# How to generate Rails models from database schemas **URL:** \ **Category:** Rails\ **Created:** [May 22, 2015, 9:46pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054 "2015-05-22T21:46:03Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\ **Post date:** [May 22, 2015, 9:46pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/1 "2015-05-22T21:46:03Z")
I’m evaluating Rails (vs Django) for a new project. A requirement of this project is that the Rails app(s) be able to work with a database (PostgreSQL, in case that matters) whose schemas (table definitions) have been created and, over time, will be modified independently of the Rails app(s). Though I’m a newbie to Rails, it already seems to be that Rails’ standard mode of operation is: (1) Models are created and modified within Rails, and then (2) Rails Migration creates and modifies the database table definitions. What I need is the opposite sequence: (1) The database table definitions are created and modified through tools external to Rails, and then (2) the Rails models are created and modified to fit the database table definitions. So my questions are: 1. First and most important, is there a Gem (or some other tool in the Ruby-Rails world) that can generate a model from a database table definition? 2. If not, presumably one could use Rails on a pre-existing database by manually editing the Rails models. Right? 3. If that’s right, what are the requirements for the table designs to enable them to work as viable Rails models? It seems that one requirement is that each table have a sequence-assigned primary key named “id”. Right? Any others? ~ Thanks in advance ~ Ken ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [May 22, 2015, 10:05pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/2 "2015-05-22T22:05:54Z")
You don’t always have to work with Rails functionality to utilize a database, not sure always true for PostgreSQL. The critical aspect is how you define your database connectivity in config/database.yml. Perhaps helpful, check out brilliant Ryan B.’ RailsCast: > **[\#342 Migrating to PostgreSQL - RailsCasts](http://railscasts.com/episodes/342-migrating-to-postgresql)** > > Short Ruby on Rails screencasts containing tips, tricks and tutorials. Great for both novice and experienced web developers. Liz ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [May 22, 2015, 10:33pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/3 "2015-05-22T22:33:22Z")
I know how to \*connect \*a Rails app to a PG database. My question is about how to align the Rails \*contents \*(model definitions) with the database contents (table definitions), so that the app can read from and write to the tables. It think perhaps you’re answering “yes” to my question 2 - that is, I can keep the app and database contents aligned without using “Rails functionality” by editing them manually. Right? That still leaves question 1 and 3 unanswered. ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [May 22, 2015, 11:08pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/4 "2015-05-22T23:08:25Z")
On 22 May 2015 at 20:44, kenatsun [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I’m evaluating Rails (vs Django) for a new project. A requirement of this > project is that the Rails app(s) be able to work with a database > (PostgreSQL, in case that matters) whose schemas (table definitions) have > been created and, over time, will be modified independently of the Rails > app(s). Google for rails legacy database and you will get lots of useful hits Colin ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [May 22, 2015, 11:07pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/5 "2015-05-22T23:07:50Z")
On Fri, May 22, 2015 at 12:44 PM, kenatsun [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > What I need is the opposite sequence: (1) The database table definitions > are created and modified through tools external to Rails, and then (2) the > Rails models are created and modified to fit the database table definitions. > > So my questions are: > > 1. First and most important, is there a Gem (or some other tool in the > Ruby-Rails world) that can generate a model from a database table > definition? If you have a table named “things”, all you need is a file named e.g. thing.rb that contains class Thing \< ActiveRecord::Base end That will give you access to all the fields of that table. > 1. If not, presumably one could use Rails on a pre-existing database by > manually editing the Rails models. Right? See above. > 1. If that’s right, what are the requirements for the table designs to > enable them to work as viable Rails models? It seems that one requirement > is that each table have a sequence-assigned primary key named “id”. Right? Not exactly. You do need a primary key, and it’s _easiest_ with an integer, and _easiest_ if the name is “id”, but not necessary; I’ve got an app using string ids based on a legacy db schema (from what was previously a Java app). > Any others? Depends on what you’re trying to do. I’d suggest just trying it 🙂 The “schemas independently modified over time” part presages some future pain, I would think; make sure you have _really good_ test coverage. ## HTH, and good luck. Hassan S. ------------------------ [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) [Hassan Schroeder | about.me](http://about.me/hassanschroeder) twitter: @hassan Consulting Availability : Silicon Valley or remote ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [May 22, 2015, 11:08pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/6 "2015-05-22T23:08:25Z")
