When I read the source of play framework 1.2.5, I found this class:
package play.classloading;
import java.util.concurrent.atomic.AtomicLong;
/**
* Each unique instance of this class represent a State of the ApplicationClassloader.
* When some classes is reloaded, them the ApplicationClassloader get a new state.
* <p/>
* This makes it easy for other parts of Play to cache stuff based on the
* the current State of the ApplicationClassloader..
* <p/>
* They can store the reference to the current state, then later, before reading from cache,
* they could check if the state of the ApplicationClassloader has changed..
*/
public class ApplicationClassloaderState {
private static AtomicLong nextStateValue = new AtomicLong();
private final long currentStateValue = nextStateValue.getAndIncrement();
#Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
ApplicationClassloaderState that = (ApplicationClassloaderState) o;
if (currentStateValue != that.currentStateValue) return false;
return true;
}
#Override
public int hashCode() {
return (int) (currentStateValue ^ (currentStateValue >>> 32));
}
}
I don't understand the hashCode method, why it uses this implementation:
return (int) (currentStateValue ^ (currentStateValue >>> 32));
The source url: https://github.com/playframework/play/blob/master/framework/src/play/classloading/ApplicationClassloaderState.java#L34
hashCode() must return an int by design. currentStateValue is a long number denoting the internal state change of the ApplicationClassloader. The play! framework is a sophisticated web framework with a so called hot-code replacement and reload feature. central part of this feature implementation is play.classloading.ApplicationClassloader.detectChanges().
As you can see, there are lots of 'new ApplicationClassloaderState()' invocations which means a (fast - depending on your developement workflow and application size) increasing currentStateValue member in the returned object.
returning to the question: the implementations goal should be to hold the maximum information to differentiate at least 2 different states from each other.
try to understand currentStateValue as a (encryption)key which encrypts itself (in kryptology terms a terrible approach) but in this context it is very useful.
perhaps you recognize the relationship.
sorry that i cant post links here but you can find some usefull hints in wikipedia searching for "Involution_%28mathematics%29", "One-time_pad", "Tabula_recta".
Related
is it possible to implement a custom hydration and persistence in Doctrine 2 on a per entity basis?
Doctrine 2 has some major limitations regarding value objects (e.g. collections and ids). I wonder if it would be possible to use custom mechanisms (or implementations) for the mapping from object properties to the database (loading and persistence).
I know there are some possibilities to "solve" this problem but I like none of them:
Fake entities require proper handling in the entity which leaks the persistence layer into the domain objects
real entities require a lot more work in persistence (more repositories and more complex handling)
Embaddables have the mentioned limitations
Custom DBAL types with serialization makes querying for certain values impossible or at least extremely slow
I know there are the lifecycle events in doctrine which may be usable. I could't find out if the postLoad event carries an already constructed entity object (with all the VOs)? Becuase in that case it would be useless to me.
best regards,
spigandromeda
Yes, you can register new hydrators in your config/packages/doctrine.yaml like this:
doctrine:
dbal: ...
orm:
hydrators:
CustomEntityHydrator: 'App\ORM\Hydrator\CustomEntityHydrator'
...
mapping: ...
...
You can then use it in your queries like this:
public function findCustomEntities(): array
{
return $this->createQueryBuilder('c')
...your query logic...
->getResult('CustomEntityHydrator');
}
Note, that you can only specify which hydrator you want to use for the root entity. If you fetch associated entities you might end up with a more complicated setup that is hard to debug.
Instead you could consider dealing with value objects (VOs) only in the interface of your entity. In other words, the fields are scalar values, but your method arguments and return values are VOs.
