The .NET Entity Framework has come a long way since its early beginnings as an NHibernate alternative and the successor to LinqToSQL. Currently in version 6.0, the ORM is stable and mature but you still have an important decision to make when you start a new project. Which of the four design workflows will you use? Here are 3 reasons why you might use the code first approach.
The workflows you have to choose from are:
Code first creating a new database
Code first to an existing database
Model designer creating a new database
Existing database to generated model
In the past I used #4 most frequently because it was the quickest path to get a system up and running. You can rapidly develop your database design in SQL Management Studio then generate the code model in just few clicks. More recently I’ve come to prefer #1 (or #2) for the following reasons.
1) Less cruft, less bloat
Using an existing database to generate a .edmx model file and the associated code models results in a giant pile of auto generated code. You’re implored never to touch these generated files lest you break something, or your changes get overwritten on the next generation. The context and initializer are jammed together in this mess as well. When you need to add functionality to your generated models, like a calculated read only property, you need to extend the model class. This ends up being a requirement for almost every model and you end up with an extension for everything.
With code first your hand coded models become your database. The exact files that you’re building are what generate the database design. There are no additional files and there is no need to create a class extension when you want to add properties or whatever else that the database doesn't need to know about. You can just add them into the same class as long as you follow the proper syntax. Heck, you can even generate a Model.edmx file to visualize your code if you want.
2) Greater Control
When you go DB first, you’re at the mercy of what gets generated for your models for use in your application. Occasionally the naming convention is undesirable. Sometimes the relationships and associations aren't quite what you want. Other times non transient relationships with lazy loading wreak havoc on your API responses.
While there is almost always a solution for model generation problems you might run into, going code first gives you complete and fine grained control from the get go. You can control every aspect of both your code models and your database design from the comfort of your business object. You can precisely specify relationships, constraints, and associations. You can simultaneously set property character limits and database column sizes. You can specify which related collections are to be eager loaded, or not be serialized at all. In short, you are responsible for more stuff but you’re in full control of your app design.
3)Database Version Control
This is a big one. Versioning databases is hard, but with code first and code first migrations, it’s much more effective. Because your database schema is fully based on your code models, by version controlling your source code you're helping to version your database. You’re responsible for controlling your context initialization which can help you do things like seed fixed business data. You’re also responsible for creating code first migrations.
When you first enable migrations, a configuration class and an initial migration are generated. The initial migration is your current schema or your baseline v1.0. From that point on you will add migrations which are timestamped and labeled with a descriptor to help with ordering of versions. When you call add-migration
The speed of going the database first or model designer first route is appealing. The result of doing so is even pretty darn good. I’ll definitely still be using the database first method when time is important or when the project is a minor internal effort. For larger efforts or for long term client projects, code first provides us the control we need to create the most efficient program and also gives us the protection and consistency of a versioned controlled database while reducing bloat. There is value in each of the 4 workflows but these are 3 reasons why you might use code first design with Entity Framework.