Assuming that I have a Scala case class that is persisted using the Salat/Casbah/Mongo stack, I want to set up pre-persistence validation logic like I could easily do in Rails using ActiveRecord hooks or in Java using JSR 303 bean validation.
Perhaps there is a better way to think about this in a functional paradigm, but I want to accomplish something like the following:
case class SomeItem(
id: ObjectId = new ObjectId,
someProperty: String) {
#PrePersistence
def validate() = {
//perform some logic
//fail document save in certain conditions
}
}
I am having trouble finding any documentation on how to do something like this in Salat. I do see a #Persist annotation but it seems focused on serializing specific values and not creating hooks.
It seems like one option is to override the save method in the SalatDAO for my case class. Does anyone have an example of this or know of a better, built-in way to handle validation tied to a pre-persistence event?
Thanks!
Salat developer here.
Yes, #Persist is simply for ensuring that fields that aren't in the constructor are serialized - this is particularly useful for manipulating data in MongoDB. One example is where you want to ensure that all the fields are populated with a value so you can sort sensibly, but the value is an Option which may not be present.
Unfortunately, the Java driver doesn't offer lifecycle callbacks like the Ruby driver :(
But what you want should be easy enough to do. Please file an issue at https://github.com/novus/salat/issues and describe how you would like the validation to behave - we can start a discussion and I can try to get something in for you in the 1.9.2 release.
Related
I'm looking for a way of condensing some of my AS3 code to avoid almost duplicate commands.
The issue is that I have multiple variables with almost the same name e.g. frenchLanguage, englishLanguage, germanLanguage, spanishLanguage
My Controller class contains public static variables (these are accessed across multiple classes) and I need a way to be able to call a few of these variables dynamically. If the variables are in the class you are calling them from you can do this to access them dynamically:
this["spanish"+"Language"]
In AS3 it's not possible to write something like:
Controller.this["spanish"+"Language"]
Is there any way to achieve this? Although everything is working I want to be able to keep my code as minimal as possible.
It is possible to access public static properties of a class this way (assuming the class name is Controller as in your example:
Controller['propertyName']
I'm not sure how this helps to have "minimal code", but this would be a different topic/question, which might need some more details on what you want to achive.
Having said that, I like the approach DodgerThud suggests in the comments of grouping similar values in a (dynamic) Object or Dictonary and give it a proper name.
Keep in mind, that if the string you pass in as the key to the class or dynamic object is created from (textual) user input you should have some checks for the validity of that data, otherwise your programm might crash or expose other fields to the user.
It would make sense to utilize a Dictionary object for a set of variables inherited: it provides a solid logic and it happens to work...
I do not think this is what you are trying to accomplish. I may be wrong.
Classes in AS3 are always wrapped within a package - this is true whether you have compiled from Flash, Flex, Air, or any other...
Don't let Adobe confuse you. This was only done in AS3 to use Java-Based conventions. Regardless, a loosely typed language is often misunderstood, unfortunately. So:
this["SuperObject"]["SubObject"]["ObjectsMethod"][ObjectsMethodsVariable"](args..);
... is technically reliable because the compiler avoids dot notation but at runtime it will collect a lot of unnecessary data to maintain those types of calls.
If efficiency becomes an issue..
Use:
package packages {
import flash.*.*:
class This implements ISpecialInterface {
// Data Objects and Function Model
// for This Class
}
package packages {
import...
class ISpecialInterface extends IEventDispatcher
When using the Grails MongoDB GORM Plugin (v 1.0.0.GA) standalone (i.e. WITHOUT the Hibernate jars), are the listener events supposed to work?
I've got domain classes with afterInsert, afterUpdate, etc but the event either doesn't fire or the methods are just not getting called.
I'm not seeing any specific guidance on this in the plugin docs. Does anyone know what's supposed to happen? Thanks.
Answering my own question for the benefit of others who may find it:
Apparently, when using MongoDB/GORM without Hibernate, GORM finds the event listeners by looking for the method signature on your domain object class. A closure won't do work (despite the fact that it will work when using Hibernate).
Thus, you cannot use a pattern like this:
class A {
int blah
String foo
def afterInsert = { ... }
}
Instead, do this:
class A {
int blah
String foo
def afterInsert() { ... }
}
Was wondering if there's a way one can handle conversion errors in a lenient way.
Given a query that returns a List[ModelObject]
If there are 5 DBObjects retrieved, one of them is throwing a ConversionException when converted to ModelObject, is there a way to return the 4 convertible objects and provide a hook for the 1 conversion failure?
