CRUD Operations
On this page
CRUD operations are those which deal with creating, reading, updating, and deleting documents.
Key-value Pair Notation
Key-value pairs appear in many different contexts in the MongoDB Ruby driver, and there are some quirks of syntax with regard to how they can be notated which depend on which version of Ruby you're using.
When constructing a document, the following syntax is acceptable and correct for Ruby version 1.9 and later:
document = { name: "Harriet", age: 36 }
If you're using Ruby version 2.2 or greater, you can optionally enclose your keys in quotes.
document = { "name": "Harriet", "age": 36 }
If you need to use any MongoDB operator which begins with $
,
such as $set
, $gte
, or $near
, you must enclose it in
quotes. If you're using Ruby version 2.2 or greater, you can notate
it as follows:
collection.update_one({ name: "Harriet" }, { "$set": { age: 42 } })
If you're using an earlier version of Ruby, use the hashrocket symbol:
collection.update_one({ name: "Harriet" }, { "$set" => { age: 42 } })
Quoted strings and hashrockets for key-value pairs will work with any version of Ruby:
collection.update_one({ "name" => "Harriet" }, { "$set" => { age: 42 } })
Creating Documents
To insert documents into a collection, select a
collection on the client and call insert_one
or insert_many
.
Insert operations return a Mongo::Operation::Result
object which
gives you information about the insert itself.
On MongoDB 2.6 and later, if the insert fails, an exception is raised, because write commands are used.
On MongoDB 2.4, an exception is only raised if the insert fails and the write concern is 1 or higher.
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') result = client[:artists].insert_one( { :name => 'FKA Twigs' } ) result.n # returns 1, because 1 document was inserted. result = client[:artists].insert_many([ { :name => 'Flying Lotus' }, { :name => 'Aphex Twin' } ]) result.inserted_count # returns 2, because 2 documents were inserted.
Specify a Decimal128
number
New in version 3.4.
Decimal128 is a BSON datatype that employs 128-bit decimal-based floating-point values capable of emulating decimal rounding with exact precision. This functionality is intended for applications that handle monetary data, such as financial and tax computations.
The following example inserts a value of type Decimal128
into
the price
field of a collection named inventory
:
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'test') price = BSON::Decimal128.new("428.79") client[:inventory].insert_one({ "_id" => 1, "item" => "26 inch monitor", "price" => price })
The above operation produces the following document:
{ "_id" : 1, "item" : "26 inch monitor", "price" : NumberDecimal("428.79") }
You can also create a Decimal128
object from a Ruby BigDecimal
object, or with Decimal128.from_string()
.
big_decimal = BigDecimal.new(428.79, 5) price = BSON::Decimal128.new(big_decimal) # => BSON::Decimal128('428.79') price = BSON::Decimal128.from_string("428.79") # => BSON::Decimal128('428.79')
Query Cache
The Ruby driver provides a query cache. When enabled, the query cache will save the results of find and aggregation queries and return those saved results when the same queries are performed again.
To read more about the query cache, visit the query cache tutorial.
Reading
The Ruby driver provides a fluent interface for queries using the find
method on the collection. Various options are available
to the find
method.
The query is lazily executed against the server only when iterating the
results - at that point the query is dispatched and a Mongo::Cursor
is
returned.
To find all documents for a given filter, call find
with the
query:
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') client[:artists].find(:name => 'Flying Lotus').each do |document| #=> Yields a BSON::Document. end
To query nested documents, specify the keys in nested order using dot notation.
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') client[:artists].find("records.releaseYear": 2008).each do |document| #=> Yields a BSON::Document. end
Legacy $query
Syntax
This usage is deprecated.
The find
method allows providing the query and the options using the
legacy $query
syntax in the first parameter:
collection.find(:'$query' => {name: 'Mr. Smith'}) # Equivalent to: collection.find(name: 'Mr. Smith') collection.find(:'$query' => {name: 'Mr. Smith'}, :'$sort' => {age: 1}) # Equivalent to: collection.find(name: 'Mr. Smith').sort(age: 1)
When the query is executed against MongoDB 3.2 or newer, the driver will use the protocol appropriate for the server version in question, automatically converting the query as needed to either a find command or an OP_MSG payload.