On May 22, 2015, at 2:32 PM, kenatsun [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > My question is about how to align the Rails contents (model definitions) with > the database contents (table definitions), so that the app can read from and write > to the tables. Largely, you just ignore migrations and mostly ignore Rails models. Inherit from ActiveRecord::Base, list the attributes that can be bulk set, and you’re done. Rails connects to the db and reads the schema. Now of course you will wind up adding validations and calculations and relations and so forth, and you may have to specify the table name if it doesn’t follow RoR conventions. But really, the answer to your question is not just “yes”, it’s “yes and it’s so easy that you’re completely missing it by looking for something harder” 😉 – Scott R. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > **[Elevated Software Development, Inc.](http://www.elevated-dev.com/)** [https://www.linkedin.com/in/scottribe/](https://www.linkedin.com/in/scottribe/) (303) 722-0567 voice ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [May 23, 2015, 8:56pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/7 "2015-05-23T20:56:22Z")
Thanks a million to Scott, Hassan, & Colin, for this rich feast of possibilities! It’s gonna take me some time to digest. Then I’ll be back with the solutions I’m finding and/or with more questions. ~ Ken ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 1, 2015, 8:57am UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/8 "2015-06-01T08:57:39Z")
I think you just need to create Toy model and then use scaffold controller [http://stackoverflow.com/questions/4333393/using-rails-generate-scaffold-when-model-already-exists](http://stackoverflow.com/questions/4333393/using-rails-generate-scaffold-when-model-already-exists) On Mon, Jun 1, 2015 at 7:06 AM, kenatsun [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > [https://groups.google.com/d/msgid/rubyonrails-talk/4a506cc5-5bf7-4f46-9628-b4dc6e7555b2%40googlegroups.com?utm\_medium=email&utm\_source=footer](https://groups.google.com/d/msgid/rubyonrails-talk/4a506cc5-5bf7-4f46-9628-b4dc6e7555b2%40googlegroups.com?utm_medium=email&utm_source=footer) > . > > For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). – Mou Dareka no, tame janakutte Jibun no Tame ni Warette Iru ( Aqua Timez - Alones ) ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 1, 2015, 8:07pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/9 "2015-06-01T20:07:44Z")
On Sun, May 31, 2015 at 5:06 PM, kenatsun [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > 1. An odd note is that there still is no schema.rb file in x/db/. If this > is what Rails uses as its “database catalog”, is the lack of it going to > cause trouble down the road? Possibly, but you can use `rake db:schema:dump` to generate it from your existing DB. > My next question is whether it is possible to sue the amazing Rails > generators - in particular, scaffold - to more quickly create an app that > works with an existing database - so it would not be necessary to go thru > all those manual steps shown above. I tried it once, and it tried to run > the migrator I’ve never seen a scaffold command automatically run migrations; can you be more specific about what led up to that? You should be able to scaffold a model and then just delete the migration file. – Hassan S. ------------------------ [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) [Hassan Schroeder | about.me](http://about.me/hassanschroeder) twitter: @hassan Consulting Availability : Silicon Valley or remote ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 1, 2015, 10:19pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/10 "2015-06-01T22:19:12Z")
Thanks, Hassan ~ The rake command does the job of building (and updating) schema.rb. ~ Ken ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 1, 2015, 10:18pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/11 "2015-06-01T22:18:02Z")
