I have 3 tables: Computers, Flaws, Patch
Flaws hasMany Computers
Computers hasMany Patches
Patches hasOne Computers
So When I have a flaw concerning a computer, the computer is patched, the problem is that when I try to retrieve the Flaw with it's computers and patches, I get all patched, related to any flaw and not only the one requested.
class Computer extends \Eloquent {
public function patches()
{
return $this->hasMany('App\Models\Patch', 'computer_id');
}
}
class Flaw extends \Eloquent {
public function computer()
{
return $this->belongsTo('App\Models\Device\Computer\Computer', 'computer_id');
}
}
class Patch extends \Eloquent{
public function computer()
{
return $this->belongsTo('App\Models\Device\Computer\Computer', 'computer_id');
}
}
How can I retrieve, with this Eloquent query, ONLY the patches regarding the current flaw ?
Flaw::with(['computers', 'computers.patches'])->findOrFail($flawId);
Related
I have my Grails Domain classes annotated with #Resource with the uri specifications in UrlMappings where I declare the resource nesting. But even though according to https://docs.grails.org/latest/guide/theWebLayer.html#restfulMappings it seems that just declaring this the right way, I should have the correct behavior that I wanted, which is that a URL pattern such as /nesting/1/nested will list the nested domain that belonged to the nesting domain with ID 1, the observed behavior is that it just lists out all nested domain objects.
So for that, my workaround is to have a controller implemented that overrides the listResources to filter the nested domain by the nesting domain. But what's weird to me is why I even have to do that at all. The documentation said it defaults to the index action but said index action seems to just behave as if it's the index() of nested (without taking nesting into account).
My domain entities are WeightSensor:
#Resource(formats = ['json', 'xml'])
class WeightSensor extends Sensor<WeightData>
{
Set<WeightData> data
static constraints = {
}
}
its superclass Sensor
#Resource(formats = ['json', 'xml'])
class Sensor<T extends SensorData>
{
Set<T> data
static hasMany = [data: SensorData]
String name
static constraints = {
name unique: true
}
}
and WeightData
class WeightData extends SensorData
{
Float weight
static constraints = {
weight nullable: false
}
}
and its superclass SensorData
class SensorData
{
#BindingFormat('yyyy-MM-dd HH:mm:ss.S') // 2019-07-11 22:00:28.909
Date timestamp
static belongsTo = [sensor: Sensor]
static constraints = {
timestamp nullable: false
}
}
In my UrlMappings I have the following:
"/sensor/weight"(resources: 'weightSensor') {
"/data"(resources: "weightData")
}
My WeightDataController extends from a SensorDataController:
class WeightDataController extends SensorDataController<WeightSensor, WeightData>
{
#SuppressWarnings("GroovyUnusedDeclaration")
static responseFormats = ['json', 'xml']
WeightDataController()
{
super(WeightData, WeightSensor, "weightSensorId")
}
}
And SensorDataController in turn extends RestfulController, and overrides the listAllResources method as below.
import grails.rest.RestfulController
class SensorDataController<S extends Sensor, T extends SensorData> extends RestfulController<T>
{
String idProperty
Class<S> sensorType
#SuppressWarnings("GroovyUnusedDeclaration")
static responseFormats = ['json', 'xml']
protected SensorDataController(Class<T> dataType, Class<S> sensorType, String idProperty)
{
super(dataType)
this.idProperty = idProperty
this.sensorType = sensorType
}
#Override
protected List<T> listAllResources(Map params)
{
Long sensorId = params.get(idProperty) as Long
if (sensorId)
{
resource.withCriteria() {
eq 'sensor.id', sensorId
maxResults params.max ?: 10
firstResult params.offset ?: 0
} as List<T>
}
else
{
super.listAllResources(params)
}
}
}
Note because in order for me to have my WeightDataController class be used, I needed to remove the #Resource on top of WeightData domain entity above, another nice little gem of wisdom I had to discover with trial and error.
I can probably blame this on the fact that the documentation for nested resources seems a bit open to interpretation. But when we see in the documentation a URL like GET books/${bookId}/authors, doesn't that look like it should return the list of Author objects that belongs to the Book instance IDed by bookId?
I know that I'm not alone as I did find this online of someone asking the same question I have - https://gist.github.com/mnellemann/7cfff1c721ef32f0be6c63574795f795 but no one answered them either. I also came across another SO post nested RESTful resources that was abandoned 5 years ago as well.
