mongodb - Most efficient way to change a string field value to its substring -

i have collection filled documents this:

{     data: 11,     version: "0.0.32"   } 

and have test suffix version:

{     data: 55,     version: "0.0.42-test"   } 

the version field has different values conforms pattern: 0.0.xxx. update documents this:

{     data: 11,     version: 32   } 

and suffixed version (for test documents - version should negative):

{     data: 55,     version: -42   } 

the collection these documents used our critical system, needs turned off while updating data - want update/change fast possible. there 66_000_000 documents in collection, , it's 100gb in size.

which type of mongodb operation efficient one?

the efficient way in upcoming release of mongodb of writing using $split operator split our string shown here assign last element in array variable using $let variable operator , $arrayelemat operators.

next, use $switch operator perform logical condition processing or case statement against variable.

the condition here $gt returns true if value contains "test", , in case in in expression split string , return $concatenated value of first element in newly computed array , -. if condition evaluates false, return variable.

of course in our case statement, use $indexofcp returns -1 if there no occurrences of "test".

let cursor = db.collection.aggregate(     [         { "$project": {              "data": 1,              "version": {                  "$let": {                      "vars": {                          "v": {                              "$arrayelemat": [                                 { "$split": [ "$version", "." ] },                                  -1                             ]                         }                     },                      "in": {                          "$switch": {                              "branches": [                                  {                                      "case": {                                          "$gt": [                                              { "$indexofcp": [ "$$v", "test" ] },                                             -1                                          ]                                     },                                      "then": {                                          "$concat": [                                              "-",                                              "",                                              { "$arrayelemat": [                                                 { "$split": [ "$$v", "-" ] },                                                  0                                              ]}                                          ]                                     }                                 }                             ],                              "default": "$$v"                          }                     }                 }             }         }}     ] ) 

the aggregation query produces this:

{ "_id" : objectid("57a98773cbbd42a2156260d8"), "data" : 11, "version" : "32" } { "_id" : objectid("57a98773cbbd42a2156260d9"), "data" : 55, "version" : "-42" } 

as can see, "version" field data string. if data type field not matter then, can use $out aggregation pipeline stage operator write result new collection or replace collection.

{ "out": "collection" } 

if need convert data floating point number then, way this, because mongodb doesn't not provides way type conversion out of box except integer string, iterate aggregation cursor object , convert value using parsefloat or number update documents using $set operator , bulkwrite() method maximum efficiency.

let requests = []; cursor.foreach(doc => {      requests.push({          "updateone": {              "filter": { "_id": doc._id },              "update": {                  "$set": {                      "data": doc.data,                      "version": parsefloat(doc.version)                  },                 "$unset": { "person": " " }             }          }      });      if ( requests.length === 1000 ) {          // execute per 1000 ops , re-init         db.collection.bulkwrite(requests);          requests = [];      }}  );   // clean queues if(requests.length > 0) {     db.coll.bulkwrite(requests); } 

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while aggregation query work in mongodb 3.4 or newer our best bet mongodb 3.2 backwards mapreduce bulkwrite() method.

var results = db.collection.mapreduce(     function() {          var v = this.version.split(".")[2];          emit(this._id, v.indexof("-") > -1 ? "-"+v.replace(/\d+/g, '') : v)     },      function(key, value) {},      { "out": { "inline": 1 } } )["results"]; 

results looks this:

[     {         "_id" : objectid("57a98773cbbd42a2156260d8"),         "value" : "32"     },     {         "_id" : objectid("57a98773cbbd42a2156260d9"),         "value" : "-42"     } ] 

from here use previous .foreach loop update documents.

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from mongodb 2.6 3.0 need use deprecated bulk() api , associated method show in answer here.