I am trying to create a small personal project which uses EF to handle data access. My project architecture has a UI layer, a service layer, a business layer and a data access layer. The EF is contained within the DAL. I don't think it's right to then make reference to my DAL, from my UI. So I want to create custom classes for 'business objects' which is shared between all my layers.
Example: I have a User table. EF creates a User entity. I have a method to maybe GetListOfUsers(). That, in the presentation, shouldn't reply on a List, as the UI then has a direct link to the DAL. I need to maybe have a method exposed in the DAL to maybe be something like:
List<MyUserObject> GetListOfUsers();
That would then call my internal method which would GetListOfUsers which returns a list of user entities, and then transforms them into my MyUserObejcts, which is then passed back through the layers to my UI.
Is that correct design? I don't feel the UI, or business layer for that matter, should have any knowledge of the entity framework.
What this may mean, though, is maybe I need a 'Transformation layer' between my DAL and my Business layer, which transforms my entities into my custom objects?
Edit:
Here is an example of what I am doing:
I have a data access project, which will contain the Entity Framework. In this project, I will have a method to get me a list of states.
public class DataAccessor
{
taskerEntities te = new taskerEntities();
public List<StateObject> GetStates()
{
var transformer = new Transformer();
var items = (from s in te.r_state select s).ToList();
var states = new List<StateObject>();
foreach (var rState in items)
{
var s = transformer.State(rState);
states.Add(s);
}
return states;
}
}
My UI/Business/Service projects mustn't know about entity framework objects. It, instead, must know about my custom built State objects. So, I have a Shared Library project, containing my custom built objects:
namespace SharedLib
{
public class StateObject
{
public int stateId { get; set; }
public string description { get; set; }
public Boolean isDefault { get; set; }
}
}
So, my DAL get's the items into a list of Entity objects, and then I pass them through my transformation method, to make them into custom buily objects. The tranformation takes an EF object, and outputs a custom object.
public class Transformer
{
public StateObject State (r_state state)
{
var s = new StateObject
{
description = state.description,
isDefault = state.is_default,
stateId = state.state_id
};
return s;
}
}
This seems to work. But is it a valid pattern?
So, at some point, your UI will have to work with the data and business objects that you have. It's a fact of life. You could try to abstract farther, but that would only succeed in the interaction being deferred elsewhere.
I agree that business processes should stand alone from the UI. I also agree that your UI should not directly act with how you access your data. What have you suggested (something along the lines of "GetListOfUsers()") is known as the Repository Pattern.
The purpose of the repository pattern is to:
separate the logic that retrieves the data and maps it to the entity
model from the business logic that acts on the model. The business
logic should be agnostic to the type of data that comprises the data
source layer
My recommendation is to use the Repository Pattern to hide HOW you're accessing your data (and, allow a better separation of concerns) and just be concerned with the fact that you "just want a list of users" or you "just want to calculate the sum of all time sheets" or whatever it is that you want your application to actually focus on. Read the link for a more detailed description.
First, do you really need all that layers in your 'small personal project'?
Second, I think your suggested architecture is a bit unclear.
If I get you right, you want to decouple your UI from your DAL. For that purpose you can for example extract interface of MyUserObject (defined in DAL obviously) class, lets call it IMyUserObject, and instead of referencing DAL from UI, reference some abstract project, where all types are data-agnostic. Also, I suggest that you'd have some service layer which would provide your presentation layer (UI) with concrete objects. If you utilize MVC you can have a link to services from your controller class. Service layer in turn can use Repository or some other technique to deal with DAL (it depends on the complexity you choose)
Considering transformation layer, I think people deal with mapping from one type to another when they have one simple model (DTO) to communicate with DB, another one - domain model, that deals with all the subtleties of business logic, and another one - presentational model, that is suited best to let user interact with. Such layering separates concerns to good measure, making each task simpler, but making app more complicated in general.
So you may end having MyUserObjectDTO, MyUserObject and MyUserObjectView and some mapping or transformation btw them.
Related
I'm currently wondering what's the suggested way to separate plain model classes (for e.g. using them in Entity Framework, Web API, MVC, WCF...) from their application logic parts (server side tasks, threads etc.) utilizing the DRY principe.
