Extract statements api

[Giorgi]

Remaining tasks before it can be merged:

• Tests
• Check error message marshaling on non-Windows platforms

[coveralls]

Pull Request Test Coverage Report for Build 4780141643

• 87 of 96 (90.63%) changed or added relevant lines in 4 files are covered.
• 10 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-1.5%) to 84.267%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
DuckDB.NET.Data/DuckDBDataReader.cs	41	42	97.62%
DuckDB.NET.Data/Internal/PreparedStatement.cs	16	19	84.21%
DuckDB.NET.Data/DuckDBCommand.cs	21	26	80.77%

Files with Coverage Reduction	New Missed Lines	%
DuckDB.NET.Data/DuckDBDataReader.cs	1	90.73%
DuckDB.NET.Data/Internal/PreparedStatement.cs	9	80.15%

Totals
Change from base Build 4629118895:	-1.5%
Covered Lines:	733
Relevant Lines:	867

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💛 - Coveralls

[Seddryck]

Hi Giorgi, I'm a bit not sure about the implementation but I'm clearly not a specialist of DuckDB so I could miss the point.

In ADO.Net the class DbCommand handles a single command, when you have multiple commands, it's the class DbBatch that is handling that. It doesn't sound too important but my fear is especially regarding the method ExecuteReader where the classical behaviour is impacted. Merging together the readers isn't intuitive for me and my experience of ADO.net

[Giorgi]

You definitely can execute multiple statements with a single command:

Retrieving multiple result sets using NextResult

[Seddryck]

Yes, correct. Nevertheless, .NET introduced the Batch API (materialized by the DbBatch class) a couple of years ago mainly because the feature to support multiple statements into a single DbCommand was clumsy. See https://www.infoq.com/news/2022/06/Database-Command-Batching/

In a modern ADO.Net provider, it sounds more suitable to implement this in a DbBatch class than a DbCommand class. If you want I can create a pull request with an implementation of DbBatch. Optionally, we could use the same trick as PostgreSQL to allow/deny this option on the DbCommand class (Probably won't be able to do it in the next two weeks).

[Giorgi]

Yes, it would be nice to implement the Batch API but I think it should be left in the DbCommand class too. Two weeks is perfectly OK, I plan to release a new version in May once DuckDB 0.8 is released. I'll create a ticket and you can assign it to you if you plan to work on it.

[Giorgi]

Created #105