I have MVC 3 web app where I get record(s) from DB which is used to render page elements and populate different partial views.
I have classes that represent these DB objects (service layer).
I have also separate set of classes which holds models get returned by the controllers to the view(s).
In my controller, I query DB that returns object to represent DB record.
Then I transfer (MAP) that DB Object to object that Represent the model used by the view(s)
These classes are big and I have to write lots of code in the controller to map.
In most cases I only have some properties which are different.
It seems lots of extra work to do this mapping & lots of code to do the mapping
That is why I am asking.
Is this the correct design approach of developing in MVC framework?
If no, then do you have some pointers that outline the best practice on this aspect.
The Model or ViewModel should only contain information that is used by the View. In some cases, this can be almost identical to what the objects you get from the database are,but this is not always the case. Keeping these concerns separate is good for a number of reasons beyond the scope of a stackoverflow answer. On a side note, I hope you have a separate data access layer and am not querying the database , entity framework or service directly from the controller, again, just to keep those concerns separate.
You can use AutoMapper to map between your DB objects and view models automatically.
Example:
SomeViewModel model = Mapper.Map<SomeViewModel>(someDbObj);
Getting started guide.
Related
I've recently started developing in .NET core.
When developing I encountered the situation that I have to make very similair models that aren't quite the same. For example, let's talk about a booking model:
Frontend: Here I need a model that gets posted as a JSON to my backend and gets deserliazed to a sort of FrontendBooking model.
Backend: I need to add Customer data to the booking, therefore I need to add fields like: CustomerName and CustomerAddress, based on their CustomerId. The backend needs to provide this data, I do not want the frontend to determine these fields. I combine these models to prepare it for an API call. To a model called RequestBooking.
API: I sent RequestBooking to an API and get a response with a similair object that has for example a Status and BookingId added, this was added to the model by the API. So I need to deserialize this to an object called: ResponseBooking.
Database: Finally I wish to store the object to a database, not all properties of the model are relevant however, therefore I create another model called: DatabaseBooking and store this to the databse.
When a property is added, removed or changed. Then I'll have to change it for each of these models.
Is there a design pattern or some other solution, so this is more manageable?
Also, what is best practise for naming these models? Naming them all Booking doesn't feel quite right and adding what they're used for doesn't feel quite right either.
Thanks in advance.
Well, in general you will need different (although similar) models at least at these levels:
Server: here you can make use of Domain Driven Design. You will have an object Booking that is responsible for its logic and contain all properties and methods like e.g. MarkAsCancelled. You can use Entity Framework to use the same object in the database, which will correspond to a database table. EF allows you to mark some properties as not being saved in the DB. Also you can set up EF in the DbContext class and thus not use DB specific attributes in the class. So one object for DB and backend business logic.
API: obviously you cannot send your domain object to the API, e.g. REST. In the API you may want to combine properties of several domain objects or hide some properties. You will have to define a set of Data Transfer Objects (DTOs), e.g. BookingDto. How to convert your domain objects to DTOs? Solutions like AutoMapper may help. You just set up convertion rules once.
Now you can describe your API in e.g. Swagger. With Swagger Codegen you can than generate code for your server (.net) and client (e.g. JS).
In the end you will have to support the following:
API definition (e.g. Swagger). Code for server DTOs and client
objects is autogenerated. You modify API definition once, both sides
get new objects.
DDD Models that also are used for the Database. They
may be faily independent from your DTOs. Mapping is handled for you
semi-automatically by e.g. Automapper
All said is just a suggestion. All the layers and number of objects can and should be adapted to the specific needs of your project. E.g. you may want to use separate objects for the database if you are not using a relational mapper like EF or do not want to mix DB and logic.
I know the title sounds like a duplicate of quite a few existing posts, but I've read quite a few of them and my situation is actually quite different. I would really appreciate it if anyone experienced with Entity Framework could offer some advice on the best architecture for the following scenario.
I have a wpf application with a 3-tier layout, Data Access Layer, Business Logic Layer, and UI Presentation Layer. The UI uses MVVM. DAL uses Entity Framework. UI and Data Access Layer each have their own models, UIModel and DataModel.
The current design uses a global DbContext for Entity Framework across the application. For a simple update operation, an entity is retrieved from the database as a DataModel, converted into a GUIModel, wired to the ViewModel and View for updates, and converted back into a DataModel to update in the database. And here's the problem: when the new DataModel is created from the conversion, it is no longer related to the original entity retrieved, and Entity Framework cannot perform the update because it now has two duplicate models of the same primary key attached to the same DbContext.
