I'm having a look at Entity Framework and everything I'm reading takes a data centric approach to explaining EF. By that I mean that the fundamental relationships of the system are first defined in the database and objects are generated that reflect those relationships.
Examples
Quickstart (Entity Framework)
Using Entity Framework entities as business objects?
The EF documentation implies that it's not necessary to start from the database layer, e.g.
Developers can work with a consistent
application object model that can be
mapped to various storage schemas
When designing a new system (simplified version), I tend to first create a class model, then generate business objects from the model, code business layer stuff that can't be generated, and then worry about persistence (or rather work with a DBA and let him worry about the most efficient persistence strategy). That object centric approach is well supported by ORM technologies such as (n)Hibernate.
Is there a reasonable path to an object centric approach with EF? Will I be swimming upstream going that route? Any good starting points?
Model First approach seems to be what you need.
We suggest to take a look at the ADO.NET Team Blog article also.
A while after asking this, I discovered that EF 4 supports POCO (Plain Old CLR Objects), allowing an object-centric design with (relative) ignorance of persistence.
This article was the best one I came across discussing that approach, while this article explains how to use code generation templates to ease the work.
Related
I am using Entity Framework 6 database-first. I am converting the project to implement the onion architecture to move towards better separation of concerns. I have read many articles and watched many videos but having some issues deciding on my solution structure.
I have 4 projects: Core, Infrastructure, Web & Tests.
From what I've learned, the .edmx file should be placed under my "Infrastructure" folder. However, I have also read about using the Repository and Unit of Work patterns to assist with EF decoupling and using Dependency Injection.
With this being said:
Will I have to create Repository Interfaces under CORE for ALL entities in my model? If so, how would one maintain this on a huge database? I have looked into automapper but found issues with it presenting IEnumererables vs. IQueryables but there is an extension available it has to hlep with this. I can try this route deeper but want to hear back first.
As an alternative, should I leave my edmx in Infrastructure and move the .tt T4 files for my entities to CORE? Does this present any tight coupling or a good solution?
Would a generic Repository interface work well with the suggestion you provide? Or maybe EF6 already resolves the Repository and UoW patterns issue?
Thank you for looking at my question and please present any alternative responses as well.
I found a similar post here that was not answered:
EF6 and Onion architecture - database first and without Repository pattern
Database first doesn't completely rule out Onion architecture (aka Ports and Adapters or Hexagonal Architecture, so you if you see references to those they're the same thing), but it's certainly more difficult. Onion Architecture and the separation of concerns it allows fit very nicely with a domain-driven design (I think you mentioned on twitter you'd already seen some of my videos on this subject on Pluralsight).
You should definitely avoid putting the EDMX in the Core or Web projects - Infrastructure is the right location for that. At that point, with database-first, you're going to have EF entities in Infrastructure. You want your business objects/domain entities to live in Core, though. At that point you basically have two options if you want to continue down this path:
1) Switch from database first to code first (perhaps using a tool) so that you can have POCO entities in Core.
2) Map back and forth between your Infrastructure entities and your Core objects, perhaps using something like AutoMapper. Before EF supported POCO entities this was the approach I followed when using it, and I would write repositories that only dealt with Core objects but internally would map to EF-specific entities.
As to your questions about Repositories and Units of Work, there's been a lot written about this already, on SO and elsewhere. You can certainly use a generic repository implementation to allow for easy CRUD access to a large set of entities, and it sounds like that may be a quick way for you to move forward in your scenario. However, my general recommendation is to avoid generic repositories as your go-to means of accessing your business objects, and instead use Aggregates (see DDD or my DDD course w/Julie Lerman on Pluralsight) with one concrete repository per Aggregate Root. You can separate out complex business entities from CRUD operations, too, and only follow the Aggregate approach where it is warranted. The benefit you get from this approach is that you're constraining how the objects are accessed, and getting similar benefits to a Facade over your (large) set of database entities.
Don't feel like you can only have one dbcontext per application. It sounds like you are evolving this design over time, not starting with a green field application. To that end, you could keep your .edmx file and perhaps a generic repository for CRUD purposes, but then create a new code first dbcontext for a specific set of operations that warrant POCO entities, separation of concerns, increased testability, etc. Over time, you can shift the bulk of the essential code to use this, while still keeping the existing dbcontext so you don't lose and current functionality.
I am using entity framework 6.1 in my DDD project. Code first works out very well if you want to do Onion Architecture.
In my project we have completely isolated Repository from the Domain Model. Application Service is what uses repository to load aggregates from and persist aggregates to the database. Hence, there is no repository interfaces in the domain (core).
Second option of using T4 to generate POCO in a separate assembly is a good idea. Please remember that your domain model (core) should be persistence-ignorant.
While generic repository are good for enforcing aggregate-level operations, I prefer using specific repository more, simply because not every Aggregate is going to need all of those generic repository operations.
http://codingcraft.wordpress.com/
I am new to entity framework and MVC, and trying to understand what constitutes a good design approach for a new application.
