I am struggling to understand the right way to implement association mapping between two entities from different bounded contexts using Doctrine 2. Suppose that there are two "User" and "Post" entities that belong to "User" and "Content" bounded contexts, respectively. There is also a "User" concept in "Content" context that determines the author of a "Post" through a Many-To-One association. Therefore, "User" in "Content" context is simply a value object containing the user id.
My question is that how should I implement this association using Doctrine 2? I have two solutions that both have their own issues:
Solution 1:
/**
* #ORM\Entity
* #ORM\Table(name="posts")
* #ORM\HasLifecycleCallbacks()
*/
class Post
{
...
/**
* #ORM\ManyToOne(targetEntity="UserBC\User", inversedBy="posts")
* #ORM\JoinColumn(name="user_id", referencedColumnName="id")
*/
private $user;
...
}
Solution 2:
/**
* #ORM\Entity
* #ORM\Table(name="posts")
* #ORM\HasLifecycleCallbacks()
*/
class Post
{
...
/**
* #ORM\Column(type="integer")
*/
private $user_id;
...
}
In the first solution, "User" entity from "User" context has been used inside "Content" context that violates DDD rules on BCs being independent of each other. The second solution respects DDD rules but affects database schema (removes database-level relationship between "users" and "posts" tables through a Foreign key constraint).
So, what is the right way to implement such associations?
The second solution is correct.
As you correctly observe, associations between different BCs should be avoided. The right way to reference an entity in another BC is by ID.
This has the consequence that the BCs don't have constraints between them in the DB. After all, you try to make them independent. If you feel that this is wrong, then the only way around this is to reconsider your BC design, i.e. merge the two BCs. This is however a decision that should not be driven by code smells, but by your context map.
Note: Referencing entities from other BCs by ID is only allowed if they are aggregate roots. If the referenced entity is not an AR, you have another design smell right there. Not a serious one, but still one that needs consideration.
Also for me the second solution is the correct one. And I try to answer to the #EresDev question:
"In solution 2, how do you know that $ user_id is correct and already exists?"
To do this you should use events. For example you could dispatch a PostPublicationEvent which contains the user id as well as post data. This event is listened by the User BC. Here you can verify that the user exists and dispatch a new UserValidatedEvent which is listened to by the Post BC. Now you can publish your post knowing that the user is valid.
While creating an app in Laravel 4 after reading T. Otwell's book on good design patterns in Laravel I found myself creating repositories for every table on the application.
I ended up with the following table structure:
Students: id, name
Courses: id, name, teacher_id
Teachers: id, name
Assignments: id, name, course_id
Scores (acts as a pivot between students and assignments): student_id, assignment_id, scores
I have repository classes with find, create, update and delete methods for all of these tables. Each repository has an Eloquent model which interacts with the database. Relationships are defined in the model per Laravel's documentation: http://laravel.com/docs/eloquent#relationships.
When creating a new course, all I do is calling the create method on the Course Repository. That course has assignments, so when creating one, I also want to create an entry in the score's table for each student in the course. I do this through the Assignment Repository. This implies the assignment repository communicates with two Eloquent models, with the Assignment and Student model.
My question is: as this app will probably grow in size and more relationships will be introduced, is it good practice to communicate with different Eloquent models in repositories or should this be done using other repositories instead (I mean calling other repositories from the Assignment repository) or should it be done in the Eloquent models all together?
Also, is it good practice to use the scores table as a pivot between assignments and students or should it be done somewhere else?
I am finishing up a large project using Laravel 4 and had to answer all of the questions you are asking right now. After reading all of the available Laravel books over at Leanpub, and tons of Googling, I came up with the following structure.
One Eloquent Model class per datable table
One Repository class per Eloquent Model
A Service class that may communicate between multiple Repository classes.
