I noticed in the protobuf-net changelog that IList<> was supported but I'm getting the "Cannot create an instance of an interface" exception. If I change to IEnumerable<> then life is good. Does this sound correct?
// Client call
public override IList<IApplicationWorkflow> Execute(IRoleManagement service)
{
IList<ApplicationWorkflowMessagePart> list = service.RetrieveWorkflows(roleNames);
IList<IApplicationWorkflow> workflows = new List<IApplicationWorkflow>(list.Count);
foreach (ApplicationWorkflowMessagePart a in list)
{
workflows.Add(new ApplicationWorkflowImpl(a));
}
return workflows;
}
// Service contract
[OperationContract, ProtoBehavior]
[ServiceKnownType(typeof (ServiceFault))]
[FaultContract(typeof (ServiceFault))]
IList<ApplicationWorkflowMessagePart> RetrieveWorkflows(string[] roleNames);
// Service implementation
public IList<ApplicationWorkflowMessagePart> RetrieveWorkflows(string[] roleNames)
{
IList<IApplicationWorkflow> workflows = manager.RetrieveApplicationWorkflows(roleNames);
IList<ApplicationWorkflowMessagePart> workflowParts = new List<ApplicationWorkflowMessagePart>();
if (workflows != null)
{
foreach (IApplicationWorkflow workflow in workflows)
{
workflowParts.Add(
ModelMediator.GetMessagePart<ApplicationWorkflowMessagePart, IApplicationWorkflow>(workflow));
}
}
return workflowParts;
}
Thanks,
Mike
Also, is there document site that has this and other answers? I hate to be asking newb questions. :)
Currently it will support IList<T> as a property, as long as it doesn't have to create it - i.e. allowing things like (attributes not shown for brevity):
class Order {
private IList<OrderLine> lines = new List<OrderLine>();
public IList<OrderLine> Lines {get {return lines;}}
}
I would have to check, but for similar reasons, I expect it would work with Merge, but not Deserialize (which is what the WCF hooks use). However, I can't think of a reason it couldn't default to List<T>... it just doesn't at the moment.
The simplest option is probably to stick with List<T> / T[] - but I can have a look if you want... but I'm in a "crunch" on a (work) project at the moment, so I can't lift the bonnet today.
Re "this and other answers"... there is a google group, but that is not just protobuf-net (protobuf-net is simply one of many "protocol buffers" implementations).
You are also free to log an issue on the project site. I do mean to collate the FAQs and add them to the wiki on the site - but time is not always my friend...
But hey! I'm here... ;-p
Related
Topos it .NET Event Processing library, similar to Rebus. Unlike Rebus, it is not so much for messages, as for event processing.
Rebus supports Sagas out of the "box", including in terms of persistence, correlation and concurrency. How to implement a Saga on Topos?
If Topos supports Sagas, is there an example of a Saga implementation somewhere?
Topos does not have any kind of built-in sagas, unfortunately.
In Fleet Manager (the Rebus management app that comes with Rebus Pro, and the reason I made Topos) I made a saga-like event processor that uses MongoDB or LiteDB for persistence.
This implementation is completely proprietary though, as it's part of a commercial software product, and it's not quite generic enough to be suited for reuse. I can tell you a little bit about it here anyway, hopefully to give you some inspiration on how you could go about building something like it yourself. 🙂
The event processor is hosted in a Topos consumer, which dispatches all received events to a bunch of "projections", thus implementing the classic event sourced "left-fold" (current_state + event => new_state).
Fleet Manager has projections in two flavors: process managers (i.e. projections that cause other events to be emitted by issuing commands) and views. The two types combined would be what you call a "saga" 🙂
One possible view could be implemented like this (with lots of stuff removed for brevity):
public class QueueInstanceView : ViewInstance<InstancePerQueue>, IExpire, IHaveAccountId, IHaveQueueName, ICanBeHidden
{
public string AccountId { get; set; }
public string QueueName { get; set; }
public DateTime LastActivity { get; set; }
public bool Hidden { get; set; }
protected override void DispatchEvent(AuditEvent auditEvent)
{
if (auditEvent.Body is EntityHidden entityHidden)
{
QueueName ??= entityHidden.Id;
Hidden = !entityHidden.Reverse;
}
else
{
QueueName ??= auditEvent.GetQueueName();
}
LastActivity = auditEvent.GetTime();
}
}
Note how the view class inherits from the generic ViewInstance<> class, closing it with the InstancePerQueue type. The base class keeps track of the ID of the view instance and some other stuff used to implement idempotency, and then InstancePerQueue defines how events are mapped to view instances.