Here is an example with an entity that has a id of type Uuid, a location (some numeric identifier), status (e.g. ternary true/false/null). These are only there to showcase how to deal with different type of value objects:
/**
* #ORM\Entity()
*/
class CustomEntity
{
/**
* #ORM\Id()
* #ORM\Column(type="string", length=64)
*/
private string $id;
/**
* #ORM\Column(type="int")
*/
private int $location;
/**
* #ORM\Column(type="bool, nullable=true)
*/
private bool $status;
private function __construct(Uuid $id, Location $location, Status $status)
{
$this->id = (string) $id;
$this->location = $location->getValue();
$this->status = $status->get();
}
public static function new(Location $location, Status $status): self
{
return new self(Uuid::v4(), $location, $status);
}
public function getId(): Uuid
{
return Uuid::fromString($this->id);
}
public function getLocation(): Location
{
return new Location($this->location);
}
public function activate(): void
{
$this->status = true;
}
public function deactivate(): void
{
$this->status = false;
}
public function isActive(): bool
{
$this->status === true;
}
public function isInactive(): bool
{
$this->status === false;
}
public function isUninitialized(): bool
{
$this->status === null;
}
public function getStatus(): Status
{
if ($this->status === null) {
return new NullStatus();
}
if ($this->status === true) {
return new ActiveStatus();
}
return new InactiveStatus();
}
}
As you can see, you could replace new() with a public constructor. It would work similar with setters. I sometimes even use (private) setters for this in the constructor. In case of the status you don't even need setters if you instead use multiple methods that set the value internally. Similarly you might want to return scalar values instead of a VO in some cases (or the other way around as shown with the status getter and issers).
The point is, your entity looks from the outside as if it would use your VOs, but internally it already switches to a representation that works better with Doctrine ORM. You could even mix this with using VOs and custom types, e.g. for the UUID. You just have to be careful, when your VO needs more info for being constructed than you want to store in the database, e.g. if the numeric location in our example would also use a locale during creation, then we would need to store this (which makes sense as it seems to be related to the numeric id) or we have to hardcode it in the entity or add an abstraction above, that has access to the locale, in which case your entity would likely not return a Location or at least not a LocalizedLocation.
You might also want to consider not having a VO for each and every property in your entity. While it definitely can be helpful, e.g. to wrap an Email into a custom VO to ensure validity instead of just type hinting for string, it might be less useful for something as generic as a (user's) name, which should be very lenient with which strings it accepts as there are a wide variety of names. Using the approach above you can easily introduce a VO later, by adding a new getter for the VO, changing new() or any other method that mutates your property and then not having to change anything in the data model below (unless there is a more drastic change to how the value is represented).
For few test cases I'm trying to follow a DRY principle, where only the interactions are different with same test case conditions. I'm not able to find a way to implement multiple methods in the interaction { } block.
As mentioned in http://spockframework.org/spock/docs/1.3/interaction_based_testing.html#_explicit_interaction_blocks, I'm using interaction { } in the then: block like below:
Java Code:
// legacy code (still running on EJB 1.0 framework, and no dependency injection involved)
// can't alter java code base
public voidGetData() {
DataService ds = new DataService();
ds = ds.findByOffset(5);
Long len = ds.getOffset() // happy path scenario; missing a null check
// other code
}
// other varieties of same code:
public voidGetData2() {
ItemEJB tmpItem = new ItemEJB();
ItemEJB item = tmpItem.findByOffset(5);
if(null != item) {
Long len = item.getOffset();
// other code
}
}
public voidGetData3() {
ItemEJB item = new ItemEJB().findByOffset(5);
if(null != item) {
Long len = item.getOffset();
// other code
}
}
Spock Test:
def "test scene1"() {
given: "a task"
// other code ommitted
DataService mockObj = Mock(DataService)
when: "take action"
// code omitted
then: "action response"
interaction {
verifyNoDataScenario() // How to add verifyErrorScenario() interaction to the list?
}
}
private verifyDataScenario() {
1 * mockObj.findByOffset(5) >> mockObj // the findByOffset() returns an object, so mapped to same mock instance
1 * mockObj.getOffset() >> 200
}
private verifyErrorScenario() {
1 * mockObj.findByOffset(5) >> null // the findByOffset() returns null
0 * mockObj.getOffset() >> 200 // this won't be executed, and should ie expected to throw NPE
}
The interaction closure doesn't accept more than one method call. I'm not sure if it's design limitation. I believe more can be done in the closure than just mentioning the method name. I also tried interpolating the mockObj as a variable and use data pipe / data table, but since it's referring the same mock instance, it's not working. I'll post that as a separate question.
