Add key In all MongoDB collection objects

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Adding key in all collection object is bit tricky in mongoDB as there is nothing like alter table

db.collection.update( criteria, ourobj, upsert, multi )
  1. criteria is used to select objects which will be updated. e.g {“name”:”testName”}
  2. ourobject is the document which will be appended or overwrite fields of object found by criteria
  3. upsert  stand for update or insert true/false
  4. multi will the query effect multiple object true/false

In our case since we want to add a single key value to all objects existing in our database we will have

1.criteria  : {}  empty object to act like *

2. ourobject :{$set:{“our_key”:”test_value”}}  $set is for appending

3.upsert: false  since we want to update existing objects only we will set it to false

4. multi: true since we have to update more then one object so mutli is set to true

then our query becomes

db.collection.update( {}, {'$set': {our_key:test_value}}, false, true)