I have used EntitFramework before to do codefirst with MVC; however, I have never reverse engineered an existing database to get my models.
So what I'd like to do is reverse engineer the existing DB then switch to codefirst so that changes made to the models will be reflected in the database automagically by the Entity Framework gods. How would I do this, specifically the reverse engineer then the switch to codefirst? Please have mercy if this is poorly worded or w/e I'm very new to MVC still.
It basically boils down to using tools to autogenerate the POCO classes that represent your domain, then using those classes as the basis for EF Code First and future migrations.
Here's a msdn article outlining the process
Code First to an Existing Database
You can reverse an existing Database by creating an Entity Data Model.
Check the following link. Here is described step by step the how to reverse a database to a CodeFirst approach with all of the navigation properties and required relationships. This scenario is also very useful for those entity relations that CodeFirst cannot resolve by its own and the configuration in not very intuitive.
Reverse from ModelFirst to CodeFirst
Related
I am new to Entity Framework. I have created an EF Model and successfully added some tables and relation. Then I Clicked Generate Database from Model and My DB has been updated. Then I renamed some columns and I don't know how to revert or apply the changes. And Update Model from database does not seems to work because the columns names are different yet.
I need to graphically sync DB with Model. I prefer the model data rather than db data.
Thanks in advance.
You might want to look into the Code-First approach of Entity Framework. Using that approach you'll define your model in your code, and when changing anything you can create a Migration which allows you to up- and down-grade the DB to a specific version from the package manager console (or just create the respective SQL scripts).
For more information on this subject please see this article on MSDN
Note that you can also reverse engineer the code first model from an existing database (see 3. Reverse Engineer Model in this MSDN article), and then enable migrations for that model (see Step 2: Enable Migrations in this MSDN article)
What I do when I make "updates" is do it on both sides manually, in db and then in model (by right click properties) if the change is small. If adding a "new" table I drag it over to model from db server connections panel.
The alternative I've seen others prefer to use in this cases is to stay away from Entity Framework and use Dapper where you pass queries to it and it handles the rest.
Dapper (Wins!) vs Entity Framework vs ADO.NET Performance Benchmarking
I would like to use a tool to generate C# CodeFirst Entities and Mappings. I have used Entity Framework Power Tools and am looking for a better solution.
Using Entity Framework Power Tools as an example. This allows all tables in a database to be reverse engineered with C# classes generated for each Entity and Mapping. The problem is that you have to generate them all and cannot select just a few.
Is there such a tool that can generate these C# Entities and Mappings for the tables that you select? I do not want to hand-code these C# Code First classes.
If you have an existing database you probably could use model first approach with DbContext templates. Take a look at this walkthrough http://blogs.msdn.com/b/adonet/archive/2011/09/28/ef-4-2-model-amp-database-first-walkthrough.aspx. You can modify your model after creating it from the database. Also, when doing this this blog post may be useful too: http://blog.oneunicorn.com/2012/02/26/dont-use-code-first-by-mistake/
I know that I can create the POCO files from .edmx, but this only give's you a part of the code, because if you are going to use code first approach you need to provide more info to the POCO clases for example the key and foreign key by annotations or mapping, Now I was wondering , if exit's some way about how can I created this POCO classes with the annotations from a existing database.
what you are describing is not code first, is database first!
here is the answer you need to check: Entity Framework 4.1 - Code First with existing Database, how to define classes, using Attributes or EntityTypeConfiguration? What is the difference?
the EF power tools can generate pocos fro your db
link
As far as I can tell (correct me if I'm wrong), there are two main approaches to using Entity Framework:
Model First: start with a predefined database and let EF create the code for you.
Code First: write the code, and let EF create the database for you.
I have an existing database and I'd like to write the code myself. Is this "Code Only" approach supported? Does such an approach even make sense in the context of EF?
I disagree with most of the other answers. From what I've seen, the EF "Code First" technology is really just a way to define your model using conventions, annotations, or a fluent mapping definition, rather than an EDMX file. If you write your "Code First" files to mirror your database schema, there is no reason that Entity Framework would be unable to produce the appropriate queries and statements using LINQ to Entities.
For more information, see Scott Guthrie's post on Using EF "Code First" with an existing database.
Entity Framework Power Tools allows you to reverse engineer a database to generate code first like code (that won't re-generate your database). Then you can tweak it from there as you need.
I believe you have to decide what your system of reference is -- the code (Code First) or the database (Model First). If you have an existing database, then go with a Code First approach, it will be hard to keep your changes in synch without generating your model from your code, or your code from your model.
If you have an existing database, but want to extend your model beyond the generated code, you could implement partial classes to accomplish this.
If you want to manually map your EF4 code and your database, you could consider this approach. However, this eliminates some of the benefit of an ORM, which is to set up the mapping for you.
Well I guess you can't have your cake and eat it too in this case - there has to be one definite source on what your model is, it is either the database (DB first), which then generates matching code for you, or the code (Code first) which will then create a matching DB.
The Entity Framework team answered these questions on their blog:
http://blogs.msdn.com/b/adonet/archive/2011/03/07/when-is-code-first-not-code-first.aspx
Background:
I started to create logical database model for ASP.NET MVC web site. I used visual designer for Entity framework that ships with VS because I have used it before.
But now I already have 33 classes and I'm not finished (including quite some inheritance and a lot of associations). I'm afraid that it would be too complicated and time consuming for me to manually set all the table mappings and than generate database tables. I've no experience with it - I've done it the other way: classes from database tables and it took me a lot of time to get it work in a smaller project.
Question:
How can I easily and quickly create database tables for logical model (class diagram) in .NET / VS ? It would be great if it was possible automatically. I have never worked with LinqToSQL visual designer and it seems to be no reference on the web on how to create database tables from LinqToSQL classes. Is it possible at all ? If not is there any way to create database tables with Entity framework automatically - without having to specify table mappings ?
And one side question: if I used LinqToSQL classes are that going to commit changes to database every time I change properties ? Or is some caching taking place there ?
Entity framework has a concept called "Model First", which generates the database model from you model, hence the name.
You can read about that here: http://msdn.microsoft.com/en-us/data/ff830362
However, my personal favourite when it comes to Object Relational Mappers is NHibernate with the addition Fluent NHibernate. They have a concept where you work with your domain model rather than you data model and you use conventions to control your mappings. It's pretty neat. You can get started with some pretty good examples by looking at this code here: https://github.com/sharparchitecture/Northwind/tree/master/app
Linq2Sql is too limited for the case you are talking about. And it has no capability to generate data models from code. In fact, Linq2Sql works the other way around - it generates a set of classes from your data model, much like Entity Framework also can do.
Neither Linq 2 SQL or Entity Framework commit anything until you explicitly choose to do so. They both have a notion of a object context which keeps track of all changes made. When you call "Save", they transform those changes into SQL which is then executed in the database.
Like MikeEast, I've had a very good experience with Fluent NHibernate.
On my project, I use the Automapping feature, which allows me to change my data model almost at will, and the database schema automagically gets updated.
No SQL, no worrying about foreign keys, etc, etc, etc - I love it!
Fluent NHibernate Automapping
Finally I have sticked with Entity framework - tables generating is really plainless once I learnt how to deal with database connections...