A bit late, but this answer might help someone else's search
I agree it would be nice to do this on a policy basis - at the moment, if you get a single conversion error, you get no list at all. I think there are use cases where this is a valid need.
However, since you can't, you need to register a custom converter for your ModelObject that converts leniently...
public class DBObjectToModelObjectConverter implements Converter<DBObject,ModelObject>{
public ModelObject convert(DBObject s) {
... Read from the DBObject into your ModelObject and work around the bad data
}
}
and then register this as a custom converter in your bean definitions. Something like:
<bean id="lenientModelReadConverter" class="com.my.DBObjectToModelObjectConverter"/>
<mongo:custom-converters>
<mongo:converter ref="lenientModelReadConverter"/>
</mongo:custom-converters>
I know it's not directly possible to serialize a function/anonymous class to the database but what are the alternatives? Do you know any useful approach to this?
To present my situation: I want to award a user "badges" based on his scores. So I have different types of badges that can be easily defined by extending this class:
class BadgeType(id:Long, name:String, detector:Function1[List[UserScore],Boolean])
The detector member is a function that walks the list of scores and return true if the User qualifies for a badge of this type.
The problem is that each time I want to add/edit/modify a badge type I need to edit the source code, recompile the whole thing and re-deploy the server. It would be much more useful if I could persist all BadgeType instances to a database. But how to do that?
The only thing that comes to mind is to have the body of the function as a script (ex: Groovy) that is evaluated at runtime.
Another approach (that does not involve a database) might be to have each badge type into a jar that I can somehow hot-deploy at runtime, which I guess is how a plugin-system might work.
What do you think?
My very brief advice is that if you want this to be truly data-driven, you need to implement a rules DSL and an interpreter. The rules are what get saved to the database, and the interpreter takes a rule instance and evaluates it against some context.
But that's overkill most of the time. You're better off having a little snippet of actual Scala code that implements the rule for each badge, give them unique IDs, then store the IDs in the database.
e.g.:
trait BadgeEval extends Function1[User,Boolean] {
def badgeId: Int
}
object Badge1234 extends BadgeEval {
def badgeId = 1234
def apply(user: User) = {
user.isSufficientlyAwesome // && ...
}
}
You can either have a big whitelist of BadgeEval instances:
val weDontNeedNoStinkingBadges = Map(
1234 -> Badge1234,
5678 -> Badge5678,
// ...
}
def evaluator(id: Int): Option[BadgeEval] = weDontNeedNoStinkingBadges.get(id)
def doesUserGetBadge(user: User, id: Int) = evaluator(id).map(_(user)).getOrElse(false)
... or if you want to keep them decoupled, use reflection:
def badgeEvalClass(id: Int) = Class.forName("com.example.badge.Badge" + id + "$").asInstanceOf[Class[BadgeEval]]
... and if you're interested in runtime pluggability, try the service provider pattern.
You can try and use Scala Continuations - they can give you the ability to serialize the computation and run it at later time or even on another machine.
Some links:
Continuations
What are Scala continuations and why use them?
Swarm - Concurrency with Scala Continuations
Serialization relates to data rather than methods. You cannot serialize functionality because it is a class file which is designed to serialize that and object serialization serializes the fields of an object.
So like Alex says, you need a rule engine.
Try this one if you want something fairly simple, which is string based, so you can serialize the rules as strings in a database or file:
http://blog.maxant.co.uk/pebble/2011/11/12/1321129560000.html
Using a DSL has the same problems unless you interpret or compile the code at runtime.
Is there any way to create a fake from a System.Type object in FakeItEasy? Similar to:
var instance = A.Fake(type);
I try to write a fake container for AutoFac that automatically return fakes for all resolved types. I have looked in the code for FakeItEasy and all methods that support this is behind internal classes but I have found the interface IFakeObjectContainer that looks pretty interesting, but the implementations still need registration of objects that is the thing that I want to come around.
As of FakeItEasy 2.1.0 (but do consider upgrading to the latest release for more features and better bugfixes), you can create a fake from a Type like so:
using FakeItEasy.Sdk;
…
object fake = Create.Fake(type);
If you must use an earlier release, you could use some reflection based approach to create a method info for the A.Fake() method. (since it's about auto mocking this shouldn't be a problem really).
This is best done using a registration handler. You should look into how AutofacContrib.Moq implements its MoqRegistrationHandler. You'll see that it is actually using the generic method MockRepository.Create to make fake instances. Creating a similar handler for FakeItEasy should be quite simple.