Add new field to every document in a MongoDB collection

mongodb field nosql
itsme picture itsme · Oct 10, 2011 · Viewed 327.6k times · Source

How can I add a new field to every document in an existent collection?

I know how to update an existing document's field but not how to add a new field to every document in a collection. How can I do this in the mongo shell?

Answer

RameshVel picture RameshVel · Oct 10, 2011

Same as the updating existing collection field, $set will add a new fields if the specified field does not exist.

Check out this example:

> db.foo.find()
> db.foo.insert({"test":"a"})
> db.foo.find()
{ "_id" : ObjectId("4e93037bbf6f1dd3a0a9541a"), "test" : "a" }
> item = db.foo.findOne()
{ "_id" : ObjectId("4e93037bbf6f1dd3a0a9541a"), "test" : "a" }
> db.foo.update({"_id" :ObjectId("4e93037bbf6f1dd3a0a9541a") },{$set : {"new_field":1}})
> db.foo.find()
{ "_id" : ObjectId("4e93037bbf6f1dd3a0a9541a"), "new_field" : 1, "test" : "a" }

EDIT:

In case you want to add a new_field to all your collection, you have to use empty selector, and set multi flag to true (last param) to update all the documents

db.your_collection.update(
  {},
  { $set: {"new_field": 1} },
  false,
  true
)

EDIT:

In the above example last 2 fields false, true specifies the upsert and multi flags.

Upsert: If set to true, creates a new document when no document matches the query criteria.

Multi: If set to true, updates multiple documents that meet the query criteria. If set to false, updates one document.

This is for Mongo versions prior to 2.2. For latest versions the query is changed a bit

db.your_collection.update({},
                          {$set : {"new_field":1}},
                          {upsert:false,
                          multi:true})

Related questions

String field value length in mongoDB

The data type of the field is String. I would like to fetch the data where character length of field name is greater than 40. I tried these queries but returning error. 1. db.usercollection.find( {$where: "(this.name.length > 40)"} ).limit(2); …

Read More
Searching for value of any field in MongoDB without explicitly naming it

I looked through the MongoDB documentation and googled this question but couldn't really find a suitable answer. So, here is what I'm looking for. Assume I have a collection with elements like this: { "foo" : "bar", "test" : "test", "key" : "value", } What …

Read More
How to query MongoDB with "like"?

I want to query something with SQL's like query: SELECT * FROM users WHERE name LIKE '%m%' How to do I achieve the same in MongoDB? I can't find an operator for like in the documentation.

Read More