It looks like this:
public class InstancePerQueue : ViewLocator
{
public override string[] GetViewIds(AuditEvent auditEvent)
{
if (auditEvent.Body is EntityHidden entityHidden)
{
if (entityHidden.HasType(EntityTypeNames.Queue))
{
var accountId = auditEvent.GetAccountId();
return new[] { $"{accountId}/{entityHidden.Id}" };
}
return Array.Empty<string>();
}
var queueName = auditEvent.GetQueueNameOrNull();
if (queueName == null) return Array.Empty<string>();
var accountId = auditEvent.GetAccountId();
return new[] { $"{accountId}/{queueName}" };
}
}
thus correlating events with IDs on the form "/" (where "account" in Fleet Manager terminology is basically just an environment, i.e. the queue names get to IDENTIFY the queues within an account).
Of course lots of logic is then implemented in the projection implementations, but while it's lengthy, it's also fairly straightforward.
I hope that this could give you some inspiration on how you might want to approach building "sagas" for Topos. 🙂
Btw. I cannot take credit for this particular design. I was originally exposed to a design very similar to this back in 2013-2014 by Emil Krog Ingerslev, who came up with it for an event-sourced application we were building at d60.
I later imitated all of the moving parts to implement persistent projections for Cirqus, which we used for a couple of event-sourced apps.
And finally I made my current implementation for Fleet Manager, back in 2016 when I needed something similar, only without the aggregate root stuff present in Cirqus, and working on Kafka instead of normal databases.
I have a controller that modifies appointments in a calendar. I want to use my SignalR hub to notify users à la "User X changed {appointmentTitle}: List: {Property} {OriginalValue} {NewValue}"
I'm a beginner in C# (Syntax-wise it's ok, but OOP concepts are new); I'm trying to use events to achieve the above.
Below are the handlers and arguments, an extract from the controller and a summary of my questions.
Code is abbreviated!
EventArgs
public class AppointmentChangeEventArgs : EventArgs
{
public EntityState AppointmentState = EntityState.Unchanged;
public EntityEntry Entity = null;
public ScheduleData Appointment = null;
}
EventHandler
// maybe this could be just one, and let the consumer decide based on EntityState?
public EventHandler<AppointmentChangeEventArgs> AppointmentChanged;
public EventHandler<AppointmentChangeEventArgs> AppointmentAdded;
public EventHandler<AppointmentChangeEventArgs> AppointmentRemoved;
protected virtual void OnAppointment(AppointmentChangeEventArgs appointmentChangeEventArgs)
{
switch (appointmentChangeEventArgs.AppointmentState)
{
case EntityState.Added:
AppointmentAdded?.Invoke(this, appointmentChangeEventArgs);
break;
case EntityState.Deleted:
AppointmentRemoved?.Invoke(this, appointmentChangeEventArgs);
break;
case EntityState.Modified:
AppointmentChanged?.Invoke(this, appointmentChangeEventArgs);
break;
default:
break;
}
}
Controller
public async Task<IActionResult> Batch([FromBody] ScheduleEditParameters param)
switch (param.Action) {
case "insert":
await _dbContext.Appointments.AddAsync(appointment);
break;
case "update":
// .. get Appointment from DB
appointment.Subject = value.Subject;
appointment.StartTime = value.StartTime;
// ...