I ended up repeating the test case twice just to invoke different interaction methods. Down the line I see more scenarios, and wanted to avoid copy & paste approach. Appreciate any pointers to achieve this.
Update:
Modified shared java code as the earlier DataService name was confusing.
As there's no DI involved, and I didn't find a way to mock method variables, so I mock them using PowerMockito, e.g. PowerMockito.whenNew(DataService.class).withNoArguments().thenReturn(mockObj)
Your application code looks very strange. Is the programming style in your legacy application really that bad? First a DataService object is created with a no-arguments constructor, just to be overwritten in the next step by calling a method on that instance which again returns a DataService object. What kind of programmer creates code like that? Or did you just make up some pseudo code which does not have much in common with your real application? Please explain.
As for your test code, it also does not make sense because you instantiate DataService mockObj as a local variable in your feature method (test method), which means that in your helper method mockObj cannot be accessed. So either you need to pass the object as a parameter to the helper methods or you need to make it a field in your test class.
Last, but not least, your local mock object is never injected into the class under test because, as I said in the first paragraph, the DataService object in getData() is also a local variable. Unless your application code is compeletely fake, there is no way to inject the mock because getData() does not have any method parameter and the DataService object is not a field which could be set via setter method or constructor. Thus, you can create as many mocks as you want, the application will never have any knowledge of them. So your stubbing findByOffset(long offset) (why don't you show the code of that method?) has no effect whatsoever.
Bottom line: Please provide an example reflecting the structure of your real code, both application and test code. The snippets you provide do not make any sense, unfortunately. I am trying to help, but like this I cannot.
Update:
In my comments I mentioned refactoring your legacy code for testability by adding a constructor, setter method or an overloaded getData method with an additional parameter. Here is an example of what I mean:
Dummy helper class:
package de.scrum_master.stackoverflow.q58470315;
public class DataService {
private long offset;
public DataService(long offset) {
this.offset = offset;
}
public DataService() {}
public DataService findByOffset(long offset) {
return new DataService(offset);
}
public long getOffset() {
return offset;
}
#Override
public String toString() {
return "DataService{" +
"offset=" + offset +
'}';
}
}
Subject under test:
Let me add a private DataService member with a setter in order to make the object injectable. I am also adding a check if the ds member has been injected or not. If not, the code will behave like before in production and create a new object by itself.
package de.scrum_master.stackoverflow.q58470315;
public class ToBeTestedWithInteractions {
private DataService ds;
public void setDataService(DataService ds) {
this.ds = ds;
}
// legacy code; can't alter
public void getData() {
if (ds == null)
ds = new DataService();
ds = ds.findByOffset(5);
Long len = ds.getOffset();
}
}
Spock test:
Now let us test both the normal and the error scenario. Actually I think you should break it down into two smaller feature methods, but as you seem to wish to test everything (IMO too much) in one method, you can also do that via two distinct pairs of when-then blocks. You do not need to explicitly declare any interaction blocks in order to do so.
package de.scrum_master.stackoverflow.q58470315
import spock.lang.Specification
class RepeatedInteractionsTest extends Specification {
def "test scene1"() {
given: "subject under test with injected mock"
ToBeTestedWithInteractions subjectUnderTest = new ToBeTestedWithInteractions()
DataService dataService = Mock()
subjectUnderTest.dataService = dataService
when: "getting data"
subjectUnderTest.getData()
then: "no error, normal return values"
noExceptionThrown()
1 * dataService.findByOffset(5) >> dataService
1 * dataService.getOffset() >> 200
when: "getting data"
subjectUnderTest.getData()
then: "NPE, only first method called"
thrown NullPointerException
1 * dataService.findByOffset(5) >> null
0 * dataService.getOffset()
}
}
Please also note that testing for exceptions thrown or not thrown adds value to the test, the interaction testing just checks internal legacy code behaviour, which has little to no value.
