= Transformations

Connectors can be configured with transformations to make lightweight per message modifications. {prodname} provides several link:{link-kafka-docs}/#connect_transforms[single message transformations] (SMTs) that you can use to either modify records before they are sent to Apache Kafka (by applying them to the {prodname} connectors), or when they are read from Kafka by a sink connector. Also xref:{link-debezium-server}[{prodname} Server] supports the usage of SMTs.

The following SMTs are provided by {prodname}:

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|===
|Transform
|Description

|xref:transformations/topic-routing.adoc[Topic Routing]
|Re-routes records to different topics based on a regular expression applied to the original topic name.

|xref:transformations/content-based-routing.adoc[Content-Based Routing]
|Reroute selected events to other topics, based on the event content.

|xref:transformations/event-flattening.adoc[New Record State Extraction]
|Extracts the flat structure of field names and values from Debezium change events, facilitating sink connectors which cannot process Debezium's complex event structure.

|xref:transformations/mongodb-event-flattening.adoc[MongoDB New Document State Extraction]
|The MongoDB-specific counter-part to the xref:transformations/event-flattening.adoc[New Record State Extraction] SMT.

|xref:transformations/outbox-event-router.adoc[Outbox Event Router]
|Provides a way to safely and reliably exchange data between multiple (micro) services.

|xref:transformations/mongodb-outbox-event-router.adoc[MongoDB Outbox Event Router]
|The MongoDB-specific counter-part to the xref:transformations/outbox-event-router.adoc[Outbox Event Router] SMT.

|xref:transformations/filtering.adoc[Message Filtering]
|Applies a filter to the change events emitted by the connectors, based on their content. This lets you propagate only those records that are relevant to you.

|xref:transformations/header-to-value.adoc[HeaderToValue]
|Moves or copies headers into the record value.

|xref:transformations/partition-routing.adoc[Partition Routing]
|Re-routes records to specific partitions based on configured payload fields.

|xref:transformations/timezone-converter.adoc[Timezone Converter]
|Converts {prodname} and Kafka Connect timestamp fields in event records to a specified timezone.

|xref:transformations/timescaledb.adoc[TimescaleDB Integration]
|Routes and enriches messages that the {prodname} PostgreSQL connector captures from a TimescaleDB.

|xref:transformations/decode-logical-decoding-message-content.adoc[Decode Logical Decoding Message Content]
|Converts the binary content of logical decoding messages captured by the {prodname} PostgreSQL connector into a structured form.

|xref:transformations/vitess-use-local-vgtid.adoc[Vitess Use Local VGTID]
|A transformation that reduces the size of VGTIDs that the Vitess connector emits.
To reduce the amount of data in the event message, the SMT writes only the VGTID for the shard in which a change occurs.
The VGTIDs for other shards are removed.
This transformation is designed for use only with the {prodname} connector for Vitess.

|xref:transformations/vitess-remove-field.adoc[Vitess Remove Field]
|The Vitess-specific transformation to remove fields to reduce the size of the messages written (e.g., redundant VGTID fields).

|xref:transformations/vitess-replace-field-value.adoc[Vitess Replace Field Value]
|The Vitess-specific transformation to replace the value of a field to reduce the size of the messages written (e.g., redundant VGTID fields).

|xref:transformations/vitess-filter-transaction-topic-records.adoc[Vitess Filter Transaction Topic Records]
|A transformation that filters out all messages that the connector emits to the transaction topic (when transaction metadata is enabled).
This transformation is designed for use only with the {prodname} connector for Vitess.

|===

By means of xref:transformations/applying-transformations-selectively.adoc[SMT Predicates] you can apply any of the transformations selectively, so that it modifies only that subset of change event messages that share a common characteristic.

[NOTE]
====
Most of the above SMTs are available by default with the {prodname} container image, but you need to opt-in for the scripting-based ones (Message Filtering or Content-based Routing). See the link:https://github.com/debezium/container-images/tree/main/connect/1.7#enable_debezium_scripting[README] file of the container image for more details.
====
