I have a Symfony2/AngularJS application and using FOSRestBundle with JMS Serializer Bundle.
For normal entities every thing works great but in one of my entities that contains a collection of messages (topic entity) I need to return subset of messages in different situations.
For example for the Topic Entity Owner I want to return all messages of the topic for message owner I want to return just the message that posts with the message owner and for other users I don't want to return any messages but they can post a message on topic.
I'm not sure where to implement this. In the topic entity or in the controller or ...
The short answer is: In the controller.
Long version:
That you have a Topic entity that holds a collection of messages does not mean that you are not allowed to use just the message entity. Thus in case you don't need a whole topic then you should not use it also. Instead use an (array of the) message entity directly in your controller. You can use the findBy() or findOneBy() function to retrieve the message(s) you need.
Related
I'm creating a design for a Twitter application to practice DDD. My domain model looks like this:
The user and tweet are marked blue to indicate them being a aggregate root. Between the user and the tweet I want a bounded context, each will run in their respective microservice (auth and tweet).
To reference which user has created a tweet, but not run into a self-referencing loop, I have created the UserInfo object. The UserInfo object is created via events when a new user is created. It stores only the information the Tweet microservice will need of the user.
When I create a tweet I only provide the userid and relevant fields to the tweet, with that user id I want to be able to retrieve the UserInfo object, via id reference, to use it in the various child objects, such as Mentions and Poster.
The issue I run into is the persistance, at first glance I thought "Just provide the UserInfo object in the tweet constructor and it's done, all the child aggregates have access to it". But it's a bit harder on the Mention class, since the Mention will contain a dynamic username like so: "#anyuser". To validate if anyuser exists as a UserInfo object I need to query the database. However, I don't know who is mentioned before the tweet's content has been parsed, and that logic resides in the domain model itself and is called as a result of using the tweets constructor. Without this logic, no mentions are extracted so nothing can "yet" be validated.
If I cannot validate it before creating the tweet, because I need the extraction logic, and I cannot use the database repository inside the domain model layer, how can I validate the mentions properly?
Whenever an AR needs to reach out of it's own boundary to gather data there's two main solutions:
You pass in a service to the AR's method which allows it to perform the resolution. The service interface is defined in the domain, but most likely implemented in the infrastructure layer.
e.g. someAr.someMethod(args, someServiceImpl)
Note that if the data is required at construction time you may want to introduce a factory that takes a dependency on the service interface, performs the validation and returns an instance of the AR.
e.g.
tweetFactory = new TweetFactory(new SqlUserInfoLookupService(...));
tweet = tweetFactory.create(...);
You resolve the dependencies in the application layer first, then pass the required data. Note that the application layer could take a dependency onto a domain service in order to perform some reverse resolutions first.
e.g.
If the application layer would like to resolve the UserInfo for all mentions, but can't because it doesn't know how to parse mentions within the text it could always rely on a domain service or value object to perform that task first, then resolve the UserInfo dependencies and provide them to the Tweet AR. Be cautious here not to leak too much logic in the application layer though. If the orchestration logic becomes intertwined with business logic you may want to extract such use case processing logic in a domain service.
Finally, note that any data validated outside the boundary of an AR is always considered stale. The #xyz user could currently exist, but not exist anymore (e.g. deactivated) 1ms after the tweet was sent.
I have used rest servlet binding to expose route as a service.
I have used employeeClientBean as a POJO , wrapping the actual call to employee REST service within it, basically doing the role of a service client.
So, based on the method name passed, I call the respective method in employee REST service, through the employeeClientBean.
I want to know how how I can handle the scenarios as added in commments in the block of code.
I am just new to Camel, but felt POJO binding is better as it does not couple us to camel specific APIs like exchange and processor or even use
any specific components.
But, I am not sure how I can handle the above scenarios and return appropriate JSON responses to the user of the route service.
Can someone help me on this.
public void configure() throws Exception {
restConfiguration().component("servlet").bindingMode(RestBindingMode.json)
.dataFormatProperty("prettyPrint", "true")
.contextPath("camelroute/rest").port(8080);
rest("/employee").description("Employee Rest Service")
.consumes("application/json").produces("application/json")
.get("/{id}").description("Find employee by id").outType(Employee.class)
.to("bean:employeeClientBean? method=getEmployeeDetails(${header.id})")
//How to handle and return response to the user of the route service for the following scenarios for get/{id}"
//1.Passed id is not a valid one as per the system
//2.Failure to return details due to some issues
.post().description("Create a new Employee ").type(Employee.class)
.to("bean:employeeClientBean?method=createEmployee");
//How to handle and return correct response to the user of the route service for the following scenarios "
//1. Employee being created already exists in the system
//2. Some of the fields of employee passed are as not as per constraints on them
//3. Failure to create a employee due to some issues in server side (For Eg, DB Failure)
}
I fear you are putting Camel to bad use - as per the Apache documentation the REST module is supporting Consumer implementations, e.g. reading from a REST-endpoint, but NOT writing back to a caller.
