javascript - 在 promise 中链接三个查询

Question

我如何在一个 promise 中将这 3 个查询链接在一起？它们会一个接一个地运行还是并行运行？

SELECT * FROM books where book_id = $1

SELECT * FROM username where username = $2

SELECT * FROM saved where saved_id = $3

编辑:

我不知道我应该为函数 getBookIdQuery 返回什么。它给出了错误:

getBookIdQuery is not a function

function getBookIdQuery(){
    return client.query(getBookId, [bookId]);
 }

那么为了让我的链接工作，我应该为该函数返回什么？

return new Promise((resolve, reject) => {



        getBookIdQuery
        .then(data => {


        })
        .catch(err => {
            reject(err);
        });

});

Answer 1

不确定您使用的是哪个数据库。但总的来说，您可以按照您想要的方式串行或并行执行查询。

Serial:

async serial(){
    queryResult1 = await client.query('SELECT * FROM books where book_id = $1', ['bookid']);
    queryResult2 = await client.query('SELECT * FROM username where username = $2',['username']);
    queryResult3 = await client.query('SELECT * FROM saved where saved_id = $3',['saved_id']);
    console.log(queryResult1);
    console.log(queryResult2);
    console.log(queryResult3);
}


Parallerl:

async parallel(){
   Promise.all([client.query('SELECT * FROM books where book_id = $1', ['bookid']), client.query('SELECT * FROM username where username = $2',['username']), client.query('SELECT * FROM saved where saved_id = $3',['saved_id']))
   .then(queryResults => {
        console.log(queryResults[0]);
        console.log(queryResults[1]);
        console.log(queryResults[2]);
   })
}