first vs Model/Database

 

What are the pros & cons of using Entity Framework 4.1 Code-first over Model/Database-first with EDMX diagram?

I'm trying to fully understand all the approaches to building data access layer using EF 4.1. I'm using Repository pattern and IoC .

I know I can use code-first approach: define my entities and context by hand and use ModelBuilder to fine-tune the schema.

I can also create an EDMX diagram and choose a code generation step that uses T4 templates to generate the same POCO classes.

In both cases I end up with POCO object which are ORM agnostic and context that derives from DbContext .

Database-first seems to be most appealing since I can design database in Enterprise Manager, quickly synch the model and fine-tune it using the designer.

So what is the difference between those two approaches? Is it just about the preference VS2010 vs Enterprise Manager?

I think the differences are:

Code first

  • Very popular because hardcore programmers don't like any kind of designers and defining mapping in EDMX xml is too complex.
  • Full control over the code (no autogenerated code which is hard to modify).
  • General expectation is that you do not bother with DB. DB is just a storage with no logic. EF will handle creation and you don't want to know how it does the job.
  • Manual changes to database will be most probably lost because your code defines the database.

    • Database first

  • Very popular if you have DB designed by DBAs, developed separately or if you have existing DB.
  • You will let EF create entities for you and after modification of mapping you will generate POCO entities.
  • If you want additional features in POCO entities you must either T4 modify template or use partial classes.
  • Manual changes to the database are possible because the database defines your domain model. You can always update model from database (this feature works quite good).
  • I often use this together VS Database projects (only Premium and Ultimate version).

    • Model first

  • IMHO popular if you are designer fan (= you don't like writing code or SQL).
  • You will "draw" your model and let workflow generate your database script and T4 template generate your POCO entities. You will lose part of the control on both your entities and database but for small easy projects you will be very productive.
  • If you want additional features in POCO entities you must either T4 modify template or use partial classes.
  • Manual changes to database will be most probably lost because your model defines the database. This works better if you have Database generation power pack installed. It will allow you updating database schema (instead of recreating) or updating database projects in VS.

    • I expect that in case of EF 4.1 there are several other features related to Code First vs. Model/Database first. Fluent API used in Code first doesn't offer all features of EDMX. I expect that features like stored procedures mapping, query views, defining views etc. works when using Model/Database first and DbContext (I didn't try it yet) but they don't in Code first.

    I think this simple "decision tree" by Julie Lerman the author of "Programming Entity Framework" should help making the decision with more confidence:

    一个决策树可以帮助您选择不同的EF方法

    More info Here.

    Database first and model first has no real differences. Generated code are the same and you can combine this approaches. For example, you can create database using designer, than you can alter database using sql script and update your model.

    When you using code first you can't alter model without recreation database and losing all data. IMHO, this limitation is very strict and does not allow to use code first in production. For now it is not truly usable.

    Second minor disadvantage of code first is that model builder require privileges on master database. This doesn't affect you if you using SQL Server Compact database or if you control database server.

    Advantage of code first is very clean and simple code. You have full control of this code and can easily modify and use it as your view model.

    I can recommend to use code first approach when you creating simple standalone application without versioning and using modeldatabase first in projects that requires modification in production.

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