Go: Variable from PostgreSQL in template not output value (Echo framework) - postgresql

Many codes taken from Martini example, but this using Echo framework.
I can make it works in Martini but not in Echo.
server.go:
package main
import (
"database/sql"
"github.com/labstack/echo"
_ "github.com/lib/pq"
"html/template"
"io"
"log"
"net/http"
)
type Book struct {
Title, Author, Description string
}
type (
Template struct {
templates *template.Template
}
)
func (t *Template) Render(w io.Writer, name string, data interface{}) error {
return t.templates.ExecuteTemplate(w, name, data)
}
func main() {
e := echo.New()
db, err := sql.Open("postgres", "user=postgres password=apassword dbname=lesson4 sslmode=disable")
if err != nil {
log.Fatal(err)
}
t := &Template{
templates: template.Must(template.ParseFiles("public/views/testhere.html")),
}
e.Renderer(t)
e.Get("/post/:idnumber", func(c *echo.Context) {
rows, err := db.Query("SELECT title, author, description FROM books WHERE id=$1", c.Param("idnumber"))
if err != nil {
log.Fatal(err)
}
books := []Book{}
for rows.Next() {
b := Book{}
err := rows.Scan(&b.Title, &b.Author, &b.Description)
if err != nil {
log.Fatal(err)
}
books = append(books, b)
}
c.Render(http.StatusOK, "onlytestingtpl", books)
})
e.Run(":4444")
}
public/views/testhere.html:
{{define "onlytestingtpl"}}Book title is {{.Title}}. Written by {{.Author}}. The book is about {{.Description}}.{{end}}
I cannot figure out since no error message, and no SQL documentation of this framework. When running, it gives:
Book title is
(The variable not output value)

As I mentioned in a comment, you shouldn't execute a template that takes a struct with a slice of structs. Either use {{range}} in your template, or do
c.Render(http.StatusOK, "onlytestingtpl", books[0])

Related

What is the bson syntax for $set in UpdateOne for the official mongo-go-driver

I am trying to get some familiarity with the official mongo-go-driver and the right syntax for UpdateOne.
My simplest full example follows:
(NOTE: in order to use this code you will need to substitute in your own user and server names as well as export the login password to the environment as MONGO_PW):
package main
import (
"context"
"fmt"
"os"
"go.mongodb.org/mongo-driver/bson"
"go.mongodb.org/mongo-driver/bson/primitive"
"go.mongodb.org/mongo-driver/mongo"
"go.mongodb.org/mongo-driver/mongo/options"
)
type DB struct {
User string
Server string
Database string
Collection string
Client *mongo.Client
Ctx context.Context
}
var db = DB{
User: <username>,
Server: <server_IP>,
Database: "test",
Collection: "movies",
Ctx: context.TODO(),
}
type Movie struct {
ID primitive.ObjectID `bson:"_id" json:"id"`
Name string `bson:"name" json:"name"`
Description string `bson:"description" json:"description"`
}
func main() {
if err := db.Connect(); err != nil {
fmt.Println("error: unable to connect")
os.Exit(1)
}
fmt.Println("connected")
// The code assumes the original entry for dunkirk is the following
// {"Name":"dunkirk", "Description":"a world war 2 movie"}
updatedMovie := Movie{
Name: "dunkirk",
Description: "movie about the british evacuation in WWII",
}
res, err := db.UpdateByName(updatedMovie)
if err != nil {
fmt.Println("error updating movie:", err)
os.Exit(1)
}
if res.MatchedCount < 1 {
fmt.Println("error: update did not match any documents")
os.Exit(1)
}
}
// UpdateByName changes the description for a movie identified by its name
func (db *DB) UpdateByName(movie Movie) (*mongo.UpdateResult, error) {
filter := bson.D{{"name", movie.Name}}
res, err := db.Client.Database(db.Database).Collection(db.Collection).UpdateOne(
db.Ctx,
filter,
movie,
)
if err != nil {
return nil, err
}
return res, nil
}
// Connect assumes that the database password is stored in the
// environment variable MONGO_PW
func (db *DB) Connect() error {
pw, ok := os.LookupEnv("MONGO_PW")
if !ok {
fmt.Println("error: unable to find MONGO_PW in the environment")
os.Exit(1)
}
mongoURI := fmt.Sprintf("mongodb+srv://%s:%s#%s", db.User, pw, db.Server)
// Set client options and verify connection
clientOptions := options.Client().ApplyURI(mongoURI)
client, err := mongo.Connect(db.Ctx, clientOptions)
if err != nil {
return err
}
err = client.Ping(db.Ctx, nil)
if err != nil {
return err
}
db.Client = client
return nil
}
The function signature for UpdateOne from the package docs is:
func (coll *Collection) UpdateOne(ctx context.Context, filter interface{},
update interface{}, opts ...*options.UpdateOptions) (*UpdateResult, error)
So I am clearly making some sort of mistake in creating the update interface{} argument to the function because I am presented with this error
error updating movie: update document must contain key beginning with '$'
The most popular answer here shows that I need to use a document sort of like this
{ $set: {"Name" : "The Matrix", "Decription" "Neo and Trinity kick butt" } }
but taken verbatim this will not compile in the mongo-go-driver.
I think I need some form of a bson document to comply with the Go syntax. What is the best and/or most efficient syntax to create this bson document for the update?
After playing around with this for a little while longer I was able to solve the problem after A LOT OF TRIAL AND ERROR using the mongodb bson package by changing the UpdateByName function in my code above as follows:
// UpdateByName changes the description for a movie identified by its name
func (db *DB) UpdateByName(movie Movie) (*mongo.UpdateResult, error) {
filter := bson.D{{"name", movie.Name}}
update := bson.D{{"$set",
bson.D{
{"description", movie.Description},
},
}}
res, err := db.Client.Database(db.Database).Collection(db.Collection).UpdateOne(
db.Ctx,
filter,
update,
)
if err != nil {
return nil, err
}
return res, nil
}
Note the use of bson.D{{$"set", .... It is unfortunate the way MongoDB has implemented the bson package this syntax still does not pass the go-vet. If anyone has a comment to fix the lint conflict below it would be appreciated.
go.mongodb.org/mongo-driver/bson/primitive.E composite literal uses unkeyed fields
In many cases you can replace construction
filter := bson.D{{"name", movie.Name}}
with
filter := bson.M{"name": movie.Name}
if arguments order dowsn't matter

