Azure Schema Registry client library for Python

Azure Schema Registry is a schema repository service hosted by Azure Event Hubs, providing schema storage, versioning, and management. The registry is leveraged by encoders to reduce payload size while describing payload structure with schema identifiers rather than full schemas. This package provides:

1. A client library to register and retrieve schemas and their respective properties.

2. An JSON schema-based encoder capable of encoding and decoding payloads containing Schema Registry schema identifiers, corresponding to JSON schemas used for validation, and encoded content.

[Source code][source_code] | [Package (PyPi)][pypi] | Package (Conda) | [API reference documentation][api_reference] | [Samples][sr_samples] | [Changelog][change_log]

Disclaimer

Azure SDK Python packages support for Python 2.7 has ended on 01 January 2022. For more information and questions, please refer to https://github.com/Azure/azure-sdk-for-python/issues/20691

Getting started

Install the package

Install the Azure Schema Registry client library for Python with [pip][pip]:

pip install azure-schemaregistry

To use the built-in jsonschema validators with the JSON Schema Encoder, install jsonencoder extras:

pip install azure-schemaregistry[jsonencoder]

Prerequisites:

To use this package, you must have:

• Azure subscription - [Create a free account][azure_sub]
• [Azure Schema Registry][schemaregistry_service] - [Here is the quickstart guide][quickstart_guide] to create a Schema Registry group using the Azure portal.
• Python 3.8 or later - [Install Python][python]

Authenticate the client

Interaction with Schema Registry starts with an instance of SchemaRegistryClient class. The client constructor takes an Azure Event Hubs fully qualified namespace and an Azure Active Directory credential:

• The fully qualified namespace of the Schema Registry instance should follow the format: <yournamespace>.servicebus.windows.net.

• An AAD credential that implements the [TokenCredential][token_credential_interface] protocol should be passed to the constructor. There are implementations of the TokenCredential protocol available in the [azure-identity package][pypi_azure_identity]. To use the credential types provided by azure-identity, please install the Azure Identity client library for Python with [pip][pip]:

pip install azure-identity

• Additionally, to use the async API, you must first install an async transport, such as aiohttp:

pip install aiohttp

Create client using the azure-identity library:

from azure.schemaregistry import SchemaRegistryClient
from azure.identity import DefaultAzureCredential

credential = DefaultAzureCredential()
# Namespace should be similar to: '<your-eventhub-namespace>.servicebus.windows.net/'
fully_qualified_namespace = os.environ['SCHEMAREGISTRY_FULLY_QUALIFIED_NAMESPACE']
schema_registry_client = SchemaRegistryClient(fully_qualified_namespace, credential)

Create JsonSchemaEncoder using the azure-schemaregistry library:

import os
from azure.schemaregistry import SchemaRegistryClient
from azure.schemaregistry.encoder.jsonencoder import JsonSchemaEncoder
from azure.identity import DefaultAzureCredential

credential = DefaultAzureCredential()
# Namespace should be similar to: '<your-eventhub-namespace>.servicebus.windows.net'
fully_qualified_namespace = os.environ['SCHEMAREGISTRY_FULLY_QUALIFIED_NAMESPACE']
group_name = os.environ['SCHEMAREGISTRY_GROUP']
schema_registry_client = SchemaRegistryClient(fully_qualified_namespace, credential)
encoder = JsonSchemaEncoder(client=schema_registry_client, group_name=group_name)

Key concepts

Client concepts

• Schema: Schema is the organization or structure for data. More detailed information can be found [here][schemas].

• Schema Group: A logical group of similar schemas based on business criteria, which can hold multiple versions of a schema. More detailed information can be found [here][schema_groups].

• SchemaRegistryClient: SchemaRegistryClient provides the API for storing and retrieving schemas in schema registry.

Encoder concepts

• JsonSchemaEncoder: Provides API to encode content to and decode content from Binary Encoding, validate content against a JSON Schema, and cache schemas/schema IDs retrived from the registry using the SchemaRegistryClient locally.

