Filtering and sorting an SQL query to recreate a nested struct - sql

Question

I am new to Go and I'm trying to populate a struct called Reliefworker from an SQL query which I can send as a JSON payload.
Essentially I have a Reliefworker who may be assigned to many communities and the community can consist of multiple regions.
I suspect there is a clever way of doing this other than what I intend which is a primitive solution that will add a sort to the SQL (by Community) and create a function that detects if the community being added is different to the previous one, in which case I would create a new community struct type object to be appended.
type Reliefworker struct {
Name string `json:"name"`
Communities []Community `json:"community"`
Deployment_id string `json:"deployment_id"`
}
type Community struct{
Name string `json:"name"`
community_id string `json:"community_id"`
Regions []Region `json:"regions"`
}
type Region struct{
Name string `json:"name"`
Region_id string `json:"region_id"`
Reconstruction_grant string `json:"reconstruction_grant"`
Currency string `json:"currency"`
}
Currently I have created a struct that reflects what I am actually getting from SQL whilst pondering my next move. Perhaps this might be a good stepping stone instead of attempting an on-the-fly transformation ?
type ReliefWorker_community_region struct {
Deployment_id string
Community_title int
Region_name string
Reconstruction_grant int
}
func GetReliefWorkers(deployment_id string) []Reliefworker {
fmt.Printf("Confirm I have a deployment id:%v\n", deployment_id)
rows, err := middleware.Db.Query("select deployment_id, community_title, region_name, reconstruction_grant WHERE Deployment_id=$1", brand_id)
if err != nil {
return
}
for rows.Next() {
reliefworker := Reliefworker{}
err = rows.Scan(&deployment_id, &community_title, &region_name, &reconstruction_grant)
if err != nil {
return
}
}
rows.Close()
return
}

Answer 1

I think a sort makes a lot of sense, primitive solutions can be the most efficient:
func GetReliefWorkers(deployment_id string) []Reliefworker {
// Added sort to query
q := "select worker_name, community_title, region_name, reconstruction_grant WHERE deployment_id=? ORDER BY community_title"
rows, err := middleware.Db.Query(q, deployment_id)
if err != nil {
return
}
defer rows.Close() // So rows get closed even on an error
c := Community{} // To keep track of the current community
cmatrix := [][]string{[]string{}} // Matrix of communities and workers
communities := []Community{} // List of communities
workers := make(map[string]Reliefworker) // Map of workers
var ccount int // Index of community in lists
for rows.Next() {
w := Reliefworker{Deployment_id: deployment_id}
r := Region{}
var ctitle string // For comparison later
err = rows.Scan(&w.Name, &ctitle, &r.Name, &r.Reconstruction_grant)
if err != nil {
return
}
if ctitle != c.Name {
communities = append(communities, c)
c = Community{}
c.Name = ctitle
ccount++
cmatrix = append(cmatrix, []string{})
}
c.Regions = append(c.Regions, r)
cmatrix[ccount] = append(cmatrix[ccount], w.Name)
workers[w.Name] = w
}
for i, c := range communities {
for _, id := range cmatrix[i] {
w := workers[id] // To avoid error
w.Communities = append(w.Communities, c)
workers[id] = w
}
}
out := []Reliefworker{}
for _, w := range workers {
out = append(out, w)
}
return out
}
Though it might make even more sense to create seperate tables for communities, regions, and workers, then query them all with a JOIN: https://www.w3schools.com/sql/sql_join_inner.asp
UPDATE: Since you only want to retrieve one Reliefworker, would something like this work?
type ReliefWorker struct {
Name string `json:"name"`
Communities []Community `json:"community"`
}
type Community struct {
Name string `json:"name"`
Regions []Region `json:"regions"`
}
type Region struct {
Name string `json:"name"`
Region_id string `json:"region_id"`
Reconstruction_grant int `json:"reconstruction_grant"`
Currency string `json:"currency"`
}
func GetReliefWorkers(deployment_id string) Reliefworker {
reliefworker := Reliefworker{}
communities := make(map[string]Community)
rows, err := middleware.Db.Query("select name, community_title, region_name, region_id, reconstruction_grant WHERE Deployment_id=$1", deployment_id)
if err != nil {
if err == sql.ErrNoRows {
fmt.Printf("No records for ReliefWorker:%v\n", deployment_id)
}
panic(err)
}
defer rows.Close()
for rows.Next() {
c := Community{}
r := Region{}
err = rows.Scan(&reliefworker.Name, &c.Name, &r.Name, &r.Region_id, &r.Reconstruction_grant)
if err != nil {
panic(err)
}
if _, ok := communities[c.Name]; ok {
c = communities[c.Name]
}
c.Regions = append(c.Regions, r)
communities[c.Name] = c
}
for _, c := range commmunities {
reliefworker.Communities = append(reliefworker.Communities, c)
}
return reliefworker
}