I did a little bit of research and found a couple of possible ways to fix this. One is to use a single model entity across all layers instead of separating GUIModel and DataModel, and break the global DbContext into unit of work. This seems to be a very common design, but my concerns with this approach is that the merge of GUIModel and DataModel violates the separation of responsibilities, and using unit of work required Business Layer to control the lifetime of DbContext, which also blurs the boundary between BLL and DAL.
The second alternative would be to use a local DbContext for every database query with a using block. This seems most memory efficient. But doing it this way makes lazy loading not possible, and eager loading all navigation properties in every query would likely affect performance. Also the short lived DbContexts require working completely in disconnected graph, which becomes quite complicated in terms of change tracking.
A third possibility would be to cache all original DataModels and update on those entities after the update.
I am new to Entity Framework and I'm sure there should be other ways to fix this issue too. I'll really appreciate it if anyone could offer some insights on the best way to approach this.
Better approach is when you are going for update call in your repository firstly get the entity by primary key now you are in dbContext with required entity to be updated then assign updated fields and update the Context.
Here is code:
public void UpdateEntity(Entity updatedEntity)
{
using (var db = new DBEntities())
{
var entity = db.Entities.Find(updatedEntity.Id);
if (entity!= null)
{
entity.Name = updatedEntity.Name;
entity.Description = updatedEntity.Description;
entity.LastModifiedBy = updatedEntity.LastModifiedBy;
entity.Value = updatedEntity.Value;
entity.LastModifiedOn = DateTime.Now;
db.SaveChanges();
}
}
}
I would recommend using separate Business Objects as described in your second alternative. In a multi-tier scenario, you would create reusable objects that support your use case from the UI perspective, modelling the behavior of your business domain (as you call them "GUIModel"). Those models should focus on the behavior of your system and only contain the data needed to support this behavior. This is in direct contrast to entity classes that focus on data.
Example: Northwind Database, Customers Table. The entity would be a class containing all properties of a customer, probably having navigation properties to related things. Would you really want to use this model when you need to display a list of condensed customer information in the dropdown of an auto completion search box? Would you want to use the same model to display customers together with their aggregated invoice data in a grid? You would need to load all customer information together with related invoices to your presentation tier. You probably don't want to do that.
If you had different models for different use cases, things would make more sense from an object oriented point of view:
Class CustomerSearchResult: Id, Name. GetCustomerEdit method.
Class CustomerInvoiceInfo: Id, Name, Aggregated invoice values. GetCustomerEdit method.
Class CustomerEdit: All properties you want to display and edit, timestamp for optimistic concurrency checks. Change tracking logic, validation logic. Methods that model behavior that you need while editing a customer.
Class CustomerEntity: this is your data object that resembles the customers table. You use it as DTO to initialize the other objects from the database or push changes back into the database. You don't send it across the wire.
This way, when you get to the data access layer, you can put your DbContext into using blocks and respect the unit of work pattern. Of course, you will need to reflect changes made to the CustomerEdit instance by creating a new CustomerEntity from it and reattach it to the context as modified:
context.Entry(entity).State = EntityState.Modified;
context.SaveChanges();
This seems complex and burdensome at first, but actually, Entity Framework doesn't contain any magic that helps you much in a disconnected (n-tier) scenario. If you try using things like lazy loading or keeping DbContext instances open all the time, things get out of hand pretty fast.
If you're looking for a framework that helps in creating Business Objects and supports multi tier architectures, take a look into CSLA.net. Disclaimer: Many people here don't like it. It will make things worse if used wrong. Still, it helped me in some projects and I'm happy with it.
You can attach entity to an existing dbContext by using the
following code, also here is a good post about entities states from MSDN
var existingBlog = new Blog { BlogId = 1, Name = "ADO.NET Blog" };
using (var context = new BloggingContext())
{
context.Entry(existingBlog).State = EntityState.Modified;
// Do some more work...
context.SaveChanges();
}
Regarding 3-Tier, I would like to start by giving small description with .net context for each tier
Presentation, This is the layer that return the results to the use and it could be in the form of ASP.Net Website, Windows Forms, Web Api, WCF service or anything else
Business, this should include the domain model of your business, business logic and services that provide business across multiple domain entities
Data access/ persistence, This layer should include the logic to persist and retrieve the domain model into durable media such as DB, file system,...
