Update Documents
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Overview
In this guide, you can learn how to use the C++ driver to update
documents in a MongoDB collection. You can call the update_one()
method
to update a single document or the update_many()
method to update multiple
documents.
Sample Data
The examples in this guide use the restaurants
collection in the sample_restaurants
database from the Atlas sample datasets. To access this collection
from your C++ application, instantiate a mongocxx::client
that connects to an Atlas cluster
and assign the following values to your db
and collection
variables:
auto db = client["sample_restaurants"]; auto collection = db["restaurants"];
To learn how to create a free MongoDB Atlas cluster and load the sample datasets, see the Get Started with Atlas guide.
Update Operations
You can perform update operations in MongoDB by using the following methods:
update_one()
, which updates the first document that matches the search criteriaupdate_many()
, which updates all documents that match the search criteria
Each update method requires the following parameters:
Query filter document: Specifies which documents to update. For more information about query filters, see the Query Filter Documents section in the MongoDB Server manual.
Update document: Specifies the update operator, or the kind of update to perform, and the fields and values to change. For a list of update operators and their usage, see the Field Update Operators guide in the MongoDB Server manual.
Update One Document
The following example uses the update_one()
method to update the name
value of a document in the restaurants
collection from "Bagels N Buns"
to "2 Bagels 2 Buns"
:
auto query_filter = make_document(kvp("name", "Bagels N Buns")); auto update_doc = make_document(kvp("$set", make_document(kvp("name", "2 Bagels 2 Buns")))); auto result = collection.update_one(query_filter.view(), update_doc.view());
Update Many Documents
The following example uses the update_many()
method to update all documents
that have a cuisine
value of "Pizza"
. After the update, the documents have
a cuisine
value of "Pasta"
.
auto query_filter = make_document(kvp("cuisine", "Pizza")); auto update_doc = make_document(kvp("$set", make_document(kvp("cuisine", "Pasta")))); auto result = collection.update_many(query_filter.view(), update_doc.view());
Customize the Update Operation
You can modify the behavior of the update_one()
and update_many()
methods by
passing an instance of the mongocxx::options::update
class as an optional
parameter. The following table describes the fields you can set in a
mongocxx::options::update
instance:
Field | Description |
---|---|
upsert | Specifies whether the update operation performs an upsert operation if no
documents match the query filter. For more information, see the upsert
statement
in the MongoDB Server manual. Defaults to false . |
bypass_document_validation | Specifies whether the update operation bypasses document validation. This lets you
update documents that don't meet the schema validation requirements, if any
exist. For more information about schema validation, see Schema
Validation in the MongoDB
Server manual. Defaults to false . |
collation | Specifies the kind of language collation to use when sorting
results. For more information, see Collation
in the MongoDB Server manual. |
array_filters | Specifies which array elements an update applies to if the operation modifies
array fields. |
hint | Sets the index to scan for documents.
For more information, see the hint statement
in the MongoDB Server manual. |
write_concern | Sets the write concern for the operation.
For more information, see Write Concern
in the MongoDB Server manual. |
let | Specifies a document with a list of values to improve operation readability.
Values must be constant or closed expressions that don't reference document
fields. For more information, see the let statement in the
MongoDB Server manual. |
comment | A comment to attach to the operation. For more information, see the insert command
fields guide in the
MongoDB Server manual for more information. |
The following example uses the update_many()
method to find all documents that
have borough
value of "Manhattan"
. It then updates the borough
value
in these documents to "Manhattan (north)"
. Because the upsert
option is
set to true
, the C++ driver inserts a new document if the query filter doesn't
match any existing documents.
mongocxx::options::update opts{}; opts.upsert(true); auto query_filter = make_document(kvp("borough", "Manhattan")); auto update_doc = make_document(kvp("$set", make_document(kvp("borough", "Manhattan (north)")))); auto result = collection.update_many(query_filter.view(), update_doc.view(), opts);
Return Value
The update_one()
and update_many()
methods return an instance of
the mongocxx::result::update
class. This class contains the following
member functions:
Function | Description |
---|---|
matched_count() | Returns the number of documents that matched the query filter, regardless of
how many were updated. |
modified_count() | Returns number of documents modified by the update operation. If an updated
document is identical to the original, it is not included in this
count. |
result() | Returns the raw result document for the operation. |
upserted_count() | Returns the number of document that were upserted into the database. |
upserted_id() | Returns the ID of the document that was upserted in the database, if the driver
performed an upsert. |
The following example uses the update_many()
method to update the name
field
of matching documents from "Dunkin' Donuts"
to "Dunkin'"
. It calls the
modified_count()
member function to print the number of modified documents:
auto query_filter = make_document(kvp("name", "Dunkin' Donuts")); auto update_doc = make_document(kvp("$set", make_document(kvp("name", "Dunkin'")))); auto result = collection.update_many(query_filter.view(), update_doc.view()); std::cout << "Modified documents: " << result->modified_count() << std::endl;
Modified documents: 206
Additional Information
To learn more about creating query filters, see the Specify a Query guide.
API Documentation
To learn more about any of the methods or types discussed in this guide, see the following API documentation: