Through Associations

rubyonrails-talk
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

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.

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

insha wrote:

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

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.

5

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

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