Difference between multi field and copy-to in Elastic Search? - elasticsearch

Question

I use multi-fields in a lot of my mappings. In the doc of Elastic Search there is an indication that multi-fields should be replaced with the "fields" parameter. See http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/_multi_fields.html#_multi_fields
This works fine. However, to access a multi-field as a single field the documentation recommends to specify the copy_to parameter instead of the path parameter (see http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/mapping-core-types.html#_accessing_fields)
Can somebody provide an example of such a mapping definition (thus using the "fields" parameter combined with "copy_to").
I have the impression that if you use the fields parameter you still need to specify the path parameter. And if you use copy_to, you no longer need to use a multi-fields approach; the fields just become separate fields and data of one field is copied to another at index time.
Hope somebody can help.
thx
Marc

Answer 1

I think that the copy_to option can be viewed as a cleaner variant of the Multi-fields feature (that is, the fields option). Both of these are easy to use when you want to "copy" values of a field to one or more other fields (to apply different mapping rules). However, if you need to "copy" values from multiple fields to the same field (that is, when you want a custom _all field), you must add the path option to the mapping, if you're using Multi-fields. On the other hand, with the copy_to option, you can simply point multiple source fields to the same destination field.

Answer 2

See this: https://www.elastic.co/guide/en/elasticsearch/reference/1.6/_multi_fields.html
copy_to would allow you to merge different fields like first_name and last_name into full_name
while multi field is used when you want to define several ways to index your field. For example
// Document mapping
{
"properties": {
"name": {
"fields": {
"name_metaphone": {
"type": "string",
"analyzer": "mf_analyzer"
},
"name_exact": {
"index": "not_analyzed",
"type": "string"
}
},
"type": "multi_field"
}
}
}