So let's say I'm building a movie database. I would have at least the following following Eloquent Model classes:
Movie
Studio
Director
Actor
Review
A repository class would encapsulate each Eloquent Model class and be responsible for CRUD operations on the database. The repository classes might look like this:
MovieRepository
StudioRepository
DirectorRepository
ActorRepository
ReviewRepository
Each repository class would extend a BaseRepository class which implements the following interface:
interface BaseRepositoryInterface
{
public function errors();
public function all(array $related = null);
public function get($id, array $related = null);
public function getWhere($column, $value, array $related = null);
public function getRecent($limit, array $related = null);
public function create(array $data);
public function update(array $data);
public function delete($id);
public function deleteWhere($column, $value);
}
A Service class is used to glue multiple repositories together and contains the real "business logic" of the application. Controllers only communicate with Service classes for Create, Update and Delete actions.
So when I want to create a new Movie record in the database, my MovieController class might have the following methods:
public function __construct(MovieRepositoryInterface $movieRepository, MovieServiceInterface $movieService)
{
$this->movieRepository = $movieRepository;
$this->movieService = $movieService;
}
public function postCreate()
{
if( ! $this->movieService->create(Input::all()))
{
return Redirect::back()->withErrors($this->movieService->errors())->withInput();
}
// New movie was saved successfully. Do whatever you need to do here.
}
It's up to you to determine how you POST data to your controllers, but let's say the data returned by Input::all() in the postCreate() method looks something like this:
$data = array(
'movie' => array(
'title' => 'Iron Eagle',
'year' => '1986',
'synopsis' => 'When Doug\'s father, an Air Force Pilot, is shot down by MiGs belonging to a radical Middle Eastern state, no one seems able to get him out. Doug finds Chappy, an Air Force Colonel who is intrigued by the idea of sending in two fighters piloted by himself and Doug to rescue Doug\'s father after bombing the MiG base.'
),
'actors' => array(
0 => 'Louis Gossett Jr.',
1 => 'Jason Gedrick',
2 => 'Larry B. Scott'
),
'director' => 'Sidney J. Furie',
'studio' => 'TriStar Pictures'
)
Since the MovieRepository shouldn't know how to create Actor, Director or Studio records in the database, we'll use our MovieService class, which might look something like this:
public function __construct(MovieRepositoryInterface $movieRepository, ActorRepositoryInterface $actorRepository, DirectorRepositoryInterface $directorRepository, StudioRepositoryInterface $studioRepository)
{
$this->movieRepository = $movieRepository;
$this->actorRepository = $actorRepository;
$this->directorRepository = $directorRepository;
$this->studioRepository = $studioRepository;
}
public function create(array $input)
{
$movieData = $input['movie'];
$actorsData = $input['actors'];
$directorData = $input['director'];
$studioData = $input['studio'];
// In a more complete example you would probably want to implement database transactions and perform input validation using the Laravel Validator class here.
// Create the new movie record
$movie = $this->movieRepository->create($movieData);
// Create the new actor records and associate them with the movie record
foreach($actors as $actor)
{
$actorModel = $this->actorRepository->create($actor);
$movie->actors()->save($actorModel);
}
// Create the director record and associate it with the movie record
$director = $this->directorRepository->create($directorData);
$director->movies()->associate($movie);
// Create the studio record and associate it with the movie record
$studio = $this->studioRepository->create($studioData);
$studio->movies()->associate($movie);
// Assume everything worked. In the real world you'll need to implement checks.
return true;
}
So what we're left with is a nice, sensible separation of concerns. Repositories are only aware of the Eloquent model they insert and retrieve from the database. Controllers don't care about repositories, they just hand off the data they collect from the user and pass it to the appropriate service. The service doesn't care how the data it receives is saved to the database, it just hands off the relevant data it was given by the controller to the appropriate repositories.
Keep in mind you're asking for opinions :D
Here's mine:
TL;DR: Yes, that's fine.
You're doing fine!
I do exactly what you are doing often and find it works great.
I often, however, organize repositories around business logic instead of having a repo-per-table. This is useful as it's a point of view centered around how your application should solve your "business problem".
A Course is a "entity", with attributes (title, id, etc) and even other entities (Assignments, which have their own attributes and possibly entities).
Your "Course" repository should be able to return a Course and the Courses' attributes/Assignments (including Assignment).
