# What is the proper role of seed data?

**URL:** <https://www.ruby-forum.com/t/what-is-the-proper-role-of-seed-data/185228>\
**Category:** Rails\
**Created:** [March 16, 2010, 1:40pm UTC](https://www.ruby-forum.com/t/what-is-the-proper-role-of-seed-data/185228 "2010-03-16T13:40:43Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Grary](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/91b2a8/32.png) [@Grary](https://www.ruby-forum.com/u/Grary)\
**Post date:** [March 16, 2010, 1:40pm UTC](https://www.ruby-forum.com/t/what-is-the-proper-role-of-seed-data/185228/1 "2010-03-16T13:40:43Z")

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Hi,

In my Rails app, I have some parameters whose values change only  
infrequently. These parameters are used in computations. Where is the  
place for data like this – data that is particular to the  
application?

On the one hand, I might think a flat file (yaml) is appropriate, but  
maybe I shouldn’t sacrifice the benefit of modeling my parameters as  
seed data in the seed.rb file.

Thanks for any comment,

Grar

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<div class="post-metadata">

**Author:** ![Grary](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/91b2a8/32.png) [@Grary](https://www.ruby-forum.com/u/Grary)\
**Post date:** [March 16, 2010, 2:26pm UTC](https://www.ruby-forum.com/t/what-is-the-proper-role-of-seed-data/185228/2 "2010-03-16T14:26:19Z")

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Grary wrote:

> Hi,
> 
> In my Rails app, I have some parameters whose values change only  
> infrequently. These parameters are used in computations. Where is the  
> place for data like this – data that is particular to the  
> application?
> 
> On the one hand, I might think a flat file (yaml) is appropriate, but  
> maybe I shouldn’t sacrifice the benefit of modeling my parameters as  
> seed data in the seed.rb file.

I use seed data in basically two ways:

1. As a starting point for the production database.

This provides a mean to pre-plan the starting point for the production  
database. This might include things like setting up an admin user, user  
roles, collections for pull-down lists, etc.

1. For populating development data.

This provides a convenient way to reset my development database to match  
the data where my production environment will start.

I would not, however, use seed data in the way you’re describing.  
Instead I would use either a static configuration file or use the  
database. For data that I would never want the users to be able to  
change I would use a configuration file (a sort of property list). For  
data that could possibly be altered by the users, or administrators, I  
would use the database to store the values.

Think of seed data as a means of “bootstrapping” your database. You  
would likely only ever run the seed data script once on the production  
database, but possibly many times on the development database.

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<div class="post-metadata">

**Author:** ![Grary](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/91b2a8/32.png) [@Grary](https://www.ruby-forum.com/u/Grary)\
**Post date:** [March 16, 2010, 2:46pm UTC](https://www.ruby-forum.com/t/what-is-the-proper-role-of-seed-data/185228/3 "2010-03-16T14:46:52Z")

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Robert,

Thanks for your reply, you really nail it:

> Instead I would use either a static configuration file or use the  
> database. For data that I would never want the users to be able to  
> change I would use a configuration file (a sort of property list). For  
> data that could possibly be altered by the users, or administrators, I  
> would use the database to store the values.

Please appreciate that, for a novice, the integration of database with  
model is so tight, it’s hard to think about a Rails web app using a  
database without going through a model!

So, I think that my data should be accessible by administrators, but  
what is the Rails mechanism for that access? Am I going to be issuing  
raw SQL commands?

Thanks for any additional comment,

Grary

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<div class="post-metadata">

**Author:** ![Grary](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/91b2a8/32.png) [@Grary](https://www.ruby-forum.com/u/Grary)\
**Post date:** [March 16, 2010, 3:29pm UTC](https://www.ruby-forum.com/t/what-is-the-proper-role-of-seed-data/185228/4 "2010-03-16T15:29:16Z")

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Grary wrote:

> So, I think that my data should be accessible by administrators, but  
> what is the Rails mechanism for that access? Am I going to be issuing  
> raw SQL commands?

Essentially, anything that can be stored in a database table can be  
modeled. From what I understand from your original post, you have a set  
of values that could possibly be changed, but not often.

Let’s make sure I understand your requirements:

- You need to store a list of values that are to be used in in  
calculations.
- There is a fixed number of different parameters. Let’s call them (x, y  
& z).
- The parameters x, y & z will be initialized to known values.
- The values of x, y & z are normally fixed, but can be altered by users  
(administrators) at runtime.

Here are some options:

1. Use a configuration file to store key/value pairs.
2. Use a database with a single row containing the values in the columns  
of the table.

±—±-----±-----±------+  
| id | x | y | z |  
±—±-----±-----±------+  
| 1 | 10.0 | 12.5 | 0.124 |  
±—±-----±-----±------+

1. Use a database table with multiple rows to simulate a key/value  
store.

±—±------±------+  
| id | key | value |  
±—±------±------+  
| 1 | x | 10.0 |  
| 2 | y | 12.5 |  
| 3 | z | 0.124 |  
±—±------±------+

The advantage here is that the number of parameters the is not fixed. No  
need to add a new column to add a new key/value.

1. Use an actual key/value persistent store  
([Google Code Archive - Long-term storage for Google Code Project Hosting.](http://code.google.com/p/redis/)).

This is very probably overkill for your situation.

In all of these cases you could use seeds.rb to initialize your values.  
From what I can glean I’d most likely go with option 1. Use a  
configuration file (YAML). If the administrator needs to change the  
configuration then just update the file with the new parameter. You will  
also like want to cache these values in some form of memory cache so you  
don’t have to read the values from disk/database on every request. Take  
a look at memcached.

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<div class="post-metadata">

**Author:** ![Grary](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/91b2a8/32.png) [@Grary](https://www.ruby-forum.com/u/Grary)\
**Post date:** [March 16, 2010, 6:18pm UTC](https://www.ruby-forum.com/t/what-is-the-proper-role-of-seed-data/185228/5 "2010-03-16T18:18:10Z")

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Robert,

Another high quality response, thank you.

Let me respond briefly, selectively to your reply…

> - The parameters x, y & z will be initialized to known values.
> - The values of x, y & z are normally fixed, but can be altered by users  
> (administrators) at runtime.

Yes, very infrequently, e.g., once a year, parameters used as  
constants in application computations will change and will need to be  
changed by an administrator. So, these parameters are global.

> 1. Use a configuration file to store key/value pairs \<…\> Use a  
> configuration file (YAML). If the administrator needs to change the  
> configuration then just update the file with the new parameter. You will  
> also like want to cache these values in some form of memory cache so you  
> don’t have to read the values from disk/database on every request. Take  
> a look at memcached.

I agree with you that this is likely the best approach for my  
situation.

Borrowing from [http://railsforum.com/viewtopic.php?id=15295](http://railsforum.com/viewtopic.php?id=15295), I might  
read/write to my file via the following mechanism:

a\_config = YAML.load\_file “#{RAILS\_ROOT}/config/application.yml”  
a\_config[“user”][“pwd\_days”] = params[:days]  
File.open(“#{RAILS\_ROOT}/config/application.yml”, ‘w’) { |f|  
YAML.dump(a\_config, f) }

Look good?

Two final questions for you:

1. Regarding the use of memcached for efficiency, it is a efficiency  
option available for flat file and database persisted data, alike,  
right? So, I might look forward to its use in varied manner of  
performance tuning?

2. 

> In all of these cases you could use seeds.rb to initialize your  
> values.

So, seeds is kind of like providing a user with a place to start,  
e.g., standardized settings, that they may then wish to change? It is  
not really for classic configuration, i.e., it does not involve global  
settings.

Grar