I have Data Access Layer objects which represent data retrieved from a webservice.
In other hand, I have MVC Model objects which represent the same data structure but enforced with Data Annotation attributes in order to perform UI validation, etc.
Apparently, I have to swap data between DAL and Model objects for every read/write operation.
The question is whether I can simplify this approach to have just one set of objects and use them for both layers (Data Access and Model). What is the best practice?
I know there are some NuGets to sync data between those two kinds of objects. Could you please suggest which one to use? Thank you.
The best practice is to have a separate set of domain objects and mvc models. That way you can wire up all of your annotations on your viewmodel and people won't be able to post fields that you don't want the user to edit
You can also use AutoMapper to simplify binding between the two
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Where to write Database and Business logic in MVC?
I have just started with MVC3 pattern. How do we do data access in MVC3? Do we make the 'MODEL' as Data Access Layer or Do we add another 'DAL' layer and call it from 'MODEL' Layer?
Your model should be independent of data-access stuff, which will allow you to change your DAL strategy in the future.
You should be feeding the model from the DAL, but the model shouldn't know how it is being constructed, and certainly shouldn't have any database-specific code in it.
If you take the approach I suggest, look at AutoMapper - a very useful tool for mapping data between DAL and model classes.
When I was working with my last MVC3 project, my understanding from the various samples (such as GeekDinner) was that the Entity Framework serves as the Data Access Layer.
Your Model can be a directly mapped data access object, but don't necessarily have to be. They could just as well be proxies through to your backend DAL which is always going to be the better option depending on your requirements and longevity of the project.
The way I tend to handle it for larger projects is to have a separate namespace called Project.Entities which contains my Entity Framework data models. My Project.Models would contain models which use the Entities as a backing store for their data, and provide common methods (Where necessary) to manipulate that data. It may not be the best way to do it, but provides the most flexibility, and sticks to keeping data models separate from the backing store which allows more abstraction. For example, you can always switch out the underlying data layer to in-memory storage, another DAL than Entity Framework or whatever else.
For smaller/temporary/test projects, my Entity Framework data models will be straight in Project.Models and used directly as it's quicker and doesn't require so much thought.
No, model is not data access. Model is a buch of classes to hold data, and it generally does not contain code other than, possibly, to verify the assigned values are permitted.
You access data from controllers. In which way you do that is completely up to you and MVC is not concerned.
Model is your view model, not your domain model.
If you want to do DAL activity, I would tend to wrap it in repository/service that can be injected into your controllers.
This stops your controllers getting bloated and also allows you to mock your DAL layer for unit testing the controllers.
I am using AutoMapper.org to map my DTO objects to Model objects in MVC4. DTO objects are retrieved from SOAP web services. The operations on the services are mostly CRUD.
This works nicely.
I have 2 questions. Firstly, is it bad practise to map both ways (2 way mapping). So when I update on screen map the Model to a DTO, as well as the orginal mapping of DTO to Model?
Second question, is it possible for AutoMapper to map enums?
I map both ways without issue - I map from the DTOs to the business objects to get the data, and map back the other way to save the data. This is so that the DTOs that are used in my WCF service are reusable (I'm using CSLA framework and the data portal model in CSLA doesn't really let 3rd parties consume the service without having access to my bizobj library).
It does mean that some of the business logic is repeated in the web layer, but since the rules are sparse this isn't a big issue
In my case I don't think it's a bad thing. I have a very simple data model which is mostly reads, there is only the occasional time when data goes back across to be modified.
As far as I know it maps enums natively (assuming it's a direct enum to enum - since enum is just a primitive underneath), but you can always provide your own custom type converters to resolve any enum issues or if you need to do string parsing for enums.
Please help on choosing the right way to use the entities in n-tier web application.
At the present moment I have the following assembleis in it:
The Model (Custom entities) describes the fields of the classes that the application use.
The Validation is validating the data integrity from UI using the reflection attributes method (checks data in all layers).
The BusinessLogicLayer is a business facade for additional logic and caching that use abstract data providers from DataAccessLayer.
The DataAccessLayer overrides the abstarct data providers using LinqtoSql data context and Linq queries. And here is the point that makes me feel i go wrong...