Well, I'm looking for the best way to refactor a (huge) legacy code-base and introducing some tests in it..There was no test framework. (yeah, I mean not at all)
It was an JEE 5 application. The goal is to revamp that in JEE7
Let me introduce a quick overview .
The end-users (those of them who are authorized) are free to evolve , configure many aspect of the application behavior by setting in the UI a bunch of preferences.
Theses are stored in an SQL table for the main part (the rest in some xml and properties files).
To fulfill this requirement, there is an #Startup object dedicated to build a sort-of huge map with all key-values.
Then all across the code base when a use case needs to adapt it's processing it checks the current value of the parameter(s) needed to its task.
A real case is that the app has to do a few operations on images;
For instance, Class ImgProcessing has to create thumbnail of a picture via this method :
Optional<Path> generateThumb_fromPath(Path origImg);
for this the method generateThumb_fromPath, calls Thumbnailer,
which uses a generic ImageProcessingHelper,
which holds a few set of generic image related tools and methods,
and specially an static method returning the wished dimensions of the thumbnail to be generated based on the original image constraints and some thumbnail preferences (keys = "THUMBNAIL_WIDTH" and "THUMBNAIL_HEIGHT").
These preferences are the user wishes for what size a thumbnail should have.
So far so good, nothing special.
Now the dark side of this :
The original JEE5 config loader is an bad old fashioned infamous singleton pattern as :
OldBadConfig {
private static OldBadConfig instance ;
public static getInstance(){
if(instance==null){
// create, initialize and populate our big preferences' map
}
return instance;
}
}
Then all across the whole code-base these preferences are used. In my refactoring effort I've already done using #Inject for injecting the singleton object.
But in static utilities ( no injection point available ) you have lots of this nasty calls :
OldBadConfig.getInstance.getPreference(key, defaultValue)
(Briefly I will explain that I use testNg + Mockito, I don't think the tools are relevant here, it seems to be more about an original terrible design,
but if I HAVE to change my toolbox (Junit or whatever) I will. But again I don't think the tooling is the root problem here. )
Trying to refactor the image part and make it test-friendly., I want to do this test with cut = instance of my Class Under Test:
#Test
public void firstTest(){
Optional<Path> op = cut.generateThumb_fromPath(targetPath);
// ..assertThatTheThumbnailWasCreated........
}
So in a few words ,
the execution flow will be like :
class under test --> some business implementation --> someutilities --> static_global_app_preference ---> other_class-othermethod.finalizingProcessing,
then return to the caller.
My testing effort halts here. How to mock the static_global_app_preference ?
How can I refactor the static_global_app_preference part from
*OldBadConfig.getInstance.getPreference(key, defaultValue)*
to something mockable where I could mock like :
Mockito.when(gloablConf.getPreference("THUMBNAIL_WIDTH", anyString)).thenReturn("32");
I've spent quite a time reading boks, blog posts etc all saying
'(these kind of) Singleton is EVIL'. You should NOT do that !
I think we all agree , thanks.
But what about a real word and effective solution to such really trivial, common tasks?
I can not add the singleton instance (or the preferences'map ) as parameters (because as it is already spread all across the code-base it will pollute all and every classes and methods . For instance in the exposed use case, it will pollute 5 methods in 4 classes just for one, poor, miserable, access to a parameter.
It's really not feasible.
So far I tried to refactor OldBadConfig class in two part : one with all initialization/write stuff,
and the other with only the read parts. that way I can at least make this a real JEE #Singleton and benefits from concurrent access once the startup is over and the configuration all loaded.
Then I tried to make this SharedGlobalConf accessible via a factory, called like :
SharedGlobalConf gloablConf= (new SharedGlobalConfFactory()).getShared();
then gloablConf.getPreference(key, defaultValue); is accessible.
It seems to be a little better than the original bottleneck, but didn't help at all for the testing part.
I thought the factory will ease everything but nothing like that comes out.