Thank you, byakugie\* ~\* Your link led me to the gem “schema-to-scaffold”, which enabled the following scenario: The aim is to get all the components generated automatically, but based on the database schema. I did it my using the gem \*schema\_to\_scaffold, \*which simply generates a script (one command in this case) that runs the \*scaffold \*generator in a way that drives off of the database schema for the new table (_users_). 1. Created a new database table, _users_: sqlite\> CREATE TABLE “users” (“id” INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, “name” text, “email” textuser); sqlite\> INSERT INTO users (name) VALUES (‘Jo’); sqlite\> SELECT \* FROM users; 1|Jo| 1. Installed \*schema\_to\_scaffold \*gem: sqlite\> gem install schema\_to\_scaffold 1. Ran _schema\_to\_scaffold_ for _users_: [sunward@web324 x]$ scaffold -p db Looking for schema.rb in db 1. db/schema.rb Select a path to the target schema: Loaded tables: 1. toys 2. users Options are: 4 for table 4; (4…6) for table 4 to 6; [4,6] for tables 4 and 6; \* for all Tables Select a table: 1 Script for scaffold: rails generate scaffold User name:text email:text --no-migration 1. Ran the script produced by _schema\_to\_scaffold_: [sunward@web324 x]$ rails generate scaffold User name:text email:text –no-migration ``` invoke active_record create app/models/user.rb invoke test_unit create test/models/user_test.rb create test/fixtures/users.yml invoke resource_route route resources :users invoke scaffold_controller create app/controllers/users_controller.rb invoke erb create app/views/users create app/views/users/index.html.erb create app/views/users/edit.html.erb create app/views/users/show.html.erb create app/views/users/new.html.erb create app/views/users/_form.html.erb invoke test_unit create test/controllers/users_controller_test.rb invoke helper create app/helpers/users_helper.rb invoke test_unit invoke jbuilder create app/views/users/index.json.jbuilder create app/views/users/show.json.jbuilder invoke assets invoke coffee create app/assets/javascripts/users.coffee invoke scss create app/assets/stylesheets/users.scss invoke scss create app/assets/stylesheets/scaffolds.scss ``` 1. \*It **work** s! \*See [http://x.sunward.webfactional.com/users/](http://x.sunward.webfactional.com/users/). Amazing! Next step will be to make a change in the database schema and see if/how I can get Rails to automagically update its model, controller, and views to fit. Any how-to hints would be welcome. ~ Ken ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 1, 2015, 2:08am UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/12 "2015-06-01T02:08:10Z")
Yaay! I’m happy to report success with my first attempt to make a Rails app that works from an existing database. This first experiment used (a) the simplest “instructions” I could find (basically, Hassan’s); (b) a streamlined version of the “Getting Started Guide” process for setting up a Rails app (but - this is crucial - _omitting_ the step of running the migrator); and (c) a pre-existing (“legacy”) database that conforms to the Rails naming conventions. For the benefit of other Rails newbies (or oldbies) that need to build apps on existing DBs, a play-by-play of what I did follows. 1. Created new Rails app, _x_: [sunward@web324 rails\_eval]$ rails new x 2. Populated the “legacy” SQLite database with table toys, and added one row to that table: [sunward@web324 x]$ rails dbconsole SQLite version 3.6.20 sqlite\> CREATE TABLE toys (“id” INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, “name” TEXT); sqlite\> INSERT INTO toys (name) VALUES (“Tinker”); sqlite\> SELECT \* FROM toys; 1|Tinker|58 3. Added the \*toys \*resource and root to _routes.rb_: Rails.application.routes.draw do resources :toys root ‘toys#index’ end 4. Used \*rake \*to see the resulting routes: [sunward@web324 x]$ rake routes Prefix Verb URI Pattern Controller#Action toys GET /toys(.:format) toys#index POST /toys(.:format) toys#create new\_toy GET /toys/new(.:format) toys#new edit\_toy GET /toys/:id/edit(.:format) toys#edit toy GET /toys/:id(.:format) toys#show PATCH /toys/:id(.:format) toys#update PUT /toys/:id(.:format) toys#update DELETE /toys/:id(.:format) toys#destroy 5. Generated \*toys \*controller: [sunward@web324 x]$ rails generate controller toys create app/controllers/toys\_controller.rb invoke erb create app/views/toys invoke test\_unit create test/controllers/toys\_controller\_test.rb invoke helper create app/helpers/toys\_helper.rb invoke test\_unit invoke assets invoke coffee create app/assets/javascripts/toys.coffee invoke scss create app/assets/stylesheets/toys.scss 6. Added the necessary CRUD methods to the \*toys \*controller: class ToysController \< ApplicationController def index @toys = Toy.all end 7. Made\* index.html.erb, show.html.erb, new.html.erb, edit.html.erb, \_form.html.erb, index.json.jbuilder, show.json.jbuilder,\* following the pattern in [Getting Started with Rails — Ruby on Rails Guides](http://guides.rubyonrails.org/getting_started.html). 8. Created the \*Toy \*model file, toy.rb: class Toy \< ActiveRecord::Base end 9. In my browser, tried [http://x.sunward.webfactional.com/toys](http://x.sunward.webfactional.com/toys). Feel free to try it yourself. (However, this is a temporary site that may be gone by the time you read this.) _It works_!!! That is, all the CRUDs execute as they should. 10. An odd note is that there still is no _schema.rb_ file in _x/db/_. If this is what Rails uses as its “database catalog”, is the lack of it going to cause trouble down the road? Thanks again to Scott, Hassan, & Colin for your key clues. My next question is whether it is possible to sue the amazing Rails generators - in particular, scaffold - to more quickly create an app that works with an existing database - so it would not be necessary to go thru all those manual steps shown above. I tried it once, and it tried to run the migrator and croaked when it found that the DB table was already there. But that may have been pilot error on my part. Comments and advice would be welcome. ~ Ken ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 4, 2015, 10:23pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/13 "2015-06-04T22:23:01Z")
