尝试在我的代码中使用 await with promise - 怎么做？

Question

我试过了，但没能弄清楚 javascript promises 和 await 是如何工作的！我以某种方式设法拼凑了一个函数来执行我在 node.js 微服务中所需的功能，但我不确定我是否以正确（最佳）的方式进行操作。此外，我在没有等待的情况下使用 promise 实现了我想要的，但我也没有对我的代码进行任何广泛的测试以查看它是否确实运行正是我认为的那样。这是我目前拥有并可以使用的代码，但我不确定我是否缺少使用 await 来正常运行：

  const QryAllBooks = {
        type: new GraphQLList(BookType),
        args: {},
        resolve(){
              return new Promise((resolve, reject) => {
                 let sql = singleLineString`
                      select distinct t.bookid,t.bookname,t.country
                      from books_tbl t
                      where t.ship_status = 'Not Shipped'
                  `;
                 pool.query(sql, (err, results) => {
                   if(err){
                      reject(err);
                   }
                   resolve(results);

                const str = JSON.stringify(results);
                const json = JSON.parse(str);

                const promises = [];
                for (let p = 0; p < results.length; p++){
                   const book_id = json[p].bookid;
                   const query = `mutation updateShipping
                                  {updateShipping
                                   (id: ${book_id}, input:{
                                      status: "Shipped"
                                   })
                                   { bookid
                                     bookname }}`
                    promises.push(apolloFetch({ query }));
               }

              //I need an await function so that previous apolloFetch  
              //goes in sequence of bookid, one after the other

              Promise.all( promises ).then(( result) => {
                      errorLogger(27, 'Error', result);
                      })
                     .catch(( e ) => {
                         errorLogger( 29, 'Error', e );
                     )};
                      });
                });
            }
          };

       module.exports = {
              QryAllBooks,
              BookType
       };

Answer 1

避免 Promise constructor antipattern - 你不应该在承诺执行器中调用 resolve 之后做任何事情。将所有这些东西放在 new Promise:

上的 then 回调中

resolve() {
    return new Promise((resolve, reject) => {
        let sql = singleLineString`
            select distinct t.bookid,t.bookname,t.country
            from books_tbl t
            where t.ship_status = 'Not Shipped'
        `;
        pool.query(sql, (err, results) => {
            if(err) reject(err);
            else resolve(results);
        });
    }).then(results => {
        const str = JSON.stringify(results);
        const json = JSON.parse(str);

        const promises = [];
        for (let p = 0; p < results.length; p++){
            const book_id = json[p].bookid;
            const query = `mutation updateShipping {
                updateShipping(id: ${book_id}, input:{
                    status: "Shipped"
                }) { bookid
                     bookname }
                }`;
            promises.push(apolloFetch({ query }));
        }
        return Promise.all(promises);
    }).then(result => {
        errorLogger(27, 'Result', result);
        return result;
    }, err => {
        errorLogger(29, 'Error', err);
        throw err;
    )};
}

您现在可以用 await 语法替换那些 then 调用。并且还将 Promise.all 交换为循环中的顺序 awaiting：

async resolve() {
   try {
        const results = await new Promise((resolve, reject) => {
//                      ^^^^^
            let sql = singleLineString`
                select distinct t.bookid,t.bookname,t.country
                from books_tbl t
                where t.ship_status = 'Not Shipped'
            `;
            pool.query(sql, (err, results) => {
                if(err) reject(err);
                else resolve(results);
            });
        });
        const promises = results.map(res => {
            const book_id = res.bookid;
            const query = `mutation updateShipping {
                updateShipping(id: ${book_id}, input:{
                    status: "Shipped"
                }) { bookid
                     bookname }
                }`;
            return apolloFetch({ query });
        });
        const result = await Promise.all(promises);
//                     ^^^^^
        errorLogger(27, 'Result', result);
        return result;
    } catch(err) {
        errorLogger(29, 'Error', err);
        throw err;
    }
}

async resolve() {
    const results = await new Promise((resolve, reject) => {
//                  ^^^^^
        let sql = singleLineString`
            select distinct t.bookid,t.bookname,t.country
            from books_tbl t
            where t.ship_status = 'Not Shipped'
        `;
        pool.query(sql, (err, results) => {
            if(err) reject(err);
            else resolve(results);
        });
    });
    const fetches = [];
    for (let p = 0; p < results.length; p++){
        const book_id = results[p].bookid;
        const query = `mutation updateShipping {
            updateShipping(id: ${book_id}, input:{
                status: "Shipped"
            }) { bookid
                 bookname }
            }`;
        fetches.push(await apolloFetch({ query }));
//                   ^^^^^
    }
    return fetches;
}

尝试在我的代码中使用 await with promise - 怎么做？

Trying to use await with promise in my code here - how to?

javascript

node.js

async-await

es6-promise