Single Message Transforms (SMT), introduced withKIP-66, have greatly improved Connector's usability by enabling the transformation of input/output data formats and contents without the need for additional streaming applications.

However, these benefits have been limited by SMTs SMT's limitation to only act on fields available at the root of the data structure.

...

Proposed Changes

Nested notation

Using dots Dotted notation tends to be the most intuitive way to describe the path paths to nested fields in a record structures, structure and will cover most of the scenarios. e.g. jq already uses it[1], and will cover most of the scenarios.

However, dots are already allowed as part of element names on JSON (i.e. Schemaless) records(e.field names in JSON could include dots(e.g. {'nested.keyfield': {'value':42}}).

Therefore, the nested notation must support escaping dots that could be valid field names.

Instead of escaping dots with backslashes — which in JSON configurations will lead leads to unfriendly configurations — it's proposed to follow a similar approach as the JSONata[2] where backticks are used to add define field names with dots using backticks, e.g. `nested.key`.valuefield`

[1] https://stedolan.github.io/jq/manual/#Basicfilters

...

> Field references containing whitespace or reserved tokens can be enclosed in backticks

Rules

1. If field names do not contain dots (.), then only use dots to represent nested fieldsfield paths.
2. If field names contain dots, then:
- wrap the field name with a backtick pair (`...`) by
  - adding an opening backtick at the beginning of the field name (beginning of a path, or after a dot)
  - adding a closing backtick at the end of the field name (end of the path, or before the next dot)
- if If a field is wrapped and doesn't contain dots, is processed the same way: field name within the wrapping backticks is used
3. If a field name includes backticks, then:
- if the backticks are in a wrapping position (opening or closing a field name), then need to If a backtick is followed by a dot in the field name, then the backtick should be escaped with a backslash to signal that the backtick is part of the name and not closing a backtick pair.
  - Backslashes (\) do not need to be escaped. If the backslash happen happens to be part of the field name and before a backtick is to be escaped, then add another backslash.
- else, backticks do not require escape
4. If wrapping backtick pairs are incomplete, the Connect configuration must fail fast to avoid getting ambiguous paths deployed.

...

Scenario	Nested struct	Path
Normal (no dots or backticks on field names)	foo: bar: baz: val	OK: foo.bar.baz
2. Field names including dots	foo: bar.baz: val	OK: foo.`bar.baz`
2.1 Using backticks within a field name without dots	foo: bar: baz: val	OK: foo.bar.baz ERROR: foo.`bar.baz: no pair ERROR: foo.bar`.baz: no pair
3. Field names including backticks	foo: ba`r: baz: val	OK: foo.ba`r.baz OK: foo.`ba`r`.baz
3.1. Field names including backticks at the wrapping position	foo: bar`.`baz: val	OK: foo.`bar\`.\`baz` ERROR: foo.`bar\`.`baz`: no pair ERROR: foo.`bar`.`baz`: valid but different path (see 2.1)
3.2. Field names including dots and backticks between a backtick pair	foo: b`ar.baz: val	OK: foo.`b`ar.baz`
3.3. Field names including backslash and backticks at the wrapping position	foo: bar\`.`baz: val	OK: foo.`bar\\`.\`baz`
3.4. Field names wrapped by backticks	foo: `bar`: baz: val	OK: foo.`\`bar\``.baz ERROR: foo.`bar`.baz: valid but different path (see 2.1)

...

These SMTs will include support for nested structurestructures:

Cast
ExtractField
HeaderFrom
MaskField
ReplaceField
TimestampConverter
ValueToKey
InsertField
HoistField

...

Name Type Default Importance Documentation

field.syntax.version

STRING

V1

HIGH

Permitted values: V1 , V2 . Defines the version of the syntax to access fields. If set to "V1", then the field paths are limited to access the elements at the root level of the struct or map. If set to "V2", the syntax will support accessing nested elements. o To access nested elements, dotted notation is used. If dots are already included in the field name, then backtick pairs can be used to wrap field names containing dots. e.g. to access elements from a struct/map named "foo.bar", the following format can be used to access its elements: "`foo.bar`.baz".

This configuration will affect all the field paths used by the transform.

...

Extend spec to support nested notation.

Examples:

scenario

input

smtSMT

output

1. Nested field.

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.Cast$Value",
"transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.spec": "k1:string,parent.child.k2:int64"
}

Code Block

language	js

{
  "k1": "123",
  "parent": {
    "child": {
      "k2": 123    
    }
  }
}

2. Nested field, when field names include dots

Code Block

language	js

{
  "k1": 123,
  "parent.child": {
    "k2": "123"
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.Cast$Value",
"transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.spec": "k1:string,`parent.child`.k2:int64"
}

Code Block

language	js

{
  "k1": "123",
  "parent.child": {
    "k2": 123
  }
}

...

