Add more tests and docs for issue indexer, add db indexer type for searching from database (#6144)

* add more tests and docs for issue indexer, add db indexer type for searching from database

* fix typo

* fix typo

* fix lint

* improve docs

modules/indexer/issues/db.go

@@ -0,0 +1,45 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package issues
+
+import "code.gitea.io/gitea/models"
+
+// DBIndexer implements Indexer inteface to use database's like search
+type DBIndexer struct {
+}
+
+// Init dummy function
+func (db *DBIndexer) Init() (bool, error) {
+	return false, nil
+}
+
+// Index dummy function
+func (db *DBIndexer) Index(issue []*IndexerData) error {
+	return nil
+}
+
+// Delete dummy function
+func (db *DBIndexer) Delete(ids ...int64) error {
+	return nil
+}
+
+// Search dummy function
+func (db *DBIndexer) Search(kw string, repoID int64, limit, start int) (*SearchResult, error) {
+	total, ids, err := models.SearchIssueIDsByKeyword(kw, repoID, limit, start)
+	if err != nil {
+		return nil, err
+	}
+	var result = SearchResult{
+		Total: total,
+		Hits:  make([]Match, 0, limit),
+	}
+	for _, id := range ids {
+		result.Hits = append(result.Hits, Match{
+			ID:     id,
+			RepoID: repoID,
+		})
+	}
+	return &result, nil
+}