Add an example for r2dbc connection URL

[62mkv]

it was really difficult to figure out proper H2 r2dbc URL for a "file" database.

Eventually it worked as follows:

r2dbc:h2:file://././build/h2db/db/dbname;DB_CLOSE_DELAY=-1;USER=username

can we add a section on this, because I could not find this information anywhere and had to debug ConnectionFactoryProvider

[mp911de]

Sorry that you had a hard time figuring out how to construct the URL. Do you want to submit a pull request that explains H2 specifics when constructing an URL?

[62mkv]

Hi Mark, thanks for this suggestion; I would gladly take this assignment however there're too many unknowns for me unfortunately. I am not even certain where to begin with that. For example, "r2dbc" URL parser seems to really demand a "schema", whereas in the H2 official URL (those are for jdbc, though) "schema" is mostly missing: http://www.h2database.com/html/features.html#database_url

also, I can't understand why first thing after schema is parsed as a "host", even though there's a "file" in it. If only I knew where to find the proper spec for an R2DBC H2 URL...

[mp911de]

R2DBC H2 is basically a wrapper for H2 that attempts to bridge what H2 provides into the R2DBC world. The H2 documentation is really only a first starting point but it cannot cover how R2DBC URL's get built.

You might be interested in the general URL scheme: https://r2dbc.io/spec/0.8.1.RELEASE/spec/html/#overview.connection.url

Basically, URL's can contain the host part ("authority") (r2dbc:h2:tcp://remote-host/database) or they can be built without (r2dbc:h2:file:///absolute/file/path) depending on what you're trying to express. Getting feedback on the documentation and the idea how you approach configuration helps us to learn which aspects we can improve.

[katzyn]

file: in H2 is also optional and assumed by default, jdbc:h2:/path/to/database is a perfectly valid JDBC URL. It actually means the I/O method; there are others, such as async: and nioMapped:.

[62mkv]

thanks, Mark! so basically my problem was that I was trying to refer to "relative" file path, and a leading "." was parsed as a "host", which lead to problems later.

So I had to begin the path with that "././" thing. It might even be a defect, not just a documentation missing.. I am not sure