Issue

This Content is from Stack Overflow. Question asked by Mehdi M

consider there are 3 collections :

Company : {
    name
}

Department: {
    name,
    company_id
}

Person: {
    name,
    department_id
}

and we want to get all persons in a company, by company name.

i know the way to first get the company id in one query, and then get the list of department_ids in another query, and then get the list of persons, in another query with the list of Ids :

    async function query(){
        let companyId = await Company.findOne({name}).distinct('_id').exec();
        let departmentIds = await Department.find({company_id : companyId } ).distinct('_id').exec();
        let persons = await Person.find({department_id : departmentIds}).exec();
    }

I want to know is there any better way to do this, I mean is it possible to use populate method or aggregation here? and if yes how?
thanks in advance.

Solution

You may try to use aggregate from Company document. Then one more aggregation with lookup to reach company document.

After reached company Document, you can easily match the name value.

return await Company.aggregate([
  {
    $lookup: {
      from: "departments",
      localField: "_id",
      foreignField: "company_id",
      as: "PersonCompanyTable",
    },
  },
  {
       $unwind: '$PersonCompanyTable'
  },
  {
       $lookup: {
          from: 'persons',
          localField: 'PersonCompanyTable._id',
          foreignField: 'department_id',
          as: 'PersonsTable'
  }
        },
  {
    $match: {
      name: name,
    },
  },
])

I hope, it is useful for you.

This Question was asked in StackOverflow by Mehdi M and Answered by Onur Doğan It is licensed under the terms of CC BY-SA 2.5. - CC BY-SA 3.0. - CC BY-SA 4.0.