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Count limits #86

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merged 6 commits into from
Aug 29, 2021
Merged

Count limits #86

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cc9c070
Count limits
Tinche Aug 24, 2021
0793c10
Work around mypy
Tinche Aug 24, 2021
caf2e5b
Appease mypy more
Tinche Aug 24, 2021
86e83b3
Spin out counting with a limit into a different test
Tinche Aug 25, 2021
acf87c0
Restore variable name
Tinche Aug 26, 2021
7f697b0
Rework count_with_limit test
Tinche Aug 27, 2021
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7 changes: 7 additions & 0 deletions docs/changelog.rst
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Original file line number Diff line number Diff line change
@@ -1,6 +1,13 @@
Changelog
=========

UNRELEASED
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----------

Release Date: UNRELEASED

* Added the `limit` parameter to :py:meth:`aiodynamo.client.Client.count`

21.8
----

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11 changes: 9 additions & 2 deletions src/aiodynamo/client.py
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Expand Up @@ -271,13 +271,15 @@ async def count(
start_key: Optional[Dict[str, Any]] = None,
filter_expression: Optional[Condition] = None,
index: Optional[str] = None,
limit: Optional[int] = None,
) -> int:
return await self.client.count(
self.name,
key_condition,
start_key=start_key,
filter_expression=filter_expression,
index=index,
limit=limit,
)

async def update_item(
Expand Down Expand Up @@ -745,6 +747,7 @@ async def count(
start_key: Optional[Dict[str, Any]] = None,
filter_expression: Optional[Condition] = None,
index: Optional[str] = None,
limit: Optional[int] = None,
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Documentation needs to be updated :)

) -> int:
params = Parameters()

Expand All @@ -764,7 +767,7 @@ async def count(
payload.update(params.to_request_payload())

count_sum = 0
async for result in self._depaginate("Query", payload):
async for result in self._depaginate("Query", payload, limit):
count_sum += result["Count"]
return count_sum

Expand Down Expand Up @@ -907,6 +910,7 @@ async def _depaginate(
task: Optional[asyncio.Task[Dict[str, Any]]] = asyncio.create_task(
self.send_request(action=action, payload=payload)
)
is_count = payload.get("Select") == "COUNT"
try:
while task:
result = await task
Expand All @@ -919,7 +923,10 @@ async def _depaginate(
task = None
else:
if limit is not None:
limit -= len(result["Items"])
consumed: int = (
result["Count"] if is_count else len(result["Items"])
)
limit -= consumed
if limit > 0:
payload["Limit"] = limit
else:
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14 changes: 14 additions & 0 deletions tests/integration/test_client.py
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Expand Up @@ -92,6 +92,20 @@ async def test_count(client: Client, table: TableName):
)


async def test_count_with_limit(client: Client, table: TableName):
hk = HashKey("h", "k")
assert await client.count(table, hk, limit=1) == 0
await client.put_item(table, {"h": "k", "r": "0"})
for i in range(1, 20):
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what's the reason for repeating this 20 times?

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I wanted to call it more than a few times to ensure the limit parameter was being correctly applied. The number 20 is arbitrary.

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@ojii ojii Aug 26, 2021 •
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I like that idea, but I think the loop adds little value. Instead, how about testing these scenarios:

  • 1 item table, limit 1 (tests a full count despite limit)
  • 2 item table, limit 1 (tests a single page partial count)
  • table above page size, limit larger than page size but not all items (tests a multi page partial count)

There's lots of other potential scenarios, but I feel like these are the most important. The main point I'm trying to suggest is to test specific scenarios, rather than the same one 20 times.

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Sounds good, but what is the page size? I know from experience on our production DynamoDB instances some tables would return around 10k items using a single query. I think it depends on the sizes of the items?

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Hm I see

aiodynamo/tests/integration/test_client.py

Line 259 in 29c7ae7

async def test_query_with_limit(client: Client, high_throughput_table: TableName):
already dealing with pagination, maybe I can use this approach for the test.

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@ojii Test reworked!

assert await client.count(table, hk, limit=30) == i
assert await client.count(table, hk, limit=i) == i

await client.put_item(table, {"h": "k", "r": str(i)})

assert await client.count(table, hk, limit=i) == i
assert await client.count(table, hk, limit=i + 1) == i + 1


async def test_update_item(client: Client, table: TableName):
item = {
"h": "hkv",
Expand Down