Answer 2

Ok, my crude solution doesn't contain a shred of the intelligence #Absentbird demonstrates but I'm here to learn.
#Absentbird I love your use of maps and multidimensional arrays to hold a matrix of communities and workers. I will focus on making this part of my arsenal over the weekend.
I can accept and adapt #Absentbird's solution once I have a solution to why it gives the error "cannot assign to struct field workers[id].Communities in mapcompilerUnaddressableFieldAssign" for the line workers[id].Communities = append(workers[id].Communities, c)
Firstly apologies as I had to correct two things. Firstly I only needed to return ReliefWorkers (not an array of ReliefWorkers). Secondly ReliefWorker struct did not need to contain the Deployment_id since I already knew it.
I am new to Go so I'd really appreciate feedback on what I can do to better leverage the language and write more concise code.
My structs and solution is currently as follows:
type ReliefWorker struct {
Name string `json:"name"`
Communities []Community `json:"community"`
}
type Community struct {
Name string `json:"name"`
Regions []Region `json:"regions"`
}
type Region struct {
Name string `json:"name"`
Region_id string `json:"region_id"`
Reconstruction_grant int `json:"reconstruction_grant"`
Currency string `json:"currency"`
}
type ReliefWorker_community_region struct {
Name string
Community_title string
Region_name string
Reconstruction_grant int
}
func GetReliefWorkers(deployment_id string) Reliefworker {
var reliefworker Reliefworker
var communitiesOnly []string
var name string
var allReliefWorkerData []ReliefWorker_community_region
rows, err := middleware.Db.Query("select name, community_title, region_name, reconstruction_grant WHERE Deployment_id=$1", deployment_id)
for rows.Next() {
reliefWorker_community_region := ReliefWorker_community_region{}
err = rows.Scan(&reliefWorker_community_region.Name, &reliefWorker_community_region.Community_title, &reliefWorker_community_region.Region_name, &reliefWorker_community_region.Reconstruction_grant)
if err != nil {
panic(err)
}
name = reliefWorker_community_region.Name
allReliefWorkerData = append(allReliefWorkerData, reliefWorker_community_region)
communitiesOnly = append(communitiesOnly, reliefWorker_community_region.Community_title) //All communities go in here, even duplicates, will will create a unique set later
}
rows.Close()
if err != nil {
if err == sql.ErrNoRows {
fmt.Printf("No records for ReliefWorker:%v\n", deployment_id)
}
panic(err)
}
var unique []string //Use this to create a unique index of communities
for _, v := range communitiesOnly {
skip := false
for _, u := range unique {
if v == u {
skip = true
break
}
}
if !skip {
unique = append(unique, v)
}
}
fmt.Println(unique)
reliefworker.Name = name
var community Community
var communities []Community
for _, v := range unique {
community.Name = v
communities = append(communities, community)
}
// Go through each record from the database held within allReliefWorkerData and grab every region belonging to a Community, when done append it to Communities and finally append that to ReliefWorker
for j, u := range communities {
var regions []Region
for i, v := range allReliefWorkerData {
if v.Community_title == u.Name {
var region Region
region.Name = v.Region_name
region.Reconstruction_grant = v.Reconstruction_grant
regions = append(regions, region)
}
}
communities[j].Regions = regions
}
reliefworker.Communities = communities
return reliefworker
}