Azure Cosmos DB's API for MongoDB (3.6 version): supported features and syntax

• 03/02/2021
• 8 minutes to read
• • g
  • S
  • c
  • r
  • t
  • +5

APPLIES TO: Azure Cosmos DB API for MongoDB

Azure Cosmos DB is Microsoft's globally distributed multi-model database service. You can communicate with the Azure Cosmos DB's API for MongoDB using any of the open-source MongoDB client drivers. The Azure Cosmos DB's API for MongoDB enables the use of existing client drivers by adhering to the MongoDB wire protocol.

By using the Azure Cosmos DB's API for MongoDB, you can enjoy the benefits of the MongoDB you're used to, with all of the enterprise capabilities that Cosmos DB provides: global distribution, automatic sharding, availability and latency guarantees, encryption at rest, backups, and much more.

Protocol Support

The Azure Cosmos DB's API for MongoDB is compatible with MongoDB server version 3.6 by default for new accounts. The supported operators and any limitations or exceptions are listed below. Any client driver that understands these protocols should be able to connect to Azure Cosmos DB's API for MongoDB. Note that when using Azure Cosmos DB's API for MongoDB accounts, the 3.6 version of account has the endpoint in the format *.mongo.cosmos.azure.com whereas the 3.2 version of account has the endpoint in the format *.documents.azure.com.

Query language support

Azure Cosmos DB's API for MongoDB provides comprehensive support for MongoDB query language constructs. The following sections show the detailed list of server operations, operators, stages, commands, and options currently supported by Azure Cosmos DB.

Database commands

Azure Cosmos DB's API for MongoDB supports the following database commands:

Query and write operation commands

Authentication commands

Administration commands

Diagnostics commands

Aggregation pipeline

Aggregation commands

Aggregation stages

Boolean expressions

Set expressions

Comparison expressions

Arithmetic expressions

String expressions

Text search operator

Array expressions

Variable operators

System variables

Literal operator

Date expressions

Conditional expressions

Data type operator

Accumulator expressions

Merge operator

Data types

Indexes and index properties

Indexes

Index properties

Operators

Logical operators

Element operators

Evaluation query operators

In the $regex queries, left-anchored expressions allow index search. However, using 'i' modifier (case-insensitivity) and 'm' modifier (multiline) causes the collection scan in all expressions.

When there's a need to include '$' or '|', it is best to create two (or more) regex queries. For example, given the following original query: find({x:{$regex: /^abc$/}), it has to be modified as follows:

find({x:{$regex: /^abc/, x:{$regex:/^abc$/}})

The first part will use the index to restrict the search to those documents beginning with ^abc and the second part will match the exact entries. The bar operator '|' acts as an "or" function - the query find({x:{$regex: /^abc |^def/}) matches the documents in which field 'x' has values that begin with "abc" or "def". To utilize the index, it's recommended to break the query into two different queries joined by the $or operator: find( {$or : [{x: $regex: /^abc/}, {$regex: /^def/}] }).

Array operators

Comment operator

Projection operators

Update operators

Field update operators

Array update operators

Update modifiers

Bitwise update operator

Geospatial operators

Sort operations

When using the findOneAndUpdate operation, sort operations on a single field are supported but sort operations on multiple fields are not supported.

Unique indexes

Unique indexes ensure that a specific field doesn't have duplicate values across all documents in a collection, similar to the way uniqueness is preserved on the default "_id" key. You can create unique indexes in Cosmos DB by using the createIndex command with the unique constraint parameter:

globaldb:PRIMARY> db.coll.createIndex( { "amount" : 1 }, {unique:true} )
{
        "_t" : "CreateIndexesResponse",
        "ok" : 1,
        "createdCollectionAutomatically" : false,
        "numIndexesBefore" : 1,
        "numIndexesAfter" : 4
}

Compound indexes

Compound indexes provide a way to create an index for groups of fields for up to 8 fields. This type of index differs from the native MongoDB compound indexes. In Azure Cosmos DB, compound indexes are used for sorting operations that are applied to multiple fields. To create a compound index you need to specify more than one property as the parameter:

globaldb:PRIMARY> db.coll.createIndex({"amount": 1, "other":1})
{
        "createdCollectionAutomatically" : false, 
        "numIndexesBefore" : 1,
        "numIndexesAfter" : 2,
        "ok" : 1
}

GridFS

Azure Cosmos DB supports GridFS through any GridFS-compatible MongoDB driver.

Replication

Cosmos DB supports automatic, native replication at the lowest layers. This logic is extended out to achieve low-latency, global replication as well. Cosmos DB does not support manual replication commands.

Retryable Writes

Azure Cosmos DB does not yet support retryable writes. Client drivers must add retryWrites=false to their connection string.

Sharding

Azure Cosmos DB supports automatic, server-side sharding. It manages shard creation, placement, and balancing automatically. Azure Cosmos DB does not support manual sharding commands, which means you don't have to invoke commands such as addShard, balancerStart, moveChunk etc. You only need to specify the shard key while creating the containers or querying the data.

Sessions

Azure Cosmos DB does not yet support server-side sessions commands.

Time-to-live (TTL)

Azure Cosmos DB supports a time-to-live (TTL) based on the timestamp of the document. TTL can be enabled for collections from the Azure portal.

User and role management

Azure Cosmos DB does not yet support users and roles. However, it supports Azure role-based access control (Azure RBAC) and read-write and read-only passwords or keys that can be obtained through the connection string pane in the Azure portal.

Write Concern

Some applications rely on a Write Concern which specifies the number of responses required during a write operation. Due to how Azure Cosmos DB handles replication, all writes are automatically majority quorum by default when using strong consistency. Any write concern specified by the client code is ignored. To learn more, see Using consistency levels to maximize availability and performance article.

Next steps

• For further information check Mongo 3.6 version features
• Learn how to use Studio 3T with Azure Cosmos DB's API for MongoDB.
• Learn how to use Robo 3T with Azure Cosmos DB's API for MongoDB.
• Explore MongoDB samples with Azure Cosmos DB's API for MongoDB.