_Next step_: I have succeeded in adding a column to a database table, then using the generator tools to update the Rails objects that implement that model. The process, which I share for what it’s worth to others, is: 1. ``` Add attribute *toys.color* (text): ``` sqlite\> ALTER TABLE toys ADD COLUMN color TEXT; sqlite\> INSERT INTO toys (name, color) VALUES (‘Tinker’, ‘Green’); sqlite\> select \* from toys; 1|Tinker|Green 1. ``` Ran rake db:schema:dump to update schema.rb: ``` ActiveRecord::Schema.define(version: 0) do create\_table “toys”, force: :cascade do |t| ``` t.text "name" *t.text "color"* ``` end 1. ``` Ran *schema_to_scaffold* for *toys*: ``` [sunward@web324 x]$ scaffold -p db … Loaded tables: 1. toys 2. users … Select a table: 0 Script for scaffold: rails generate scaffold Toy name:text color:text --no-migration 1. ``` Ran *scaffold *using that script: ``` [sunward@web324 x]$ rails generate scaffold Toy name:text color:text –no-migration ``` invoke active_record conflict app/models/toy.rb ``` Overwrite /home/sunward/webapps/rails\_eval/x/app/models/toy.rb? (enter “h” for help) [Ynaqdh] Y ``` force app/models/toy.rb invoke test_unit create test/models/toy_test.rb create test/fixtures/toys.yml invoke resource_route route resources :toys invoke scaffold_controller conflict app/controllers/toys_controller.rb ``` Overwrite /home/sunward/webapps/rails\_eval/x/app/controllers/toys\_controller.rb? (enter “h” for help) [Ynaqdh] Y ``` force app/controllers/toys_controller.rb invoke erb exist app/views/toys conflict app/views/toys/index.html.erb Overwrite ``` /home/sunward/webapps/rails\_eval/x/app/views/toys/index.html.erb? (enter “h” for help) [Ynaqdh] Y ``` force app/views/toys/index.html.erb conflict app/views/toys/edit.html.erb Overwrite ``` /home/sunward/webapps/rails\_eval/x/app/views/toys/edit.html.erb? (enter “h” for help) [Ynaqdh] Y ``` force app/views/toys/edit.html.erb conflict app/views/toys/show.html.erb Overwrite ``` /home/sunward/webapps/rails\_eval/x/app/views/toys/show.html.erb? (enter “h” for help) [Ynaqdh] Y ``` force app/views/toys/show.html.erb conflict app/views/toys/new.html.erb Overwrite ``` /home/sunward/webapps/rails\_eval/x/app/views/toys/new.html.erb? (enter “h” for help) [Ynaqdh] Y ``` force app/views/toys/new.html.erb conflict app/views/toys/_form.html.erb Overwrite ``` /home/sunward/webapps/rails\_eval/x/app/views/toys/\_form.html.erb? (enter “h” for help) [Ynaqdh] Y ``` force app/views/toys/_form.html.erb invoke test_unit conflict test/controllers/toys_controller_test.rb Overwrite ``` /home/sunward/webapps/rails\_eval/x/test/controllers/toys\_controller\_test.rb? (enter “h” for help) [Ynaqdh] Y ``` force test/controllers/toys_controller_test.rb invoke helper ``` identical app/helpers/toys\_helper.rb ``` invoke test_unit invoke jbuilder conflict app/views/toys/index.json.jbuilder Overwrite ``` /home/sunward/webapps/rails\_eval/x/app/views/toys/index.json.jbuilder? (enter “h” for help) [Ynaqdh] Y ``` force app/views/toys/index.json.jbuilder conflict app/views/toys/show.json.jbuilder Overwrite ``` /home/sunward/webapps/rails\_eval/x/app/views/toys/show.json.jbuilder? (enter “h” for help) [Ynaqdh] Y ``` force app/views/toys/show.json.jbuilder invoke assets invoke coffee ``` identical app/assets/javascripts/toys.coffee ``` invoke scss conflict app/assets/stylesheets/toys.scss Overwrite ``` /home/sunward/webapps/rails\_eval/x/app/assets/stylesheets/toys.scss? (enter “h” for help) [Ynaqdh] Y ``` force app/assets/stylesheets/toys.scss invoke scss ``` identical 1. ``` *It **work** s!* See http://x.sunward.webfactional.com/toys/. ``` _However_: This process has only a limited ability to update the Rails objects to handle the database change while preserving manually entered changes to them. Specifically: For each Rails file where the new (generated) version differs from the existing (possibly manually modified) version, you get to choose between keeping the old version (so it doesn’t match the database changes) or replacing it with the new version (so any manual updates to the old version are lost). In other words, I haven’t found a way to generate a new file that is a combination of the old and the new - that is, it is identical to the old file in all respects except that it implements the database schema changes. So… _Next question_: Are there any Rails tools