[Mono-list] Bug (?) in SqliteDataReader
nikki at trumphurst.com
Wed May 17 13:53:44 EDT 2006
Joshua Tauberer wrote:
> Just declare the column DATETIME and insert your favorite nonintegral
> number (with or without quotes!). Sqlite ignores the types of the
> columns (sometimes...?), which is among the reasons why there's so much
> trouble fitting Sqlite into the db adapter paradigm.
> As I suspected, if you do this, and with your patch (that returns
> typeof(DateTime) in GetSchemaTable for DATETIME columns), an
> InvalidCastException is thrown in
> System.Data.Common.AbstractDataContainer when reading the data back.
> Since there's no native way to store DateTimes in Sqlite, it's possible
> someone would want to put a floating point representation of a DateTime
> into a DATETIME column (like the return of DateTime.ToOADate()).
Thats a point against my patch.
> OTOH, if you insert a string that can't be parsed as a DateTime, a
> FormatException is thrown instead in
> Mono.Data.SqliteClient.SqliteDataReader (with or without the patch)
> since we assume strings in a DateTime columns are parseable. (We could
> aggressively convert doubles to DateTimes too, which would partially get
> around the problem above.)
That's a point against the existing implementation.
> The next best thing we can do, I think, is to have GetSchemaTable return
> the result of GetFieldType. GetFieldType is implemented to look at the
> first row of the result set and return the type of the object it's
> actually going to return (or to return typeof(string) if the result set
> is empty). This way, so long as the column contains fields of a
> consistent type, it'll be ok. However, even this is possible to mess
> up. If I declare the column as INT and then insert first an integer and
> then a string (let's say by accident), a FormatException is thrown in
> AbstractDataContainer when reading it back.
That's a point against this proposed fix.
> Lastly, since SqliteDataReader buffers all of the results, a solution
> could be to return a type that surely all of the values in a column can
> be converted to. If a double is found in a DATETIME column, it could
> automatically return typeof(string) and convert all of the values
> appropriately. However, this would be doing a lot of behind-the-scenes
> conversions that don't seem too friendly.
That sounds horrible.
> So my inclination after all of this is to recommend not using the
> DataTable class with Sqlite. But what do you say?
That's a cop-out :-)
What about putting in some type checking when the data is _written_ to the
database, instead? OK, it wouldn't stop exceptions being thrown if the data
was written by a some other app, but at least it would make things work
> And finally, if there's really a bug in DateTime.Parse reversing the
> dates on non-US locales, fixing that might make all of this moot (for
> your application, at least).
That would help - at least I could put in some MONO-specific code which
would work for my application.
Could I have a copy of the test code you used to try all this out? I want
to run it on the Microsoft/Finisar version, to see what happens.
Nikki Locke, Trumphurst Ltd. PC & Unix consultancy & programming
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