case "remove":
// .. get Appointment from DB
_dbContext.Appointments.Remove(appointment);
}
var modifiedEntries = _dbContext.ChangeTracker
.Entries()
.Where(x => x.State != EntityState.Unchanged && x.State != EntityState.Detached)
.Select(x => new AppointmentChangeEventArgs() { Entity = (EntityEntry) x.Entity, AppointmentState = x.State, Appointment = appointment })
.ToList();
if (modifiedEntries.Any())
{
var notificationService = new NotificationService(signalRHub, notificationLogger);
AppointmentAdded += notificationService.OnAppointmentChanged;
AppointmentChanged += notificationService.OnAppointmentChanged;
AppointmentRemoved += notificationService.OnAppointmentChanged;
}
await _dbContext.SaveChangesAsync();
Questions
Is it ok to use EntityEntry and EntityState in event arguments?
for each modified Entry, I can obtain _dbContext.Entry(modifiedEntry).Properties.Where(x => x.IsModified).ToList(); - but does this belong in the NotificationService class? In order to do that, I'd also need to pass the DbContext over to NotificationService.
Might there be a simpler way to achieve this? Adding and Removing handlers are easy ("User X has added|removed ... appointment {Title}"), but in order to figure out the exact changes I'll have to look at the modified properties.
I'd be grateful if you could provide an insight into how you would structure & handle this task. Thank you.
To start off, I would generally recommend you not to use events here. Events are something that may sound very useful but due to the way they work (synchronously), they aren’t really the best way to achieve this in a web context, especially in a primarily asynchronous framework like ASP.NET Core.
Instead, I would recommend you to simply declare your own type, e.g. IAppointmentChangeHandler like this:
public interface IAppointmentChangeHandler
{
Task AddAppointment(ScheduleData appointment);
Task UpdateAppointment(ScheduleData appointment);
Task RemoveAppointment(ScheduleData appointment);
}
Your NotificationService can just implement that interface to be able to handle those events (obviously just send whatever you need to send there):
public class NotificationService : IAppointmentChangeHandler
{
private readonly IHubContext _hubContext;
public NotificationService(IHubContext hubContext)
{
_hubContext = hubContext;
}
public AddAppointment(ScheduleData appointment)
{
await _hubContext.Clients.InvokeAsync("AddAppointment", appointment);
}
public UpdateAppointment(ScheduleData appointment)
{
await _hubContext.Clients.InvokeAsync("UpdateAppointment", appointment);
}
public RemoveAppointment(ScheduleData appointment)
{
await _hubContext.Clients.InvokeAsync("RemoveAppointment", appointment);
}
}
And inside of your controller, you just inject that IAppointmentChangeHandler then and call the actual method on it. That way you have both the controller and the notification service completely decoupled: The controller does not need to construct the type first and you also do not need to subscribe to some events (which you would also have to unsubscribe from at some point again btw). And you can leave the instantiation completely to the DI container.
To answer your individual questions:
Is it ok to use EntityEntry and EntityState in event arguments?
I would avoid using it in a context outside of your database. Both are an implementation detail of your database setup, since you are using Entity Framework here. Not only would this couple your event handlers strongly with Entity Framework (meaning that everyone that wanted to be an event handler would need to reference EF even if they didn’t do anything with it), you are also leaking possibly internal state that may change later (you don’t own the EntityEntry so who knows what EF does with it afterwards).
for each modified Entry, I can obtain _dbContext.Entry(modifiedEntry).Properties.Where(x => x.IsModified).ToList();
If you look at your code, you are first calling Add, Update or Remove on your database set; and then you are using some logic to look at some internal EF stuff to figure out the exact same thing really. You could make this a lot less complex if you constructed the AppointmentChangeEventArgs within those three switch cases directly.
but does this belong in the NotificationService class? In order to do that, I'd also need to pass the DbContext over to NotificationService.
Does a notification service have anything to do with a database? I would say no; unless you are persisting those notifications into the database. When I think about a notification service, then I expect to be able to call something on it to actively trigger a notification, instead of having some logic within the service to figure out what notifications it could possibly trigger.
Might there be a simpler way to achieve this? Adding and Removing handlers are easy ("User X has added|removed ... appointment {Title}"), but in order to figure out the exact changes I'll have to look at the modified properties.
Think about it in the simplest way first: Where do you update the values of the database entity? Within that update case. So at that point, where you are copying over values from the passed object, you can also just check which properties you are actually changing. And with that, you can record easily which properties you need to notify about.
