column_count can panic

[Timmmm]

Statement::column_count() just returns a usize, yet it can easily fail. In that case it panics because it calls result_unwrap() as shown by this backtrace.

   4: duckdb::raw_statement::RawStatement::result_unwrap
             at .../.cargo/registry/src/index.crates.io-6f17d22bba15001f/duckdb-0.9.2/src/raw_statement.rs:72:9
   5: duckdb::raw_statement::RawStatement::column_count
             at .../.cargo/registry/src/index.crates.io-6f17d22bba15001f/duckdb-0.9.2/src/raw_statement.rs:168:49
   6: duckdb::column::<impl duckdb::statement::Statement>::column_count
             at .../.cargo/registry/src/index.crates.io-6f17d22bba15001f/duckdb-0.9.2/src/column.rs:49:9

All I did was this:

    let mut stmt = conn.prepare(&sql)?;
    let cols = stmt.column_count();

There's no indication that that will panic!

[pengye91]

Hi team, facing with the same issue here, is there any solution now?

[gmosx]

Can column_count be called after prepare or it can be called only after execute/query?

[AlphaJack]

I'm also interested in @gmosx question, it seems that the Rust API only allows column_count after execute/query, but it would be great to know count and types already after prepare

[mlafeldt]

As of today, column_count only works (i.e., doesn't panic) if the statement has already been executed.

While DuckDB itself can derive the number of columns from prepared statements, this functionality is currently missing in the C API (and therefore in duckdb-rs as well).

#541 will improve the situation a bit until we have better C API support.