Fix columntable materialization on stored schema #360
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Fixes #357. The issue here is for stored schema, the type of the schema is `Schema{nothing, nothing}` which usually indicates tables with many columns. Some tables implementations, however, like ARFFFiles.jl, may choose to explicitly store _all_ schemas, even for very narrow tables. We already have a generated branch which checks for a specialization threshold for the known-schema case, so the fix here is fairly straightforward in just actually checking if the stored schema # of columns is actually too many or not. In the end, users should be aware that `Tables.columntable` isn't a perfect, 100% kind of table implementation that is always expected to work. It was originally meant as just a test implementation that then turned out to be fairly convenient for REPL use. Users should note that generating a named tuple of columns from stored schema doesn't have a way to be particularly efficient, since it necessarily has to generate the NamedTuple type at runtime.
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Fixes #357.
The issue here is for stored schema, the type of the schema is
Schema{nothing, nothing}which usually indicates tables with many columns. Some tables implementations, however, like ARFFFiles.jl, may choose to explicitly store all schemas, even for very narrow tables. We already have a generated branch which checks for a specialization threshold for the known-schema case, so the fix here is fairly straightforward in just actually checking if the stored schema # of columns is actually too many or not.In the end, users should be aware that
Tables.columntableisn't a perfect, 100% kind of table implementation that is always expected to work. It was originally meant as just a test implementation that then turned out to be fairly convenient for REPL use. Users should note that generating a named tuple of columns from stored schema doesn't have a way to be particularly efficient, since it necessarily has to generate the NamedTuple type at runtime.