Query Options
To add options to a query, chain the appropriate methods after the
find
method. Note that the underlying object, the Mongo::Collection::View
,
is immutable and a new object will be returned after each method call.
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') documents = client[:artists].find(:name => 'Flying Lotus').skip(10).limit(10) documents.each do |document| #=> Yields a BSON::Document. end
The following is a full list of the available options that can be added when querying and their corresponding methods as examples.
Option | Description | |||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
allow_disk_use | When set to true, the server can write temporary data to disk while
executing the find operation. This option is only available on MongoDB
server versions 4.4 and newer. | |||||||||||||||||||
allow_partial_results | For use with sharded clusters. If a shard is down, allows the query
to return results from the shards that are up, potentially only getting
a portion of the results. | |||||||||||||||||||
batch_size(Integer) | Specifies the size of each batch of documents the cursor will return on
each GETMORE operation. | |||||||||||||||||||
comment(String) | Adds a comment to the query. | |||||||||||||||||||
explain(**opts) | Returns the query plan for the query. Pass the explain options via the keyword arguments using symbol keys.
The explain operation supports
If the read preference option is specified on the client or on the collection, it will be passed to the explain operation:
Note that the session option is not accepted when creating a collection object. The explain command does not support passing the read concern option. If the read concern is specifed on the client or collection level, or if the read concern is specified as a find option, it will NOT be passed by the driver to the explain command. The information returned by the server for the The return value of the ``explain`` method is not part of the driver's public API and depends on the server version and deployment topology. | |||||||||||||||||||
hint(Hash) | Provides the query with an
index hint to use. | |||||||||||||||||||
let(Hash) | Mapping of variables
to use in the query. | |||||||||||||||||||
limit(Integer) | Limits the number of returned documents to the provided value. | |||||||||||||||||||
max_scan(Integer) | Sets the maximum number of documents to scan if a full collection scan
would be performed. Deprecated as of MongoDB server version 4.0. | |||||||||||||||||||
max_time_ms(Integer) | The maximum amount of time to allow the query to run, in milliseconds. | |||||||||||||||||||
no_cursor_timeout | MongoDB automatically closes inactive cursors after a period of 10
minutes. Call this for cursors to remain open indefinitely on the server. | |||||||||||||||||||
projection(Hash) | Specifies the fields to include or exclude from the results.
| |||||||||||||||||||
read(Hash) | Changes the read preference for this query only.
| |||||||||||||||||||
session(Session) | The session to use. | |||||||||||||||||||
show_disk_loc(Boolean) | Tells the results to also include the location of the documents on disk. | |||||||||||||||||||
skip(Integer) | Skip the provided number of documents in the results. | |||||||||||||||||||
snapshot | Execute the query in snapshot mode. Deprecated as of MongoDB server version 4.0. | |||||||||||||||||||
sort(Hash) | Specifies sort criteria for the query.
|
Additional Query Operations
count_documents
- Get the total number of documents matching a filter, or the total number of documents in a collection.
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') client[:artists].find(:name => 'Flying Lotus').count_documents
estimated_document_count
Get an approximate number of documents in the collection.
Note that unlike
count_documents
,estimated_document_count
does not accept a filter.The
count
server command is used to implementestimated_document_count
. More information can be found via Count: Behavior.Due to an oversight in MongoDB versions 5.0.0-5.0.7, the
count
command, whichestimated_document_count
uses in its implementation, was not included in v1 of the Stable API. Therefore, users of the Stable API withestimated_document_count
are recommended to upgrade their server version to 5.0.8+ or setapi_strict: false
to avoid encountering errors.
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') client[:artists].estimated_document_count
count
Get an approximate number of documents matching a filter, or an approximate number of documents in the collection.