Extend field to support nested notation.

Example:

scenario

input

smtSMT

output

1. Nested field.

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.ExtractField$Value",
"transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.field": "parent.child.k2"
}

Code Block

language	js

"123"

2. Nested field, when field names include dots

Code Block

language	js

{
  "k1": 123,
  "parent.child": {
    "k2": "123"
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.ExtractField$Value",
"transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.field": "`parent.child`.k2"
}

Code Block

language	js

"123"

3. Nested field, an object returned.

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.ExtractField$Value",
"transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.field": "parent.child"
}

Code Block

language	js

{ "k2": "123" }

...

Extend fields to support nested notation.

Example:

scenario

input

smtSMT

output

1. Nested field.

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.HeaderFrom$Value",
"transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.fields": "k1,parent.child.k2",
"transforms.smt1.headers": "k1,k2"
}

Code Block

language	js

headers:
- k1=123
- k2="123"

2. Nested field, when field names include dots

Code Block

language	js

{
  "k1": 123,
  "parent.child": {
    "k2": "123"
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.HeaderFrom$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.fields": "k1,`parent.child`.k2",
"transforms.smt1.headers": "k1,k2"
}

Code Block

language	js

headers:
- k1=123
- k2="123"

...

Extend fields to support nested notation.

Example:

scenario

input

smtSMT

output

1. Nested field.

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.MaskField$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.fields": "parent.child.k2"
}

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": ""    
    }
  }
}

2. Nested field, when field names include dots

Code Block

language	js

{
  "k1": 123,
  "parent.child": {
    "k2": "123"
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.MaskField$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.fields": "`parent.child`.k2"
}

Code Block

language	js

{
  "k1": 123,
  "parent.child": {
    "k2": ""
  }
}

...

Extend theinclude and exclude lists

Example:

scenario

input

smtSMT

output

1. Nested field. Drop field

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.ReplaceField$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.exclude": "parent.child.k2"
}

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
    }
  }
}

2. Nested field. Drop struct

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.ReplaceField$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.exclude": "parent.child"
}

Code Block

language	js

{
  "k1": 123,
  "parent": {
  }
}

3. Nested field. Include field

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123",
      "k3": "234"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.ReplaceField$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.include": "parent.child.k2"
}

Code Block

language	js

{
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

4. Nested field. Include struct

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123",
      "k3": "234"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.ReplaceField$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.include": "parent.child"
}

Code Block

language	js

{
  "parent": {
    "child": {
      "k2": "123",
      "k3": "234"    
    }
  }
}

5. Nested field, when field names include dots

Code Block

language	js

{
  "k1": 123,
  "parent.child": {
    "k2": "123"
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.ReplaceField$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.renames": "`parent.child`.k2:field2"
}

Code Block

language	js

{
  "k1": 123,
  "parent.child": {
   "field2": "123"
  }
}

...

Extend fields to support nested notation.

Example:

scenario

input

smtSMT

output

1. Nested field.

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": 1556204536000         }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.TimestampConverter$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.field": "parent.child.k2",
"transforms.smt1.format": "yyyy-MM-dd",
"transforms.smt1.target.type": "string"
}

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "2014-04-25"         }
  }
}

2. Nested field, when field names include dots

Code Block

language	js

{
  "k1": 123,
  "parent.child": {
      "k2": 1556204536000         }
  }
}

Code Block

language	js



{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.TimestampConverter$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.field": "`parent.child`.k2",
"transforms.smt1.format": "yyyy-MM-dd",
"transforms.smt1.target.type": "string"
}

Code Block

language	js

{
  "k1": 123,
  "parent.child": {      "k2": "2014-04-25"   }
}

...

Extend fields to support nested notation.

Example:

scenario

input

smtSMT

output

1. Nested field.

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.ValueToKey", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.fields": "parent.child.k2"
}

Code Block
"123"

2. Nested struct to Key.

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.ValueToKey", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.fields": "parent.child"
}

Code Block
{ "k2": "123" }

3. Nested field, when field names include dots

Code Block

language	js

{
  "k1": 123,
  "parent.child": {
    "k2": "123"
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.ValueToKey", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.fields": "`parent.child`.k2"
}

Code Block

language	js

"123"

...

Name	Type	Default	Importance	Documentation
`field.on.missing.parent`	STRING	create	`MEDIUM`	Permitted values: `create`, `ignore`. Defines how to react when the field to act on does not have a parent and "field.style" is "nested". If set to "create", then the SMT will create the parent struct/map when it does not exist. If set to "ignore", then it will SMT have no effect.
`field.on.existing.field`	STRING	overwrite	`MEDIUM`	Permitted values: `overwrite`, `ignore`. Defines how to react when the field to act on already exists. If set to "overwrite", then the SMT will be applied to the existing field. If set to "ignore", then it will SMT have no effect.

