exposed-wiki/FAQ.md

Q: Can I use multiple Database Connections?

A: Yes. At the moment the connection usage is implicit (ie: via ThreadLocal), and it is not possible to specify connection explicitly. So switching between connections is not supported at the moment. There is an open issue about it: https://github.com/JetBrains/Exposed/issues/93.

Q: Is Array column type supported?

A: Not at the moment. More info here: https://github.com/JetBrains/Exposed/issues/150
The complete list of supported data types can be found here: Data Types.

Q: Is upsert supported?

A: Upsert is an instruction to the Database to insert a new row or update existing row based on a table key. It is not supported as part of the library but it is possible to implement on top of it. See this issue: https://github.com/JetBrains/Exposed/issues/167 and example here: https://medium.com/@OhadShai/first-steps-with-kotlin-exposed-cb361a9bf5ac

Q: Is json type supported?

A: Not at the moment. Here is the issue: https://github.com/JetBrains/Exposed/issues/127
The complete list of supported data types can be found here: Data Types.

Q: Is it possible to use native sql / sql as a string?

A: It is not supported as part of the library but it is possible to implement on top of it and use it like this:

fun <T:Any> String.execAndMap(transform : (ResultSet) -> T) : List<T> {
     val result = arrayListOf<T>()
     TransactionManager.current().exec("") { rs ->
          while (rs.next()) {
               result += transform(rs)
          }
     }
     return result
}

"select u.name, c.name from user u inner join city c where blah blah".execAndMap { rs ->
    rs.getString("u.name") to rs.getString("c.name") 
}

More info in this issue: https://github.com/JetBrains/Exposed/issues/118