Deprecated: The
count
method is deprecated and does not work in transactions. Please usecount_documents
to obtain an exact count of documents potentially matching a filter orestimated_document_count
to obtain an approximate number of documents in the collection.
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') client[:artists].find(:name => 'Flying Lotus').count
distinct
- Filters out documents with duplicate values. Equivalent to the SQL
distinct
clause.
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') client[:artists].find.distinct(:name )
Tailable Cursors
For capped collections you may use a tailable cursor that remains open after the client exhausts the results in the initial cursor. The following code example shows how a tailable cursor might be used:
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') client[:artists].drop client[:artists, capped: true, size: 512].create result = client[:artists].insert_many([ { :name => 'Flying Lotus' }, { :name => 'Aphex Twin' } ]) enum = client[:artists].find({}, cursor_type: :tailable_await).to_enum while true doc = enum.next # do something sleep(1) end
Read Concern
Read concern can be set on the client or on the collection:
client = Mongo::Client.new(['localhost:14420'], database: 'music', read_concern: {level: :local}) client['collection'].find.to_a collection = client['collection', read_concern: {level: :majority}] collection.find.to_a
The driver does not currently support setting read concern on an individual query.
Read concern can be specified when starting a transaction. When a transaction is active, any read concern specified on the client or on the collection is ignored.
When using the generic command helper, the read concern can be specified as part of the command:
client.database.command(dbStats: 1, readConcern: {level: :majority})
Read Preference
Read preference determines the candidate replica set
members to which a query or command can be sent. They consist of a mode
specified as a symbol, an array of hashes known as tag_sets,
the hedge
option, which is a Hash specifying hedged read behavior, and two
timing options: local_threshold and server_selection_timeout.
local_threshold
- Defines the upper limit in seconds of the latency window between the nearest server and suitable servers to which an operation may be sent. The default is 15 milliseconds, or 0.015 seconds.
server_selection_timeout
- Defines how long to block for server selection before throwing an exception. The default is 30,000 milliseconds, or 30 seconds.
Note
Read preference does not apply to Standalone deployments. When a client is connected to a Standalone deployment, any application-specified read preference is ignored.
For more information on the algorithm used to select a server, please refer to the Server Selection documentation, available on GitHub.
Read preference can be set as an option on the client or passed an option when a command is run on a database:
# Set read preference on a client, used for all operations client = Mongo::Client.new([ '127.0.0.1:27017' ], read: { mode: :secondary, tag_sets: [ { 'dc' => 'nyc' } ] } ) # Set read preference for a given command client.database.command( { dbStats: 1 }, read: { mode: secondary, tag_sets: [ { 'dc' => 'nyc' } ] } )
Read preference can also be set for specific operations on a collection
using the with
method:
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') artists = client[:artists] artists.with(:read => { :mode => :primary_preferred }).find.to_a
Mode
There are five possible read preference modes: :primary
, :secondary
,
:primary_preferred
, :secondary_preferred
and``:nearest``.
Please see the read preference documentation in the MongoDB Manual for an explanation of the modes.
Note
When a client is directly connected to a server using the :direct_connection
Ruby option or the directConnection
URI option, read preference mode
is automatically set to :primary_preferred
to permit read operations
against secondaries. If the application specified a :primary
read
preference mode, the mode is automatically converted to :primary_preferred
.
If another read preference mode is specified, it is passed to the server
unchanged.
Tag sets
The tag_sets
parameter is an ordered list of tag sets used to
restrict the eligibility of servers for selection, such as for data
center awareness. Please see the read preference documentation in
the MongoDB Manual for an explanation of tag sets.
A read preference tag set (T) matches a server tag set (S) – or equivalently a server tag set (S) matches a read preference tag set (T) — if T is a subset of S.
For example, the read preference tag set { dc: 'ny', rack: 2 }
matches a secondary server with tag set { dc: 'ny', rack: 2, size: 'large' }
.
