How to execute mongodb find query in a loop in nodejs

Question

I am trying to execute mongodb find query in a loop. I have an object with some properties. The value of each property will be checked in the mongodb to get its updated value. Once all the property values are updated, i want to perform some other actions.

But before getting the updated object(updatedVehObj), the next line of code (function updatedVehicleData ) is getting executed and its throwing some error,since i dont have the updated values.

Thanks in advance for any help to solve this issue or any better methods for achieving this result.

const processVehData = async (vehData) => {
  const vehObj = {
    make: 'AUD',
    model: 'A12',
    type: 'S',
  }
  const updatedVehObj = await getDBMapping(vehObj)
  // Do some preocessing with the updated vehicle obj
  const processedDataRes = updatedVehicleData(updatedVehObj)
  return processedDataRe;
}

const getDBMapping = async (vehObj) => {
  let updatedVeh = {}
  MongoClient.connect(connectionStr, mongoOptions, async (err, client) => {
    if (err) {
      console.log('Error in connecting to DB')
    }
    const dbo = client.db('VehicleDataBase')
    for (const key of Object.keys(vehObj)) {
      // Iterating every element in the object
      await dbo
        .collection(key)  // key name will be the collection name in mongodb
        .find({         
          code: vehObj[key],
        })
        .toArray()
        .then(result => {
          updatedVeh[key] = result[0] // Framing new object with updated values
        })
        .catch(err => {
          console.log(' Error in getting mapping', err)
        })
    }
    return updatedVeh;
    /*** Expected result
      updatedVeh = {
        "make": "AUDI",
        "model" : "A3 Auto",
        "type" : "Sedan"
      }
    ****/
  })
}

const updatedVehicleData = vehData => {
  // Do something
}

zken · Accepted Answer · 2020-05-31 13:41:36Z

Your problem came from the callback of MongoClient.connect(), when performing await getDBMapping(vehObj) you are not waiting for something to be resolved.

Also, you combined await and then on update queries.

A solution could be to use a Promise in getDBMapping function :

const getDBMapping = async (vehObj) => new Promise((resolve, reject) => {
  let updatedVeh = {}
  MongoClient.connect(connectionStr, mongoOptions, async (err, client) => {
    if (err) {
      console.log('Error in connecting to DB')
      return reject(err); // reject is there is an error
    }

    const dbo = client.db('VehicleDataBase')
    for (const key of Object.keys(vehObj)) {
      // use try / catch instead of combined await / then
      try {
        const result = await dbo
          .collection(key)
          .find({         
            code: vehObj[key],
          })
          .toArray();

        updatedVeh[key] = result[0];
      } catch (err) {
        console.log('Error in getting mapping', err)
        // reject(err); => you can also reject here, but it could break batch update transaction
      }
    }

    return resolve(updatedVeh);
  })
});

turivishal · Accepted Answer · 2020-05-31 13:52:05Z

0

As per your problem "But before getting the updated object(updatedVehObj), the next line of code (function updatedVehicleData ) is getting executed and its throwing some error,since i dont have the updated values."

You have to write same async and await before this function,

const processedDataRes = await updatedVehicleData(updatedVehObj)

const updatedVehicleData = async vehData => {
  // Do something
}

edited May 31, 2020 at 13:52

answered May 31, 2020 at 13:44

turivishal

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