optimize FindKeyByField

db/db_impl.cc

@@ -1220,13 +1220,10 @@ std::vector DBImpl::FindKeysByField(Field &field) {
   iter->SeekToFirst();
   while (iter->Valid()) {
     std::string key = iter->key().ToString();
-    FieldArray field_array = iter->fields().GetFieldArray();
+    Fields fields = iter->fields();
 
-    for (const auto& field_db : field_array) {
-      if (field_db.first == field.first &&
-          field_db.second == field.second) {
-        keys.push_back(key);
-      }
+    if (fields.find(field.first) == field.second) {
+      keys.emplace_back(key);
     }
     iter->Next();
   }

db/fields.cc

@@ -64,10 +64,19 @@ namespace leveldb {
     FieldArray field_array;
 
     for (const auto& _field : this->_fields) {
-      field_array.push_back(Field(_field.first, _field.second));
+      field_array.emplace_back(_field.first, _field.second);
     }
 
     return field_array;
   }
 
+  std::string Fields::find(const std::string& field_name) const {
+    auto it = this->_fields.find(field_name);
+    if (it == this->_fields.end()) {
+      return "";
+    }
+    return it->second;
+  }
+
+
 }  // namespace leveldb

db/fields.h

@@ -32,6 +32,9 @@ namespace leveldb {
 
     // 将Fields编码为存入LevelDB的Value
     std::string Serialize() const;
+
+    // 通过field_name得到相应的字段值
+    std::string find(const std::string& field_name) const;
   private:
     std::map<std::string, std::string> _fields;
   };