takahe/api/pagination.py

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import dataclasses
import urllib.parse
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from django.db import models
from django.http import HttpRequest
@dataclasses.dataclass
class PaginationResult:
#: A list of objects that matched the pagination query.
results: list[models.Model]
#: The actual applied limit, which may be different from what was requested.
limit: int
sort_attribute: str
def next(self, request: HttpRequest, allowed_params: list[str]):
"""
Returns a URL to the next page of results.
"""
if not self.results:
return None
params = self.filter_params(request, allowed_params)
params["max_id"] = self.results[-1].pk
return f"{request.build_absolute_uri(request.path)}?{urllib.parse.urlencode(params)}"
def prev(self, request: HttpRequest, allowed_params: list[str]):
"""
Returns a URL to the previous page of results.
"""
if not self.results:
return None
params = self.filter_params(request, allowed_params)
params["min_id"] = self.results[0].pk
return f"{request.build_absolute_uri(request.path)}?{urllib.parse.urlencode(params)}"
@staticmethod
def filter_params(request: HttpRequest, allowed_params: list[str]):
params = {}
for key in allowed_params:
value = request.GET.get(key, None)
if value:
params[key] = value
return params
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class MastodonPaginator:
"""
Paginates in the Mastodon style (max_id, min_id, etc)
"""
def __init__(
self,
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anchor_model: type[models.Model],
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sort_attribute: str = "created",
default_limit: int = 20,
max_limit: int = 40,
):
self.anchor_model = anchor_model
self.sort_attribute = sort_attribute
self.default_limit = default_limit
self.max_limit = max_limit
def paginate(
self,
queryset,
min_id: str | None,
max_id: str | None,
since_id: str | None,
limit: int | None,
):
if max_id:
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try:
anchor = self.anchor_model.objects.get(pk=max_id)
except self.anchor_model.DoesNotExist:
return []
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queryset = queryset.filter(
**{self.sort_attribute + "__lt": getattr(anchor, self.sort_attribute)}
)
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if since_id:
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try:
anchor = self.anchor_model.objects.get(pk=since_id)
except self.anchor_model.DoesNotExist:
return []
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queryset = queryset.filter(
**{self.sort_attribute + "__gt": getattr(anchor, self.sort_attribute)}
)
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if min_id:
# Min ID requires items _immediately_ newer than specified, so we
# invert the ordering to accommodate
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try:
anchor = self.anchor_model.objects.get(pk=min_id)
except self.anchor_model.DoesNotExist:
return []
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queryset = queryset.filter(
**{self.sort_attribute + "__gt": getattr(anchor, self.sort_attribute)}
).order_by(self.sort_attribute)
else:
queryset = queryset.order_by("-" + self.sort_attribute)
limit = min(limit or self.default_limit, self.max_limit)
return PaginationResult(
results=list(queryset[:limit]),
limit=limit,
sort_attribute=self.sort_attribute,
)