query_single_or_default_async

query_single_or_default_async can execute a query and serialize the first result, or return a default value if the result set is empty; this method throws an exception if there is more than one element in the result set.

Parameters

name	type	description	optional	default
sql	str	the sql query str to execute
default	Any	any object to return if the result set is empty
param	ParamType	params to substitute in the query		None
model	Any	the callable to serialize the model; callable must be able to accept column names as kwargs.		dict

First, Single and Default

Be careful to use the right method. first and single methods are very different.

method	no item	one item	many items
first	NoResultException	item	first item
single	NoResultException	item	MoreThanOneResultException
first_or_default	default	item	first item
single_or_default	default	item	MoreThanOneResultException

Example

Execute a query and map the result to a dataclass.

import asyncio
import datetime
from dataclasses import dataclass

from pydapper import connect_async


@dataclass
class Task:
    id: int
    description: str
    due_date: datetime.date
    owner_id: int


sentinel = object()


async def main():
    async with connect_async() as commands:
        task = await commands.query_single_or_default_async(
            "select * from task where id = -1", model=Task, default=sentinel
        )

    if task is sentinel:
        print("No results found!")
    # No results found!


asyncio.run(main())

(This script is complete, it should run "as is")