My DataLayer right before it sends data to the business layer, maps (converts) the data retrieved from DB to the Model classes (Custom entities) using the mappers. It looks like this:
internal static model.City ToModel(this City city)
{
if (city == null)
{
return null;
}
return new model.City
{
Id = city.CountryId,
CountryId = city.CountryId,
AddedDate = city.AddedDate,
AddedBy = city.AddedBy,
Title = city.Title
};
}
So the mapper maps data object to the describing model. Is that right and common way to work with entities or do I have to use the data object as entities (to gain a time)? Am I clear enough?
You could use your data entities in your project if they are POCOs. Otherwise I would create separate models as you have done. But do keep them in a separate assembly (not in the DataAccess project)
But I would not expose them through a webservice.
Other suggestions
imho people overuse layers. Most applications do not need a lot of layers. My current client had a architecture like yours for all their applications. The problem was that only the data access layer and the presentation layer had logic in them, all other layers just took data from the lower layer, transformed it, and sent it to the layer above.
The first thing I did was to tell them to scrap all layers and instead use something like this (requires a IoC container):
Core (Contains business rules and dataaccess through an orm)
Specification (Seperated interface pattern. Contains service interfaces and models)
User interface (might be a webservice, winforms, webapp)
That works for most application. If you find that Core grows and becomes too large too handle you can split it up without affecting any of the user interfaces.
You are already using an ORM and have you thought about using a validation block (FluentValidation or DataAnnotations) for validation? Makes it easy to validate your models in all layers.
It may be a common practice to send out DTOs from serivce boundary (WCF service, etc.) but if you are directly using your "entities" in your presentation model, I don't see any benefit in doing that.
As to the code snippet you have provided, why not use AutoMappter? It helps by eliminating writing of boiler-plate mapping codes and does that for you if you have a set of convention in place.
Get rid of the model now, before removing it later will require refactoring the whole application. The last project i worked on used this architecture and maintaining the DTO layer and mappings to the database model layer is a huge pain in the arse and offers no usefull benefits. One of the main things that is anoying is that LinkToSql does not effectively support a disconnected data model. You cannot update a database table by creating a new DB entity with a primary key matching an existing record and then stick it into the data context. You have to first retrieve the entity from the database, update it then commit the changes. Managing this results in really nasty update methods to map all the properties from your DTOs to your LinqtoSql classes. It also breaks the whole deferred execution model of LinqToSql. Don't even get me started on the problems it causes with properties on parent classes that are collections of child DTOs (e.g. a customer DTO with an Orders property that contains a collection of order DTOs), managing those mappings is really really fiddly, i had to do some extensive optimisations because retrieving a few hundred records ended up causing LinqToSql to make 200,000 database calls (admittedly there was also some pretty dumbass code as well but you get the picture).
The only valid reason to use DTOs is if you want to have multiple pluggable Data Access Layers e.g. LinqToSql and NHibernate for supporting different DB servers. That way you can swap out the data access later without having to change any other layers. If you don't need to do this then save yourself a world of pain and just use the LinqToSql entities.
I have seen lots of tutorials and examples using Model-View UI design patterns, and they all implement them pretty differently, especially the Model part. In some examples Model is data (actual object representation of some DB) in some it's data access layer (like repository pattern) in some it's service layer...
If someone tells you he is using MV* pattern in his app, what will it tell you about app design? Does it maintain in-memory representation of database in object graph and use it as data source or some data access layer to query data base...
What you will choose as a Model for data oriented smart client app containing mostly Tab Pages with Tables?
The word model is used in, at least, two senses. There is your domain model. Here the sense is how you represent your data. There are many ways to structure your data and also many ways to access it. When we talk about the model in this sense we're not particularly concerned with how you are accessing the structures that make it up, i.e., the data access or persistence layer, although you may also hear people speak of the model of persistence. By this, people mean the particular philosophy that the persistence implementation uses, such as ActiveRecord or Repository. You might also hear these referred to as patterns.
Finally, the word model has a very specific meaning in MVC, MVP, and MVVM in the context of a view. In that context it means that particular data object associated with a view, the view model. This could be one of your domain objects, but more typically it is a view-specific object that encapsulates data from one or more domain objects along with ancillary data such as user data that is used by a particular view.