There are several ways of using Entity Framework. However, for my project, the best looking option is DB First. I've played around with an EDMX file, and I have got as far as using the DbContext code generator to create my wrapper classes.
I plan on using the repository and unit-of-work patterns, and using ninject for DI.
However, it does not seem "proper", from a SoC point of view, that whilst my respository will hide the implementation of the data store (EF) from my code, the model classes themselves are very much EF flavoured.
It seems that using EDMX-based approaches to EF blur the separation of concerns. Only POCO support seems to allow a true separation, but POCO has some other limitations that I don't like.
Am I missing something, or does using EDMX have this drawback?
Are people using an auto mapper to convert between the entity model and another, clean, SoCced model?
thanks
Tian
I don't have a strong opinion on the Separation Of Concerns question, but I have used both the standard ADO.Net version of EF and POCO and it is not difficult at all to customise the output of the the T4 code generation script for POCO to address any concerns you have about the structure of the objects created. That sounds like it would probably be a good starting point for what you are looking to do.
Once you know you are looking for T4 templates there are quite a few tutorials and a lot of helpful SO questions that can give you an idea of what you need to do.
I'm developping a line of business application using WPF as a presentation layer (of course with MVVM).
I'm using ADO.Net Entity Framework to map the DataBase.
I don't want to use entities directly in code (in the business layer). I want to separate my project into 3 layers:
Presentation layer
Business Layer
Data Access Layer
According to this post I want to implement a full encapsulation of the Entity Framework to provide a separation of concerns and to not be dependant on EF as ORM in the future.
Can you help me by giving me some exemples to encapsulate the EF and how to implement this in code.
Regarding this
I want to implement a Full encapsulation of the Entity Framework. to
provide a separation of concerns and to not be dependant on EF in the
future as ORM
Normally, you will create yourself a lot of problems if you go that route. If you choose EF, you really should make full use of the features, not hiding that behind another abstraction.
EF itself is already an abstraction layer over DB, there is no need to create another abstraction on top of that.
I would take a look at this post wich implements UnitOfWork and Repository patterns to implement what, I understand, you want to achieve.
http://blogs.msdn.com/b/adonet/archive/2009/06/16/using-repository-and-unit-of-work-patterns-with-entity-framework-4-0.aspx
There is one way of doing it, using POCO. Entity Framework 4.0 comes with the support of POCO (Plain CLR Objects). But POCO has its own complexities, when u have to deal with Relationship and associations. You can refer to the blog by Julie Lerman (a nice article)
http://thedatafarm.com/blog/data-access/agile-entity-framework-4-repository-part-1-model-and-poco-classes/
I guess that EF4.1 is recent to EF4.0, but I didn't find any book on EF4.1, but 2 books on EF4.0.
can I still buy the book on EF4.0 expecting that I will get most of the concept??
Thanks for helping.
According to The ADO.NET Team blog, there are two main features:
The DbContext API is a simplified abstraction over ObjectContext and a number of other types that were included in previous releases of the ADO.NET Entity Framework. The DbContext API surface is optimized for common tasks and coding patterns. DbContext can be used with Database First, Model First and Code First development.
Code First is a new development pattern for the ADO.NET Entity Framework and provides an alternative to the existing Database First and Model First patterns. Code First is focused around defining your model using C#/VB.NET classes, these classes can then be mapped to an existing database or be used to generate a database schema. Additional configuration can be supplied using Data Annotations or via a fluent API.
EF 4.0 books are good unless you are using one of those 2 features, because you won't find them in there.
But you have plenty of resources online about those new features (especially Code First).
You even have official tutorials:
Using DbContext
Code First walkthrough
HI Guys,
I was watching these videos series about Entity Framework:
http://msdn.microsoft.com/en-us/data/ff191186.aspx
is that easy building application in real world programming??? and is it ....reliable...has good performance...
"I am a graduate.."
thanks
Entity Framework is a valid real world data access tool. It is very easy to get up and running with EF. You simply import (or create in EF 4) your data model. You then can rename it to make it more code friendly. And then you are off querying databases.
Performance
I have been on multiple projects that use it, some which require high throughput, others that have low performance requirements. Entity Framework out of the box is not the fastest solution in the world, so there are a lot of performance tweaks that have to go on, but its all do able.
Reliability
We never have issues with reliability. We have never had an issue with EF in general, its always data content related. Trying to insert duplicated data, etc.
Other Tangibles
EF follows a pattern which allows for you to do some fun stuff with templates and abstract classes. All entities inerit from a class, entities that have references inherit from other classes. All Entity Contexts inherit from ;) ObjectContext classes, which provide a base set of functionality that allows you to create generic DAO implementations that can be reused throughout the enterprise.
If you are using UI dev, you can also use Data Services that wrap EF, as a fast gateway to your databse. The only downside of this is that you dont have access to the full suite of the Entity Framework.