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import typing
from flask import jsonify, request
from peewee import Model, ModelSelect
_V = typing.TypeVar('_V', bound=Model)
def model_paginator(model: typing.Type[_V], mapping: typing.Callable[[_V], dict]):
return query_paginator(model.select(), mapping)
class ConstrainFailed(Exception):
def __init__(self, description: str, parameter: str, reason: str):
self.reason = reason
self.parameter = parameter
self.description = description
def try_or_fail_contrain(func: typing.Callable, parameter: str, value=None, default=None):
if value is None:
value = request.args.get(parameter, default)
try:
return func(value)
except BaseException as e:
func = func.__name__
raise ConstrainFailed(f"{func}({parameter}) failed with an exception", parameter,
f"{func} raised {type(e).__name__}")
def max_constrain(max: int, parameter: str, value=None, default=None):
value = try_or_fail_contrain(int, parameter, value, default)
if value > max:
raise ConstrainFailed(f"requested {parameter} too big", parameter, f'> {max}')
return value
def min_constrain(min: int, parameter: str, value=None, default=None):
value = try_or_fail_contrain(int, parameter, value, default)
if value < min:
raise ConstrainFailed(f"requested {parameter} too big", parameter, f'< {min}')
return value
def query_paginator(query: ModelSelect, mapping: typing.Callable[[_V], dict]):
size = try_or_fail_contrain(int, 'size', default='50')
max_constrain(50, 'size', size)
min_constrain(2, 'size', size)
offset = try_or_fail_contrain(int, 'offset', default='0')
min_constrain(0, 'offset', offset)
res = []
for obj in query.limit(size + 1).offset(offset):
res.append(mapping(obj))
more = len(res) > size
if more:
res[-1:] = []
return jsonify({
'more': more,
'next': offset + size if more else None,
'results': res,
})
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