You can accomplish that with Eloquent, luckily.
(I often end up with a repository per table, but some repositories are used much more than others, and so have many more methods. Your "courses" repository may be much more full-featured than your Assignments repository, for instance, if your application centers more around Courses and less about a Courses' collection of Assignments).
The tricky part
I often use repositories inside of my repositories in order to do some database actions.
Any repository which implements Eloquent in order to handle data will likely return Eloquent models. In that light, it's fine if your Course model uses built-in relationships in order to retrieve or save Assignments (or any other use case). Our "implementation" is built around Eloquent.
From a practical point of view, this makes sense. We're unlikely to change data sources to something Eloquent can't handle (to a non-sql data source).
ORMS
The trickiest part of this setup, for me at least, is determing if Eloquent is actually helping or harming us. ORMs are a tricky subject, because while they help us greatly from a practical point of view, they also couple your "business logic entities" code with the code doing the data retrieval.
This sort of muddles up whether your repository's responsibility is actually for handling data or handling the retrieval / update of entities (business domain entities).
Furthermore, they act as the very objects you pass to your views. If you later have to get away from using Eloquent models in a repository, you'll need to make sure the variables passed to your views behave in the same way or have the same methods available, otherwise changing your data sources will roll into changing your views, and you've (partially) lost the purpose of abstracting your logic out to repositories in the first place - the maintainability of your project goes down as.
Anyway, these are somewhat incomplete thoughts. They are, as stated, merely my opinion, which happens to be the result of reading Domain Driven Design and watching videos like "uncle bob's" keynote at Ruby Midwest within the last year.
I like to think of it in terms of what my code is doing and what it is responsible for, rather than "right or wrong". This is how I break apart my responsibilities:
Controllers are the HTTP layer and route requests through to the underlying apis (aka, it controls the flow)
Models represent the database schema, and tell the application what the data looks like, what relationships it may have, as well as any global attributes that may be necessary (such as a name method for returning a concatenated first and last name)
Repositories represent the more complex queries and interactions with the models (I don't do any queries on model methods).
Search engines - classes that help me build complex search queries.
With this in mind, it makes sense every time to use a repository (whether you create interfaces.etc. is a whole other topic). I like this approach, because it means I know exactly where to go when I'm needing to do certain work.
I also tend to build a base repository, usually an abstract class which defines the main defaults - basically CRUD operations, and then each child can just extend and add methods as necessary, or overload the defaults. Injecting your model also helps this pattern to be quite robust.
Think of Repositories as a consistent filing cabinet of your data (not just your ORMs). The idea is that you want to grab data in a consistent simple to use API.
If you find yourself just doing Model::all(), Model::find(), Model::create() you probably won't benefit much from abstracting away a repository. On the other hand, if you want to do a bit more business logic to your queries or actions, you may want to create a repository to make an easier to use API for dealing with data.
I think you were asking if a repository would be the best way to deal with some of the more verbose syntax required to connect related models. Depending on the situation, there are a few things I may do:
Hanging a new child model off of a parent model (one-one or one-many), I would add a method to the child repository something like createWithParent($attributes, $parentModelInstance) and this would just add the $parentModelInstance->id into the parent_id field of the attributes and call create.
Attaching a many-many relationship, I actually create functions on the models so that I can run $instance->attachChild($childInstance). Note that this requires existing elements on both side.
Creating related models in one run, I create something that I call a Gateway (it may be a bit off from Fowler's definitions). Way I can call $gateway->createParentAndChild($parentAttributes, $childAttributes) instead of a bunch of logic that may change or that would complicate the logic that I have in a controller or command.
I have a strange requirement, and do not know how to solve it.
I have a context that holds all my main entities.
One of the entity is "customers".
Now i have an other application with they're entities in a separate context.
However that application should be able to access the customers from the main context.
I don't mind if there is no relation. I know the key of the customer and can access it manually.
I thought about something like this: (example is pseudo vb.net)
Imports MainModels
Namespace OtherApplication
Dim myMainContext as new MainModels.MainContext
Dim myAppContext as new AppContext
Dim myOrder as order = AppContext.Orders.Find(OrderIdent)
Dim myCustomer as customer = MainModels.MainContext.Customers.Find(myOrder.CustomerKey)
Is there a common way of solving those kind of requirements?
Reason for me to separate the two context is, that the MainContext is not going to change anymore, while the AppContext could be extended. There could even be a App2Context for some other application.
I have found following post:
Choosing the subset by exposing foreign keys
http://blogs.msdn.com/b/adonet/archive/2008/11/24/working-with-large-models-in-entity-framework-part-1.aspx
Found similar question:
Entity Framework: Multiple models - the current state of thinking?
Context
I have a Core Data entity called "LPFile" that represents a file on disk. It has an optional relationship to itself that allows files to "import" each other, like so:
imports<<---->>importedBy
Question
Now, suppose I have this situation with Files 1, 2, 3, and 4:
File 1 is importedBY 2 and 3. Files 2 & 3 are importedBY 4. What I want to know is: if I start at file 1, what's the most efficient approach for finding the "base" or "end" file of this relationship (in this case, that's file 4)? I can write a simple recursive function that looks at each entity in the importedBy relationship, and follows the chain until it finds an entity with zero entities in the importedBy relationship, but I wanted to see if Core Data has a pre-baked method to do this.
Thanks!
Core Data has no pre-baked method to find a root. So your way of looping through it is fine.
Altough this questions has been answered, I solved a similiar problem on a tree made by same entities by adding an attribute called with much fantasy "breadcrumb" and filling that at runtime so that if I have entity model
X {
name NSString
breadcrumb NSString
to-many X relationship
}
A,B,C,D,E like that:
A-->B
-->C-->D
-->E
I end up with this:
A {
breadcrumb /A
relationship B,C,E
}
B {
breadcrumb /A/B
relationship nil
}
C {
breadcrumb /A/C
relationship D
}
D {
breadcrumb /A/C/D
relationship nil
}
E {
breadcrumb /A/D
relationship nil
}
I can say that indexing breadcrumb, make things faster, and I can do regex search.
Important, when I have an entity I can easily find its root without cycling.
Of course I had some mechanism to avoid loop and uniqueness of breadcrumb, based on 'name' attribute.
Starting with a List of entities and needing all dependent entities through an association, is there a way to use the corresponding navigation-propertiy to load all child-entities with one db-round-trip? Ie. generate a single WHERE fkId IN (...) statement via navigation property?
More details
I've found these ways to load the children:
Keep the set of parent-entities as IQueriable<T>
Not good since the db will have to find the main set every time and join to get the requested data.
Put the parent-objects into an array or list, then get related data through navigation properties.
var children = parentArray.Select(p => p.Children).Distinct()
This is slow since it will generate a select for every main-entity.
Creates duplicate objects since each set of children is created independetly.
Put the foreign keys from the main entities into an array then filter the entire dependent-ObjectSet
var foreignKeyIds = parentArray.Select(p => p.Id).ToArray();
var children = Children.Where(d => foreignKeyIds.Contains(d.Id))
Linq then generates the desired "WHERE foreignKeyId IN (...)"-clause.
This is fast but only possible for 1:*-relations since linking-tables are mapped away.
Removes the readablity advantage of EF by using Ids after all
The navigation-properties of type EntityCollection<T> are not populated
Eager loading though the .Include()-methods, included for completeness (asking for lazy-loading)
Alledgedly joins everything included together and returns one giant flat result.
Have to decide up front which data to use
It there some way to get the simplicity of 2 with the performance of 3?
You could attach the parent object to your context and get the children when needed.
foreach (T parent in parents) {
_context.Attach(parent);
}
var children = parents.Select(p => p.Children);
Edit: for attaching multiple, just iterate.
I think finding a good answer is not possible or at least not worth the trouble. Instead a micro ORM like Dapper give the big benefit of removing the need to map between sql-columns and object-properties and does it without the need to create a model first. Also one simply writes the desired sql instead of understanding what linq to write to have it generated. IQueryable<T> will be missed though.