But 3 people having the same question and no one responding to our questions (I asked mine on the Grails Slack community) usefully because there is a work-around is not acceptable. At the risk of having my question taken down for a slew of different reasons, I question the usefulness of even having the grails nested resource URL mapping in the first place because I could have done everything manually myself without having to "declare" such a nesting in UrlMappings.
In closing, what I'm trying to find out is whether or not there's more "configuration" I need to do to get Grails nested Resources to behave in the way that I expected, which is how the documentation painted, correctly. Because just doing what was described doesn't get me that.
It's a common situation but I somehow couldn't manage to find a reasonable solution so far. Basically I need the following:
I have the model House which contains a couple of other models (e.g. Brick, 'Stick', 'Chair' etc.). Each one of them has a belongsTo relation to the House (so basically in the sticks, chairs and bricks table there is a house_id column). Each model contains a public function house() method which returns the house they're part of. Now comes the problem that I'd like to get all of a house's supplies by a method, let's say for example public function supplies(), which should return a collection of instances of the classes Stick, Chair and Brick. Is there any convenient way to achieve that? Could I for example unite those classes by a trait and somehow point to that trait in the house's method or maybe with a BaseClass, let's say Supply, that all the supplies should inherit? Any recommendances? Any help is greatly appreciated and thanks in advance!
There is no built-in support for this in Laravel.
You can define separate HasMany relationships and then merge them with an accessor:
class House extends Model {
public function bricks() {
return $this->hasMany(Brick::class);
}
public function chairs() {
return $this->hasMany(Chair::class);
}
public function sticks() {
return $this->hasMany(Stick::class);
}
public function getSuppliesAttribute() {
return $this->bricks->toBase()->merge($this->chairs)->merge($this->sticks);
}
}
$supplies = $house->supplies;
+++ UPDATE +++
I've created a package for merging relationships using views:
https://github.com/staudenmeir/laravel-merged-relations
First, create the merge view in a migration:
use Staudenmeir\LaravelMergedRelations\Facades\Schema;
Schema::createMergeView(
'supplies', [(new House)->bricks(), (new House)->chairs(), (new House)->sticks()]
);
Then define the relationship:
class House extends Model
{
use \Staudenmeir\LaravelMergedRelations\Eloquent\HasMergedRelationships;
public function supplies()
{
return $this->mergedRelation('supplies');
}
}
Use it like any other relationship:
House::find($id)->supplies;
House::find($id)->supplies()->paginate();
House::with('supplies')->get();
i have a question on mongodb, model cakephp and relationships.
I'd create the following relations:
User -> hasMany -> City
City -> belongsTo -> User
In MongoDB, I have two tables:
users
cities (with key user_id)
In cakephp, I have 2 model:
User.php
class User extends Model {
public $name = 'User';
public $actsAs = array('Containable');
public $hasMany = array ('City');
..
}
and:
City.php
class City extends Model {
public $name = 'City';
public $actsAs = array('Containable');
public $belongsTo = array('User');
..
}
In my controller I use :
$user = $this->User->find('all');
but it doesn't work. In sql dump, cakephp uses a find only on tbl users.
Why? Where I wrong?
I normally place recursive to -1 and containable in app model, so it applies to all models you create unless you override specifically.
class AppModel extends Model {
public $actsAs = array('Containable');
public $recursive = -1;
}
Your relationships are fine, although I usually add className and foreignKey just to be safe and clear. In your controller you should do something like this:
$users = $this->User->find('all', array(
'contain' => array(
'City'
)
));
Recursive will prevent any associated records being included by default, this is good as sometimes you do not need the recursive data and extra data will help slow down your application.
Next adding contain into your find call may seem like a chore but it will be clear and concise what you are querying, any 3rd party developer will understand exactly what you are doing if they know how to use Cake. Hope this helps.
I am designing a system that has a simple Entity Framework backed domain object that has fields I need to update based on a series of rules - I want to implement these rules progressively (in an agile style) and as I am using EF I am sceptical about putting each rule into the domain object. However, I want to avoid writing "procedural code" and using anemic domain models. This all needs to be testable as well.