Decouple this completely from EF and you will be a lot more flexible in the long run.
My silverlight solution has 3 project files
Silverlight part(Client)
Web part(Server)
Entity model(I maintained the edmx along with Metadata in a seperate project)
Metadata file is a partial class with relavent dataannotation validations.
[MetadataTypeAttribute(typeof(User.UserMetadata))]
public partial class User
{
[CustomValidation(typeof(UsernameValidator), "IsUsernameAvailable")]
public string UserName { get; set; }
}
Now my question is where I need to keep this class UsernameValidator
If my Metadata class and edmx are on Server side(Web) then I know I need to create a .shared.cs class in my web project, then add the proper static method.
My IsUserAvailable method intern will call a domainservice method as part of asyc validation.
[Invoke]
public bool IsUsernameAvailable(string username)
{
return !Membership.FindUsersByName(username).Cast<MembershipUser>().Any();
}
If my metadata class is in the same project as my domain service is in then I can call domain service method from my UsernameValidator.Shared.cs class.
But here my entity models and Metadata are in seperate library.
Any idea will be appreciated
Jeff wonderfully explained the asyc validation here
http://jeffhandley.com/archive/2010/05/26/asyncvalidation-again.aspx
but that will work only when your model, metadata and Shared class, all are on server side.
There is a kind of hack to do this. It is not a clean way to do it it, but this is how it would probably work.
Because the .shared takes care of the code generation it doesn't complain about certain compile errors in the #if brackets of the code. So what you can do is create a Validator.Shared.cs in any project and just make sure it generates to the silverlight side.
Add the following code. and dont forget the namespaces.
#if SILVERLIGHT
using WebProject.Web.Services;
using System.ServiceModel.DomainServices.Client;
#endif
#if SILVERLIGHT
UserContext context = new UserContext();
InvokeOperation<bool> availability = context.DoesUserExist(username);
//code ommited. use what logic you want, maybe Jeffs post.
#endif
The compiler will ignore this code part because it does not meet the condition of the if statement. Meanwhile on the silverlight client side it tries to recompile the shared validator where it DOES meet the condition of the if-statement.
Like I said. This is NOT a clean way to do this. And you might have trouble with missing namespaces. You need to resolve them in the non-generated Validator.shared.cs to finally let it work in silverlight. If you do this right you can have the validation in silverlight with invoke operations. But not in your project with models and metadata like you would have with Jeff's post.
Edit: I found a cleaner and better way
you can create a partial class on the silverlight client side and doing the following
public partial class User
{
partial void OnUserNameChanging(string value)
{
//must be new to check for this validation rule
if(EntityState == EntityState.New)
{
var ctx = new UserContext();
ctx.IsValidUserName(value).Completed += (s, args) =>
{
InvokeOperation invop = (InvokeOperation) s;
bool isValid = (bool) invop.Value;
if(!isValid)
{
ValidationResult error = new ValidationResult(
"Username already exists",
new string[] {"UserName"});
ValidationErrors.Add(error;
}
};
}
}
}
This is a method generated by WCF RIA Services and can be easily partialled and you can add out-of-band validation like this. This is a much cleaner way to do this, but still this validation now only exists in the silverlight client side.
Hope this helps
Here is the situation:
Silverlight 3 Application hits an asp.net hosted WCF service to get a list of items to display in a grid. Once the list is brought down to the client it is cached in IsolatedStorage. This is done by using the DataContractSerializer to serialize all of these objects to a stream which is then zipped and then encrypted. When the application is relaunched, it first loads from the cache (reversing the process above) and the deserializes the objects using the DataContractSerializer.ReadObject() method. All of this was working wonderfully under all scenarios until recently with the entire "load from cache" path (decrypt/unzip/deserialize) taking hundreds of milliseconds at most.
On some development machines but not all (all machines Windows 7) the deserialize process - that is the call to ReadObject(stream) takes several minutes an seems to lock up the entire machine BUT ONLY WHEN RUNNING IN THE DEBUGGER in VS2008. Running the Debug configuration code outside the debugger has no problem.
