在Rails应用程序中定义模型的常用方法是什么？

Question

All of the tutorials I've seen so far for RoR have shown me generating models like:

rails generate User name:string placeofbirth:string

This generates a class for the model, and only actually references an attribute if I apply a validation of some kind.

So my question is, how do I use a 'code' first approach when creating my models. Or is it the rails way to just right down on paper the attributes you want, run the generate command with each attribute you want and it's type, then run the rake db:migrate command?

I'd love some more proven patterns on this subject because so far the way I've seen seems too empty.

Answer 1

Yes, this is the rails way- migration comes first and generates the code and the database- and the model class inspects the database to see what fields are there and make accessible via methods.

You can do gem install annotate_models if you want to get some comments in your model class with the attribute names and types.

See here for an example: https://github.com/ctran/annotate_models

Answer 2

Rails uses an active record pattern for models which basically means that a model object will automatically map each DB column to an attribute so you don't have to specify all attributes in the model. It's a feature, but I agree that it might not be perfect for everyone. If you're using Rails 3 it should be easy to use another ORM of your choice if ActiveRecord's approach doesn't suit you. Here are some alternative ORMs that you could use.

Answer 3

Usually when you are developing some database backed web application, you know the database design(name of the tables, name of the columns in those tables and associations between different tables) beforehand.

Rails, as mentioned by maarons in his answer, uses Active Record pattern. Your models are classes that represent a table in your database, an instance of your model class a row in that table and different attributes of an object represent values under different columns in the same table.

When you create a model, usually, you are creating a class that represents one of the tables in your database. And while you are creating a model, you are also going to create a table in your database. That means knowing the name of the table and columns within that table.

So to answer your question, you must know all the columns, required for the time being, that will be in your tables. And hence available as attribute methods for your model objects. You specify these columns to added in the table in the migration generated by rails generator while generating this model. This is what usually everyone does.

You can take a code first approach by creating a class, without running the rails model generator,under app/models/ but not inheriting it from ActiveRecord::Base . As you move forward in your development, you can generate migrations by $ rails generate migration MigrationName and creating table and adding columns using [add_column][2] to that table as required. Once you have created a table for this model, you will have to inherit that model from ActiveRecord::Base so that you can get all the Rails magic in your application.