Extract elements from a string representing an array

Question

My message object has a link attribute @message.link, which is a string. Before saving message.link to db I URI.extract from message.body:

["http://getbootstrap.com/javascript/#tabs", "http://paulgraham.com/re.html"]

Once I save it to the db message.link will be saved as:

"[\"http://getbootstrap.com/javascript/#tabs\", \"http://paulgraham.com/re.html\"]"

When I fetch the data from db later on how can I get the array from the message.link string like this?

["http://getbootstrap.com/javascript/#tabs", "http://paulgraham.com/re.html"]

To display the links from all message objects, how should I extract the links? Let's say message(1).link has one link, message(2) has three links, and I'd like to display all the four links as separated elements of @message_links or whatever instance variable.

UPDATE

Method works but can't display the :created_at and do the pagination properly since @message_links2 will be an array of links.

@message_links = @conversation.messages.with_link.order(created_at: :desc).paginate(page: params[:page], per_page: 12)
@message_links2 = @message_links.map(&:link).flatten

You fixed where you shouldn't have. Now, it's wrong in the other way. — sawa
– sawa, Commented Jan 13, 2016 at 18:11
sawa, I'm confused. If I do the URI extract from message.body I get: ["getbootstrap.com/javascript/#tabs", "paulgraham.com/re.html"], and then I save it to the db as message.link. Then I fetch the data from the db and I get back "[\"getbootstrap.com/javascript/#tabs\", \"paulgraham.com/re.html\"]" — Sean Magyar
– Sean Magyar, Commented Jan 13, 2016 at 18:16

Community · Accepted Answer · 2017-05-23 12:15:19Z

1

This is where you want a serialized column. Then you won't need to do the conversion yourself. see: Using Rails serialize to save hash to database

edited May 23, 2017 at 12:15

CommunityBot

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answered Jan 13, 2016 at 18:02

court3nay

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6 Comments

court3nay Over a year ago

you can display all the items from an array using flatten and map: @messages.map(&:link).flatten => [link, link, link, link]

Sean Magyar Over a year ago

court3nay, what I don't get is how you can mix the different objects. In this example the first link belongs to message(1) and the other three to message(2)?

court3nay Over a year ago

Yes. Since it's not obvious what you want to do with the links, I'm giving you some general ruby ideas :) You might want to make a separate class/table for links with has_many association

Sean Magyar Over a year ago

Basically, when a user creates a chat message the link gets saved, so the users can find all the links from a conversation. I'm not sure if I need a new class. I will just display the links as a list (kinda index page), and if user click on one of them then gets to the given page. So besides recognizing links in chat messages and displaying them I do nothing with the links. What do you think? Do I need a separate class?

Sean Magyar Over a year ago

court3nay, plz take a look at the updated question. I would like to display 12 links with created_at attribute, but since @message_links2 is an array I can't call the pagination on it and it doesn't contain the created_at date. If I call the pagination on the message.with_links objects like in the current code then the number of links will vary since it's unknown how many links an object has.

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