Scala Anorm-如何正确使用

Question

Scala's play framework claims that Anorm, and writing your own SQL is better that ORM's. One of the reasons is that you anyway most often want only transfer data between database and frontend as json. However, most tutorials, and even Play documentation give examples of parsing sql's returned values into case classes, in order to parse it again into json. We still have an object relational mapping anyway, or am I missing a point?

In my database there exists a table with 33 columns. Declaring a case class takes me 33 lines, declaring a parser with ~ operator, takes another 33. Using case statement to create an Object, another 66! Seriously, what am I doing wrong? Is there any shortcut? In django the same thing takes only 33 lines.

Answer 1

If you're using Anorm within a Play application, then the mapping into a Json object of your case class (assuming it has fairly normal apply and unapply functions defined for it, which most do) should be pretty much as simple as defining an implicit which uses the >2.10 macro based Json-inception methods...so all you actually need is a definition like this:

implicit val myCaseFormats = Json.format[MyCaseClass]

where 'MyCaseClass' is the name of your case type. You could even bake this into the parser combinator you use for de-serialising row-sets back from the database...that would dramatically clean up your code and cut down the amount of code you have to write.

See here for details on the Json macros: https://www.playframework.com/documentation/2.1.1/ScalaJsonInception

I use this quite extensively in a pretty large code-base and it does make things quite clean.

In terms of your parsers for Anorm, remember that you don't have to produce a case-class instance as a result of a parse...you can actually return anything you like, which could just be an indexed sequence of your column values (if you're using something like Shapeless to allow for mixed-type lists etc...) or some other structure.

You do hav macro support in Anorm as well so the the parsers for your case classes can be one liners like this:

import norm.{Macro, Rowset}

val parser = Macro.namedParser[MyCaseClass] 

If you want to do something custom, (such as parse direct to JsValue) then you have the flexibility to just hand-craft a more crafty parser.

HTH