Add a multivalued property to field mappings (#16420)

[normanj-bitquill]

Description

A mapping for a field can now contain a property multivalued. multivalued must have a boolean value. It can only be applied to field types that support multiple values.

If the multivalued property has never been set for a field, then it is assumed to be false and will not be returned in the index mapping.

If multivalued is set to false, then there is not change in behaviour except for including multivalued in the index mapping.

If multivalued is set to true, then it is returned in the index mapping. In addition, any new documents inserted must have an array value for the field with multivalued set to true.

The multivalued property is intended to be useful to services that consume index mappings. It indicates that the field will should only contain array values. As an example, the SQL plugin can this to decide on how to process an aggregate operation such as MIN or MAX.

An example mapping that uses multivalued:

{
  "test_integer": {
    "mappings": {
      "properties": {
        "x": {
          "type": "long"
        },
        "y": {
          "type": "integer",
          "multivalued": true
        }
      }
    }
  }
}

Related Issues

Resolves #16420
Relates to: SQL #3137
Relates to: SQL #3138

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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