So there is my question :
For myself, I can split the OldBadConfig to an startup artefact doing the init and refesh, and to an SharedGlobalConf which is a JEE7 pure Singleton,
#Singleton
#ConcurrencyManagement(ConcurrencyManagementType.BEAN)
#Lock(LockType.READ)
Then, as for the legacy use case described here, How Can I make this reasonably mock-able ? Real word solutions are all welcomed.
Thanks sharing your wisdom and skills !
I will like to share my own answer.
Let's say we got these classes after the initial large OldBadConfig class was splitted :
#Startup AppConfigPopulator in charge of loading all information and populating the kind-of internal cache,
which is now a distinct SharedGlobalConf object. The populator is the only one in charge of feeding the SharedGlobalConf via :
#Override
public SharedGlobalConf sharedGlobalConf() {
if (sharedGlobalConf.isDirty()) {
this.refreshSharedGlobalConf();
}
return sharedGlobalConf;
}
private void refreshSharedGlobalConf() {
sharedGlobalConf.setParams(params);
sharedGlobalConf.setvAppTempPath_temp(getAppTempPath_temp());
}
In all components (by that I mean all Classes holding valid injection points) you just do your classic
#Inject private SharedGlobalConf globalConf;
For static utilities that can not do #Inject, we got an SharedGlobalConfFactory which handles the shared data to everything in a one-liner :
SharedGlobalConf gloablConf = (new SharedGlobalConfFactory()).getShared();
That way our old code base can be smoothly upgraded : #Inject in all valid components, And the (too many) old utilities that we can not reasonably rewrite them all in this refactoring step can get these
*OldBadConfig.getInstance.getPreference(key, defaultValue)*
,simply replaced by
(new SharedGlobalConfFactory()).getShared().getPreference(key, defaultValue);
And we are test-compliant and mockable !
Proof of concept :
A really critical Business demands is modeled in this class :
#Named
public class Usage {
static final Logger logger = LoggerFactory.getLogger(Usage.class);
#Inject
private SharedGlobalConf globalConf;#Inject
private BusinessCase bc;public String doSomething(String argument) {
logger.debug(" >>doSomething on {}", argument);
// do something using bc
Object importantBusinessDecision = bc.checks(argument);
logger.debug(" >>importantBusinessDecision :: {}", importantBusinessDecision);
if (globalConf.isParamFlagActive("StackOverflow_Required", "1")) {
logger.debug(" >>StackOverflow_Required :: TRUE");
// Do it !
return "Done_SO";
} else {
logger.debug(" >>StackOverflow_Required :: FALSE -> another");
// Do it another way
String resultStatus = importantBusinessDecision +"-"+ StaticHelper.anotherWay(importantBusinessDecision);
logger.debug(" >> resultStatus " + resultStatus);
return "Done_another_way " + resultStatus;
}
}
public void err() {
xx();
}
private void xx() {
throw new UnsupportedOperationException(" WTF !!!");
}
}
To get it's job done , we need a hand from our old companion StaticHelper :
class StaticHelper {
public static String anotherWay(Object importantBusinessDecision) {// System.out.println("zz #anotherWay on "+importantBusinessDecision);
SharedGlobalConf gloablConf = (new SharedGlobalConfFactory()).getShared();
String avar = gloablConf.getParamValue("deeperParam", "deeperValue");
//compute the importantBusinessDecision based on avar
return avar;
}
}
Usage of this =
#Named public class Usage {
static final Logger logger = LoggerFactory.getLogger(Usage.class);
#Inject
private SharedGlobalConf globalConf;
#Inject
private BusinessCase bc;
public String doSomething(String argument) {
logger.debug(" >>doSomething on {}", argument);
// do something using bc
Object importantBusinessDecision = bc.checks(argument);
logger.debug(" >>importantBusinessDecision :: {}", importantBusinessDecision);
if (globalConf.isParamFlagActive("StackOverflow_Required", "1")) {
logger.debug(" >>StackOverflow_Required :: TRUE");
// Do it !