One thing that seems to look suspicious is that when you turn on stop on Exceptions, you can see that the ReadObject() throws many, many System.FormatException's indicating that a number was not in the correct format. When I turn off "Just My Code" thousands of these get dumped to the screen. None go unhandled. These occur both on the read back from the cache AND on a deserialization at the conclusion of a web service call to get the data from the WCF Service. HOWEVER, these same exceptions occur on my laptop development machine that does not experience the slowness at all. And FWIW, my laptop is really old and my desktop is a 4 core, 6GB RAM beast.
Again, no problems unless running under the debugger in VS2008. Anyone else seem this? Any thoughts?
Here is the bug report link: https://connect.microsoft.com/VisualStudio/feedback/details/539609/very-slow-performance-deserializing-using-datacontractserializer-in-a-silverlight-application-only-in-debugger
EDIT: I now know where the FormatExceptions are coming from. It seems that they are "by design" - they occur when when I have doubles being serialized that are double.NaN so that that xml looks like NaN...It seems that the DCS tries to parse the value as a number, that fails with an exception and then it looks for "NaN" et. al. and handles them. My problem is not that this does not work...it does...it is just that it completely cripples the debugger. Does anyone know how to configure the debugger/vs2008sp1 to handle this more efficiently.
cartden,
You may want to consider switching over to XMLSerializer instead. Here is what I have determined over time:
The XMLSerializer and DataContractSerializer classes provides a simple means of serializing and deserializing object graphs to and from XML.
The key differences are:
1.
XMLSerializer has much smaller payload than DCS if you use [XmlAttribute] instead of [XmlElement]
DCS always store values as elements
2.
DCS is "opt-in" rather than "opt-out"
With DCS you explicitly mark what you want to serialize with [DataMember]
With DCS you can serialize any field or property, even if they are marked protected or private
With DCS you can use [IgnoreDataMember] to have the serializer ignore certain properties
With XMLSerializer public properties are serialized, and need setters to be deserialized
With XmlSerializer you can use [XmlIgnore] to have the serializer ignore public properties
3.
BE AWARE! DCS.ReadObject DOES NOT call constructors during deserialization
If you need to perform initialization, DCS supports the following callback hooks:
[OnDeserializing], [OnDeserialized], [OnSerializing], [OnSerialized]
(also useful for handling versioning issues)
If you want the ability to switch between the two serializers, you can use both sets of attributes simultaneously, as in:
[DataContract]
[XmlRoot]
public class ProfilePerson : NotifyPropertyChanges
{
[XmlAttribute]
[DataMember]
public string FirstName { get { return m_FirstName; } set { SetProperty(ref m_FirstName, value); } }
private string m_FirstName;
[XmlElement]
[DataMember]
public PersonLocation Location { get { return m_Location; } set { SetProperty(ref m_Location, value); } }
private PersonLocation m_Location = new PersonLocation(); // Should change over time
[XmlIgnore]
[IgnoreDataMember]
public Profile ParentProfile { get { return m_ParentProfile; } set { SetProperty(ref m_ParentProfile, value); } }
private Profile m_ParentProfile = null;
public ProfilePerson()
{
}
}
Also, check out my Serializer class that can switch between the two:
using System;
using System.IO;
using System.Runtime.Serialization;
using System.Text;
using System.Xml;
using System.Xml.Serialization;
namespace ClassLibrary
{
// Instantiate this class to serialize objects using either XmlSerializer or DataContractSerializer
internal class Serializer
{
private readonly bool m_bDCS;
internal Serializer(bool bDCS)
{
m_bDCS = bDCS;
}
internal TT Deserialize<TT>(string input)
{
MemoryStream stream = new MemoryStream(input.ToByteArray());
if (m_bDCS)
{
DataContractSerializer dc = new DataContractSerializer(typeof(TT));
return (TT)dc.ReadObject(stream);
}
else
{
XmlSerializer xs = new XmlSerializer(typeof(TT));
return (TT)xs.Deserialize(stream);
}
}
internal string Serialize<TT>(object obj)
{
MemoryStream stream = new MemoryStream();
if (m_bDCS)
{
DataContractSerializer dc = new DataContractSerializer(typeof(TT));
dc.WriteObject(stream, obj);
}
else
{
XmlSerializer xs = new XmlSerializer(typeof(TT));