Generally the common issue here is which model goes into which layer for example should class X goes into presentation or business and I recommend an easy way to help you take your decision which is introducing new sibling layer so ask your self if you would like to build another presentation layer as console instead of windows will you copy and paste that logic into the new layer? if yes then there is good probability that your classes not in the right place.
Finally some concrete recommendations,
Keep each layer having its models as each layer has unique
responsibility, also there are good frameworks that might help you in
mapping between models such as AutoMapper
Don't transfer Entity Framework models across the layers as this will ruin the separation of concerns also it has more and more issues if you enabled lazy loading.
Try to avoid lazy loading unless you know what you are doing, one of the common pitfalls is Select N+1 and here is a good article describing it.
Also if you have a complex business, try to separate between querying the system and updating it by applying CQRS pattern, and there are some frameworks that can help you such as Dapper
Is it possible to call multiple stored procedures (not multiple result sets from a procedure) and display results on a single page in ASP.NET MVC 3 application?
From what I understand only one Model can created on any single page and my stored procedure is already tied to that Model. I would like to call another procedure and display that result as well on my page
I think the root problem is to understand the meaning of the Model in the MVC pattern.
First of all,
The model consists of application data and business rules, and the controller mediates input, converting it to commands for the model or view.[3] A view can be any output representation of data, such as a chart or a diagram
source
In ASP.Net MVC you link a model to your view, this model should not be part of your domain logic or any domain object
The real model (using the meaning of the MVC pattern) is represented by your domain objects.
So what should you put inside the object that you link to your view??
These objects should contain a representation of the view, in other words simple DTO's containing only the data that is going to be used in the view and nothing more. These models should represent the data being used in the view. If you follow this approach, and you need to display more data in the page, you only need to add another property to this model and voila, you can use it from your view.
In a CQRS architecture, these DTO's should be populated by the Query repositories.
If you do not have a CQRS architecture, just populate these objects in your domain, repositories, etc. Do not do it inside the controller, keep your controllers clean and simple, by making calls to your real domain using services or repositories
Try to avoid the reuse of these DTO's, they should belong to one view only. And do yourself a favor and do not try to reuse a domain object instead of a DTO just to use it as the model.
Following this approach your view-models will be clean, since they will be only DTO's and only containing the data needed by the view. And you can fill these DTO's from different sources, even from different databases if you want.
When you want to perform an action you would read from the model the data provided by the user, and with this data you would call your domain through repositories, services or in a CQRS arc. using commands
The simple answer to your question is "yes".
I suggest you do some more research (ie reading articles and looking at sample apps) into MVC and concentrate on understanding these points:
The Model is a class used to group the data you want to display in the View. It can be populated by a variety of methods and does not have to be the domain object or the pure representation of the database result.
A "page" (the concept of what a user sees in their browser window) can be made up from one or more Views. Each View can be responsible for displaying one type of Model allowing for reuse, but a "page" can have multiple Views.
Models are not "tied" to stored procedures. Perhaps you are using an ORM tool that returns a DTO class (which you call model)? This doesn't have to be the Model used by the View. The Controller could compose several of these DTO classes into one Model class.
N-tier application design where database access is separated from the display logic. MVC tries to encourage this but it still has to be done correctly to avoid tying yourself in knots.
Good luck!
I have been reading about entity framework over the past couple of days and have managed to get a fair idea of using it but I still have a couple of questions some of which might seem a bit too basic. For perspective I am using entity framework 4.0 in an asp.net web application.If you can answer any of the questions please go ahead.
What advantage do I get by using POCO templates. I understand that if I wish to get persistence ignorance and keep my Entities clear of any information related to storage POCO entities are the way to go. Also I could switch from Entity framework to say NHibernate with relative ease when using POCO entities? Apart from loose coupling is there any significant reason for me to go towards POCO entities. Also if I do use POCO do I end up losing anything. I still get change tracking and lazy loading with the help of proxies?
Is it normal practice to use the Entities of the EF model as Data transfer Objects or Business Objects. i.e for example I have a separate class library for my entity model.Supposing I am using MVP , where I want a list of Employee's in a company. The presenter would request my business logic functions which would query the entity model for the list of Employee's and return the list of entities to the presenter. In this case my presenter would need to have a reference to the EF model. Is this the correct way? In the case of my asp.net web applciation it shouldnt be a problem but if I am using web services how does this work? Is this the reason to go towards POCO entities?