return "Done_SO";
} else {
logger.debug(" >>StackOverflow_Required :: FALSE -> another");
// Do it another way
String resultStatus = importantBusinessDecision +"-"+ StaticHelper.anotherWay(importantBusinessDecision);
logger.debug(" >> resultStatus " + resultStatus);
return "Done_another_way " + resultStatus;
}
}
public void err() {
xx();
}
private void xx() {
throw new UnsupportedOperationException(" WTF !!!");
}}
As you see the old shared key/value holder is still used every where but this time, we can test
public class TestingAgainstOldBadStaticSingleton {
private final Boolean boolFlagParam;
private final String deepParam;
private final String decisionParam;
private final String argument;
private final String expected;
#Factory(dataProvider = "tdpOne")
public TestingAgainstOldBadStaticSingleton(String argument, Boolean boolFlagParam, String deepParam, String decisionParam, String expected) {
this.argument = argument;
this.boolFlagParam = boolFlagParam;
this.deepParam = deepParam;
this.decisionParam = decisionParam;
this.expected = expected;
}
#Mock
SharedGlobalConf gloablConf = (new SharedGlobalConfFactory()).getShared();
#Mock
BusinessCase bc = (new BusinessCase());
#InjectMocks
Usage cut = new Usage();
#Test
public void testDoSomething() {
String result = cut.doSomething(argument);
assertEquals(result, this.expected);
}
#BeforeMethod
public void setUpMethod() throws Exception {
MockitoAnnotations.initMocks(this);
Mockito.when(gloablConf.isParamFlagActive("StackOverflow_Required", "1")).thenReturn(this.boolFlagParam);
Mockito.when(gloablConf.getParamValue("deeperParam", "deeperValue")).thenReturn(this.deepParam);
SharedGlobalConfFactory.setGloablConf(gloablConf);
Mockito.when(bc.checks(ArgumentMatchers.anyString())).thenReturn(this.decisionParam);
}
#DataProvider(name = "tdpOne")
public static Object[][] testDatasProvider() {
return new Object[][]{
{"**AF-argument1**", false, "AF", "DEC1", "Done_another_way DEC1-AF"},
{"**AT-argument2**", true, "AT", "DEC2", "Done_SO"},
{"**BF-Argument3**", false, "BF", "DEC3", "Done_another_way DEC3-BF"},
{"**BT-Argument4**", true, "BT", "DEC4", "Done_SO"}};
}
The test is with TestNG and Mockito : it shows how we don't need to do the complex stuff (reading the sql table, the xml files etc..) but simply mock different set of values targeting just our sole business case. (if a nice fellow would accept to translate in other frameworks for those interested...)
As for the initial request was about the design allowing to reasonably refactor a -huge- existing code-base away from the 'static singleton anti-pattern' , while introducing tests and mocks I assume this a quite valid answer.
Will like to hear about your opinion and BETTER alternatives
I have some questions about writing a custom OutputAttributeProcessor.
I use WSO2 CEP 2.1.0 and siddhi 1.1.0.
I want to create a custom OutputAttributeProcessor, so I create two java classes, TestFactory implements OutputAttributeProcessorFactory and Test implements OutputAttributeProcessor.
Package of two classes is org.wso2.siddhi.extention.
TestFactory must override createAggregator and getProcessorType, and Test must override createNewInstance, getType, processInEventAttribute, and processRemoveEventAttribute.
First question is about each methods.
What should be written in getProcessorType?
And also, what is different between processInEventAttribute, and processRemoveEventAttribute?
In addition, I have one more question.
I will create jar file consits of two java classes.
I add the jar file to the class path at /repository/components/lib, and the fully-qualified class name for TestFactory to the siddhi.extension file located at /repository/conf/siddhi.
What is content of siddhi.extension?
Is the following a line?
org.wso2.siddhi.extention.TestFactory
If there is sample program about a custom OutputAttributeProcessor, please teach me.
Thank you in advance.
What should be written in getProcessorType?
