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Make fetch_val call fetch_one for type conversion #246

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vmarkovtsev merged 3 commits into from
Sep 26, 2020
Merged

Make fetch_val call fetch_one for type conversion #246

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b076fb0
Make fetch_val call fetch_one for type conversion
se7entyse7en Sep 22, 2020
a443b6f
Add fetch_val tests
vmarkovtsev Sep 26, 2020
bb5c265
Add the comment to explain the replacement of fetchval
vmarkovtsev Sep 26, 2020
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14 changes: 11 additions & 3 deletions databases/backends/postgres.py
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Original file line number Diff line number Diff line change
Expand Up @@ -178,9 +178,17 @@ async def fetch_one(self, query: ClauseElement) -> typing.Optional[typing.Mappin
async def fetch_val(
self, query: ClauseElement, column: typing.Any = 0
) -> typing.Any:
assert self._connection is not None, "Connection is not acquired"
query, args, _ = self._compile(query)
return await self._connection.fetchval(query, *args, column=column)
# we are not calling self._connection.fetchval here because
# it does not convert all the types, e.g. JSON stays string
# instead of an object
# see also:
# https://github.com/encode/databases/pull/131
# https://github.com/encode/databases/pull/132
# https://github.com/encode/databases/pull/246
row = await self.fetch_one(query)
if row is None:
return None
return row[column]

async def execute(self, query: ClauseElement) -> typing.Any:
assert self._connection is not None, "Connection is not acquired"
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12 changes: 12 additions & 0 deletions tests/test_databases.py
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Expand Up @@ -155,6 +155,18 @@ async def test_queries(database_url):
result = await database.fetch_val(query=query)
assert result == "example1"

# fetch_val() with no rows
query = sqlalchemy.sql.select([notes.c.text]).where(
notes.c.text == "impossible"
)
result = await database.fetch_val(query=query)
assert result is None

# fetch_val() with a different column
query = sqlalchemy.sql.select([notes.c.id, notes.c.text])
result = await database.fetch_val(query=query, column=1)
assert result == "example1"

# row access (needed to maintain test coverage for Record.__getitem__ in postgres backend)
query = sqlalchemy.sql.select([notes.c.text])
result = await database.fetch_one(query=query)
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