Dot expander processor | Elasticsearch Guide [8.2]

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Dot expander processoredit

Expands a field with dots into an object field. This processor allows fields with dots in the name to be accessible by other processors in the pipeline. Otherwise these fields can’t be accessed by any processor.

Table 14. Dot Expand Options

Name	Required	Default	Description
`field`	yes	-	The field to expand into an object field. If set to `*`, all top-level fields will be expanded.
`path`	no	-	The field that contains the field to expand. Only required if the field to expand is part another object field, because the `field` option can only understand leaf fields.
`override`	no	false	Controls the behavior when there is already an existing nested object that conflicts with the expanded field. When `false`, the processor will merge conflicts by combining the old and the new values into an array. When `true`, the value from the expanded field will overwrite the existing value.
`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.

{
  "dot_expander": {
    "field": "foo.bar"
  }
}

For example the dot expand processor would turn this document:

{
  "foo.bar" : "value"
}

into:

{
  "foo" : {
    "bar" : "value"
  }
}

If there is already a bar field nested under foo then this processor merges the foo.bar field into it. If the field is a scalar value then it will turn that field into an array field.

For example, the following document:

{
  "foo.bar" : "value2",
  "foo" : {
    "bar" : "value1"
  }
}

is transformed by the dot_expander processor into:

{
  "foo" : {
    "bar" : ["value1", "value2"]
  }
}

Contrast that with when the override option is set to true.

{
  "dot_expander": {
    "field": "foo.bar",
    "override": true
  }
}

In that case, the value of the expanded field overrides the value of the nested object.

{
  "foo" : {
    "bar" : "value2"
  }
}

The value of field can also be set to a * to expand all top-level dotted field names:

{
  "dot_expander": {
    "field": "*"
  }
}

The dot expand processor would turn this document:

{
  "foo.bar" : "value",
  "baz.qux" : "value"
}

into:

{
  "foo" : {
    "bar" : "value"
  },
  "baz" : {
    "qux" : "value"
  }
}

If any field outside of the leaf field conflicts with a pre-existing field of the same name, then that field needs to be renamed first.

Consider the following document:

{
  "foo": "value1",
  "foo.bar": "value2"
}

Then the foo needs to be renamed first before the dot_expander processor is applied. So in order for the foo.bar field to properly be expanded into the bar field under the foo field the following pipeline should be used:

{
  "processors" : [
    {
      "rename" : {
        "field" : "foo",
        "target_field" : "foo.bar"
      }
    },
    {
      "dot_expander": {
        "field": "foo.bar"
      }
    }
  ]
}

The reason for this is that Ingest doesn’t know how to automatically cast a scalar field to an object field.

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