Depending on the use case, you can return one of the AGGREGATOR or CONVERTER types here:
#Override
public ProcessorType getProcessorType() {
return OutputAttributeProcessorFactory.ProcessorType.AGGREGATOR;
}
What exactly is your use case? As the name implies, you can use AGGREGATOR type if it does aggregations (i.e. something like calculating an average, taking min() of several events etc.)
And also, what is different between processInEventAttribute, and processRemoveEventAttribute?
These are the two methods that are used to add and remove events to/from your OutputAttributeProcessor. For an example, if you are taking an average, it needs to be done for a specific set of events (like a sliding window, usually not all events received so far), which changes dynamically. So when you receive an event through processInEventAttribute(), you can update your average including that event. Similary when processRemoveEventAttribute() is called, you can update the average removing that event.
For an example, see the below code sample which calculates the average as a double value.
private double value = 0.0;
private long count=0;
public Attribute.Type getType() {
return Attribute.Type.DOUBLE;
}
#Override
public Object processInEventAttribute(Object obj) {
count++;
value += (Double) obj;
if (count == 0) {
return 0;
}
return value / count;
}
#Override
public Object processRemoveEventAttribute(Object obj) {
count--;
value -= (Double) obj;
if (count == 0) {
return 0;
}
return value / count;
}
What is content of siddhi.extension?
It's just one line as you've mentioned. Just the fully qualified class name.
org.wso2.siddhi.extention.TestFactory
I'm sure I missing something simple here but I can't figure out why my NUnit object comparison test continues to fail.
I have a simple object:
public virtual int Id { get; private set; }
public virtual string Description { get; set; }
public virtual string Address { get; set; }
public virtual string Ports { get; set; }
public virtual string Password { get; set; }
public virtual ServerGroup ServerGroup { get; set; }
I am persisting an instance of this object to my database and then fetching it out using NHibernate. My NUnit unit test compares the object saved to the object retrieved and compares them. I understand that AreSame() would fail as they are not the same reference to an object but I would expect that AreEqual() pass.
If I debug the test I can see that both objects appear to have the same values in these properties my test still fails. Can someone tell me why?
Thanks!
You have to override Equals() method on your class. Otherwise NUnit will use the base implementation, which compares references (which is certainly not what you are after here)
As suggested you need to override Equals. You do need to be aware of the side effects.
You should also override GetHashCode or you could end up with objects where .Equals will be true, but using your Id class as the key in a Dictionary the hash would not match resulting in multiple entries with "Equal" Ids.
Also, you would need to override the == and != operators to maintain consistent behavior.
Imagine the confusion if .Equals were true but == were false.
You do need to override Equals as Grzenio suggests, but watch out for a subtle source of confusion that can occur with NHibernate. Specifically, when lazy loading is enabled, a type comparison test can fail. To illustrate, here is a piece of a well written Equals method:
// override object.Equals
public override bool Equals(object obj)
{
//
// See the full list of guidelines at
// http://go.microsoft.com/fwlink/?LinkID=85237
// and also the guidance for operator== at
// http://go.microsoft.com/fwlink/?LinkId=85238
//
if (GetType() != obj.GetType())
{
return false;
}
....
}
But when lazy loading is enabled, the way NHib works is to generate a proxy of the actual object (thereby deferring unnecessary database hits). If an equality check is made between one object that has been 'proxified' by NHib and another that hasn't been, it will fail because of the mismatch in Types. The solution (courtesy of the S#arp Architecture project, is to modify the type test to be something like this:
public override bool Equals(object obj) {
...
if (GetType() != obj.GetTypeUnproxied())
{
return false;
}
...
}
protected virtual Type GetTypeUnproxied() { return GetType(); }
This effectively returns the type of the underlying object in all cases, even when the compareTo object is a NHib proxy.
An Equals method can be as tricky as it is important to get just right, so ideally you can factor that into some sort of Layer Supertype (Fowler). Lots of open source projects, including the S#arp one I mentioned earlier, provide examples of how to do this.
HTH,
Berryl