Exercises in Java

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Exercises
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The (broken) site layout with a particularly long word
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Listing 1142 A helper to wrap long words
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app/helpers/microposts_helperrb
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module MicropostsHelper def wrap(content) raw(contentsplitmap{ |s| wrap_long_string(s) }join(' ')) end private def wrap_long_string(text, max_width = 30) zero_width_space = "​" regex = /{1,#{max_width}}/ (textlength < max_width) text : textscan(regex)join(zero_width_space) end end
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C HAPTER 12
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Following Users
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In this chapter, we will complete the core sample application by adding a social layer that allows users to follow (and unfollow) other users, resulting in each user s Home page displaying a status feed of the followed users microposts We will also make views to display both a user s followers and the users each user is following We will learn how to model user following in Section 121, and then make the web interface in Section 122 (including an introduction to Ajax) Finally, we ll end by developing a fully functional status feed in Section 123 This final chapter contains some of the most challenging material in the tutorial, including a complicated data model and some Ruby/SQL trickery to make the status feed Through these examples, you will see how Rails can handle even rather intricate data models, which should serve you well as you go on to develop your own applications with their own specific requirements To help with the transition from tutorial to independent development, Section 124 contains suggested extensions to the core sample application, along with pointers to more advanced resources As usual, Git users should create a new topic branch:
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$ git checkout -b following-users
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Because the material in this chapter is particularly challenging, before writing any code we ll pause for a moment and take a tour of user following As in previous chapters, at this early stage we ll represent pages using mockups1 The full page flow runs as
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1 The photographs in the mockup tour are from http://wwwflickrcom/photos/john_lustig/2518452221/ and http://wwwflickrcom/photos/30775272@N05/2884963755/
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12: Following Users
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A mockup of the current user s profile
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follows: a user (John Calvin) starts at his profile page (Figure 121) and navigates to the Users page (Figure 122) to select a user to follow Calvin navigates to the profile of a second user, Thomas Hobbes (Figure 123), clicking on the Follow button to follow that user This changes the Follow button to Unfollow , and increments Hobbes s followers count by one (Figure 124) Navigating to his home page, Calvin now sees an incremented following count and finds Hobbes s microposts in his status feed (Figure 125) The rest of this chapter is dedicated to making this page flow actually work
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The Relationship Model
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A mockup of finding a user to follow
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121 The Relationship Model
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Our first step in implementing user following and followers is to construct a data model, which is not as straightforward as it seems Na vely, it seems that a has_many relationship should do: a user has_many following and has_many followers As we will see, there is a problem with this approach, and we ll learn how to fix it using has_many :through It s likely that many of the ideas in this section won t seem obvious at first, and it may take a while for the rather complicated data model to sink in If you find yourself getting confused, try pushing forward to the end; then, read the section a second time through to see if things are clearer
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12: Following Users
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A mockup of the profile of another user, with a follow button
1211 A Problem with the Data Model (and a Solution)
As a first step toward constructing a data model for user following, let s examine a typical case For instance, consider a user who follows a second user: we could say that, eg, Calvin is following Hobbes, and Hobbes is followed by Calvin, so that Calvin is the follower and Hobbes is followed Using Rails default pluralization convention, the set of all such followed users would be called the followeds, but that is ungrammatical and clumsy; instead, we will override the default and call them following, so that userfollowing will contain an array of the users being followed Similarly, the set of all users following