As an example, the object is:
class Employee {
private string Name;
private float Salary;
private float PensionPot;
private bool _pension;
private bool _eligibleForPension;
}
I need to build rules such as "if Salary is higher than 100,000 and _eligibleForPension is false then set _eligibleForPension as true" and "if _pension is true then set _eligibleForPension as true".
There are approximately 20 such rules and I am looking for advice whether they should be implemented in the Employee class or in something like an EmployeeRules class? My first thought was to create a separate class for each rule inheriting from "Rule" and then apply each rule to the Employee class, maybe using the Visitor pattern but I'd have to expose all the fields to the rules to do this so it feels wrong. Having each rule on the Employee class though doesn't feel quite right either. How would this be implemented?
The second concern is that the actual Employees are Entity Framework entities backed to the DB so I don't feel happy adding logic to these "Entities" - especially when I need to mock the objects for unit testing each rule. How could I mock them if they have the rules I'm testing on the same object?
I have been thinking of using AutoMapper to convert to a simpler domain object before applying rules but then need to manage the updates to the fields myself. Any advice on this too?
One approach is to make the rules inner classes of Employee. The benefit of this approach is that the fields can remain private. Also, the invocation of the rules can be enforced by the Employee class itself, ensuring that they are always invoked when needed:
class Employee
{
string id;
string name;
float salary;
float pensionPot;
bool pension;
bool eligibleForPension;
public void ChangeSalary(float salary)
{
this.salary = salary;
ApplyRules();
}
public void MakeEligibleForPension()
{
this.eligibleForPension = true;
ApplyRules(); // may or may not be needed
}
void ApplyRules()
{
rules.ForEach(rule => rule.Apply(this));
}
readonly static List<IEmployeeRule> rules;
static Employee()
{
rules = new List<IEmployeeRule>
{
new SalaryBasedPensionEligibilityRule()
};
}
interface IEmployeeRule
{
void Apply(Employee employee);
}
class SalaryBasedPensionEligibilityRule : IEmployeeRule
{
public void Apply(Employee employee)
{
if (employee.salary > 100000 && !employee.eligibleForPension)
{
employee.MakeEligibleForPension();
}
}
}
}
One problem here is that the Employee class has to contain all rule implementations. This isn't a major problem since the rules embody business logic associated with employee pensions and so they do belong together.
Business rules are usually an interesting topic. There may certainly be a difference between an aggregate / entity invariant and a business rule. Business rules may need external data and I wouldn't agree with a rule changing an aggregate / entity.
You should think specification pattern for rules. The rule should basically just return whether it was broken or not with possibly a description of sorts.
In your example SalaryBasedPensionEligibilityRule, as used by eulerfx, may need some PensionThreshold. This rule really does look more like a task since the rule really isn't checking any validity of the entity.
So I would suggest that rules are a decision mechanism and tasks are for changing the state.
That being said you probably want to ask the entity for advice here since you may not want to expose the state:
public class Employee
{
float salary;
bool eligibleForPension;
public bool QualifiesForPension(float pensionThreshold)
{
return salary > pensionThreshold && !eligibleForPension;
}
public void MakeEligibleForPension()
{
eligibleForPension = true;
}
}
This sticks with the command/query separation idea.
If you are building directly from your ORM objects and do not want to, or cannot, include all the behaviour then that is OK --- but it certainly would help :)
Does anyone know the best way to refactor a God-object?
Its not as simple as breaking it into a number of smaller classes, because there is a high method coupling. If I pull out one method, i usually end up pulling every other method out.
It's like Jenga. You will need patience and a steady hand, otherwise you have to recreate everything from scratch. Which is not bad, per se - sometimes one needs to throw away code.
Other advice:
Think before pulling out methods: on what data does this method operate? What responsibility does it have?
Try to maintain the interface of the god class at first and delegate calls to the new extracted classes. In the end the god class should be a pure facade without own logic. Then you can keep it for convenience or throw it away and start to use the new classes only
Unit Tests help: write tests for each method before extracting it to assure you don't break functionality
I assume "God Object" means a huge class (measured in lines of code).
The basic idea is to extract parts of its functions into other classes.
In order to find those you can look for
fields/parameters that often get used together. They might move together into a new class
methods (or parts of methods) that use only a small subset of the fields in the class, the might move into a class containing just those field.
primitive types (int, String, boolean). They often are really value objects before their coming out. Once they are value object, they often attract methods.
look at the usage of the god object. Are there different methods used by different clients? Those might go in separate interfaces. Those intefaces might in turn have separate implementations.
