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Quick Start

On this page

  • Prerequisites
  • Make a Connection
  • Access a Database and a Collection
  • Insert a Document
  • Query the Collection
  • Update Documents
  • Delete Documents
  • Create Indexes
  • Complete Sample App
  • A running MongoDB instance on localhost using the default port, 27017.

  • The Ruby MongoDB driver. See installation for instructions on how to install the MongoDB driver.

  • The following statement at the top of your code:

require 'mongo'

Use Mongo::Client to establish a connection to a running MongoDB instance.

client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'test')

You can also use a URI connection string:

client = Mongo::Client.new('mongodb://127.0.0.1:27017/test')

Tip

See also:

The following examples demonstrate how to access a particular database and show its collections:

client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'test')
db = client.database
db.collections # returns a list of collection objects
db.collection_names # returns a list of collection names
db.list_collections # returns a list of collection metadata hashes

To access a collection, refer to it by name.

collection = client[:restaurants]

If the collection does not exist, the server will create it the first time you put data into it.

To insert a single document into a collection, use the insert_one method.

client = Mongo::Client.new('mongodb://127.0.0.1:27017/test')
collection = client[:people]
doc = {
name: 'Steve',
hobbies: [ 'hiking', 'tennis', 'fly fishing' ],
siblings: {
brothers: 0,
sisters: 1
}
}
result = collection.insert_one(doc)
result.n # returns 1, because one document was inserted

To insert multiple documents into a collection, use the insert_many method.

docs = [ { _id: 1, name: 'Steve',
hobbies: [ 'hiking', 'tennis', 'fly fishing' ],
siblings: { brothers: 0, sisters: 1 } },
{ _id: 2, name: 'Sally',
hobbies: ['skiing', 'stamp collecting' ],
siblings: { brothers: 1, sisters: 0 } } ]
result = collection.insert_many(docs)
result.inserted_count # returns 2 because two documents were inserted

Use the find method to create collection queries.

An empty query filter returns all documents in the collection.

client = Mongo::Client.new('mongodb://127.0.0.1:27017/test')
collection = client[:people]
collection.find.each do |document|
#=> Yields a BSON::Document.
end

Use a query filter to find only matching documents.

client = Mongo::Client.new('mongodb://127.0.0.1:27017/test')
collection = client[:people]
puts collection.find( { name: 'Sally' } ).first

The example should print the following:

{"_id" => 2, "name" => "Sally", "hobbies" => ["skiing", "stamp collecting"], "siblings" => { "brothers": 1, "sisters": 0 } }

Query nested documents by specifying the keys and values you want to match.

client = Mongo::Client.new('mongodb://127.0.0.1:27017/test')
collection = client[:people]
puts collection.find("siblings.sisters": 1 ).first

The example should print the following:

{"_id"=>1, "name"=>"Steve", "hobbies"=>["hiking", "tennis", "fly fishing"], "siblings"=>{"brothers"=>0, "sisters"=>1}}

There are several update methods, including update_one and update_many. update_one updates a single document, while update_many updates multiple documents at once.

Both methods take as arguments a query filter document and a second document with the update data. Use $set to add or update a particular field or fields. Without $set, the entire existing document is replaced with the update data.

client = Mongo::Client.new('mongodb://127.0.0.1:27017/test')
collection = client[:people]
result = collection.update_one( { 'name' => 'Sally' }, { '$set' => { 'phone_number' => "555-555-5555" } } )
puts collection.find( { 'name' => 'Sally' } ).first

The example should print the following:

{"_id" => 2, "name" => "Sally", "hobbies" => ["skiing", "stamp collecting"], "phone_number" => "555-555-5555"}

The following example uses update_many with a blank query filter to update all the documents in the collection.

client = Mongo::Client.new('mongodb://127.0.0.1:27017/test')
collection = client[:people]
result = collection.update_many( {}, { '$set' => { 'age' => 36 } } )
puts result.modified_count # returns 2 because 2 documents were updated

Use the delete_one or delete_many methods to delete documents from a collection (either singly or several at once).

client = Mongo::Client.new('mongodb://127.0.0.1:27017/test')
collection = client[:people]
result = collection.delete_one( { name: 'Steve' } )
puts result.deleted_count # returns 1 because one document was deleted

The following example inserts two more records into the collection, then deletes all the documents with a name field which matches a regular expression to find a string which begins with "S".

client = Mongo::Client.new('mongodb://127.0.0.1:27017/test')
collection = client[:people]
collection.insert_many([ { _id: 3, name: "Arnold" }, { _id: 4, name: "Susan" } ])
puts collection.count # counts all documents in collection
result = collection.delete_many({ name: /$S*/ })
puts result.deleted_count # returns the number of documents deleted

Use the create_one or create_many methods to create indexes singly or several at once.

client = Mongo::Client.new('mongodb://127.0.0.1:27017/test')
collection = client[:people]
collection.indexes.create_one({ name: 1 }, unique: true)

Use the create_many method to create several indexes with one statement. Note that when using create_many, the syntax is different from create_one.

client = Mongo::Client.new('mongodb://127.0.0.1:27017/test')
collection = client[:people]
collection.indexes.create_many([
{ key: { name: 1 } , unique: true },
{ key: { hobbies: 1 } },
])

Tip

See also:

A sample app using the Ruby driver for several common use cases is available for download from GitHub.

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