that _can_ generate a “combined” file in the sense just defined? Is there any way to generate a “combined” file in the sense just defined? - either with other Rails tools or with options to the tools used in the above scenarios? I know that meaningfully merging two versions of an object quickly gets us into the “hard problem” zone. But I notice that the prompts that \*scaffold \*puts out do offer to show you a “diff” of the old vs new versions of each file. It shouldn’t be too hard to give the user the opportunity to choose between the old and the new versions of each line that differs, and that would enable the user to produce the desired “combination” in most cases. Short of that, an option to tag the new file with a slightly different file name from the old file would enable the user to use an external “diff editor” to compare and manually merge the two versions fairly efficiently. So, I’m wondering, does the Rails World contain any tools that can do this? ~ Thanks yet again ~ Ken ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 4, 2015, 10:41pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/14 "2015-06-04T22:41:07Z")
On Jun 4, 2015, at 2:21 PM, kenatsun [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Next step: I have succeeded in adding a column to a database table, then using > the generator tools to update the Rails objects that implement that model. The > process, which I share for what it’s worth to others, is: > > 1. > > ``` > Add attribute toys.color (text): > > ``` > > 2. > > ``` > Ran rake db:schema:dump to update schema.rb: > > ``` > > 3. > > ``` > Ran schema_to_scaffold for toys: > > ``` > > 4. > > ``` > Ran scaffold using that script: > > ``` > > However: This process has only a limited ability to update the Rails objects… I do wonder if you really understand: steps 2 through 4 were unnecessary. You can manage your database schema using Rails & migrations, or you can manage it completely outside of Rails. Either option is pretty easy, while a mishmash combination of the two is not so easy. – Scott R. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > **[Elevated Software Development, Inc.](http://www.elevated-dev.com/)** [https://www.linkedin.com/in/scottribe/](https://www.linkedin.com/in/scottribe/) (303) 722-0567 voice ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 4, 2015, 11:01pm UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/15 "2015-06-04T23:01:34Z")
On 4 June 2015 at 21:21, kenatsun [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > it implements the database schema changes. > > So… > > Next question: Are there any Rails tools that can generate a “combined” > file in the sense just defined? Is there any way to generate a “combined” > file in the sense just defined? - either with other Rails tools or with > options to the tools used in the above scenarios? The reason no work has been done on this is that the scaffold is intended merely as a quick and dirty method of getting some basic functionality up and running. By the time you have a real application going it is most unlikely that much of the original scaffolding code will remain. Colin ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 5, 2015, 1:27am UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/16 "2015-06-05T01:27:38Z")
You’re misreading my step 1: “Add attribute toys.color (text)”. That was added to the \*database schema, \*not to the Rails model definition. So steps 2-4 (or some equivalent process in Rails) absolutely were necessary. Otherwise the Rails app would have gone on oblivious to the change in the DB schema. ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 5, 2015, 2:27am UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/17 "2015-06-05T02:27:13Z")
On Jun 4, 2015, at 5:26 PM, kenatsun [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > You’re misreading my step 1: “Add attribute toys.color (text)”. That was added > to the database schema, not to the Rails model definition. So steps 2-4 (or some > equivalent process in Rails) absolutely were necessary. Otherwise the Rails app > would have gone on oblivious to the change in the DB schema. No, I did not misread it. As I suspected, you still do not understand what we have been trying to tell you: Rails WILL READ THE SCHEMA FROM THE DATABASE. Your steps 2 through 4 were unnecessary, and, as I said before: You can manage your database schema using Rails & migrations, or you can manage it completely outside of Rails. Either option is pretty easy, while a mishmash combination of the two is not so easy. – Scott R. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > **[Elevated Software Development, Inc.](http://www.elevated-dev.com/)** [https://www.linkedin.com/in/scottribe/](https://www.linkedin.com/in/scottribe/) (303) 722-0567 voice ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 5, 2015, 1:34am UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/18 "2015-06-05T01:34:03Z")
