Elasticsearch获取日期类型的所有字段

Question

I'm using olivere's elastic v.5 Go library (https://godoc.org/gopkg.in/olivere/elastic.v5) for my Elastic queries. If I have an elastic mapping like this:

"mappings": {
        "boxes": {
            "properties": {
                "field1": {
                    "type": "string"
                },
                "field2": {
                    "type": "string"
                },
                "field3": {
                    "type": "date"
                },
                "field4": {
                    "type": "date"
                }
            }
        }

And I want to get a list of all fields that have type 'date'.

I've looked into GetFieldMapping but that doesn't seem to have an option to filter the fields based on type.

I tried this:

elasticclient.GetFieldMapping().Index("someindex").Type("boxes").Field().Type("date").Pretty(true).Do(ctx)

That just gives me all the fields and their types. Is there a different syntax to do this? Thanks!