Through Associations

Rails
1

Hi,

I’m a total noob to rails. I’m working my way through my first app and
I desperately need help with through associations in rails.

Task: get number of unread articles.

Database structure:
A. Users
has_many :activity
has_many :article, :through => :activity

B. Activity
belongs_to :user
belongs_to :article

C. Articles (user_id,feed_id,is_read)
has_many :reading
has_many :user, :through => :reading
belongs_to :feed

Any article that is in this table has been read and the “is_read”
field has been set to true.

D. Feeds
has_many :article

How do I go about getting the number of unread articles for a given
user and feed?

Any help will be greatly appreciated.

Thanks in advance.

Best,
Farhan

Sent from my iPhone

2

Farhan wrote:

Hi,

I’m a total noob to rails. I’m working my way through my first app and
I desperately need help with through associations in rails.

Through associations can be a bit complex for a beginner. Are you sure
you don’t want to start with something simpler? Have you worked through
the tutorial in AWDWR yet?

Task: get number of unread articles.

Database structure:
A. Users
has_many :activity
has_many :article, :through => :activity

Well, for starters, you should always use plurals with has_many
relationships. So, “has_many :activities, has_many :articles, :through
=> :activities”, etc. AWDWR would have taught you this, and many other
fundamental concepts.

B. Activity
belongs_to :user
belongs_to :article

good. But I’m not sure I understand the purpose of this model. What’s
an “activity” as it relates to a user and an article?

C. Articles (user_id,feed_id,is_read)
has_many :reading
has_many :user, :through => :reading
belongs_to :feed

Again, “:has_many :readings”

Any article that is in this table has been read and the “is_read”
field has been set to true.

What table? Articles? I think you forgot to post a description of
your “Reading” model.

D. Feeds
has_many :article

:articles

How do I go about getting the number of unread articles for a given
user and feed?

Not sure I can really help here without a better understanding of the
purpose of the Activity model and the structure of your Reading model.

Any help will be greatly appreciated.

Thanks in advance.

Best,
Farhan
–
http://www.5valleys.com/

3

Hi John,

Thanks for replying. I’m will be getting the AWDWR book this evening.

Okay; so I made the changes to pluralize the associations for
has_many. Thanks for the tip; makes the code more readable.

I actually made a couple of typos in the “Database Structure”. I had
changed the name of the “readings” to “activity” (now “activities”).
The new database structure is as follows with the changes you
requested:

Database structure:
A. Users
has_many :activities
has_many :articles, :through => :activities

B. Activity (user_id,feed_id,is_read)
belongs_to :user
belongs_to :article

C. Articles
has_many :activities
has_many :users, :through => :activities
belongs_to :feed

D. Feeds
has_many :articles

The activity model will keep track of all read articles for the user.
That is when a user reads an article it gets added to the “activities”
table. This table has the user_id, article_id, and the is_read
columns. Any article that is added to the activity model has the
is_read column set to “true”.

Hope this helps; otherwise let me know and I will provide more
information.

Thanks,
Farhan

4

John,

Thank you. I will try this two liner solution. Yes, in B the activity
table has the “article_id” and not “feed_id”, sorry.

Thank you for your patience,
Farhan

5

insha wrote:

requested:
C. Articles
columns. Any article that is added to the activity model has the
is_read column set to “true”.

Hope this helps; otherwise let me know and I will provide more
information.

Thanks,
Farhan

Alright, first… at B. above, you say the activity table has a
“feed_id” column, but below you say it’s “article_id”. I 'm going to
plow forward with the second and ignore the first, since that what it
should be.

Ok, so now we want to get all the read articles for a particular user.

Add something like this to your User class.
has_many :readings, :class_name => ‘Activity’, :conditions => ‘is_read =
1’
has_many :read_articles, :through => :readings

I hope that helps.

–
http://www.5valleys.com/

6

Here’s another scenario, since I’m getting confused:

I have the following Models:

A = User (name)
B = Feed (name)
C = Article (feed_id, title)
D = Reading (user_id, article_id, is_read)

What would be the simplest/easiest way to associate, using :through
associations, these models so that I can easily do the following:

  1. Get all articles that a user has read
  2. Get all articles that a user has not read

Best,
Farhan