For your use case you might want to switch framework. Syntactically, Ratpack goes in that direction.
I am currently learning more about the Google App Engine datastore, and I have some doubts regarding my understanding of the concept of defining a parent key. Now, here's the code for defining a parent key from the GAE documentation:
def guestbook_key(guestbook_name="default"):
"""Constructs a Datastore key for a Guestbook entity with guestbook_name."""
return ndb.Key('Guestbook', guestbook_name)
Note: this code is included in the source code of an application which accepts entries from a user and stores it in a datastore and displays them collectively on the homepage.
Now, this is what I understand from this code(please correct me if my understanding of this concept is not what it is supposed to be):
The 'guestbook_key' function defines a parent key, which we have named as 'default', for all the posts that the user submits into the datastore. So basically, all the posts that are submitted by the user are stored in an entity named 'Guestbook', and we define a key for it's parent(which is non-existent) named 'default'.
Please correct me wherever I went wrong with my understanding.
It really depends on how you use this key. Right now, it is just a name. If you put() it, you are putting a Guestbook type with the name "default".
However, if you are using it as a parent, then you may have code that looks like this:
post = Post(parent=guestbook_key())
post.comment = "This is a new post!"
post.put()
In this case, the new Post object will have the Guestbook object with the name "default" as a parent. Then, you could use an ancestor query to get all Posts for a given guestbook.
The reason you might choose to do this (rather than, for example, have a property on each post with the name of the guestbook) is that it guarantees strongly consistent results. This basically allows all requests to see a consistent view of a guestbook. If you didn't have strongly consistent results, you may see cases where a user writes a post but when they look at the guestbook it doesn't appear.
You are correct that you never actually need to create the Guestbook entity. When you define a parent key, it is actually creating a key where the parent key is a prefix of the child key.
I've set up a topic exchange such that the consumer queue is bound with "#.topic". I'd like to use different acknowledgement strategies based on the prefix. Is the full routing key sent to the consumer? If so, how do I access it? An answer in terms of AMQP concepts would probably be sufficient, but an answer involving rabbitmq-c would be ideal.
Even when you do a binding like you have given in your example the message received contains the full routing key. This means you can extract that in order to help you process the message. Unfortunately I only know how to do this in Java so try to extrapolate from there.
QueueingConsumer.Delivery delivery = consumer.nextDelivery();
String routingKey = delivery.getEnvelope().getRoutingKey();
The delivery object contains a body which is the payload and can be retrieve with delivery.getBody() and an Envelope object which contains other information like the full routing key.
We have ActiveMQ onto which the events that happen in the system are published. The project involves users adding entities to their watch-list and whenever there are events on those entities I would like an email to be sent out to the interested participants.
The use-case roughly translates to some one expressing an interest in a product information page on the catalog and an email being sent whenever any activity happens on that product (price goes down, there is a positive review etc.,). I had modelled this interaction as a Camel route.
So, for example, if the user says email me whenever this product's rating equals 5, then the following route would be added to the camel context:
from("activemq:topic:events.product.save").filter().xpath("/object[<object id>]/rating").isEqualTo("5").to("email:<user's email>")
Similarly if the user wants to be notified whenever there is a new comment on a product, another route would be created and so on. This could potentially, end up creating thousands of routes as each user starts adding their watches of interest.
Some questions that I have are:
Is this an acceptable way of creating dynamic routes? One option I am considering is to use recipient lists. But I haven't been able to come up with a solution that would make it elegant to route messages to the bean that would return the recipient list. For example for the case explained above would the bean have a bunch of if-else to see which recipient list to return?
The camelcontext has a method to load routes from a xml file but no method to persist the existing routes. What would be simplest (and efficient) way to persist these dynamically created routes? This thread in the camel-users list sums up my request.
Given the dynamic nature of your subscription requirements, you should use a database to store the information rather than trying to create dynamic routes. This is a much more scalable/appropriate use of technology...
Then you can only need a single static route or a POJO consumer (see below) that can process the product update messages using a simple POJO bean (bean-binding can help, etc). The POJO bean would then be responsible for querying the database to find all "interested" users and send an email using camel-mail
public class NotificationBean {
#Consume(uri="activemq:topic:events.product.save")
public void onUpdate(#XPath("/object/id") String id,
#XPath("/object/rating") String rating) {
//query database for subscriptions for this product ID/rating, etc.
//for each interested subscriber
//send email (camel-mail, etc)
}
public void addSubscription(String productID, Integer rating, String email) {
//create/update subscription entry in database, etc...
}
}