DbString - analyzer and runtime

[mgravell]

DbString is a Dapper type that allows metadata to be conveyed for string types.

However:

• it is allocatey
• it isn't touched by AOT today
• what it achieves is the same as DbValue]

Suggestions:

1. we need to verify that [DbValue] allows the size and type to be conveyed into DbParameter
2. we should emit a warning to use [DbValue] instead
3. we should probably treat DbString as a recognized type, and configure things correctly
4. for this last, I would propose (if any DbString are encountered) writing a helper method into the output (we have some prior art that copies entire files into the output; that would be fine) with a method that takes a DbParameter and DbString (global:: qualified) and does the right things:

• if the entire DbString is null, just set Value to DbNull
• set the size if appropriate
• set the type if appropriate
• set the value using AsValue, or a (object)value.Value ?? DbNull if easier

The reason we can't put this into the library is that we can't ref Dapper directly because of the Dapper/Dapper.StrongName duality - hence we need to implement it in codegen

[DeagleGross]

questions:

1. what does it mean "[DbValue] allows the size and type to be conveyed into DbParameter" (I can see both of them have System.Data.DbType member + DbParameter can handle strings (which DbString are))? Why is DbParameter in the context here?
2. where is the code that copies entire files into the output?

[mgravell]

1. when passing some member .Foo into the DB, we do that via a parameter; by default we can only guess as to the type and other properties - but sometimes the details matter, so this tribute allows the .Size and .DbType of the parameter object to be controlled more explicitly

2 do you mean this? https://github.com/DapperLib/DapperAOT/blob/main/src/Dapper.AOT.Analyzers/CodeAnalysis/Writers/InterceptorsLocationAttributeWriter.cs#L24