Consider this pseduo example:
public class HorseOfDoom {
private Thread _hungerThread;
private Laser _headMountedLaser = new Laser();
public int Age { get; set; }
public string Name { get; set; }
public int Health { get; set; }
public int HungerLevel { get; set; }
public HorseOfDoom() {
_hungerThread.Start();
}
public void PewPew() {
_headMountedLaser.PewPew();
}
}
In this class we have both - model properties that describe the model (age, name,..), but also a thread and methods. I can use this class in Entity Framework, WCF and so on.. but what if I want to use the model in a ASP.NET MVC client application without exposing the methods, threads? Do I have to write the same class again? Do I need managers, adapters and facades? Could I use the buddy class pattern?
Use a model fit for the context. DRY is not about repeating lines of code, it's about repeating behaviour. Your view model can have the same properties (copy paste ftw) as the business model, minus the methods. You can use Automapper to map one to the other. Chances are your view model will have more than only those properties, including validation attributes or other data neede by the view in a certain format.
A model to rule'm all is not good on the long term. Clean models will alow you to focus better on the context and avoid coupling to other contexts, which might use a very similar or identical model. Things change in time and it's easier to work with a specific model from the beginning even if that involves copy paste and it seems that you're repeating yourself.
I understand that a combination as you show it in your sample is not really desirable - my main point of critique would be the thread that already implies a very concrete way on how the object should behave. The probability is high that the thread contained in the class itself will make it harder to use the class in some environments. From my point of view, the platform that integrates the class should be able to choose how to orchestrate the actions of the class - of course the class can make some restrictions like "not to be used in a separate thread as the class is not implemented in a thread-safe way".
As for the point of whether to combine properties and methods in a class: I don't think that there is a clear and always valid answer. It depends very much on how big the architecture of your application is and whether you are willing to pay the price for the separation in terms of complexity and overhead.
The concept of combining properties and methods in a single class is usually referred to as "Domain Model". It is a very natural approach to design complex business logic.
If you have an architecture that sets out to separate the layers very well, you'd have a Domain Model in the business logic that implements the business rules. These classes combine properties and methods, but these classes are mapped to simpler versions (e.g. DTOs) that only transport the data to other layers. This way, you also de-couple a service interface from the domain model and change them with minimal influences on the other layers. For instance, if you have complex classes in the domain model and you want to present only a part of this information in a web interface or through a service layer, you could create one or more DTO classes that contain exactly the data that is needed. Changes to the domain model will not necessarily affect clients so that you gain freedom in this respect.
In a smaller architecture however, you might not need to separate the layers with DTOs if you can live with the consequences.
As for the mentioned example of WCF, you have separate service and data contracts that you typically implement in different classes. If you have additional methods in a class that serves as a data contract those methods will not be part of the data contract. You'd have to explicitly make the methods that you want to publish part of a service contract. If you don't share the classes with a service client (e.g. through a class library), the client will not even know that these methods exist.
Let's say that I want to create a blog application with these two simple persistence classes used with EF Code First or NHibernate and returned from repository layer:
public class PostPersistence
{
public int Id { get; set; }
public string Text { get; set; }
public IList<LikePersistence> Likes { get; set; }
}
public class LikePersistence
{
public int Id { get; set; }
//... some other properties
}
I can't figure out a clean way to map my persistence models to domain models. I'd like my Post domain model interface to look something like this:
public interface IPost
{
int Id { get; }
string Text { get; set; }
public IEnumerable<ILike> Likes { get; }
void Like();
}
Now how would an implementation underneath look like? Maybe something like this:
public class Post : IPost
{
private readonly PostPersistence _postPersistence;
private readonly INotificationService _notificationService;
public int Id
{
get { return _postPersistence.Id }
}
public string Text
{
get { return _postPersistence.Text; }
set { _postPersistence.Text = value; }
}
public IEnumerable<ILike> Likes
{
//this seems really out of place
return _postPersistence.Likes.Select(likePersistence => new Like(likePersistence ));
}
public Post(PostPersistence postPersistence, INotificationService notificationService)
{
_postPersistence = postPersistence;
_notificationService = notificationService;
}
public void Like()
{
_postPersistence.Likes.Add(new LikePersistence());
_notificationService.NotifyPostLiked(Id);
}
}
I've spent some time reading about DDD but most examples were theoretical or used same ORM classes in domain layer. My solution seems to be really ugly, because in fact domain models are just wrappers around ORM classes and it doens't seem to be a domain-centric approach. Also the way IEnumerable<ILike> Likes is implemented bothers me because it won't benefit from LINQ to SQL. What are other (concrete!) options to create domain objects with a more transparent persistence implementation?
