如何将一个mongodb请求的结果同步传入下一个请求的值？

Question

我需要将从我的第一个 MongoDB 查询中获得的 state.name 值放入下一组 MongoDB 查询中。当我 console.log 我的第一个查询时，我达到了预期的结果，但它在以下查询中显示为未定义。是它们是异步的还是我传错了？

我研究了在 Express + MongoDB 中将一个查询的结果传递给下一个查询的示例，并研究了 Promises - 不确定我是否完全理解。

// GET State Home
router.get('/:stateid', ensureAuthenticated, (req, res) => {
    const member = req.user;
    console.log(member);
    Promise.all([
        state = States.findOne({url:req.params.stateid}),
        statelegislation = StateLegislation.find({'state': state.name }),
        statepolicy = StatePolicy.find({'state': state.name }),
        stateregulation = StateRegulation.find({'state': state.name }),
        statelitigation = StateLitigation.find({'state': state.name }),
    ]).then(([state,statelegislation,statepolicy,stateregulation,statelitigation]) =>
        res.render('app/state/home', {
            state:state,
            statelegislation:statelegislation,
            statepolicy:statepolicy,
            stateregulation:stateregulation,
            statelitigation:statelitigation,
        }))
        .catch(err => res.send('Ops, something has gone wrong'));
});

在以下查询中传入字符串值而不是变量 state.name 时，我会获得该值的所需结果。

我无法从第一个 MongoDB 请求动态传递值。

感谢您的任何帮助！

Answer 1

你不能在一个Promise.all 中一次完成。在开始其余查询之前，您需要先等待 state 承诺：

router.get('/:stateid', ensureAuthenticated, (req, res) => {
    const member = req.user;
    console.log(member);
    States.findOne({url:req.params.stateid}).then(state =>
        Promise.all([
            StateLegislation.find({'state': state.name }),
            StatePolicy.find({'state': state.name }),
            StateRegulation.find({'state': state.name }),
            StateLitigation.find({'state': state.name }),
        ]).then(([statelegislation,statepolicy,stateregulation,statelitigation]) =>
            res.render('app/state/home', {
                state,
                statelegislation,
                statepolicy,
                stateregulation,
                statelitigation,
            })
        )
    )
    .catch(err => res.send('Ops, something has gone wrong'));
});