• OutboundMessageContent: Protocol defined under azure.schemaregistry that allows for JsonSchemaEncoder.encode interoperability with certain Azure Messaging SDK message types. Support has been added to:

  • azure.eventhub.EventData for azure-eventhub>=5.9.0

• InboundMessageContent: Protocol defined under azure.schemaregistry that allows for JsonSchemaEncoder.decode interoperability with certain Azure Messaging SDK message types. Support has been added to:

  • azure.eventhub.EventData for azure-eventhub>=5.9.0

OutboundMessageContent/InboundMessageContent

If a message type that follows the OutboundMessageContent protocol is provided to the JsonSchemaEncoder, it will set the corresponding content and content type properties. If a message type object that follows the InboundMessageContent protocol is provided to the encoder, it will get the corresponding content and content type properties. These are defined as:

• content: Binary-encoded, JSON schema-validated payload (in general, format-specific payload)

• content type: a string of the format application/json;serialization=Json+<schema ID>, where:

  • application/json;serialization=Json is the format indicator
  • <schema ID> is the hexadecimal representation of GUID, same format and byte order as the string from the Schema Registry service.

If EventData is passed in as the message type, the following properties will be set on the EventData object:

• The body property will be set to the encoded content value.

• The content_type property will be set to the content type value.

If message type is not provided, and by default, the encoder will create the following dict: {"content": <encoded payload>, "content_type": 'application/json;serialization=Json+<schema ID>'}

Examples

The following sections provide several code snippets covering some of the most common Schema Registry and Json Schema Encoder tasks, including:

• Register a schema

• Get the schema by id

• Get the schema by version

• Get the id of a schema

• Encode

• Decode

• Event Hubs Send Integration

• Event Hubs Receive Integration

Register a schema

Use SchemaRegistryClient.register_schema method to register a schema.

import os

from azure.identity import DefaultAzureCredential
from azure.schemaregistry import SchemaRegistryClient

token_credential = DefaultAzureCredential()
fully_qualified_namespace = os.environ['SCHEMAREGISTRY_AVRO_FULLY_QUALIFIED_NAMESPACE']
group_name = os.environ['SCHEMA_REGISTRY_GROUP']
name = "your-schema-name"
format = "Avro"
definition = """
{"namespace": "example.avro",
 "type": "record",
 "name": "User",
 "fields": [
     {"name": "name", "type": "string"},
     {"name": "favorite_number",  "type": ["int", "null"]},
     {"name": "favorite_color", "type": ["string", "null"]}
 ]
}
"""

schema_registry_client = SchemaRegistryClient(fully_qualified_namespace=fully_qualified_namespace, credential=token_credential)
with schema_registry_client:
    schema_properties = schema_registry_client.register_schema(group_name, name, definition, format)
    id = schema_properties.id

Get the schema by id

Get the schema definition and its properties by schema id.

import os

from azure.identity import DefaultAzureCredential
from azure.schemaregistry import SchemaRegistryClient

token_credential = DefaultAzureCredential()
fully_qualified_namespace = os.environ['SCHEMAREGISTRY_AVRO_FULLY_QUALIFIED_NAMESPACE']
schema_id = 'your-schema-id'

schema_registry_client = SchemaRegistryClient(fully_qualified_namespace=fully_qualified_namespace, credential=token_credential)
with schema_registry_client:
    schema = schema_registry_client.get_schema(schema_id)
    definition = schema.definition
    properties = schema.properties

Get the schema by version

Get the schema definition and its properties by schema version.

import os

from azure.identity import DefaultAzureCredential
from azure.schemaregistry import SchemaRegistryClient

token_credential = DefaultAzureCredential()
fully_qualified_namespace = os.environ['SCHEMAREGISTRY_AVRO_FULLY_QUALIFIED_NAMESPACE']
group_name = os.environ["SCHEMAREGISTRY_GROUP"]
name = "your-schema-name"
version = int("<your schema version>")

schema_registry_client = SchemaRegistryClient(fully_qualified_namespace=fully_qualified_namespace, credential=token_credential)
with schema_registry_client:
    schema = schema_registry_client.get_schema(group_name=group_name, name=name, version=version)
    definition = schema.definition
    properties = schema.properties

Get the id of a schema

Get the schema id of a schema by schema definition and its properties.

import os

from azure.identity import DefaultAzureCredential
from azure.schemaregistry import SchemaRegistryClient

token_credential = DefaultAzureCredential()
fully_qualified_namespace = os.environ['SCHEMAREGISTRY_AVRO_FULLY_QUALIFIED_NAMESPACE']
group_name = os.environ['SCHEMA_REGISTRY_GROUP']
name = "your-schema-name"
format = "Avro"
definition = """
{"namespace": "example.avro",
 "type": "record",
 "name": "User",
 "fields": [
     {"name": "name", "type": "string"},
     {"name": "favorite_number",  "type": ["int", "n