xs.Serialize(stream, obj);
}
// be aware that the Unicode Byte-Order Mark will be at the front of the string
return stream.ToArray().ToUtfString();
}
internal string SerializeToString<TT>(object obj)
{
StringBuilder builder = new StringBuilder();
XmlWriter xmlWriter = XmlWriter.Create(builder);
if (m_bDCS)
{
DataContractSerializer dc = new DataContractSerializer(typeof(TT));
dc.WriteObject(xmlWriter, obj);
}
else
{
XmlSerializer xs = new XmlSerializer(typeof(TT));
xs.Serialize(xmlWriter, obj);
}
string xml = builder.ToString();
xml = RegexHelper.ReplacePattern(xml, RegexHelper.WildcardToPattern("<?xml*>", WildcardSearch.Anywhere), string.Empty);
xml = RegexHelper.ReplacePattern(xml, RegexHelper.WildcardToPattern(" xmlns:*\"*\"", WildcardSearch.Anywhere), string.Empty);
xml = xml.Replace(Environment.NewLine + " ", string.Empty);
xml = xml.Replace(Environment.NewLine, string.Empty);
return xml;
}
}
}
This is a guess, but I think it is running slow in debug mode because for every exception, it is performing some actions to show the exception in the debug window, etc. If you are running in release mode, these extra steps are not taken.
I've never done this, so I really don't know id it would work, but have you tried just setting that one assembly to run in release mode while all others are set to debug? If I'm right, it may solve your problem. If I'm wrong, then you only waste 1 or 2 minutes.
About your debugging problem, have you tried to disable the exception assistant ? (Tools > Options > Debugging > Enable the exception assistant).
Another point should be the exception handling in Debug > Exceptions : you can disable the user-unhandled stuff for the CLR or only uncheck the System.FormatException exception.
Ok - I figured out the root issue. It was what I alluded to in the EDIT to the main question. The problem was that in the xml, it was correctly serializing doubles that had a value of double.NaN. I was using these values to indicate "na" for when the denominator was 0D. Example: ROE (Return on Equity = Net Income / Average Equity) when Average Equity is 0D would be serialized as:
<ROE>NaN</ROE>
When the DCS tried to de-serialize it, evidently it first tries to read the number and then catches the exception when that fails and then handles the NaN. The problem is that this seems to generate a lot of overhead when in DEBUG mode.
Solution: I changed the property to double? and set it to null instead of NaN. Everything now happens instantly in DEBUG mode now. Thanks to all for your help.
Try disabling some IE addons. In my case, the LastPass toolbar killed my Silverlight debugging. My computer would freeze for minutes each time I interacted with Visual Studio after a breakpoint.
Updated: 09/02/2009 - Revised question, provided better examples, added bounty.
Hi,
I'm building a PHP application using the data mapper pattern between the database and the entities (domain objects). My question is:
What is the best way to encapsulate a commonly performed task?
For example, one common task is retrieving one or more site entities from the site mapper, and their associated (home) page entities from the page mapper. At present, I would do that like this:
$siteMapper = new Site_Mapper();
$site = $siteMapper->findByid(1);
$pageMapper = new Page_Mapper();
$site->addPage($pageMapper->findHome($site->getId()));
Now that's a fairly trivial example, but it gets more complicated in reality, as each site also has an associated locale, and the page actually has multiple revisions (although for the purposes of this task I'd only be interested in the most recent one).
I'm going to need to do this (get the site and associated home page, locale etc.) in multiple places within my application, and I cant think of the best way/place to encapsulate this task, so that I don't have to repeat it all over the place. Ideally I'd like to end up with something like this:
$someObject = new SomeClass();
$site = $someObject->someMethod(1); // or
$sites = $someObject->someOtherMethod();
Where the resulting site entities already have their associated entities created and ready for use.
The same problem occurs when saving these objects back. Say I have a site entity and associated home page entity, and they've both been modified, I have to do something like this:
$siteMapper->save($site);
$pageMapper->save($site->getHomePage());
Again, trivial, but this example is simplified. Duplication of code still applies.
