# Kafka Connect Drop SMT Usage Reference for Confluent Cloud The `io.confluent.connect.transforms.Drop` Confluent Single Message Transformation (SMT) nullifies a record’s key or value. Use the `schema.behavior` property to control schema modifications: * `nullify`: Nullifies the target schema with the payload. * `retain`: Retains the schema as-is. * `validate`: Verifies that the schema is already optional. * `force_optional`: Forces the schema to be optional. Use the concrete transformation type designed for the record key (`io.confluent.connect.transforms.Drop$Key`) or value (`io.confluent.connect.transforms.Drop$Value`). ## Installation This transformation is developed by Confluent and does not ship by default with Apache Kafka® or Confluent Cloud. You can install this transformation using the [confluent connect plugin install](https://docs.confluent.io/confluent-cli/current/command-reference/connect/plugin/confluent_connect_plugin_install.html) command: ```properties confluent connect plugin install confluentinc/connect-transforms:latest ``` ## Examples The configuration snippets below show how to use and configure the `Drop` SMT. Drop the key from the message, using the default behavior for schemas, which nullifies the keys if they are not already null. ```json "transforms": "dropKeyExample", "dropValueAndForceOptionalSchemaExample", "transforms.dropKeyExample.type": "io.confluent.connect.transforms.Drop$Key" ``` Drop the value from the message. If the schema for the value isn’t already optional, forcefully overwrite it to become optional. ```json "transforms.dropValueAndForceOptionalSchemaExample.type": "io.confluent.connect.transforms.Drop$Value", "transforms.dropValueAndForceOptionalSchemaExample.schema.behavior": "force_optional" ``` Record contents using `Drop$Key` with `schema.behavior` set to `nullify`: ```json "transforms.dropValueAndForceOptionalSchemaExample.type": "io.confluent.connect.transforms.Drop$Key", "transforms.dropValueAndForceOptionalSchemaExample.schema.behavior": "nullify" ``` * Before: `key: 24`, `schema: {"type": "integer"}` * After: `key: null`, `schema: null`
The key is nullified and the schema is nullified. Record contents using `Drop$Key` with `schema.behavior` set to `retain`: ```json "transforms.dropValueAndForceOptionalSchemaExample.type": "io.confluent.connect.transforms.Drop$Key", "transforms.dropValueAndForceOptionalSchemaExample.schema.behavior": "retain" ``` * Before: `key: 24`, `schema: {"type": "integer"}` * After: `key: null`, `schema: {"type": "integer"}`
The key is nullified and the schema is unchanged. Record contents using `Drop$Key` with `schema.behavior` set to `validate` where the schema is not optional: ```json "transforms.dropValueAndForceOptionalSchemaExample.type": "io.confluent.connect.transforms.Drop$Key", "transforms.dropValueAndForceOptionalSchemaExample.schema.behavior": "validate" ``` * Before: `key: 24`, `schema: {"type": "integer"}` * After: Throws exception because the schema is not optional.
Record contents using `Drop$Key` with `schema.behavior` set to `validate`, where the schema is optional: ```json "transforms.dropValueAndForceOptionalSchemaExample.type": "io.confluent.connect.transforms.Drop$Key", "transforms.dropValueAndForceOptionalSchemaExample.schema.behavior": "validate" ``` * Before: `key: 24`, `schema: {"type": "integer", "optional": true}` * After: `key: null`, `schema: {"type": "integer", "optional": true}`
The key is nullified and the schema is unchanged. Record contents using `Drop$Key` with `schema.behavior` set to `force_optional`, where the schema is not optional: ```json "transforms.dropValueAndForceOptionalSchemaExample.type": "io.confluent.connect.transforms.Drop$Key", "transforms.dropValueAndForceOptionalSchemaExample.schema.behavior": "force_optional" ``` * Before: `key: 24`, `schema: {"type": "integer"}` * After: `key: null`, `schema: {"type": "integer", "optional": "true"}`
The key is nullified and the schema is made optional. Record contents using `Drop$Key` with `schema.behavior` set to `force_optional`, where the schema is already optional: ```json "transforms.dropValueAndForceOptionalSchemaExample.type": "io.confluent.connect.transforms.Drop$Key", "transforms.dropValueAndForceOptionalSchemaExample.schema.behavior": "force_optional" ``` * Before: `key: 24`, `schema: {"type": "integer", "optional": true}` * After: `key: null`, `schema: {"type": "integer", "optional": true}` The key is nullified and the schema is unchanged. ## Properties | Name | Description | Type | Default | Valid Values | Importance | |-------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------|-----------|---------------------------------------------|--------------| | `schema.behavior` | How to handle non-null schemas. If set to `nullify`, then the schema for the new record is null. If set to `retain`, the schema is used, regardless of whether it is optional. If set to `validate`, the schema is checked first, and if it is optional, it is used as-is; otherwise, an exception is thrown. If set to `force_optional`, the schema is overwritten to be optional, if it is not already. | string | nullify | [nullify, retain, validate, force_optional] | medium | ## Predicates Transformations can be configured with *predicates* so that the transformation is applied only to records which satisfy a condition. You can use predicates in a transformation chain and, when combined with the [Kafka Connect Filter (Kafka) SMT Usage Reference for Confluent Cloud](filter-ak.md#ak-filter), predicates can conditionally filter out specific records. For details and examples, see [Predicates](filter-ak.md#predicates).