Support use of QueryResult as a context manager, and add a get_schema method

[alexander-beedie]

Currently close() is called on QueryResult either manually or via __del__ (which is not deterministic as it relies on GC being triggered and may never actually be called).

A cleaner pattern is to use context manager syntax; this both guarantees immediate connection close on scope exit, and gracefully handles the case where an error is raised before the connection is manually closed.

Note: this syntax is optional. If you don't use it, you get the existing behaviour (it's a non-breaking addition).

Example

Manual:

Requires a potentially fallible call to close().

res = conn.execute("MATCH (a:person) WHERE a.ID = 0 RETURN a")
df = res.get_as_pl()  # <-- if this raises "close" will NOT be called
res.close()

Context manager:

Scope exit guarantees that close() will be called successfully.

with conn.execute("MATCH (a:person) WHERE a.ID = 0 RETURN a") as res:
    df = res.get_as_pl()  # <-- if this raises "close" WILL still be called

Also

• Added a handy get_schema() method (combines get_column_names() and get_column_data_types() as a dict).
• Made the chunk_size used by get_as_pl() adaptive, minimising the chance that Polars needs to rechunk the result.
• Added test coverage for all of the above updates.
• Added some "See Also" docstring sections.

CLA

I have read and agree to the terms under CLA.md 👌

[mewim]

@alexander-beedie

Thanks for your contribution.

Could you please take a look at our CLA and add “I have read and agree to the terms under CLA.md” to your PR description if you agree with the CLA?

[alexander-beedie]

Could you please take a look at our CLA and add “I have read and agree to the terms under CLA.md” to your PR description if you agree with the CLA?

Done ;)