A tag set that is an empty document matches any server, because
the empty tag set is a subset of any tag set. This means the default
tag_sets
parameter [{}]
matches all servers.
Hedge
The hedge
parameter is a Hash that specifies whether the server should use
hedged reads. With hedged reads, sharded clusters can route read operations to
two replica set members and return results from the first respondent.
The hedge
option may only be specified on non-primary read preferences. It
must be provided as Hash with the key enabled
set to true
or false
.
client = Mongo::Client.new( [ '127.0.0.1:27017' ], read: { mode: :secondary, hedge: { enabled: true } }, )
See the MongoDB Manual for more information about hedged reads.
Note
The hedge
option is only available on MongoDB server versions 4.4 and newer.
Attempting to use this option on older server versions will result in an error.
Updating
Updating documents is possible by executing a single or
multiple update, or by using the $findAndModify
command.
update_one
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') artists = client[:artists] result = artists.find(:name => 'Goldie').update_one("$inc" => { :plays => 1 } ) result.n # Returns 1. result = artists.update_one( { :name => 'Goldie' }, { "$inc" => { :plays => 1 } } ) result.n # Returns 1.
update_many
result = artists.find(:label => 'Hospital').update_many( "$inc" => { :plays => 1 } ) result.modified_count # Returns the number of documents that were updated. result = artists.update_many( { :label => 'Hospital' }, { "$inc" => { :plays => 1 } } ) result.modified_count # Returns the number of documents that were updated.
replace_one
result = artists.find(:name => 'Aphex Twin').replace_one(:name => 'Richard James') result.modified_count # Returns 1. result = artists.replace_one( { :name => 'Aphex Twin' }, { :name => 'Richard James' } ) result.modified_count # Returns 1.
To update documents and return a document via $findAndModify
, use one of
the three provided helpers: find_one_and_delete
, find_one_and_replace
,
or find_one_and_update
. You can opt to return the document before or after
the modification occurs.
find_one_and_delete
client = Mongo::Client.new( [ '127.0.0.1:27017' ], :database => 'music') artists = client[:artists] artists.find(:name => 'José James').find_one_and_delete # Returns the document.
find_one_and_replace
doc = artists.find(:name => 'José James').find_one_and_replace(:name => 'José') doc # Return the document before the update. doc = artists.find_one_and_replace({ :name => 'José James' }, { :name => 'José' }) doc # Return the document before the update. doc = artists.find(:name => 'José James'). find_one_and_replace( { :name => 'José' }, :return_document => :after ) doc # Return the document after the update.
find_one_and_update
doc = artists.find(:name => 'José James'). find_one_and_update( '$set' => { :name => 'José' } ) doc # Return the document before the update. doc = artists.find_one_and_update( { :name => 'José James' }, { '$set' => { :name => 'José' } } ) doc # Return the document before the update.
Update Options
To add options to an update command, specify them as key-value pairs in the options Hash argument.
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') artists = client[:artists] artists.indexes.create_one(name: 1) # Force the server to use the name index to perform this operation result = artists.update_one( { :name => 'Goldie' }, { "$inc" => { :plays => 1 } }, { hint: { name: 1 } } ) result.n # Returns 1.
The following is a list of the options that can be added to update operations,
including update_one
, update_many
, replace_one
,
find_one_and_delete
, find_one_and_update
, and find_one_and_replace
.
Option | Description |
---|---|
array_filters | An Array of filter documents that determine which array elements to modify
for an update operation on an array field. |
bypass_document_validation | Whether to skip document-level validation before writing the document. |
collation | Specifies a set of rules to use when comparing strings complying with the
conventions of a particular language. |
hint | The index to use for this operation. May be specified as a Hash
(e.g. { _id: 1 }) or as a String (e.g. "_id_"). Supported on MongoDB
server versions 4.2 and newer for update_one , update_many , and
replace_one commands, and on server versions 4.4 and newer for
find_one_and_delete , find_one_and_update , and find_one_and_replace
commands. |
let(Hash) | Mapping of variables
to use for this operation. |
projection | The fields to exclude or include in the operation result (only available
on find_one_and_delete , find_one_and_replace , and
find_one_and_update commands). |
return_document | A symbol specifying whether to return the updated document as it was before or
after the update. Potential values are :before or :after .