Example:

scenario

input

smtSMT

output

1. Nested field.

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.InsertField$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.static.field": "parent.child.k3"
"transforms.smt1.static.value": "v3" 
}

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123",
      "k3": "v3"   
    }
  }
}

2. Nested field, when field names include dots

Code Block

language	js

{
  "k1": 123,
  "parent.child": {
    "k2": "123"
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.InsertField$Value",  "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.static.field": "`parent.child`.k3"
"transforms.smt1.static.value": "v3" 
}

Code Block

language	js

{
  "k1": 123,
  "parent.child": {
    "k2": "123",
    "k3": "v3"
  }
}

3. Nested field with the parent missing

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.InsertField$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.static.field": "parent.other.k3"
"transforms.smt1.static.value": "v3" 
}

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"  
    },
    "other": {
      "k3": "v3"  
    }
  }
}

4. Nested field with the parent missing, and ignore is set

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.InsertField$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.static.field": "parent.other.k3"
"transforms.smt1.static.value": "v3",
"transforms.smt1.field.on.missing.parent": "ignore"
}

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"  
    }
  }
}

5. Nested field with the parent missing

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.InsertField$Value",  "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.static.field": "parent.child.k2"
"transforms.smt1.static.value": "456"
}

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "456"  
    }
  }
}

6. Nested field with the parent missing, and ignore is set

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.InsertField$Value",  "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.static.field": "parent.child.k2"
"transforms.smt1.static.value": "456",
"transforms.smt1.field.on.existing.field": "ignore"
}

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"  
    }
  }
}

...

Name	Type	Default	Importance	Documentation
`hoisted`	`STRING`	<empty>	`MEDIUM`	Path to the element to be hoisted. If empty, the root struct/map is hoisted.

Examples:

scenario

input

smtSMT

output

1. Nested field.

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "k2": "123"    
    }
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.HoistFIeld$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.hoisted": "parent.child.k2",
"transforms.smt1.field": "other"
}

Code Block

language	js

{
  "k1": 123,
  "parent": {
    "child": {
      "other": {
        "k2": "123"
      }    
    }
  }
}

2. Nested struct, when field names include dots

Code Block

language	js

{
  "k1": 123,
  "parent.child": {
    "k2": "123"
  }
}

Code Block

language	js

{
"transforms": "smt1",
"transforms.smt1.type": "org.apache.kafka.connect.transforms.HoistFIeld$Value", "transforms.smt1.field.syntax.version": "v2",
"transforms.smt1.hoisted": "`parent.child`",
"transforms.smt1.field": "other"
}

Code Block

language	js

{
  "k1": 123,
  "other": {
    "parent.child": {
      "k2": "123"
    }
  }
}

...

Existing SMT configurations will not be affected by these changes as the default field.style is plain, which represents the current behavior and users will need to opt-in the the new notation.

Rejected Alternatives

Keep `ExtractField` as it is and use it multiple times until reaching nested fields

...

However, backslashes are also used by JSON. This could lead to unfriendly configurations like "this\\\\.is\\\\.not\\\\.very\\\\.readable"

...

Even if using custom separators represent represents a more explicit configuration, there is always the possibility that all the separators are already included as part of the field name, leading to issues and request requests for changes.

To avoid this, this KIP proposes using the approach to precede dots with another to escape itself.

...

The JSONPath spec is too extensive for the use - cases included in this KIP.
A sub-set of JSONPath was proposed, but the custom spec ends up being more complex than the notation proposed here.
- A sub-set will imply not using existing dependencies. Though However, adding an existing dependency would also reduce the chance of the KIP being accepted as the risk for external vulnerabilities will increase.
- The sub-set will require users to learn JSONPath, and then what's covered and what's not by the custom implementation.

Given these cons, the KIP is preferring prefers the dotted notation.

[1] https://github.com/json-path/JsonPath

...

field.style with valid values: "plain", and "nested".

Even though this configuration is self-describing, it limits the semantics of the values.

...

Double dot is often used in JSON Path as a descendant selector, see https://www.ietf.org/id/draft-ietf-jsonpath-base-05.html

This may cause confusion on confuse users. To avoid this, the backtick approach is proposed in this KIP.

...

Adding notation for arrays (e.g. [], or array.<offset>) to access to array elements and apply SMTs to fields within the array.

...

Space shortcuts

Child pages

Versions Compared

Old Version 36

New Version Current

Key

Proposed Changes

Nested notation

Rules

Rejected Alternatives

Keep `ExtractField` as it is and use it multiple times until reaching nested fields

Space shortcuts

Child pages

Page History

Versions Compared

Old Version 36

New Version Current

Key

Proposed Changes

Nested notation

Rules

Rejected Alternatives

Keep ExtractField as it is and use it multiple times until reaching nested fields

Keep `ExtractField` as it is and use it multiple times until reaching nested fields