One of the goals of persistence in DDD is persistence ignorance which is what you seem to be striving for to some extent. One of the issues that I see with your code samples is that you have your entities implementing interfaces and referencing repositories and services. In DDD, entities should not implement interfaces which are just abstractions of itself and have instance dependencies on repositories or services. If a specific behavior on an entity requires a service, pass that service directly into the corresponding method. Otherwise, all interactions with services and repositories should be done outside of the entity; typically in an application service. The application service orchestrates between repositories and services in order to invoke behaviors on domain entities. As a result, entities don't need to references services or repositories directly - all they have is some state and behavior which modifies that state and maintains its integrity. The job of the ORM then is to map this state to table(s) in a relational database. ORMs such as NHibernate allow you to attain a relatively large degree of persistence ignorance.
UPDATES
Still I don't want to expose method with an INotificationService as a
parameter, because this service should be internal, layer above don't
need to know about it.
In your current implementation of the Post class the INotificationService has the same or greater visibility as the class. If the INotificationService is implemented in an infrastructure layer, it already has to have sufficient visibility. Take a look at hexagonal architecture for an overview of layering in modern architectures.
As a side note, functionality associated with notifications can often be placed into handlers for domain events. This is a powerful technique for attaining a great degree of decoupling.
And with separate DTO and domain classes how would you solve
persistence synchronization problem when domain object doesn't know
about its underlying DTO? How to track changes?
A DTO and corresponding domain classes exist for very different reasons. The purpose of the DTO is to carry data across system boundaries. DTOs are not in a one-one correspondence with domain objects - they can represent part of the domain object or a change to the domain object. One way to track changes would be to have a DTO be explicit about the changes it contains. For example, suppose you have a UI screen that allows editing of a Post. That screen can capture all the changes made and send those changes in a command (DTO) to a service. The service would load up the appropriate Post entity and apply the changes specified by the command.
I think you need to do a bit more research, see all the options and decide if it is really worth the hassle to go for a full DDD implementation, i ve been there myself the last few days so i ll tell you my experience.
EF Code first is quite promising but there are quite a few issues with it, i have an entry here for this
Entity Framework and Domain Driven Design. With EF your domain models can be persisted by EF without you having to create a separate "persistence" class. You can use POCO (plain old objects) and get a simple application up and running but as i said to me it s not fully mature yet.
If you use LINQ to SQL then the most common approach would be to manually map a "data transfer object" to a business object. Doing it manually can be tough for a big application so check for a tool like Automapper. Alternatively you can simply wrap the DTO in a business object like
public class Post
{
PostPersistence Post { get; set;}
public IList<LikePersistence> Likes { get; set; }
.....
}
NHibernate: Not sure, havent used it for a long time.
My feeling for this (and this is just an opinion, i may be wrong) is that you ll always have to make compromises and you ll not find a perfect solution out there. If you give EF a couple more years it may get there. I think an approach that maps DTOs to DDD objects is probably the most flexible so looking for an automapping tool may be worth your time. If you want to keep it simple, my favourite would be some simple wrappers around DTOs when required.
I'm trying to wrap my head around Domain Driven Development. I want to make sure I have a good foundation and understanding of it, so it would be great if recommendations to use AutoMapper or similar are avoided here. My architecture currently involves the following:
The WCF service is responsible for persistence (using Entity Framework) and server-side validation. It converts POCO's to DTO's, and DTO's are transferred to the client.
The Client, receives DTO's and converts them to POCO's. The class that converts POCO's and DTO's is shared between the service and the client.
The POCO's implement IValidatableObject and INotifyPropertyChanged and are used by both the server and the client, but they are not used for data transfer. The DTO's are, which are just property bags containing no behavior.
(1) Question #1. Is this architecture appropriate for a Domain Driven Design.
(2) Question #2. Is it appropriate for POCO's to contain navigation properties? It really feels wrong for POCO's to contain navigation properties in a DDD architecture to me, because it doesn't make sense to me to have a navigation property that may or may not be serialized. It would make more sense to me to have a specialized DTO.
