SQL Topic Filtering

Introduction

Conduktor Gateway's SQL topic feature uses a SQL like language to filter and project messages, based on a simple SQL statement in the form.

SELECT
    type,
    price as amount,
    color,
    CASE
        WHEN color = 'red' AND price > 1000 THEN 'Exceptional'
        WHEN price > 8000 THEN 'Luxury'
        ELSE 'Regular'
    END as quality,
    record.offset as record_offset,
    record.partition as record_partition
  FROM cars

This supports for FetchResponse only: i.e., resulting topic is read-only.

SELECT [list of fields] FROM [topic name] WHERE [field filter criteria]

Please Note: Topic names with dash - characters in them must be double quoted, as the dash is not a valid character for a SQL name. E.g. for a topic our-orders you would need to use:

SELECT * FROM "our-orders" WHERE ...

Currently

• With filter records based on more than one condition, only AND operator current supported
• Predicates are currently supported: =, >, >=, <, <=, <> and REGEXP (RegExp MySQL Operator)
• Support Case Expression
• Filtered by:
  • Record key (It supports SR):
    • Record key as string: - .. WHERE record.key = 'some thing'
    • Record key as schema: .. WHERE record.key.someValue.someChildValue = 'some thing'
  • Record value (It supports SR): .. WHERE $.someValue.someChildValue = 'some thing'
  • Partition: .. WHERE record.partition = 1
  • Timestamp: .. WHERE record.timestamp = 98717823712
  • Header: .. WHERE record.header.someHeaderKey = 'some thing'
  • Offset: .. WHERE record.offset = 1

Schemas and Projections

If your data uses a schema, then it is not possible to make use of the projection feature here because the resulting data will no longer match the original schema. For plain JSON topics you may use the select clause to alter the shape of the data returned as required - however for schema'd data (Avro and Protobuf) you must not use a projection, i.e. the select should be in the form:

SELECT * FROM ...

Filtering with the where clause is still supported.

Configuration

key	type	description
virtualTopic	String	if virtualTopic exists, fetch this topic will get the data from the statement without configure it's own statement.
statement	String	SQL Statement
schemaRegistryConfig	Schema Registry	Schema Registry Config

Schema Registry

Key	Type	Default	Description
type	string	CONFLUENT	The type of schema registry to use: choose CONFLUENT (for Confluent-like schema registries including OSS Kafka) or AWS for AWS Glue schema registries.
additionalConfigs	map		Additional properties maps to specific security-related parameters. For enhanced security, you can hide the sensitive values using environment variables as secrets.​
Confluent Like			Configuration for Confluent-like schema registries
host	string		URL of your schema registry.
cacheSize	string	50	Number of schemas that can be cached locally by this interceptor so that it doesn't have to query the schema registry every time.
AWS Glue			Configuration for AWS Glue schema registries
region	string		The AWS region for the schema registry, e.g. us-east-1
registryName	string		The name of the schema registry in AWS (leave blank for the AWS default of default-registry)
basicCredentials	string		Access credentials for AWS (see below section for structure)
AWS Credentials			AWS Credentials Configuration
accessKey	string		The access key for the connection to the schema registry.
secretKey	string		The secret key for the connection to the schema registry.
validateCredentials	bool	true	true / false flag to determine whether the credentials provided should be validated when set.
accountId	string		The Id for the AWS account to use.

If you don't supply a basicCredentials section for the AWS Glue schema registry, the client used to connect will attempt to find the connection information from the environment. The required credentials can be passed to Gateway in this way as part of core configuration.

Find out more about the setup for this from AWS documentation.

See more about schema registry here

Example

{
  "name": "mySqlTopicPlugin",
  "pluginClass": "io.conduktor.gateway.interceptor.VirtualSqlTopicPlugin",
  "priority": 100,
  "config": {
    "virtualTopic": "legal_user",
    "statement": "SELECT * FROM users WHERE age > 18",
    "schemaRegistryConfig": {
       "host": "http://schema-registry:8081"
    }
  }
}

Schema Registry with secured template

{
  "name": "mySqlTopicPlugin",
  "pluginClass": "io.conduktor.gateway.interceptor.VirtualSqlTopicPlugin",
  "priority": 100,
  "config": {
    "virtualTopic": "legal_user",
    "statement": "SELECT * FROM users WHERE age > 18",
    "schemaRegistryConfig": {
      "host": "http://schema-registry:8081",
      "additionalConfigs": {
        "schema.registry.url": "${SR_URL}",
        "basic.auth.credentials.source": "${SR_BASIC_AUTH_CRED_SRC}",
        "basic.auth.user.info": "${SR_BASIC_AUTH_USER_INFO}"
      }
    }
  }
}