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Lowercase processor

Converts a string to its lowercase equivalent. If the field is an array of strings, all members of the array will be converted.

Table 29. Lowercase Options

Name	Required	Default	Description
`field`	yes	-	The field to make lowercase
`target_field`	no	`field`	The field to assign the converted value to, by default `field` is updated in-place
`ignore_missing`	no	`false`	If `true` and `field` does not exist or is `null`, the processor quietly exits without modifying the document
`description`	no	-	Description of the processor. Useful for describing the purpose of the processor or its configuration.
`if`	no	-	Conditionally execute the processor. See Conditionally run a processor.
`ignore_failure`	no	`false`	Ignore failures for the processor. See Handling pipeline failures.
`on_failure`	no	-	Handle failures for the processor. See Handling pipeline failures.
`tag`	no	-	Identifier for the processor. Useful for debugging and metrics.

{
  "lowercase": {
    "field": "foo"
  }
}

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https://www.elastic.co/guide/en/elasticsearch/reference/7.17/lowercase-processor.html