Supposing The Employee entity has a navigation property to a company table. If I use and wrap the data context in an 'using' block , and try to access the navigation property in the BL I am assuming I would get an exception. Would I also get an exception if I turned off lazyloading and used the 'include' linq query to get the entity? On a previous post someone recommended I use an context per request implying that the context remains active even when I am in the BL. I am assuming I would still need to detach the object and attach it to the context on my next request if I wish to persist any changes I make? or Instead should I just query for the object again with the new context and update it?
This question has more to do with organizing files/best practices and is a followup to a question i posted earlier. When I am using separate files based on entities to organize my data access layer, what is the best practice to organize my queries involving joins between multiple tables. I am still a bit hazy on organization. Have tried searching online but havent had much help.
Terrific question. My first recommendation is to think in patterns. With that said...
You pretty much nailed the advantages of using POCO. There are some distinct advantages to decoupling your business objects (POCO entities) from your data access layer. But the primary reason is like you said the ability to change or modify layers below. However using POCO you are essentially following the Code First (CF) approach. Personally, I consider it Code In Parallel depending upon your software development life cycle. You still have all the bells and whistles that data or model first approach have and some since you can extend the DbContext which is ObjectContext under the hood. I read an article, which I cannot seem to find, that CF is the future of Entity Framework. Lastly the nice thing with POCO is you are able to incorporate validation rules here or else where. You can also provide projections. Lets say you have Date of Birth but you want an Age property as well. That now becomes a no brainer as the Age property is ignored when mapping to the database.
Personally I create my own business objects (POCO) for large projects that tend to have a life of its own where change is a way of life. Another thought is scalability and maintainability. What if down the road I choose to split functionality between applications where, like you mentioned web services, functionality is now delivered from two disparate locations. If you have encapsulated your business objects and DAL within the same code block separation or scalability has now become a bit more complex. However, consider the project. It may be small with very little future change so no need to throw a grenade to kill a fly. At which time data first might be the way to go and let edmx file represent your objects. So don't marry yourself to one technology or one methodology/pattern. Do what makes sense for your time and business.
Using statements are perfectly fine. In fact I've recently been turned on to then wrapping that within a TransactionScope. If an error occurs rollbacks are inherent. Next, something to consider is the UnitOfWork. UnitOfWork pattern encapsulates a snapshot of what needs to be performed where the Data Context is the boundaries from which you work within. For each UnitOfWork you have a subject for which work is to be performed on. For example an Employee. So if you are to save Employee information to keep it simple you would make a call to the BL service or repository (which ever). There you pass in the Employee Id, perform some work under that UnitOfWork where it is either instantiated in the constructor or using Dependency Injections (DI or IoC). Easy starter is StructureMap. There the service makes the necessary calls to your UnitOfWork (DbContext) then returns control back upstream (e.g. UI).
The best way to learn here is to view others code. I'd start with some Microsoft examples. I'd start with Nerd Dinner (http://nerddinner.codeplex.com/) then build off that.
Additional Reading:
Use prototype pattern or not
http://weblogs.asp.net/manavi/archive/2011/05/17/associations-in-ef-4-1-code-first-part-6-many-valued-associations.aspx
[EDIT]
NightHawk457, I'm terribly sorry for not responding to your questions. Hopefully you figured it out but for future readers...
To help everyone visualize, imagine the below Architecture using the Domain Model and Repository as an example. Remember, there are many ways to skin a cat so take this and make it your own and don't forget my Grenade comment above.
Data Layer (Data Access): MyDbContext : DbContext, IUnitOfWork, where IUnitWork contracts the CRUD operations.
Data Repository (Data Access / Business Logic): MyDomainObjectRepository : IMyDomainObjectRepository, which receives IUnitOfWork by Factory class or Dependency Injection. Calls MyDomainObject validation on CRUD operations.
Domain Model (Business Logic): MyDomainObject using [Custom] Validation Attributes. Read this for pros/cons.
MVVM / MVC / WCF (Presentation / Service Layers): What ever additional layers you chose, you now have access to your data which is wrapped nicely in smaller modules who are self encapsulating of their function. The presentation layer (e.g. ViewModel, Controller, Code-Behind, etc.) can then receive an IMyObjectRepository by a Factory class or by Dependency Injection.
