    logging.debug("BEFORE:")
    for line in contents[class_line:end_line]:
        logging.debug(line)

    original_idxs = field_map.keys()
    sorted_idxs =  [ s[0] for s in sorted_fields]
    tuples = list(zip(original_idxs, sorted_idxs))

    logging.debug("DE->PARA:")
    for o,d in tuples:
        logging.debug(f"{field_map.get(o)}{o} -> {field_map.get(d)}{d}")
        contents[o] = field_map.get(d)
        
    logging.info("AFTER:")
    for line in contents[class_line:end_line]:
        logging.info(line)


if __name__ == "__main__":
    if len(sys.argv) != 2:
        logging.error("Usage: my_script <file_to_modify.py>")
        sys.exit(1)

    filename = sys.argv[1]
    main(filename)

python -W all scripts/resort_dataclass_optional_fields.py models.py

You will need to do this on models and queries.