Question

我对Sequelize和Promises并不陌生，对于不熟悉Java脚本语言和JavaScript语言的人来说，这可能会有些混乱。无论如何，我注意到在承诺的某些实现中使用了“返回”。在其他实现中则不是。例如：

 //FILL JOIN TABLE FROM EXISTING DATA
  Blog.find({where: {id: '1'}}) .then(blog => {
    return Tag.find({where: {id: '1'}}).then(tag => {
      return blog.hasTag(tag).
      then(result => {
        // result would be false BECAUSE the blog.addTag is still not used yet
        console.log("3 RESULT IS"+ result);
        return blog.addTag(tag).
        then(() => {
          return blog.hasTag(tag).
          then(result => {
            // result would be true
            console.log("4 RESULT IS"+ result);
          })
        })
      })
    })
  })

在这里：不使用它们。

const tags = body.tags.map(tag => Tag.findOrCreate({ where: { name: tag }, defaults: { name: tag }})
                                        .spread((tag, created) => tag))

   User.findById(body.userId)    //We will check if the user who wants to create the blog actually exists
       .then(() => Blog.create(body))
       .then(blog => Promise.all(tags).then(storedTags => blog.addTags(storedTags)).then(() => blog/*blog now is associated with stored tags*/)) //Associate the tags to the blog
       .then(blog => Blog.findOne({ where: {id: blog.id}, include: [User, Tag]})) // We will find the blog we have just created and we will include the corresponding user and tags
       .then(blogWithAssociations => res.json(blogWithAssociations)) // we will show it
       .catch(err => res.status(400).json({ err: `User with id = [${body.userId}] doesn\'t exist.`}))
      };

有人可以向我解释“返回”的用法吗？由于第二个代码有效，因此显然没有必要吗？那么我什么时候必须使用它？谢谢！！

Answer 1

从技术上讲，您询问了箭头功能。

const dummyData = { foo: "lorem" };

const af1 = () => dummyData;

const af2 = () => {
    dummyData.foo = "bar";
    return dummyData;
};

const af3 = () => { foo: "bar" };

const af4 = () => ({
    foo: "bar"
});

console.log(af1()); 

console.log(af2()); 

console.log(af3()); // Be aware if you wanna return something's started with bracket

console.log(af4());

如您所见，我们在return中使用af1语句，因为我们必须在返回值之前编写另一个“逻辑”。如果您不这样做，则可以避免使用return语句（它可以提高代码的简洁性和可读性）。

何时在Sequelize承诺中使用收益？

1 个答案: