ICU Collation Keyword Fieldedit

Collations are used for sorting documents in a language-specific word order. The icu_collation_keyword field type is available to all indices and will encode the terms directly as bytes in a doc values field and a single indexed token just like a standard Keyword Field.

Defaults to using DUCET collation, which is a best-effort attempt at language-neutral sorting.

Below is an example of how to set up a field for sorting German names in phonebook order:

PUT my_index
{
  "mappings": {
    "properties": {
      "name": {   
        "type": "text",
        "fields": {
          "sort": {  
            "type": "icu_collation_keyword",
            "index": false,
            "language": "de",
            "country": "DE",
            "variant": "@collation=phonebook"
          }
        }
      }
    }
  }
}

GET _search 
{
  "query": {
    "match": {
      "name": "Fritz"
    }
  },
  "sort": "name.sort"
}

The name field uses the standard analyzer, and so support full text queries.

The name.sort field is an icu_collation_keyword field that will preserve the name as a single token doc values, and applies the German phonebook order.

An example query which searches the name field and sorts on the name.sort field.

Parameters for ICU Collation Keyword Fieldsedit

The following parameters are accepted by icu_collation_keyword fields:

doc_values

Should the field be stored on disk in a column-stride fashion, so that it can later be used for sorting, aggregations, or scripting? Accepts true (default) or false.

index

Should the field be searchable? Accepts true (default) or false.

null_value

Accepts a string value which is substituted for any explicit null values. Defaults to null, which means the field is treated as missing.

ignore_above

Strings longer than the ignore_above setting will be ignored. Checking is performed on the original string before the collation. The ignore_above setting can be updated on existing fields using the PUT mapping API. By default, there is no limit and all values will be indexed.

store

Whether the field value should be stored and retrievable separately from the _source field. Accepts true or false (default).

fields

Multi-fields allow the same string value to be indexed in multiple ways for different purposes, such as one field for search and a multi-field for sorting and aggregations.

Collation optionsedit

strength
The strength property determines the minimum level of difference considered significant during comparison. Possible values are : primary, secondary, tertiary, quaternary or identical. See the ICU Collation documentation for a more detailed explanation for each value. Defaults to tertiary unless otherwise specified in the collation.
decomposition
Possible values: no (default, but collation-dependent) or canonical. Setting this decomposition property to canonical allows the Collator to handle unnormalized text properly, producing the same results as if the text were normalized. If no is set, it is the user’s responsibility to insure that all text is already in the appropriate form before a comparison or before getting a CollationKey. Adjusting decomposition mode allows the user to select between faster and more complete collation behavior. Since a great many of the world’s languages do not require text normalization, most locales set no as the default decomposition mode.

The following options are expert only:

alternate
Possible values: shifted or non-ignorable. Sets the alternate handling for strength quaternary to be either shifted or non-ignorable. Which boils down to ignoring punctuation and whitespace.
case_level
Possible values: true or false (default). Whether case level sorting is required. When strength is set to primary this will ignore accent differences.
case_first
Possible values: lower or upper. Useful to control which case is sorted first when case is not ignored for strength tertiary. The default depends on the collation.
numeric
Possible values: true or false (default) . Whether digits are sorted according to their numeric representation. For example the value egg-9 is sorted before the value egg-21.
variable_top
Single character or contraction. Controls what is variable for alternate.
hiragana_quaternary_mode
Possible values: true or false. Distinguishing between Katakana and Hiragana characters in quaternary strength.