isnt actually updating the movie record for Inception at all its setting the

Isnt actually updating the movie record for inception

This preview shows page 188 - 190 out of 517 pages.

isn’t actually updating the movie record for Inception at all: it’s setting the movie_id field of both Alice’s and Bob’s reviews to “link” them to Inception . Of course, if we had actually modified any of Inception ’s attributes,! would try to persist them; but because save! is transactional—that is, it’s all-or-nothing—if the save! fails then every aspect of it fails, so neither the changes to Inception nor its associated Reviews would be saved. returns an Enumerable of all owned reviews[r1,r2] Replaces the set of owned reviews with the set r1,r2 , adding or deleting as appropriate, by setting the movie_id field of each of r1 and r2 to ( m ’s primary key) in the database immediately.<<r1 Adds r1 to the set of m ’s reviews by setting r1 ’s movie_id field to . The change is written to the database immediately (you don’t need to do a separate save ). r =>5) Makes r a new, unsaved Review object whose movie_id is preset to indicate that it belongs to m . Arguments are the same as for . r =>5) Like build but saves the object immediately (analogous to the difference between new and save ). Note: if the parent object m has never been saved, that is, m.new_record? is true, then the child objects aren’t saved until the parent is saved. m = Returns the Movie instance associated with this review = m Sets m as the movie associated with review r Figure 5.15: A subset of the association methods created by movie has_many :reviews and review belongs_to :movie , assuming m is an existing Movie object and r1,r2 are Review objects. Consult the ActiveRecord::Associations documentation for a full list. Method names of association methods follow convention over configuration based on the name of the associated model. Figure 5.15 lists some of the most useful methods added to a movie object by virtue of declaring that it has_many reviews. Of particular interest is that since has_many implies a collection of the owned object (Reviews), the reviews method quacks like a collection. That is, you can use all the collection idioms of Figure 3.7 on it—iterate over its elements with each , use functional idioms like sort , search and map , and so on, as in lines 8, 11 and 14 of Figure 5.13 . What about the belongs_to method calls in review.rb ? As you might guess, belongs_to :movie gives Review objects a movie instance method that looks up and returns the movie to which this review belongs. Since a review belongs to at most one movie, the method name is singular rather than plural, and returns a single object rather than an enumerable.
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has_one is a close relative of has_many that singularizes the association method name and operates on a single owned object rather than a collection.
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  • Spring '19
  • Dr.Marcos

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