Major Description
Kafka Connect's schema system defines several core types that consist of:
- STRUCT
- ARRAY
- MAP
plus these primitive types:
- INT8
- INT16
- INT32
- INT64
- FLOAT32
- FLOAT64
- BOOLEAN
- STRING
- BYTES
The Schema for these core types define several attributes, but they do not have a name.
Kafka Connect also defines several logical types that are specializations of the primitive types and do have schema names and are automatically mapped to/from Java objects:
| Schema Name | Primitive Type | Java value class | Description |
|---|---|---|---|
| o.k.c.d.Decimal | BYTES | java.math.BigDecimal | An arbitrary-precision signed decimal number. |
| o.k.c.d.Date | INT32 | java.util.Date | A date representing a calendar day with no time of day or timezone. The java.util.Date value's hours, minutes, seconds, milliseconds are set to 0. The underlying representation is an integer representing the number of standardized days (based on a number of milliseconds with 24 hours/day, 60 minutes/hour, 60 seconds/minute, 1000 milliseconds/second with n) since Unix epoch. |
| o.k.c.d.Time | INT32 | java.util.Date | A time representing a specific point in a day, not tied to any specific date. Only the java.util.Date value's hours, minutes, seconds, and milliseconds can be non-zero. This effectively makes it a point in time during the first day after the Unix epoch. The underlying representation is an integer representing the number of milliseconds after midnight. |
| o.k.c.d.Timestamp | INT32 | java.util.Date | A timestamp representing an absolute time, without timezone information. The underlying representation is a long representing the number of milliseconds since Unix epoch. |
where "o.k.c.d" is short for org.kafka.connect.data. ewencp has stated in the past that adding more logical types is challenging and generally undesirable, since everyone use Kafka Connect values have to deal with all new logical types.
This proposal adds standard semantic types that are somewhere between the core types and logical types. Basically, they are just predefined schemas that have names and are based on other primitive types. However, there is no mapping to another form other than the primitive.
The purpose of semantic types is to provide hints as to how the values can be treated. Of course, clients are free to ignore the hints of some or all of the built-in semantic types, and in these cases would treat the values as the primitive value with no extra semantics. This behavior makes it much easier to add new semantic types over time without risking incompatibilities.
Really, any source connector can define custom semantic types, but there is tremendous value in having a library of standard, well-known semantic types, including:
| Schema Name | Primitive Type | Description |
|---|---|---|
| o.k.c.d.Uuid | STRING | A UUID in string form. |
| o.k.c.d.Json | STRING | A JSON document, array, or scalar in string form. |
| o.k.c.d.Xml | STRING | An XML document in string form. |
| o.k.c.d.BitSet | STRING | A string of zero or more 0 or 1 characters. |
| o.k.c.d.ZonedTime | STRING | An ISO-8601 formatted representation of a time (with fractional seconds) with timezone or offset from UTC. |
| o.k.c.d.ZonedTimestamp | STRING | An ISO-8601 formatted representation of a timestamp with timezone or offset from UTC. |
| o.k.c.d.EpochDays | INT64 | A date with no time or timezone information, represented as the number of days since (or before) epoch, or January 1, 1970, at 00:00:00UTC. |
| o.k.c.d.Year | INT32 | The year number. |
| o.k.c.d.MilliTime | INT32 | Number of milliseconds past midnight. |
| o.k.c.d.MicroTime | INT64 | Number of microseconds past midnight. |
| o.k.c.d.NanoTime | INT64 | Number of nanoseconds past midnight. |
| o.k.c.d.MilliTimestamp | INT64 | Number of milliseconds past epoch. |
| o.k.c.d.MicroTimestamp | INT64 | Number of microseconds past epoch. |
