Repeating code using Grails domain find method - grails

Question

Initial Problem
If you have different methods that basically have only one line different, would there be a way to make it DRY by creating one method.
Example:
def showA( ) {
def instance
try {
instance = A.findById( params.id )
} catch ( Exception e ) {
def message = "Error while retrieving details for the given id ${ params.id }, $e"
log.error message
responseAsJson( 400, "Invalid id", message )
return false
}
return checkAndRender(instance, params.id);
}
def showB( ) {
def instance
try {
instance = B.findByBId( params.BId )
} catch ( Exception e ) {
def message = "Error while retrieving details for the given id ${ params.id }, $e"
log.error message
responseAsJson( 400, "Invalid id", message )
return false
}
return checkAndRender(instance, params.id);
}
So, would there be a way to make one method and simply pass as parameter:
The domain class
the ID to search for
Or would it be better to pass an SQL statement instead?
Update
Based on #dmahapatro comment, I came up with the following:
def showA( ) {
def clos = {id -> A.findByAId( id ) }
return findAndShow(clos, params.AId, params )
}
def showB( ) {
def clos = {id -> B.findByBId( id ) }
return findAndShow(clos, params.BId, params )
}
def findAndShow(Closure closure, def id, def p)
{
def instance
try {
instance = closure(id)
}
catch ( Exception e ) {
def message = "Error while retrieving instance details for the given id ${ id }, $e"
log.error message
responseAsJson( 400, "Invalid Id", message )
return false
}
return checkAndRender(instance, id);
}
Only remaining issues are:
How to cleanup even further / make it cleaner.
How to bypass warning:
The [findAndShow] action in [ApiController] accepts a parameter of
type [groovy.lang.Closure]. Interface types and abstract class types
are not supported as command objects. This parameter will be ignored.
def findAndShow(Closure closure, def id, def p)

Answer 1

First thing you should worry if you want a DRY code, is define a better exception handling. Try-catching your code everywhere to handle response to the client is not very DRY, if you put your data-access code in services, you can throw exceptions from them and use a global controller for catch the errors and handle the responses. E.g:
class ErrorController {
def serverError() {
if (request.format == 'json') {
//Code for handling errors in json request, request.exception stores the data about the exception.
} else {
//Code for handling errors in non-json request, e.g:
render(view: 'error', model: [msg: 'Something went wrong']) //add an error view for this
}
}
}
If you like, you can also add handlers for other types of errors (403, 404, etc)
Add to UrlMappings.groovy
"500"(controller: "error", action: "serverError")
Now you can refactor your code using your new error handling, and reflection:
Controller:
class MyController {
def myService
def show() {
def result = myService.myFind(params.className,params.id)
render result as JSON //Render stuff
}
}
Service:
import grails.util.Holders
class MyService {
def myFind(String className, Long id) {
def result = Holders.getGrailsApplication().getDomainClass('com.mypack.'+ className).findById(id)
if(!result) {
throw new ServiceException('really descriptive and usefull error msg')
}
}
}
I defined a ServiceException class so i can add custom logic for it in my ErrorController using the instanceOf operator.