Golang how can I make sql row a string

I am using Golang and Postgres, Postgres has an advance feature where it can return your queries in Json format. What I want to do is get that Json query results and return it but I am having trouble since it has to be a String in order to return it. This is my code
package main
import(
"fmt"
"database/sql"
_ "github.com/lib/pq"
"log"
)
func HelloServer(w http.ResponseWriter, req *http.Request) {
db, err := sql.Open("postgres", "user=postgres password=password dbname=name sslmode=disable")
if err != nil {
log.Fatal(err)
}
defer db.Close()
rows, err := db.Query("select To_Json(t) (SELECT * from cars)t")
io.WriteString(w, "hello, world!\n")
}
func main() {
http.HandleFunc("/hello", HelloServer)
log.Fatal(http.ListenAndServe(":12345", nil))
}
The Rows element returns a Json array how can I turn that Rows element into a String ? For C# and Java I would just append the .ToString() method to it and it would make it a string . As you can see from the code above the io.WriteString takes a String as a second parameter so I want to make the Rows variable a String after it has the Json returned so that I can display it in the browser by passing it to the method. I want to replace the Hello World with the String Rows.
Rows is a sql.Rows type. In order to use the data returned by your database query you will have to iterated over the "rows".
An example from the docs
age := 27
rows, err := db.Query("SELECT name FROM users WHERE age=?", age)
if err != nil {
log.Fatal(err)
}
defer rows.Close()
for rows.Next() {
var name string
if err := rows.Scan(&name); err != nil {
log.Fatal(err)
}
fmt.Printf("%s is %d\n", name, age)
}
if err := rows.Err(); err != nil {
log.Fatal(err)
}
You should instead use QueryRow because you are expecting the database to return one result. In either case once you have used "Scan" to put the data into your own variable then you can either parse the JSON or print it out.

What am I not getting about Go sql query with variables?

