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此子文檔展示,如何定義頁面以刪除 Author對象。

正如表單設計部分所討論的那樣,我們的策略是,只允許刪除“未被其他對象引用” 的對象(在這種情況下,這意味著如果作者Author被一本書Book引用,我們將不允許刪除作者)。在實現方面,這意味著,表單需要在刪除作者之前,先確認沒有關聯的書籍。如果存在關聯的書籍,則應顯示它們,並說明在刪除Author對象之前,必須刪除它們。

Controller—get route

Open /controllers/authorController.js. Find the exported author_delete_get() controller method and replace it with the following code.

// Display Author delete form on GET.
exports.author_delete_get = function(req, res, next) {

    async.parallel({
        author: function(callback) {
            Author.findById(req.params.id).exec(callback)
        },
        authors_books: function(callback) {
          Book.find({ 'author': req.params.id }).exec(callback)
        },
    }, function(err, results) {
        if (err) { return next(err); }
        if (results.author==null) { // No results.
            res.redirect('/catalog/authors');
        }
        // Successful, so render.
        res.render('author_delete', { title: 'Delete Author', author: results.author, author_books: results.authors_books } );
    });

};

The controller gets the id of the Author instance to be deleted from the URL parameter (req.params.id). It uses the async.parallel() method to get the author record and all associated books in parallel. When both operations have completed it renders the author_delete.pug view, passing variables for the title, author, and author_books.

Note: If  findById() returns no results the author is not in the database. In this case there is nothing to delete, so we immediately render the list of all authors. 

}, function(err, results) {
    if (err) { return next(err); }
    if (results.author==null) { // No results.
        res.redirect('/catalog/authors')
    }

Controller—post route

Find the exported author_delete_post() controller method, and replace it with the following code.

// Handle Author delete on POST.
exports.author_delete_post = function(req, res, next) {

    async.parallel({
        author: function(callback) {
          Author.findById(req.body.authorid).exec(callback)
        },
        authors_books: function(callback) {
          Book.find({ 'author': req.body.authorid }).exec(callback)
        },
    }, function(err, results) {
        if (err) { return next(err); }
        // Success
        if (results.authors_books.length > 0) {
            // Author has books. Render in same way as for GET route.
            res.render('author_delete', { title: 'Delete Author', author: results.author, author_books: results.authors_books } );
            return;
        }
        else {
            // Author has no books. Delete object and redirect to the list of authors.
            Author.findByIdAndRemove(req.body.authorid, function deleteAuthor(err) {
                if (err) { return next(err); }
                // Success - go to author list
                res.redirect('/catalog/authors')
            })
        }
    });
};

First we validate that an id has been provided (this is sent via the form body parameters, rather than using the version in the URL). Then we get the author and their associated books in the same way as for the GET route. If there are no books then we delete the author object and redirect to the list of all authors. If there are still books then we just re-render the form, passing in the author and list of books to be deleted.

Note: We could check if the call to findById() returns any result, and if not,  immediately render the list of all authors.  We've left the code as it is above for brevity (it will still return the list of authors if the id is not found, but this will happen after findByIdAndRemove()).

View

Create /views/author_delete.pug and copy in the text below.

extends layout

block content
  h1 #{title}: #{author.name}
  p= author.lifespan
  
  if author_books.length
  
    p #[strong Delete the following books before attempting to delete this author.]
  
    div(style='margin-left:20px;margin-top:20px')

      h4 Books
    
      dl
      each book in author_books
        dt 
          a(href=book.url) #{book.title}
        dd #{book.summary}

  else
    p Do you really want to delete this Author?
    
    form(method='POST' action='')
      div.form-group
        input#authorid.form-control(type='hidden',name='authorid', required='true', value=author._id )

      button.btn.btn-primary(type='submit') Delete

The view extends the layout template, overriding the block named content. At the top it displays the author details. It then includes a conditional statement based on the number of author_books (the if and else clauses).

  • If there are books associated with the author then the page lists the books and states that these must be deleted before this Author may be deleted.
  • If there are no books then the page displays a confirmation prompt. If the Delete button is clicked then the author id is sent to the server in a POST request and that author's record will be deleted.

Add a delete control

Next we will add a Delete control to the Author detail view (the detail page is a good place from which to delete a record).

Note: In a full implementation the control would be made visible only to authorised users. However at this point we haven't got an authorisation system in place!

Open the author_detail.pug view and add the following lines at the bottom.

hr
p
  a(href=author.url+'/delete') Delete author

The control should now appear as a link, as shown below on the Author detail page.

What does it look like?

Run the application and open your browser to http://localhost:3000/. Then select the All authors link, and then select a particular author. Finally select the Delete author link.

If the author has no books, you'll be presented with a page like this. After pressing delete, the server will delete the author and redirect to the author list.

If the author does have books, then you'll be presented with a view like the following. You can then delete the books from their detail pages (once that code is implemented!).

Note: The other pages for deleting objects can be implemented in much the same way. We've left that as a challenge.

Next steps

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