(Only available on find_one_and_update and find_one_and_replace commands). |
sort | How to sort the results of a find and modify command. Specified as a Hash
key-value pair, where the key is the name of the field to sort by, and
the value is either 1 or -1, specifying a sort in ascending or descending
order (only available on find_one_and_delete , find_one_and_replace ,
and find_one_and_update commands). |
session | The session to use for this operation. |
upsert | Whether to upsert if the document doesn't exist. Cannot be used on
find_one_and_delete operation. |
For more information about update options, see the MongoDB server documentation on the following commands:
Deleting
delete_one
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') artists = client[:artists] result = artists.find(:name => 'Björk').delete_one result.deleted_count # Returns 1. result = artists.delete_one(:name => 'Björk') result.deleted_count # Returns 1.
delete_many
result = artists.find(:label => 'Mute').delete_many result.deleted_count # Returns the number deleted. result = artists.delete_many(:label => 'Mute') result.deleted_count # Returns the number deleted.
Delete Options
To add options to a delete command, specify them as key-value pairs in the options Hash argument.
client = Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'music') artists = client[:artists] artists.indexes.create_one(name: 1) # Force the server to use the name index to perform this operation result = artists.find(:name => 'Björk').delete_one(hint: { name: 1 }) result.deleted_count # Returns 1.
The following is a full list of the available options that can be added
to delete_one
and delete_many
operations.
Option | Description |
---|---|
collation | Specifies a set of rules to use when comparing strings complying with the
conventions of a particular language. |
hint | The index to use for this operation. May be specified as a Hash
(e.g. { _id: 1 }) or as a String (e.g. "_id_"). Supported on MongoDB
server versions 4.4 and newer. |
let(Hash) | Mapping of variables
to use for this operation. |
session | The session to use for this operation. |
For more information about update options, see the MongoDB server documentation on the delete command.
Write Concern
All write operations in MongoDB are executed with a write concern which is the level of acknowledgment requested from MongoDB for the particular write. More information about write concerns in general is available in the MongoDB manual.
The Ruby driver supports specifying write concern on client, collection,
session (for transactions on that session), transaction, GridFS bucket
and write stream levels, as well as when manually issuing commands via
Database#command
.
As of driver version 2.10, all driver objects accepting write concerns do so
through the :write_concern
option, which should be given a hash with
the write concern options. Usage of the :write
option is deprecated.
In driver versions 2.9 and below, client, collection and GridFS objects
took write concern options in the :write
option with session and
transaction objects employing the :write_concern
option.
Below are some examples of passing write concerns to client and collection
objects. The :write_concern
option can be provided when constructing
new client and collection objects, or to the #with
methods.
GridFS examples are provided on the GridFS page.
client = Mongo::Client.new([ '127.0.0.1:27017' ], database: 'music', write_concern: {w: 2}) alt_client = client.with(write_concern: {w: :majority}) collection = client[:artists, write_concern: {w: 3}] alt_collection = collection.with(write_concern: {w: :majority}) # Uses w: 3 collection.insert_one({name: 'SUN Project'}) # Uses w: :majority alt_collection.insert_one({name: 'SUN Project'})
Driver versions 2.9 and earlier accepted write concerns on client and collection
level via the :write
option. This usage continues to be supported for
backwards compatibility, but is deprecated:
client = Mongo::Client.new([ '127.0.0.1:27017' ], database: 'music', write: {w: 2}) alt_client = client.with(write: {w: :majority}) collection = client[:artists, write: {w: 3}] alt_collection = collection.with(write: {w: :majority})
If both :write
and :write_concern
options are provided, their
values must be identical or an exception will be raised:
# OK client = Mongo::Client.new([ '127.0.0.1:27017' ], database: 'music', write_concern: {w: 3}, write: {w: 3}) # Error client = Mongo::Client.new([ '127.0.0.1:27017' ], database: 'music', write_concern: {w: 3}, write: {w: :majority})
When #with
methods are used to alter the options on a client or collection,
the last provided option wins in case of naming differences:
client = Mongo::Client.new([ '127.0.0.1:27017' ], database: 'music', write_concern: {w: 2}) alt_client = client.with(write: {w: 3}) alt_client.options[:write] # => {"w"=>3} alt_client.options[:write_concern] # => nil
When using transactions, write concern is only sent to the server in
commit_transaction
and abort_transaction
operations
per the transactions specification.
