Spring-Hibernate

Which component will fetch model data, supply that data to views, as well as handle the routing of incoming requests?
Controller

Controller ----->  Service -----> DAO-Data Access Object(Repository) -----> SessionFactory

Starting Your Database Server

With a terminal window open in the directory of your project that contains the H2 JAR file, the command to start your server is as follows:

java -cp h2*.jar org.h2.tools.Server

After this, a browser tab should open, and in that tab you'll need to enter the database connection URL, username and password. These should match what you have in your app.properties file.

@OneToMany(mappedBy = "category")
private List<Gif> gifs = new ArrayList<>();

mappedBy后面有一个变量fetch默认value为fetchtype.lazy
可以改成fetchtype.eager -> Every time one or more categories are fetched from the database, another query will be performed to fetch all GIF entities from the database that are associated with that category.
但是如果直接设成eager，那么即使在category index page，没有的GIFs也会被fetch
So we fetch all the GIFs for a category, only when a single category is being fetched.

@Overridepublic Category findById(Long id) {
    Session session = sessionFactory.openSession();    Category category = session.get(Category.class, id);    Hibernate.initialize(category.getGifs());    session.close();    return category;}

We were seeing that error because we tried to access a mapped collection outside of a hibernate session, which just isn't possible. 所以加入一句Hibernate.initialize(category.getGifs());

// Mark/unmark an existing GIF as a favorite@RequestMapping(value = "/gifs/{gifId}/favorite", method = RequestMethod.POST)
public String toggleFavorite(@PathVariable Long gifId, HttpServletRequest request) {
    // TODO: With GIF whose id is gifId, toggle the favorite field    Gif  gif = gifService.findById(gifId);    gifService.toggleFavourate(gif);    // TODO: Redirect to GIF's detail view    return String.format("redirect:%s", request.getHeader("referer"));}

• If you throw this in as a parameter to a controller method,
• 3:13
  it exposes all sorts of stuff related to the HTTP request including
• 3:17
  all of its headers that you recall from the HTTP basics course.
• 3:23
  One of the headers it exposes is what's called the referer header here.
• 3:29
  Check the teachers notes for the misspelling on this.
• 3:31
  This is actually the correct use.
• 3:34
  Now this referer header allows you to see what URL the user or request or
• 3:39
  was on when the HTTP request was made.
• 3:42
  In essence, it allows us to see where this request came from.
• 3:45
  So that in our case, I can send the browser right back there for the redirect.
• 3:50
  And I did this because a user might mark a GIF as a favorite from the detail or
• 3:54
  from the index view and this takes the browser back to wherever it came from.
• 3:59
  Now word of warning about this and I do want to be clear about this warning.
• 4:04
  Using a client specified value can be dangerous.
• 4:09
  If the user's browser is compromised,
• 4:12
  malicious software could set the referer to a malicious site.
• 4:17
  And suddenly our application sends the user into a danger zone
• 4:21
  simply when they mark or unmark a GIF as a favorite.
• 4:25
  So be careful.