I'm brand new to Go, and I've started working on some postgres queries, and I'm having very little luck.
I have a package that's just going to have some database queries in it. Here's my code.
main.go
package main
import (
"fmt"
)
func main() {
fmt.Println("Querying data")
myqueries.SelectAll("mytable")
}
myqueries.go
package myqueries
import (
"database/sql"
"fmt"
)
func SelectAll (table string) {
db, err := sql.Open("postgres","user=postgres dbname=mydb sslmode=disable")
if err != nil {
fmt.Println(err)
}
defer db.Close()
rows, err := db.Query("SELECT * FROM $1", table)
if err != nil {
fmt.Println(err)
} else {
PrintRows(rows)
}
}
func PrintRows(rows *sql.Rows) {
for rows.Next() {
var firstname string
var lastname string
err := rows.Scan(&firstname, &lastname)
if err != nil {
fmt.Println(err)
}
fmt.Println("first name | last name")
fmt.Println("%v | %v\n", firstname, lastname)
}
}
The error I get is pq: syntax error at or near "$1"
which is from myqueries.go file in the db.Query.
I've tried several variations of this, but nothing has worked yet. Any help is appreciated.
It looks like you are using https://github.com/lib/pq based on the error message and it's docs say that
pq uses the Postgres-native ordinal markers, as shown above
I've never known a database engine that allows the parameterized values in anything other than values. I think you are going to have to resort to string concatenation. I don't have a Go compiler available to me right now, but try something like this. Because you are inserting the table name by concatination, you need it sanitized. pq.QuoteIdentifier should be able to help with that.
func SelectAll (table string) {
db, err := sql.Open("postgres","user=postgres dbname=mydb sslmode=disable")
if err != nil {
fmt.Println(err)
}
defer db.Close()
table = pq.QuoteIdentifier(table)
rows, err := db.Query(fmt.Sprintf("SELECT * FROM %v", table))
if err != nil {
fmt.Println(err)
} else {
PrintRows(rows)
}
}
EDIT: Thanks to hobbs to pointing out pq.QuoteIdentifier

Not understanding how mongoDB Update works in Go

I'm trying to implement a MongoDB update for a Go struct. Stripped down to essentials, it looks something like this:
type MyStruct struct {
Id bson.ObjectId `bson:"_id"`
Fruit string `bson:"fruit"`
}
func TestUpdate(t *testing.T) {
obj1 := MyStruct{Id: bson.NewObjectId(),Fruit: "apple"}
var obj2 MyStruct
session, _ := mgo.Dial("whatever")
col := session.DB("test").C("collection")
col.Insert(&obj1)
obj1.Fruit = "cherry"
if err := col.Update(obj1.Id, bson.M{"$set": &obj1}); err != nil {
t.Errorf(err.Error())
}
if err := col.Find(bson.M{"Id": obj1.Id}).One(&obj2); err != nil {
t.Errorf(err.Error())
}
if obj1.Fruit != obj2.Fruit {
t.Errorf("Expected %s, got %s", obj1.Fruit, obj2.Fruit)
}
}
This generates the error message, indicating that the value wasn't updated. What am I missing?
I understand that just updating one field is possible, but given that this is in a data layer, above which the code doesn't have any knowledge of MongoDB, that would be challenging to implement in a general way. I.e. I really need to make any updates to the Go object, and then update the copy of the object in the backing store. I suppose that I could retrieve the object and do a "diff" manually, constructing a "$set" document, but that doesn't seem like adding a retrieval every time I do an update would be very efficient.
Edit: Trying a map with "_id" deleted
I've tried amending the code to the following:
package testmgo
import (
mgo "gopkg.in/mgo.v2"
"gopkg.in/mgo.v2/bson"
"github.com/fatih/structs"
"testing"
)
type MyStruct struct {
Id bson.ObjectId `bson:"_id"`
Fruit string `bson:"fruit"`
}
func TestUpdate(t *testing.T) {
obj1 := MyStruct{Id: bson.NewObjectId(),Fruit: "apple"}
var obj2 MyStruct
session, _ := mgo.Dial("localhost")
col := session.DB("test").C("collection")
col.Insert(&obj1)
obj1.Fruit = "cherry"
omap := structs.Map(&obj1)
delete(omap, "_id")
if err := col.UpdateId(obj1.Id, bson.M{"$set": bson.M(omap)}); err != nil {
t.Errorf(err.Error())
}
if err := col.Find(bson.M{"Id": obj1.Id}).One(&obj2); err != nil {
t.Errorf(err.Error())
}
if obj1.Fruit != obj2.Fruit {
t.Errorf("Expected %s, got %s", obj1.Fruit, obj2.Fruit)
}
}
and am still receiving the same results (Expected cherry, got apple). Note that the call to UpdateId() is not returning an error.
The problem was that I was using the wrong field as the key. I had mapped "Id" to "_id", but was then asking MongoDB to find a record using the Go attribute name rather than the name. This works correctly:
package testmgo
import (
mgo "gopkg.in/mgo.v2"
"gopkg.in/mgo.v2/bson"
"testing"
)
type MyStruct struct {
Id bson.ObjectId `bson:"_id"`
Fruit string `bson:"fruit"`
}
func TestUpdate(t *testing.T) {
obj1 := MyStruct{Id: bson.NewObjectId(), Fruit: "apple"}
var obj2 MyStruct
session, _ := mgo.Dial("localhost")
col := session.DB("test").C("collection")
col.Insert(&obj1)
obj1.Fruit = "cherry"
if err := col.UpdateId(obj1.Id, bson.M{"$set": &obj1}); err != nil {
t.Errorf(err.Error())
}
if err := col.Find(bson.M{"_id": obj1.Id}).One(&obj2); err != nil {
t.Errorf(err.Error())
}
if obj1.Fruit != obj2.Fruit {
t.Errorf("Expected %s, got %s", obj1.Fruit, obj2.Fruit)
}
}

