Mongoose exec() 没有正确等待

Posted 2023-03-11

【中文标题】Mongoose exec() 没有正确等待

【英文标题】：Mongoose exec() does not await properly

【发布时间】：2020-11-23 13:46:12

【问题描述】：

由于某种原因，exec() 没有在我的代码中等待：

    let team = <SOME TEAM NAME> //putting manually for testing
    let results = []

    TeamModel.find( name: team )
        .exec(async (err, docs) => 
            if (err)
                return res.send(Response("failure", "Error occured while retrieving fixtures"))
            
            for(let i = 0; i < docs.length; i++)

                let doesExist = await FixtureModel.exists( leagueName: docs[i].leagueName )

                if (doesExist) 
                    let query = FixtureModel.find( leagueName: docs[i].leagueName, $or: [ homeTeam: team ,  awayTeam: team ] )
                    await query.exec((err2, docs2) => 
                        if (err2)
                            return res.send(Response("failure", "Error occured while retrieving fixtures"))

                        docs2.forEach((doc2, index) => results.push(doc2.toObject()))
                        console.log('during await') //Executes second
                    )

                    console.log('after await') //Executes first
                
                else  //This section is not required
                    let result = await Communicator.GetFixturesFromLeague(docs[i].leagueId)

                    result.api.fixtures.forEach((fixture, index) => 
                        let newFixture = new FixtureModel(
                            fixtureId: fixture.fixture_id,
                            leagueId: fixture.league_id,
                            leagueName: fixture.league.name,
                            eventDate: fixture.event_date,
                            statusShort: fixture.statusShort,
                            homeTeam: fixture.homeTeam.team_name,
                            awayTeam: fixture.awayTeam.team_name
                        )

                        newFixture.save()
                        results.push(newFixture.toObject())
                    )                    
                          
            

            console.log(results)
            res.send(Response("success", "Retrieved fixtures", results))
        )

结果看起来像这样：

after await
[]
during await

因此，在向其中添加值之前会发送一个空的结果数组。我不确定我在这里缺少什么。

【问题讨论】：

因为当query.exec 承诺被解决时代码继续，而不是在回调完成执行时。尝试return docs2.forEach((doc2, index) => results.push(doc2.toObject())) 或docs2 = await query.exec() 然后docs2.forEach...

@dikuw 我怀疑可能是这种情况。尝试了您的解决方案，但仍然无效

query.exec() 仅在未通过回调时返回 Promise。

【参考方案1】：

如果有人想知道，这是一种解决方法。当 forLoop 完成绕过 async/await 的需要时，在 exec() 回调中发送响应。

 if (doesExist) 
                    let query = FixtureModel.find( league_name: docs[i].leagueName, $or: [ homeTeam:  team_name: team ,  awayTeam:  team_name: team ] )
                    await query.exec((err2, docs2) => 
                        if (err2)
                            return res.send(Response("failure", "Error occured while retrieving fixtures"))

                        docs2.forEach((doc2, index) => results.push(doc2.toObject()))
                        
                        if(i + 1 == docs.length)
                            return res.send(Response("success", "Retrieved fixtures", results))
                        
                    )
                

【讨论】：

恢复到计划 A 并写 let docs2 = await FixtureModel.find(.......).exec(); 并将 res.send(Response('success', 'Retrieved fixtures', results)); 留在 for 循环之外的麻烦更少。同样，let docs = await TeamModel.find( 'name': team ).exec();.

这两个 await 可以正常工作，您可以输入try /* everything */ catch(error) res.send(Response('failure', 'Error occurred while retrieving fixtures')); 。这将捕获/处理意外错误，而不仅仅是当前代码中的这两个特定错误。