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docs: add a README section for the autoincremented ids #180

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skuruppu merged 1 commit into from
Dec 24, 2021
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docs: add a README section for the autoincremented ids #180

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12 changes: 12 additions & 0 deletions README.md
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Expand Up @@ -157,6 +157,18 @@ eng = create_engine("spanner:///projects/project-id/instances/instance-id/databa
autocommit_engine = eng.execution_options(isolation_level="AUTOCOMMIT")
```

### Autoincremented IDs
Cloud Spanner doesn't support autoincremented IDs mechanism due to performance reasons ([see for more details](https://cloud.google.com/spanner/docs/schema-design#primary-key-prevent-hotspots)). Though it's not encouraged to do so, in case you *need* the feature, you can simulate it manually, for example:

@skuruppu skuruppu Dec 24, 2021

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Cloud Spanner doesn't support autoincremented IDs mechanism due to performance reasons ([see for more details](https://cloud.google.com/spanner/docs/schema-design#primary-key-prevent-hotspots)). Though it's not encouraged to do so, in case you *need* the feature, you can simulate it manually, for example:
Cloud Spanner doesn't support autoincremented IDs mechanism due to performance reasons ([see for more details](https://cloud.google.com/spanner/docs/schema-design#primary-key-prevent-hotspots)). Though it's not encouraged to do so, in case you *need* the feature, you can simulate it manually as follows:

```python
with engine.begin() as connection:
top_id = connection.execute(
select([user.c.user_id]).order_by(user.c.user_id.desc()).limit(1)
).fetchone()
next_id = top_id[0] + 1 if top_id else 1

connection.execute(user.insert(), {"user_id": next_id})
```

### Query hints
Spanner dialect supports [query hints](https://cloud.google.com/spanner/docs/query-syntax#table_hints), which give the ability to set additional query execution parameters. Usage example:
```python
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