Cast exception when reading DateTimeOffset with System.Data.SqlClient about donald

[pimbrouwers]

Awesome! This has been merged in and deployed through 6.2.3

[pimbrouwers]

Hey Daniel! Thanks for bringing this to my attention, admittedly it's not a field type I use or encounter very often. So it's no suprise that I didn't catch this myself (since I use this package everyday at work with SQL Server) and if you look carefully at the "type reader test" the mapper is missing the datetimeoffset 🤦.

So let's solve the two problems in front of us. First and most importantly, getting your code working. Here's a solution for right now.

open System.Data.SqlClient

// quick & dirty
let mapRow (rd : IDataReader) : DateTimeOffset =
    let sqlRd = rd :?> SqlDataReader
    sqlRd.GetDateTimeOffset(sqlRd.GetOrdinal("dto"))

conn
|> Db.newCommand "SELECT SYSDATETIMEOFFSET() AS dto"
|> Db.query mapRow

Now as far as the package goes, I think I have a couple ideas. Regardless of how we proceed on that, first thing should be to mark the current ReadDateTimeOffset as obsolete, release as a patch and remove it in the next major version release.

In my view the cleanest solution is to apply generics. If we change the signature of the map param to the following, you can pass in any function which receives any implementation of the interface.

let query (map : 'reader -> 'a when 'reader :> IDataReader) (cmd : IDbCommand) : DbResult<'a list> =  // ...

// now this works
let mapRow (rd : SqlDataReader) : DateTimeOffset =
    rd.GetDateTimeOffset(sqlRd.GetOrdinal("dto"))

conn
|> Db.newCommand "SELECT SYSDATETIMEOFFSET() AS dto"
|> Db.query mapRow

At first glance, I think this idea is our best approach. It's regression-proof and immediately, without any work allows people to plugin vendor specific consumption.

Thoughts?

[daniellittledev]

Hey, thanks for quick fix and all the detail!

Yeah I think that looks like a great path forward. Switching query to use generics provides easy accesses to the
more specific IDataReader type and looks like it's backwards compatible too!

[pimbrouwers]

Ref: commit 41a7b6c