In my mind it makes sense to have some sort of central object that could take care of:
Retrieving a site (or sites) and all nessessary associated entities
Creating new site entities with new associated entities
Taking a site (or sites) and saving it and all associated entities (if they've changed)
So back to my question, what should this object be?
The existing mapper object?
Something based on the repository pattern?*
Something based on the unit of work patten?*
Something else?
* I don't fully understand either of these, as you can probably guess.
Is there a standard way to approach this problem, and could someone provide a short description of how they'd implement it? I'm not looking for anyone to provide a fully working implementation, just the theory.
Thanks,
Jack
Using the repository/service pattern, your Repository classes would provide a simple CRUD interface for each of your entities, then the Service classes would be an additional layer that performs additional logic like attaching entity dependencies. The rest of your app then only utilizes the Services. Your example might look like this:
$site = $siteService->getSiteById(1); // or
$sites = $siteService->getAllSites();
Then inside the SiteService class you would have something like this:
function getSiteById($id) {
$site = $siteRepository->getSiteById($id);
foreach ($pageRepository->getPagesBySiteId($site->id) as $page)
{
$site->pages[] = $page;
}
return $site;
}
I don't know PHP that well so please excuse if there is something wrong syntactically.
[Edit: this entry attempts to address the fact that it is oftentimes easier to write custom code to directly deal with a situation than it is to try to fit the problem into a pattern.]
Patterns are nice in concept, but they don't always "map". After years of high end PHP development, we have settled on a very direct way of handling such matters. Consider this:
File: Site.php
class Site
{
public static function Select($ID)
{
//Ensure current user has access to ID
//Lookup and return data
}
public static function Insert($aData)
{
//Validate $aData
//In the event of errors, raise a ValidationError($ErrorList)
//Do whatever it is you are doing
//Return new ID
}
public static function Update($ID, $aData)
{
//Validate $aData
//In the event of errors, raise a ValidationError($ErrorList)
//Update necessary fields
}
Then, in order to call it (from anywhere), just run:
$aData = Site::Select(123);
Site::Update(123, array('FirstName' => 'New First Name'));
$ID = Site::Insert(array(...))
One thing to keep in mind about OO programming and PHP... PHP does not keep "state" between requests, so creating an object instance just to have it immediately destroyed does not often make sense.
I'd probably start by extracting the common task to a helper method somewhere, then waiting to see what the design calls for. It feels like it's too early to tell.
What would you name this method ? The name usually hints at where the method belongs.
class Page {
public $id, $title, $url;
public function __construct($id=false) {
$this->id = $id;
}
public function save() {
// ...
}
}
class Site {
public $id = '';
public $pages = array();
function __construct($id) {
$this->id = $id;
foreach ($this->getPages() as $page_id) {
$this->pages[] = new Page($page_id);
}
}
private function getPages() {
// ...
}
public function addPage($url) {
$page = ($this->pages[] = new Page());
$page->url = $url;
return $page;
}
public function save() {
foreach ($this->pages as $page) {
$page->save();
}
// ..
}
}
$site = new Site($id);
$page = $site->addPage('/');
$page->title = 'Home';
$site->save();
Make your Site object an Aggregate Root to encapsulate the complex association and ensure consistency.
Then create a SiteRepository that has the responsibility of retrieving the Site aggregate and populating its children (including all Pages).
You will not need a separate PageRepository (assuming that you don't make Page a separate Aggregate Root), and your SiteRepository should have the responsibility of retrieving the Page objects as well (in your case by using your existing Mappers).
So:
$siteRepository = new SiteRepository($myDbConfig);
$site = $siteRepository->findById(1); // will have Page children attached
And then the findById method would be responsible for also finding all Page children of the Site. This will have a similar structure to the answer CodeMonkey1 gave, however I believe you will benefit more by using the Aggregate and Repository patterns, rather than creating a specific Service for this task. Any other retrieval/querying/updating of the Site aggregate, including any of its child objects, would be done through the same SiteRepository.
Edit: Here's a short DDD Guide to help you with the terminology, although I'd really recommend reading Evans if you want the whole picture.