For example, here is a POCO/DTO looks like in my architecture.
// Enforces consistency between a POCO and DTO
public interface IExample
{
Int32 Id { get; set; }
String Name { get; set; }
}
// POCO
public class Example : IExample, INotifyPropertyChanged, IValidatableObject
{
private int id;
private string name;
public Int32 Id {
get { return this.id; }
set {
this.id = value;
OnPropertyChanged("Id");
}
}
public String Name {
get { return this.name; }
set {
this.name = value;
OnPropertyChanged("Name ");
}
}
public ICollection<Example2> ChildExamples {
get { ... }
set { ... }
}
// INotifyPropertyChanged Members
// IValidatableObject Members
}
// DTO
public class ExampleInfo : IExample
{
public Int32 Id { get; set; }
public String Name { get; set; }
public ICollection<Example2Info> ChildExamples { get; set; }
}
It doesn't seem right though, because you may not always need the navigation property, and having an empty (null) object (or collection) seems very wrong in an object-oriented architecture. You also have to deal with serializing and converting deep object hierarchies at times, which is not trivial. It would make more sense for a specialized DTO so there isn't a problem with the constant possibility of empty navigation properties that may or may not need serialized or populated.
public class ComplexInfo
{
public Example ExampleInfo { get; set; }
public ICollection<Example2Info> ChildExamples { get; set; }
}
How are these situations handled in real-world enterprise DDD style architectures and what other advice can be given here?
I agree with Jehof about sending the DTO's to your client and keeping the domain model clean on the server side under your WCF.
With respect to navigation properties, one point Eric Evans emphasizes in Domain Driven Design is to respect invariants. So, in your example above ask yourself if Id and Name are really going to change in the lifetime of the object, or are they invariants? A lot of DDD-style developers would not even put a setter on those properties. Instead build the object's invariant state through a constructor. If Name can change, you probably want a method called Rename(string newName), because there's probably some kind of business rules you'd want to put there anyway.
A red flag in your layers above is that you have your whole object model in the DAL. What you call your assemblies really isn't a big deal but I think it points to your tendency to keep thinking of the application from a data perspective. The point of DDD is to think of your object model in terms of logic and behavior, not data and structure. I (and most other DDD developers, I think) think of the data access layer as Repository classes which return Aggregate Roots. The repositories are responsible for returning your hydrated poco/entity objects from the DAL(repository) to the business layer (and above, such as an application/service layer class or your WCF in your above example). In your case of using EF, you'd have the repositories wrap your DataContext calls and return the entity objects.
I could go on and on, because your question is really targeting the basic fundamentals of DDD, of which there are several. I would recommend 1) Read Eric Evans book, "Domain Driven Design". 2) Keep in mind that DDD targets complex business software. If you're trying to apply it to a simple CRUD application which really is just UI forms and data binding to DB tables, its hard to see a DDD approach take shape, because the problems it addresses just aren't there. So keep that in perspective.
Is this architecture appropriate for a Domain Driven Design?
Not entirely. Take a look at hexagonal architecture for a description of a more modern architectural style which fits nicely with DDD. Within hexagonal, your domain is at the core and various components "attach" to it. For example, a WCF service would be considered an adapter in a hexagonal architecture because it adapts your domain to a communication technology such as TCP or HTTP. Typically, you would have an application service which establishes a facade over your domain and effectively represents use cases. This application service can be referenced by a WCF service to expose functionality over HTTP. Unfortunately, the "service" terminology can be a bit conflating.
Is it appropriate for POCO's to contain navigation properties?
It is appropriate, but the right answer is that it depends. One of the issues with navigational properties that you state is that they may or may not be serialized for a specific DTO. This is telling me that you are talking about queries. Some queries need only a subset of attributes on an aggregate/entity (POCO) and thus the corresponding DTO only has those required properties. It seems wasteful to retrieve an entire entity together with navigational properties. To address this issue you can employ lazy loading. A more salable approach however, is to use read-models for queries. Also, as stated by others, an entity/aggregate certainly can and should contain navigational properties if they are a reflection of the domain. How these "navigational" properties are implemented can vary. Sometimes it can be better to split an aggregate into multiple aggregates. Take a look at Effective Aggregate Design by Vaughn Vernon.