Yeah, I figured something like that was the case. Probably that’s the case with most/all Rails generators (like most of the generators in the world) - they’re good for a one-time kick-start, but not much good after that. Still, a generator that could write on something other than a blank slate would be a very valuable addition to the toolkit. And doable. ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 5, 2015, 5:20am UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/19 "2015-06-05T05:20:44Z")
Well, it would be nice to do in one step what I thought required four! So let me try… 1. Add another attribute _toys.size_ to the schema (this looks different from the previous step 1 only because I have replaced my SQLite DB with a PostgreSQL one, named _sunward\_x_: [sunward@web324 x]$ rails dbconsole … psql (9.1.15) SSL connection (cipher: DHE-RSA-AES256-SHA, bits: 256) sunward\_x=\> \d toys Table “public.toys” Column | Type | Modifiers --------±------------------±---------------------------------------------- id | bigint | not null default nextval(‘toy\_seq’::regclass) name | character varying | color | character varying | price | money | sunward\_x=\> ALTER TABLE toys ADD size INTEGER; ALTER TABLE sunward\_x=\> \d toys Table “public.toys” Column | Type | Modifiers --------±------------------±---------------------------------------------- id | bigint | not null default nextval(‘toy\_seq’::regclass) name | character varying | color | character varying | price | money | size | integer | If step 1 is all that’s needed, I should be able to bring up any \*toys \*page an see the new \*size \*column, right? But I don’t: As far as I can tell, at this point the app does indeed seem to be oblivious to the change in the DB schema. If so, certainly \*something \*more needs to be done to update the app. Perhaps I can go right ahead to my old step 4, which is to run \*scaffold, \*without updating schema.rb (old step 2) or running _schema\_to\_scaffold_ (old step 3). Perhaps, as you say, “Rails WILL READ THE SCHEMA FROM THE DATABASE” and gen everything up if I just do this. [sunward@web324 x]$ rails generate scaffold Toy --no-migration Well, no. What it has done is to gen up a \*Toys \*model (and supporting views) with no columns at all: Maybe step 2 is necessary to do before step 4, still skipping step 3? [sunward@web324 x]$ rake db:schema:dump [sunward@web324 x]$ rails generate scaffold Toy --no-migration That does, of course, add the new column to _schema.rb._ But the \*scaffold \*generator still puts out model objects that are devoid of columns; the \*toys \*web page looks just like it did before. Of course, I can omit step 3, because all \*schema\_to\_scaffold \*does is “READ THE SCHEMA FROM THE DATABASE” and put out a suitable command for invoking \*scaffold. \*But without it, I have to read the database schema myself and manually type the list of columns into the _scaffold_ command. Not sure what’s easier about that. So, if there really is a simpler process for doing this, I guess I need you to spell it out for me. Hmm… Maybe this statement from you is a clue to where we have miscommunicated: “You can manage your database schema using Rails & migrations, or you can manage it completely outside of Rails. Either option is pretty easy, while a mishmash combination of the two is not so easy.” This whole thread is not about _“managing my database schema”_ - as stated in the original post, I intend to create and make all changes to my DB schema entirely outside of Rails. Given that intention, this post is about _managing the Rails objects that work with the database schema_, and using Rails generators and other tools to automate that process as much as is possible. If you have any ideas for how to do that faster/better/easier than the procedures that I have cobbled together so far thru trial-and-error and the hints provided in this thread, I would be grateful to hear them. ~ Tx, Ken ---
**Author:** ![kenatsun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a9adbd/32.png) [@kenatsun](https://www.ruby-forum.com/u/kenatsun)\ **Post date:** [June 5, 2015, 5:54am UTC](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054/20 "2015-06-05T05:54:01Z")
On Jun 4, 2015, at 9:19 PM, kenatsun [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Well, it would be nice to do in one step what I thought required four! 1. Exactly as you did, add the column to the table. Now it’s there. Use it, just like any other column. Add it to any view you wish. Do anything you wish with it in a controller. Why on earth would you keep re-generating scaffolds over and over??? A scaffold is a starting point; it is not your app code. People have told you (over and over) that you do not maintain Rails apps by generating & re-generating scaffolds. – Scott R. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > **[Elevated Software Development, Inc.](http://www.elevated-dev.com/)** [https://www.linkedin.com/in/scottribe/](https://www.linkedin.com/in/scottribe/) (303) 722-0567 voice [Next page](https://www.ruby-forum.com/t/how-to-generate-rails-models-from-database-schemas/242054.md?page=2)