# Kafka Connect Cast SMT Usage Reference for Confluent Platform The Cast SMT (`org.apache.kafka.connect.transforms.Cast`) converts fields, keys, or values of a Apache Kafka® record to a specified primitive type. ## Description The Cast SMT converts record components (such as individual fields, entire keys, or values) into a specified data type, automatically updating the schema if one is present. For example, you can use it to downcast a data type, such as forcing a large integer into a smaller bit-width. `Cast` supports primitive types such as integer, float, boolean, and string. Binary data is also supported, but it can only be cast to a base64-encoded string. Use the specific transformation type designed for the record key (`org.apache.kafka.connect.transforms.Cast$Key`) or value (`org.apache.kafka.connect.transforms.Cast$Value`). ## Properties | Name | Description | Type | Valid values | Importance | |-----------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------|----------------------------------------------------------------------------------------------------|--------------| | `spec` | To cast the entire value, specify a single type (for example,
`string`). To cast individual fields of a Map or Struct, specify a
comma-separated list of `field:type` pairs (for example,
`field1:type1,field2:type2`).

Valid types are:

- `int8`, `int16`, `int32`, `int64`
- `float32`, `float64`
- `boolean`
- `string` | list | comma-separated list of colon-delimited pairs of `field:type`. For example, `foo:int32,bar:string` | high | | `replace.null.with.default` | Specifies whether to replace null fields with their defined default
values. When set to `true`, the default value is applied. Otherwise,
the field remains null. | boolean | `true` or `false`. Defaults to `true`. | medium | ## Examples `Cast` can transform an entire primitive key or value, or one or more fields of a complex (Struct or Map) key or value. The following two examples show how to use `Cast` in these two scenarios. ### Cast a value This example shows how to use `Cast` to transform a 64-bit floating point value into a string. ```json "transforms": "Cast", "transforms.Cast.type": "org.apache.kafka.connect.transforms.Cast$Value", "transforms.Cast.spec": "string" ``` Before: `63521704.02` After: `"63521704.02"` ### Cast fields in a complex key or value This example shows how to use `Cast` with a complex key or value. It shows a comma-separated `field:type` pair, where `field` is the name of the field to cast and `type` is the type to cast the field into. ```json "transforms": "Cast", "transforms.Cast.type": "org.apache.kafka.connect.transforms.Cast$Value", "transforms.Cast.spec": "ID:string,score:float64" ``` The following before-and-after example shows a Map or Struct with an `ID` field of `46290` and a `score` field of `4761`. The SMT casts the `ID` field into a string and the `score` field into a 64-bit floating point value. Before: ```json {"ID": 46290,"score": 4761} ``` After: ```json {"ID": "46290","score": 4761.0} ``` ## Predicates Configure transformations with predicates to ensure they process only records that satisfy a particular condition. You can also use predicates in a transformation chain with the [Kafka Connect Filter (Kafka) SMT Usage Reference for Confluent Platform](filter-ak.md#ak-filter) to conditionally filter specific records. For more information, see [Predicates](filter-ak.md#predicates).