For your application, choose the persistence model that best suits your development environment and language -- LINQ to SQL, LINQ to Entities, nHibernate, Castle ActiveRecord, etc. in the MS world Create view-specific models (classes) for each of your views that hold the data needed by that view. Use your controllers to query your domain model to extract the information needed by the view and map that onto the view model.
If someone says, he is using MV* pattern, it means the application is split into several parts, acting without a direct reference to a specific type, it doesn't say anything about the actual implementation. MVVM means, you have a Model, a ViewModel and View part, that's all.
The model is your data storage. This doesn't say anything of the implementation of it, it can be anything, depending on the task at hand. However, it should be accessed using interfaces, so you can quickly exchange the implementation. That, in a sense, is the whole point of the MVVM pattern - decoupling of the three tiers via interfaces.
Your description sounds alot like my project at the moment - I use sqlite as backing storage with Entity Framework as ORM. However, I also use T4 to generate Dto objects which then get mapped via automapper in the ViewModel, as those only need the data, not the persistance.
The model typically refers to the data layer, but as I discovered, in MVC this can be a little msleading when implementing an ntier approach. The reason for this is that the model is not contained in it's own assembly.
Here is some of very useful feedback I got to a similar question Confussion over MVC and entity model
A model can be considered as data container that facilitates rendering presentation component and/or persisting data to/from data source (i.e. database etc). Besides the data container elements, a model may or may not contain behavior, depending on design context of corresponding architecture.
While the term “Model” is frequently discussed and used in Model-View-Controller pattern context, it is one of most important consideration in current world of software architecture
You may want to look the following article where few popular and new design patterns that are related to presentation component and model are described.
I have an ASP.NET app with a three layer architecture:
Presentation layer: ASP.NET
Bussiness Layer: C# library.
Data Access Layer: C# library with
ADO.Net Entity Framework objects.
Some methods on Bussiness layer would return ADO.NET entity objects but, data access layer is not visible at Presentation layer I can't do that.
My question is: On a design view, Is it correct to expose Entity Objects in the Presentation Layer? I think I only have to link Data Layer library with ASP.NET app.
Thank you!
It's absolutely desirable to have your entity objects available for use and consumption in your presentation tier. That's what all the work is for.
Binding collection of objects to a grid/listview/dropdown
Splashing a single object (i.e. customer) onto a form for read/update/delete
This makes your life easier by far. Otherwise you'd have to pass string after int after double after string between your presentation and business layers.
These may be Entity objects or even your own POCO objects that were hydrated from the Entity objects.
I would even go so far as to say that your Entites should be in their own assembly separate from the DAL.
I suggest that you look into the concepts of View objects...or Data Transfer Objects (DTO). You might consider using a tool like AutoMapper or similar which will create a view specific domain object out of your entities. In general you may have screens that need an entity present to perform its work. But more often than not you will need to pass several different entities. In this case you are better off creating one DTO that contains all of these entities. By doing this you are adding a layer of separation between your presentation layer and your business layer. Often times your entities have more power than you might want to expose to your presentation layer. And...vice versa. Frequently you may need to get some UI messages out to the presentation layer based on some validation flagged in your business layer. Rather than make your ui more complex than it needs to be (by passing in your full entities) you can only pass in what the UI needs in the form of the DTO. Also, there is never a need for your business objects to care about anything specific to the presentation layer. I suggest that you not databind directly to anything as far back as the data access layer. Technically your presentation layer should know as little as possible about your business layer. In the case of MVP or MVC this is very easy to achieve by disconnecting the front end and the back end by way of this additional separation!
I think no, it is not, the best way to do that is to separate data classes from behavior, and reference only data classes in presentation level.The good approach I think to use WCF see this link
See Supervising Controller and Passive View
If you pass the Entity, you are essentially Supervising controller. Otherwise you are Passive View.
Supervising controller is less work, but less testable. Supervising Controller also says databinding is OK.
Passive view is testable but a LOT more work. No databinding. Lots of properties.
Typically I stick with Supervising Controller. You typically don't need that level of testability and it isn't worth the extra trouble.