Can't get Go http to return an error; 'No data recieved'

I am doing attempting to build a basic API using Go which returns the results of a SQL query using the PostgreSQL library.
At the moment I can make the program return the values, but I can't get it to return a failed message to the user i.e. some JSON with an error message.
I have an error function as follows :
func handleError(w http.ResponseWriter, err error) {
if err != nil {
log.Print(err.Error() + "\r\n") // Logging
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
}
However the http.Error method doesn't appear to ever return anything. The error thrown is a table that doesn't exist in the database (which gets logged to a text file: i.e. 2016/01/11 23:28:19 pq: relation "building_roof" does not exist
My programmes query code looks like this:
table := pq.QuoteIdentifier(table)
identifier := pq.QuoteIdentifier("ID")
rows, err := db.Query( fmt.Sprintf("SELECT %s, ST_AsText(geom) FROM %s WHERE %s = $1", identifier, table, identifier), feature)
handleError(w, err)
Causing an error just gives a Chrome error:
No data received
ERR_EMPTY_RESPONSE
EDIT Full Code:
package main
import (
"fmt"
"encoding/json"
"os"
"log"
"net/http"
"database/sql"
"strings"
"time"
"github.com/lib/pq"
)
func handler(w http.ResponseWriter, r *http.Request) {
f, err := os.OpenFile("pgdump_errorlog.txt", os.O_RDWR | os.O_CREATE | os.O_APPEND, 0666)
log.Print("Couldn't open file")
defer f.Close()
log.SetOutput(f)
// Timing
start := time.Now()
// Postgres Credentials
const (
DB_USER = "postgres"
DB_PASSWORD = "OMITTED" // Removed details !
DB_PORT = "OMITTED"
DB_NAME = "OMITTED"
)
// Postgres Connect
dbinfo := fmt.Sprintf("user=%s password=%s dbname=%s port=%s sslmode=disable",
DB_USER, DB_PASSWORD, DB_NAME, DB_PORT)
db, err := sql.Open("postgres", dbinfo)
handleError(w, err)
defer db.Close()
table := r.FormValue("table")
feature := r.FormValue("id")
if table != "" {
//Postgres Query
var (
id int
geom string
)
table := pq.QuoteIdentifier(table)
identifier := pq.QuoteIdentifier("ID")
rows, qerr := db.Query( fmt.Sprintf("SELECT %s, ST_AsText(geom) FROM %s WHERE %s = $1", identifier, table, identifier), feature)
handleError(w, err)
defer rows.Close()
for rows.Next() {
err := rows.Scan(&id, &geom)
handleError(w, err)
}
err = rows.Err()
handleError(w, err)
// Maniplate Strings
returngeom := strings.Replace(geom, "1.#QNAN", "", -1)
i := strings.Index(returngeom, "(")
wkt := strings.TrimSpace(returngeom[:i])
returngeom = returngeom[i:]
type WTKJSON struct {
WTKType string
Geometry string
Elapsed time.Duration
}
returnjson := WTKJSON{Geometry: returngeom, WTKType: wkt , Elapsed: time.Since(start)/1000000.0}
json.NewEncoder(w).Encode(returnjson)
}
}
func handleError(w http.ResponseWriter, err error) {
if err != nil {
log.Print(err.Error() + "\r\n") // Logging
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
}
func main() {
http.HandleFunc("/", handler)
http.ListenAndServe(":8080", nil)
}
The following appeared to allow me to return JSON Errors:
func handleError(w http.ResponseWriter, err string) {
type APIError struct {
Error string
}
re, _ := json.Marshal(APIError{Error: err})
io.WriteString(w, string(re))
}
Used like so:
rows, err := db.Query( fmt.Sprintf("SELECT %s, ST_AsText(geom) FROM %s WHERE %s = $1", identifier, table, identifier), feature)
if err != nil {
handleError(w, err.Error())
return
}
Not suggesting this is the best method, but worked in my case.
When you are using the http.Error function the error message should a string. For simple testing I would suggest take this line
http.Error(w, err.Error(), http.StatusInternalServerError)
and change it to something like
http.Error(w,"there was an error", http.StatusInternalServerError)
and see if that response comes through. If it does its likely that you are trying to pass something that isn't a string in http.Error()