For actually doing these changes you should have some infrastructure and tools at your command:
Tests: Have a (possibly generated) exhaustive set of tests ready that you can run often. Be extremely careful with changes you do without tests. I do those, but limit them to things like extract method, which I can do completely with a single IDE action.
Version Control: You want to have a version control that allows you to commit every 2 minutes, without really slowing you down. SVN doesn't really work. Git does.
Mikado Method: The idea of the Mikado Method is to try a change. If it works great. If not take note what is breaking, add them as dependency to the change you started with. Rollback you changes. In the resulting graph, repeat the process with a node that has no dependencies yet. http://mikadomethod.wordpress.com/book/
According to the book "Object Oriented Metrics in Practice" by Lanza and Marinescu, The God Class design flaw refers to classes that tend to centralize the intelligence of the system. A God Class performs too much work on its own, delegating only minor details to a set of trivial classes and using the data from other classes.
The detection of a God Class is based on three main characteristics:
They heavily access data of other simpler classes, either directly or using accessor methods.
They are large and complex
They have a lot of non-communicative behavior i.e., there is a low
cohesion between the methods belonging to that class.
Refactoring a God Class is a complex task, as this disharmony is often a cumulative effect of other disharmonies that occur at the method level. Therefore, performing such a refactoring requires additional and more fine-grained information about the methods of the class, and sometimes even about its inheritance context. A first approach is to identify clusters of methods and attributes that are tied together and to extract these islands into separate classes.
Split Up God Class method from the book "Object-Oriented Reengineering Patterns" proposes to incrementally redistribute the responsibilities of the God Class either to its collaborating classes or to new classes that are pulled out of the God Class.
The book "Working Effectively with Legacy Code" presents some techniques such as Sprout Method, Sprout Class, Wrap Method to be able to test the legacy systems that can be used to support the refactoring of God Classes.
What I would do, is to sub-group methods in the God Class which utilize the same class properties as inputs or outputs. After that, I would split the class into sub-classes, where each sub-class will hold the methods in a sub-group, and the properties which these methods utilize.
That way, each new class will be smaller and more coherent (meaning that all their methods will work on similar class properties). Moreover, there will be less dependency for each new class we generated. After that, we can further reduce those dependencies since we can now understand the code better.
In general, I would say that there are a couple of different methods according to the situation at hand. As an example, let's say that you have a god class named "LoginManager" that validates user information, updates "OnlineUserService" so the user is added to the online user list, and returns login-specific data (such as Welcome screen and one time offers)to the client.
So your class will look something like this:
import java.util.ArrayList;
import java.util.List;
public class LoginManager {
public void handleLogin(String hashedUserId, String hashedUserPassword){
String userId = decryptHashedString(hashedUserId);
String userPassword = decryptHashedString(hashedUserPassword);
if(!validateUser(userId, userPassword)){ return; }
updateOnlineUserService(userId);
sendCustomizedLoginMessage(userId);
sendOneTimeOffer(userId);
}
public String decryptHashedString(String hashedString){
String userId = "";
//TODO Decrypt hashed string for 150 lines of code...
return userId;
}
public boolean validateUser(String userId, String userPassword){
//validate for 100 lines of code...
List<String> userIdList = getUserIdList();
if(!isUserIdValid(userId,userIdList)){return false;}
if(!isPasswordCorrect(userId,userPassword)){return false;}
return true;
}
private List<String> getUserIdList() {
List<String> userIdList = new ArrayList<>();
//TODO: Add implementation details
return userIdList;
}
private boolean isPasswordCorrect(String userId, String userPassword) {
boolean isValidated = false;
//TODO: Add implementation details
return isValidated;
}
private boolean isUserIdValid(String userId, List<String> userIdList) {
boolean isValidated = false;
//TODO: Add implementation details
return isValidated;
}
public void updateOnlineUserService(String userId){
//TODO updateOnlineUserService for 100 lines of code...
}
public void sendCustomizedLoginMessage(String userId){
//TODO sendCustomizedLoginMessage for 50 lines of code...
}
public void sendOneTimeOffer(String userId){
//TODO sendOneTimeOffer for 100 lines of code...