Tips:
Pass connection string into MyDbContext so you can reuse MyDbContext.
MySql does not play well with System.Transactions.TransactionScope, example. I don't recall exactly but it was something MySql did not support. This makes Testing a bit difficult since we have created this level of separation.
Create a Test project for each layer and at the minimum test general functionality/rules.
Each Domain Object should extend base object with ID field at minimum. Also do not implement Key attributes here. Domain Object should not describe architecture but rather the specific data as an entity. Even on Code First this can be achieved by the Fluent API.
Think generics when creating MyDbContext. ;) Read Diego's post.
In ASP.NET, the repositories are nice to use with ObjectDataSources.
As you can see, there is clear separation of roles where IUnitOfWork and IMyDomainObjectRepository are the Interfaces which expose the above layers functionality. And as an example, IUnitOfWork could be NHibernate, Entity Framework, LinqToSql or ADO.NET where a change to the factory class or dependency injection registration is all that has to change. FYI, I've heard the Repository called the Service Layer as well. Personally I like the first name to not be confused with Web Services. The next big take away from this structure is realizing the scope for you Database Context (IUnitOfWork). A simple example would be a ASP.NET page where for each page there is one and only one IUnitOfWork for either each repository or for that scope of work. Same holds true for ViewModels, Controllers, etc. So let's say you need to utilize two repositories, EmployeeRepository and HRRepository. You then could share the IUnitOfWork between both or not. To cross page, ViewModel or Controller boundaries, we use the ID for entities where they are then pulled from the DB and work is performed. You could alternatively pass a DTO across boundaries and attach to the context but then you begin losing separation of layers.
To continue, POCO classes do not have to be auto generated. In fact you can create your Entity Classes from scratch and perform the mapping in your extended DbContext class inside the OnModelCreating(DbModelBuilder mb) method. Start here, then here and note the Additional Resources, google Fluent API and read this post by Diego.
As for validation, this is an interesting point because it would be GREAT if all Business Rules could be validated in one location. Well, as we all know that doesn't work real well. So here is my recommendation, keep all data level validation (i.e. required, range, format, etc.) with data annotation as much as possible in the domain object and leave process validation in the Repository with clear roles of the Repository (i.e. if (isEmployee) do this, else that). I say clear, such that you do not want to add an Employee in two different Repositories where validation has to be duplicated. To call the validation, start here. Capture the ValidationResults and send upstream with a MyRepositoryValidationException which contains a collection of validations errors (e.g. Employee is required) which can be presented to the presentation layer. With all that said, don't forget to perform validation at the presentation layer. You don't want post backs to make sure an Employee has a valid Email, for example.
Just remember to balance time and effort with complexity. For something simple, use Data First or Model First with your EDMX file. Then lay a repository on top of that which also contains all the validation rules.
I have few concerns about DTO. I am trying to create 4 level architecture for my asp.net website. I will have DTO, BLL, DAL and Presentation Layer.
Do I need to create DTO for each table? I have almost 100 tables and some of the tables have 70-100 columns.
For complicated query where I join 5-8 tables, How do I approach this? DO I need to get DTO for each table and then run Linq Query on all those DTO List in BLL then return result back to aspx page?
If there are other suggestions, please let me know. Thanks in advance for your help.
You will only need a DTO when you need to pass a simple object, perhaps from the DAL repository (where your DTO = a table, stored procedure result or view result) to a domain / BLL object which might well be an aggregate object providing a logical view of the domain rather than a one to one mapping from the database. It all depends on how you are 'growing' your application.
If you are going to have loads of similar DTO's it can be a good idea to use a tool, like AutoMapper - it will save you a lot of time writing boring mapping code.
Some people insist on having separate DTOs for every single service call you make. Depending on the complexity of the logic, this could potentially lead to much more than 100 different DTOs.
I prefer a generic approach, where you build a DTO model with a 1-1 correspondence between DTOs and domain entities. In this approach, you'll have 100 DTO tables. If you use any tool to automatically create code (Codesmith, T4), creating the DTO layer can be easy.
The other concern, returning compound results can be tackled with a generic DTO container to hold your DTO classes:
http://netpl.blogspot.com/2010/12/generic-dto-model-and-other-silverlight.html
(the section starts at the "Generic DTO Models)