As pointed out by Jehof, you should try to have clients of the WCF service only depend on the contract of that service itself, not on the domain entities (POCOs) that the service encapsulates. Typically, POCOs should not implement INotifyPropertyChanged and IValidatableObject because those interfaces support UI concerns and should be handled by the DTOs or ViewModels.
Domain Driven Design isn't about POCO's or DTO's. It's about Entities, Aggregate Roots, Value Objects. About rich domain objects that can encapsulate behavior in addition to data.
Is it appropriate for POCO's to contain navigation properties ?
It's not clear to me what the POCOs are for in your scenario, but if they are your domain entities, then they can and should certainly contain navigation properties. Actually, using the navigation properties of an Aggregate Root (a special kind of domain entity) is often the only way for external objects to access entities enclosed in that Aggregate. Navigation through association properties is a key concept in DDD.
Also, the recommended architecture in DDD looks more or less like :
Presentation Layer (UI)
Application layer
Domain Layer
Infrastructure layer (includes persistence/DAL)
The key here is the Single Responsibility Principle. You don't want a service that does persistence, server-side validation and DTO mapping at the same time. You need decoupling. You need a clear distribution of responsibilities among your layers so that they are more easily maintainable, extensible and portable.
Another suggestion: think very hard whether to share the mapping code (and by implication the classes they are mapped to) between the client the server.
There is nothing wrong with sharing code, but be careful you are not mixing client concerns and server concerns. It may start with small compromises "I need this property only on the client, but everything else is the same", but you might end up with flags to tell the class whether to use client or server behavior and other nastiness.
Having separate implementations of the POCO's may seem as code duplication at first, but it frees you to have an implementation fitted to the task.
That's why using Automapper and the like makes sense, it lowers the barrier of writing the mapping code.
Another reason to do this (which has been also mentioned) is that the DTO's should be a way to implement a communication API, and not the API itself: i.e. the DTO's are there for WCF to implement a SOAP API (or REST or whatever), but the client should be free to implement the communication layer using only the API specification, without any hidden logic in the mapping code.
This also ensures your API remains language agnostic. You might want to provide client libraries (in any of several appropriate languages) to ease the interaction with your API, but these should not be a requirement.
In my continuing journey through ASP.NET MVC, I am now at the point where I need to render an edit/create form for an entity.
My entity consists of enums and a few other models, created in a repository via LINQtoSQL.
What I am struggling with right now is finding a decent way to render the edit/create forms which will contain a few dropdown lists and a number of text fields. I realize this may not be the most user-friendly approach, but it is what I am going with right now :).
I have a repository layer and a business layer. The controllers interface with the service layer.
Is it best to simply create a viewmodel like so?
public class EventFormViewModel
{
IEventService _eventService;
public IEvent Event { get; private set; }
public IEnumerable<EventCampaign> Campaigns { get; private set; }
public IEnumerable<SelectListItem> Statuses { get; private set; }
// Other tables/dropdowns go here
// Constructor
public EventFormViewModel(IEventService eventService, IEvent ev)
{
_eventService = eventService;
Event = ev;
// Initialize Collections
Campaigns = eventService.getCampaigns().ToSelectList(); //extn method maybe?
Statuses = eventService.getStatus().ToSelectList(); /extn for each table type?
}
So this will give me a new EventFormViewModel which I'll bind to a view. But is this the best way? I'd essentially be pulling all data back from the database for a few different tables and converting them to an IEnumerable. This doesn't seem overly efficient, but I suppose I could cache the contents of the dropdowns.
Also, if all I have is methods that get data for a dropdown, should I just skip the service layer and go right to the repository?
The last part of my question: For the ToSelectList() extension method, would it be possible to write one method for each table and use it generically even if some tables have different columns ("Id" and "Name" versus "Id" and "CampaignName").
Forgive me if this is too general, I'm just trying to avoid going down a dead-end road - or one that will have a lot of potholes.
I wouldn't provide an IEventService for my view model object. I prefer to think of the view model object as a dumb data transfer object. I would let the controller take care of asking the IEventService for the data and passing it on to the view model.
I'd essentially be pulling all data
back from the database for a few
different tables and converting them
to an IEnumerable
I don't see why this would be inefficient? You obviously shouldn't pull all data from the tables. Perform the filtering and joining you need to do in the database as usual. Put the result in the view model.