}}
Now we can see that this class will be huge and complex. It is not a God class by book definition yet, since class fields are commonly used among methods now. But for the sake of argument, we can treat it as a God class and start refactoring.
One of the solutions is to create separate small classes which are used as members in the main class. Another thing you could add, could be separating different behaviors in different interfaces and their respective classes. Hide implementation details in classes by making those methods "private". And use those interfaces in the main class to do its bidding.
So at the end, RefactoredLoginManager will look like this:
public class RefactoredLoginManager {
IDecryptHandler decryptHandler;
IValidateHandler validateHandler;
IOnlineUserServiceNotifier onlineUserServiceNotifier;
IClientDataSender clientDataSender;
public void handleLogin(String hashedUserId, String hashedUserPassword){
String userId = decryptHandler.decryptHashedString(hashedUserId);
String userPassword = decryptHandler.decryptHashedString(hashedUserPassword);
if(!validateHandler.validateUser(userId, userPassword)){ return; }
onlineUserServiceNotifier.updateOnlineUserService(userId);
clientDataSender.sendCustomizedLoginMessage(userId);
clientDataSender.sendOneTimeOffer(userId);
}
}
DecryptHandler:
public class DecryptHandler implements IDecryptHandler {
public String decryptHashedString(String hashedString){
String userId = "";
//TODO Decrypt hashed string for 150 lines of code...
return userId;
}
}
public interface IDecryptHandler {
String decryptHashedString(String hashedString);
}
ValidateHandler:
public class ValidateHandler implements IValidateHandler {
public boolean validateUser(String userId, String userPassword){
//validate for 100 lines of code...
List<String> userIdList = getUserIdList();
if(!isUserIdValid(userId,userIdList)){return false;}
if(!isPasswordCorrect(userId,userPassword)){return false;}
return true;
}
private List<String> getUserIdList() {
List<String> userIdList = new ArrayList<>();
//TODO: Add implementation details
return userIdList;
}
private boolean isPasswordCorrect(String userId, String userPassword)
{
boolean isValidated = false;
//TODO: Add implementation details
return isValidated;
}
private boolean isUserIdValid(String userId, List<String> userIdList)
{
boolean isValidated = false;
//TODO: Add implementation details
return isValidated;
}
}
Important thing to note here is that the interfaces () only has to include the methods used by other classes. So IValidateHandler looks as simple as this:
public interface IValidateHandler {
boolean validateUser(String userId, String userPassword);
}
OnlineUserServiceNotifier:
public class OnlineUserServiceNotifier implements
IOnlineUserServiceNotifier {
public void updateOnlineUserService(String userId){
//TODO updateOnlineUserService for 100 lines of code...
}
}
public interface IOnlineUserServiceNotifier {
void updateOnlineUserService(String userId);
}
ClientDataSender:
public class ClientDataSender implements IClientDataSender {
public void sendCustomizedLoginMessage(String userId){
//TODO sendCustomizedLoginMessage for 50 lines of code...
}
public void sendOneTimeOffer(String userId){
//TODO sendOneTimeOffer for 100 lines of code...
}
}
Since both methods are accessed in LoginHandler, interface has to include both methods:
public interface IClientDataSender {
void sendCustomizedLoginMessage(String userId);
void sendOneTimeOffer(String userId);
}
There are really two topics here:
Given a God class, how its members be rationally partitioned into subsets? The fundamental idea is to group elements by conceptual coherency (often indicated by frequent co-usage in client modules) and by forced dependencies. Obviously the details of this are specific to the system being refactored. The outcome is a desired partition (set of groups) of God class elements.
Given a desired partition, actually making the change. This is difficult if the code base has any scale. Doing this manually, you are almost forced to retain the God class while you modify its accessors to instead call new classes formed from the partitions. And of course you need to test, test, test because it is easy to make a mistake when manually making these changes. When all accesses to the God class are gone, you can finally remove it. This sounds great in theory but it takes a long time in practice if you are facing thousands of compilation units, and you have to get the team members to stop adding accesses to the God interface while you do this. One can, however, apply automated refactoring tools to implement this; with such a tool you specify the partition to the tool and it then modifies the code base in a reliable way. Our DMS can implement this Refactoring C++ God Classes and has been used to make such changes across systems with 3,000 compilation units.