how to check whether database supports column type

[HoneyryderChuck]

I'm expanding the test suite of one of my gems to support sqlserver, via the tinytds adapter. I've seen that my tests rely on on the database supporting a JSON type, which tinyds adapter does not support (although recent versions of sqlserver seem to support it?).

In order to fallback to TEXT column in such cases, I'd need a way to verify support for a given datatype in the migration:

# smth like
if supports_datatype?(:json)
  column :data_before, :json, null: true
else
 column :data_before, :text, null: true

but I didn't find a function I could use for that effect. Is there one?

[jeremyevans]

There currently isn't a database-independent method to use to check whether a type is supported. I'm guessing the only generic approach that would work would be attempting to create a single-column table with the type, and see if it fails, and removing the table afterward. Even that is not 100%, because there are other reasons table creation could fail, such as lack of permissions.