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docs: add query hints example #153

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Nov 19, 2021
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docs: add query hints example #153

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Update README.md
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skuruppu Nov 19, 2021
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Expand Up @@ -157,6 +157,29 @@ eng = create_engine("spanner:///projects/project-id/instances/instance-id/databa
autocommit_engine = eng.execution_options(isolation_level="AUTOCOMMIT")
```

### 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
session = Session(engine)

Base = declarative_base()

class User(Base):
"""Data model."""

__tablename__ = "users"
id = Column(Integer, primary_key=True)
name = Column(String(50))


query = session.query(User)
query = query.with_hint(
selectable=User, text="@{FORCE_INDEX=index_name}"
)
query = query.filter(User.name.in_(["val1", "val2"]))
query.statement.compile(session.bind)
```

### ReadOnly transactions
By default, transactions produced by a Spanner connection are in ReadWrite mode. However, some applications require an ability to grant ReadOnly access to users/methods; for these cases Spanner dialect supports the `read_only` execution option, which switches a connection into ReadOnly mode:
```python
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