Add TermsLookup to TermsQuery

The TermsQuery was missing the TermsLookup mechanism, as described here:
https://www.elastic.co/guide/en/elasticsearch/reference/5.3/query-dsl-terms-query.html#query-dsl-terms-lookup

Close #500

search_queries_terms.go

@@ -10,24 +10,30 @@ package elastic
 // For more details, see
 // https://www.elastic.co/guide/en/elasticsearch/reference/5.2/query-dsl-terms-query.html
 type TermsQuery struct {
-	name      string
-	values    []interface{}
-	queryName string
-	boost     *float64
+	name        string
+	values      []interface{}
+	termsLookup *TermsLookup
+	queryName   string
+	boost       *float64
 }
 
 // NewTermsQuery creates and initializes a new TermsQuery.
 func NewTermsQuery(name string, values ...interface{}) *TermsQuery {
 	q := &TermsQuery{
-		name:   name,
-		values: make([]interface{}, 0),
+		name: name,
 	}
 	if len(values) > 0 {
 		q.values = append(q.values, values...)
 	}
 	return q
 }
 
+// TermsLookup adds terms lookup details to the query.
+func (q *TermsQuery) TermsLookup(lookup *TermsLookup) *TermsQuery {
+	q.termsLookup = lookup
+	return q
+}
+
 // Boost sets the boost for this query.
 func (q *TermsQuery) Boost(boost float64) *TermsQuery {
 	q.boost = &boost
@@ -47,12 +53,22 @@ func (q *TermsQuery) Source() (interface{}, error) {
 	source := make(map[string]interface{})
 	params := make(map[string]interface{})
 	source["terms"] = params
-	params[q.name] = q.values
-	if q.boost != nil {
-		params["boost"] = *q.boost
-	}
-	if q.queryName != "" {
-		params["_name"] = q.queryName
+
+	if q.termsLookup != nil {
+		src, err := q.termsLookup.Source()
+		if err != nil {
+			return nil, err
+		}
+		params[q.name] = src
+	} else {
+		params[q.name] = q.values
+		if q.boost != nil {
+			params["boost"] = *q.boost
+		}
+		if q.queryName != "" {
+			params["_name"] = q.queryName
+		}
 	}
+
 	return source, nil
 }

search_queries_terms_test.go

@@ -26,6 +26,24 @@ func TestTermsQuery(t *testing.T) {
 	}
 }
 
+func TestTermsQueryWithTermsLookup(t *testing.T) {
+	q := NewTermsQuery("user").
+		TermsLookup(NewTermsLookup().Index("users").Type("user").Id("2").Path("followers"))
+	src, err := q.Source()
+	if err != nil {
+		t.Fatal(err)
+	}
+	data, err := json.Marshal(src)
+	if err != nil {
+		t.Fatalf("marshaling to JSON failed: %v", err)
+	}
+	got := string(data)
+	expected := `{"terms":{"user":{"id":"2","index":"users","path":"followers","type":"user"}}}`
+	if got != expected {
+		t.Errorf("expected\n%s\n,got:\n%s", expected, got)
+	}
+}
+
 func TestTermQuerysWithOptions(t *testing.T) {
 	q := NewTermsQuery("user", "ki", "ko")
 	q = q.Boost(2.79)

search_terms_lookup.go

@@ -0,0 +1,74 @@
+// Copyright 2012-present Oliver Eilhard. All rights reserved.
+// Use of this source code is governed by a MIT-license.
+// See http://olivere.mit-license.org/license.txt for details.
+
+package elastic
+
+// TermsLookup encapsulates the parameters needed to fetch terms.
+//
+// For more details, see
+// https://www.elastic.co/guide/en/elasticsearch/reference/5.3/query-dsl-terms-query.html#query-dsl-terms-lookup.
+type TermsLookup struct {
+	index   string
+	typ     string
+	id      string
+	path    string
+	routing string
+}
+
+// NewTermsLookup creates and initializes a new TermsLookup.
+func NewTermsLookup() *TermsLookup {
+	t := &TermsLookup{}
+	return t
+}
+
+// Index name.
+func (t *TermsLookup) Index(index string) *TermsLookup {
+	t.index = index
+	return t
+}
+
+// Type name.
+func (t *TermsLookup) Type(typ string) *TermsLookup {
+	t.typ = typ
+	return t
+}
+
+// Id to look up.
+func (t *TermsLookup) Id(id string) *TermsLookup {
+	t.id = id
+	return t
+}
+
+// Path to use for lookup.
+func (t *TermsLookup) Path(path string) *TermsLookup {
+	t.path = path
+	return t
+}
+
+// Routing value.
+func (t *TermsLookup) Routing(routing string) *TermsLookup {
+	t.routing = routing
+	return t
+}
+
+// Source creates the JSON source of the builder.
+func (t *TermsLookup) Source() (interface{}, error) {
+	src := make(map[string]interface{})
+	if t.index != "" {
+		src["index"] = t.index
+	}
+	if t.typ != "" {
+		src["type"] = t.typ
+	}
+	if t.id != "" {
+		src["id"] = t.id
+	}
+	if t.path != "" {
+		src["path"] = t.path
+	}
+	if t.routing != "" {
+		src["routing"] = t.routing
+	}
+	return src, nil
+}

search_terms_lookup_test.go

@@ -0,0 +1,27 @@
+// Copyright 2012-present Oliver Eilhard. All rights reserved.
+// Use of this source code is governed by a MIT-license.
+// See http://olivere.mit-license.org/license.txt for details.
+
+package elastic
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestTermsLookup(t *testing.T) {
+	tl := NewTermsLookup().Index("users").Type("user").Id("2").Path("followers")
+	src, err := tl.Source()
+	if err != nil {
+		t.Fatal(err)
+	}
+	data, err := json.Marshal(src)
+	if err != nil {
+		t.Fatalf("marshaling to JSON failed: %v", err)
+	}
+	got := string(data)
+	expected := `{"id":"2","index":"users","path":"followers","type":"user"}`
+	if got != expected {
+		t.Errorf("expected\n%s\n,got:\n%s", expected, got)
+	}
+}