Come archiviare i dati in MongoDb utilizzando il modello a cascata mongoose e asincrono

prima ho salvato Edifici e sezione :

async.every(uniqueSection,function (uS,callback) {
      if (uS != undefined) {
          console.log(uS);
            Buildings.findOne({buildingname:uS.building}, function (err,doc) {
                if (doc) {
                    // console.log(doc);
                    Sections.findOne({buildings:doc._id,section_type:uS.section},function (er,sd) {
                        if (sd) {
                            // then dont save
                            console.log(sd);
                        }
                        if (er) {
                            console.log(er);
                        }
                        if (!sd) {
                            // then save
                            var sect = new Sections();
                            sect.buildings = doc._id;
                            sect.section_type = uS.section;
                            sect.status = 'active';
                            sect.save(function (err,st) {
                                if(err) console.log(err);
                                console.log(st);
                            })
                        }
                    })  
                } 
                if (!doc) {
                 if (uS.building != undefined) {
                    var building = new Buildings();
                    building.buildingname = uS.building;
                    building.status = "active";
                    building.save(function (er,dc) {
                        if (dc) {
                            // console.log(dc);
                            Sections.findOne({buildings:dc._id,section_type:uS.section},function (er,sd) {
                                if (sd) {
                                    // then dont save
                                    console.log(sd);
                                }
                                if (er) {
                                    console.log(er);
                                }
                                if (!sd) {
                                    // then save
                                    var sect = new Sections();
                                    sect.buildings = dc._id;
                                    sect.section_type = uS.section;
                                    sect.status = 'active';
                                    sect.save(function (err,st) {
                                        if(err) console.log(err);
                                        console.log(st);
                                    })
                                }
                            })  
                        } 
                        if (er) {
                            console.log(er);
                        }
                    })
                  }
                }
                if (err) {
                    console.log(err);
                }
              })
            }
        })

quindi ho salvato Unità di :

   async.waterfall([
                function(callback) {
                    Buildings.findOne({buildingname:d.building}, function (err,doc) {
                        if (doc) {
                            buildingId = doc._id;
                            callback(null, doc);
                        } 
                        if (err) {
                            console.log(err);
                        }
                      })

                },
                function(doc,callback) {
                    Sections.findOne({buildings: buildingId,section_type:d.section},function (er,sd) {
                        if (sd) {
                            sectionId = sd._id;
                           callback(null,doc,sd);  
                        }
                        if (er) {
                            console.log(er);
                        }

                    })  
                },
                function (bld,st,callback) {
                var s = d.shares.replace(",","");
                var unit = {
                    unit_type: d.unit_type,
                    unit_num: d.residenceone_unit_id,
                    unit_ac_num: d.official_unit_id,
                    buildings: bld._id, 
                    sections: st._id,
                    shares: s
                 }
                 Units.findOne(unit,function (err,unt) {
                     if (err) {
                         console.log(err);
                     } 
                     if(unt) {
                         console.log(unt)
                     }
                     if (!unt) {
                        var units = new Units();
                        units.unit_type = d.unit_type;
                        units.unit_num = d.residenceone_unit_id;
                        units.unit_ac_num = d.official_unit_id;
                        units.buildings = bld._id; 
                        units.sections = st._id;
                        units.shares = s;

                        units.save(function (er,doc) {
                            if (er) console.log(er);
                            console.log(doc);
                        }) 
                     }
                 })
                }
            ], function(err) {
                console.log(err)
            });