Write concern may be set via the :write_concern
option in a
with_transaction
or start_transaction
call, or via
default_transaction_options
option on a session object.
If neither of these is set, write concern of the client is used; note
that transactions ignore write concerns of collections that are involved
in their operations. Note that when setting the write concern as a
transaction option, the :write
option is not recognized by any
driver version.
client = Mongo::Client.new([ '127.0.0.1:27017' ], database: 'music', write_concern: {w: 2}) collection = client[:artists, write_concern: {w: :majority}] session = client.start_session session.with_transaction do collection.insert_one({test: 1}, session: session) # Uses w: 2 when committing end session = client.start_session(default_transaction_options: {write_concern: {w: 3}) ) session.with_transaction do collection.insert_one({test: 1}, session: session) # Uses w: 3 when committing end session = client.start_session session.with_transaction(write_concern: {w: 3}) do collection.insert_one({test: 1}, session: session) # Uses w: 3 when committing end
When write concerns are inherited, inheritance applies to the entire
write concern hash rather than individual elements. For example, j: true
is not inherited in the following case:
client = Mongo::Client.new([ '127.0.0.1:27017' ], database: 'music', write_concern: {w: 1, j: true}) collection = client[:artists, write_concern: {w: 2}] collection.write_concern.options # => #<Mongo::WriteConcern::Acknowledged:0x47289650367880 options={:w=>2}>
Although CRUD operations accept an options hash, they currently do not
recognize the :write_concern
option:
client = Mongo::Client.new([ '127.0.0.1:27017' ], database: 'music', write_concern: {w: 2}) collection = client[:artists, write_concern: {w: :majority}] # Still uses w: :majority collection.insert_one({name: 'SUN Project'}, write_concern: {w: 1})
The easiest workaround for this is to use #with
to obtain a new collection
instance with the desired write concern:
# Uses w: 1 collection.with(write_concern: {w: 1}).insert_one(name: 'SUN Project')
Write concern can also be manually specified in Database#command
:
client.database.command(create: 'foo-collection', writeConcern: {w: :majority})
Note that writeConcern here is part of the operation rather than options, and the syntax is the camel case one that MongoDB server recognizes, not the underscore one that Ruby driver uses.
Field Names with Dots/Periods (.) and Dollar Signs ($)
Starting in Mongo Ruby Driver version 2.18.0, the ability to work with fields
that begin with dollar signs ($) and fields with dots/periods (.) in them is available.
In Driver version 2.17.0 and earlier, any attempt to work with dotted or dollared
fields would result in an IllegalKey
error being raised. See the MongoDB docs
on Field Names with Periods (.) and Dollar Signs ($)
for more information on working with these types of fields.
A Note about the BSON Symbol type
Because the BSON specification deprecated the BSON symbol type, the bson
gem
will serialize Ruby symbols into BSON strings when used on its own. However, in
order to maintain backwards compatibility with older datasets, the Ruby driver
overrides this behavior to serialize Ruby symbols as BSON symbols. This is
necessary to be able to specify queries for documents which contain BSON
symbols as fields. Despite this, new documents with symbol type fields should
not be stored in the database; instead, use string fields.
To override default behavior and configure the driver to encode symbol values as strings, include the following code snippet in your project:
class Symbol def bson_type BSON::String::BSON_TYPE end end