func (s *IndicesGetFieldMappingService) Do(ctx context.Context) (map[string]interface{}, error) {
	var ret map[string]interface{}
	if err := s.Validate(); err != nil {
		return nil, err
	}
	path, params, err := s.buildURL()
	if err != nil {
		return nil, err
	}
	res, err := s.client.PerformRequest(ctx, "GET", path, params, nil)
	if err != nil {
		return nil, err
	}
	if err := s.client.decoder.Decode(res.Body, &ret); err != nil {
		return nil, err
	}
	return ret, nil
}
Do executes the operation. It returns mapping definitions for an index
or index/type.
package elastic
import (
	"context"
	"fmt"
	"net/url"
	"strings"
	"gopkg.in/olivere/elastic.v5/uritemplates"
)
type IndicesGetFieldMappingService struct {
	client            *Client
	pretty            bool
	index             []string
	typ               []string
	field             []string
	local             *bool
	ignoreUnavailable *bool
	allowNoIndices    *bool
	expandWildcards   string
}
func NewGetFieldMappingService(client *Client) *IndicesGetFieldMappingService {
	return NewIndicesGetFieldMappingService(client)
}
func NewIndicesGetFieldMappingService(client *Client) *IndicesGetFieldMappingService {
	return &IndicesGetFieldMappingService{
		client: client,
	}
}
func (s *IndicesGetFieldMappingService) Index(indices ...string) *IndicesGetFieldMappingService {
	s.index = append(s.index, indices...)
	return s
}
func (s *IndicesGetFieldMappingService) Type(types ...string) *IndicesGetFieldMappingService {
	s.typ = append(s.typ, types...)
	return s
}
func (s *IndicesGetFieldMappingService) Field(fields ...string) *IndicesGetFieldMappingService {
	s.field = append(s.field, fields...)
	return s
}
func (s *IndicesGetFieldMappingService) AllowNoIndices(allowNoIndices bool) *IndicesGetFieldMappingService {
	s.allowNoIndices = &allowNoIndices
	return s
}
func (s *IndicesGetFieldMappingService) ExpandWildcards(expandWildcards string) *IndicesGetFieldMappingService {
	s.expandWildcards = expandWildcards
	return s
}
func (s *IndicesGetFieldMappingService) Local(local bool) *IndicesGetFieldMappingService {
	s.local = &local
	return s
}
func (s *IndicesGetFieldMappingService) IgnoreUnavailable(ignoreUnavailable bool) *IndicesGetFieldMappingService {
	s.ignoreUnavailable = &ignoreUnavailable
	return s
}
func (s *IndicesGetFieldMappingService) Pretty(pretty bool) *IndicesGetFieldMappingService {
	s.pretty = pretty
	return s
}
func (s *IndicesGetFieldMappingService) buildURL() (string, url.Values, error) {
	var index, typ, field []string
	if len(s.index) > 0 {
		index = s.index
	} else {
		index = []string{"_all"}
	}
	if len(s.typ) > 0 {
		typ = s.typ
	} else {
		typ = []string{"_all"}
	}
	if len(s.field) > 0 {
		field = s.field
	} else {
		field = []string{"*"}
	}
	path, err := uritemplates.Expand("/{index}/_mapping/{type}/field/{field}", map[string]string{
		"index": strings.Join(index, ","),
		"type":  strings.Join(typ, ","),
		"field": strings.Join(field, ","),
	})
	if err != nil {
		return "", url.Values{}, err
	}
	params := url.Values{}
	if s.pretty {
		params.Set("pretty", "1")
	}
	if s.ignoreUnavailable != nil {
		params.Set("ignore_unavailable", fmt.Sprintf("%v", *s.ignoreUnavailable))
	}
	if s.allowNoIndices != nil {
		params.Set("allow_no_indices", fmt.Sprintf("%v", *s.allowNoIndices))
	}
	if s.expandWildcards != "" {
		params.Set("expand_wildcards", s.expandWildcards)
	}
	if s.local != nil {
		params.Set("local", fmt.Sprintf("%v", *s.local))
	}
	return path, params, nil
}
func (s *IndicesGetFieldMappingService) Validate() error {
	return nil
}