feat(region):完成行政区划获取的功能。

service/region.go

@@ -0,0 +1,21 @@
+package service
+
+import (
+	"electricity_bill_calc/global"
+	"electricity_bill_calc/model"
+
+	"xorm.io/builder"
+)
+
+type _RegionService struct{}
+
+var RegionService _RegionService
+
+func (_RegionService) FetchSubRegions(parent string) ([]model.Region, error) {
+	regions := make([]model.Region, 0)
+	err := global.DBConn.Where(builder.Eq{"parent": parent}).Asc("code").Find(&regions)
+	if err != nil {
+		return make([]model.Region, 0), err
+	}
+	return regions, err
+}