Return a single element while iterating over segments #523
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wendigo
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This makes the usage of the segment cursor more natural:
```
cur = conn.cursor('segment')
cur.execute(sql)
spooled_result = cur.fetchall()
for spooled_data in spooled_result:
row_mapper = RowMapperFactory().create(columns=cur._query.columns, legacy_primitive_types=False)
rows = list(SegmentIterator(spooled_data, row_mapper))
```
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| legacy_primitive_types=self._legacy_primitive_types, | ||
| fetch_mode="segments") | ||
| self._iterator = iter(self._query.execute()) | ||
| self._iterator = map(lambda tuple: tuple[0], iter(self._query.execute())) |
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Note this is a breaking change, but i agree it is a nicer API.
However, how can the client retrieve the encoding?
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See the usage in the integration test
| for spooled_data, spooled_segment in rows: | ||
| segments = cur.fetchall() | ||
| assert len(segments) > 0 | ||
| row_mapper = trino.mapper.RowMapperFactory().create(columns=cur._query.columns, legacy_primitive_types=False) |
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change import to from trino.mapper import RowMapperFactory
| def __next__(self) -> Tuple["SpooledData", "Segment"]: | ||
| return self, next(self._segments_iterator) | ||
| segment = next(self._segments_iterator) | ||
| return SpooledData(self._encoding, [segment]), segment |
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Why not also change SpooledData to contain a single segment, rather than a list?
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Because SpooledData can contain multiple segments. I think we should not reuse this object as the iterable object but return another class that has all the required fields. Let's get rid of Tuple["SpooledData", "Segment"].
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Right, each response can contain multiple segment URLs, so we need the transfer object to reflect that, but the abstraction we expose to the client doesn't need to mirror that.
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This makes the usage of the segment cursor more natural:
This allows for the usage that is intuitive to the user:
This will produce: