尝试在我的代码中使用 await with promise - 如何？

Question

我已经尝试过，但未能清楚地掌握 javascript 的 promise 和 await 是如何工作的！我以某种方式设法拼凑了一个功能，该功能在我的 node.js 微服务中执行我需要的功能，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，但我还没有对我的代码进行任何广泛的测试，以查看它是否确实按照我认为的方式运行。这是我目前拥有和工作的代码，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

避免使用Promise constructor antipattern - 在promise 执行器内部调用resolve 之后，您不应该做任何事情。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。并在循环中将Promise.all 替换为连续的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;
}