Also, if all I have is methods that
get data for a dropdown, should I just
skip the service layer and go right to
the repository?
If your application is very simple, then a service layer may be an unneeded layer of abstraction / indirection. But if your application is just a bit complex (from what you've posted above, I would guess that this is the case), consider what you will by taking a shortcut and going straight to a repository and compare this to what you will win in maintainability and testability if you use a service layer.
The worst thing you could do, would be to go through a service layer only when you feel there is a need for it, and go straight to the repository when the service layer will not be providing any extra logic. Whatever you do, be consistent (which almost always means: go through a service layer, even when your application is simple. It won't stay simple).
I would say if you're thinking of "skipping" a layer than you're not really ready to use MVC. The whole point of the layers, even when they're thin, is to facilitate unit testing and try to enforce separation of concerns.
As for generic methods, is there some reason you can just use the OOB objects and then extend them (with extension methods) when they fail to meet your needs?
I've commonly seen examples like this on business objects:
public void Save()
{
if(this.id > 0)
{
ThingyRepository.UpdateThingy(this);
}
else
{
int id = 0;
ThingyRepository.AddThingy(this, out id);
this.id = id;
}
}
So why here, on the business object? This seems like contextual or data related more so than business logic.
For example, a consumer of this object might go through something like this...
...Get form values from a web app...
Thingy thingy = Thingy.CreateNew(Form["name"].Value, Form["gadget"].Value, Form["process"].Value);
thingy.Save();
Or, something like this for an update...
... Get form values from a web app...
Thingy thingy = Thingy.GetThingyByID(Int32.Parse(Form["id"].Value));
Thingy.Name = Form["name"].Value;
Thingy.Save();
So why is this? Why not contain actual business logic such as calculations, business specific rules, etc., and avoid retrieval/persistence?
Using this approach, the code might look like this:
... Get form values from a web app...
Thingy thingy = Thingy.CreateNew(Form["name"].Value, Form["gadget"].Value, Form["process"].Value);
ThingyRepository.AddThingy(ref thingy, out id);
Or, something like this for an update...
... get form values from a web app ...
Thingy thingy = ThingyRepository.GetThingyByID(Int32.Parse(Form["id"].Value));
thingy.Name = Form["Name"].Value;
ThingyRepository.UpdateThingy(ref thingy);
In both of these examples, the consumer, who knows best what is being done to the object, calls the repository and either requests an ADD or an UPDATE. The object remains DUMB in that context, but still provides it's core business logic as pertains to itself, not how it is retrieved or persisted.
In short, I am not seeing the benefit of consolidating the GET and SAVE methods within the business object itself.
Should I just stop complaining and conform, or am I missing something?
This leads into the Active Record pattern (see P of EAA p. 160).
Personally I am not a fan. Tightly coupling business objects and persistence mechanisms so that changing the persistence mechanism requires a change in the business object? Mixing data layer with domain layer? Violating the single responsibility principle? If my business object is Account then I have the instance method Account.Save but to find an account I have the static method Account.Find? Yucky.
That said, it has its uses. For small projects with objects that directly conform to the database schema and have simple domain logic and aren't concerned with ease of testing, refactoring, dependency injection, open/closed, separation of concerns, etc., it can be a fine choice.
Your domain objects should have no reference to persistance concerns.
Create a repository interface in the domain that will represent a persistance service, and implement it outside the domain (you can implement it in a separate assembly).
This way your aggregate root doesn't need to reference the repository (since it's an aggregate root, it should already have everyting it needs), and it will be free of any dependency or persistance concern. Hence easier to test, and domain focused.
While I have no understanding of DDD, it makes sense to have 1 method (which will do UPSERT. Insert if record doesn't exist, Update otherwise).
User of the class can act dumb and call Save on an existing record and Update on a new record.
Having one point of action is much clearer.
EDIT: The decision of whether to do an INSERT or UPDATE is better left to the repository. User can call Repository.Save(....), which can result in a new record (if record is not already in DB) or an update.
If you don't like their approach make your own. Personally Save() instance methods on business objects smell really good to me. One less class name I need to remember. However, I don't have a problem with a factory save but I don't see why it would be so difficult to have both. IE
class myObject
{
public Save()
{
myObjFactory.Save(this);
}
}
...
class myObjectFactory
{
public void Save(myObject obj)
{
// Upsert myObject
}
}