Golang：多个SQL查询会产生额外的空{{range。}}

Question

In the application, I will use totally different query for the second query. The second query will be quite long SELECT SIMILARITY query. In this question, I give simple query to make it easier to understand

I need to print data from PostgreSQL in template. Everything works fine but output HTML has extra range.

Below is the HTML output. You can see the extra range that have no value:

<table>
    <tr>
        <th>Title</th>
        <th>Content</th>
    </tr>

    <tr>
        <td>Nation</td>
        <td>Nation has various meanings, and the meaning has changed over time</td>
    </tr>

    <tr>
        <td></td>
        <td></td>
    </tr>

</table>

<h1>ID number:</h1>

<h3></h3>

<h3>5</h3>

Below is server.go

package main

import (
    "database/sql"
    "github.com/labstack/echo"
    _ "github.com/lib/pq"
    "html/template"
    "io"
    "log"
    "net/http"
)

type Gallery struct {
    Title, Content, Idnumber string
}

type (
    Template struct {
        templates *template.Template
    }
)

func (t *Template) Render(w io.Writer, name string, data interface{}) *echo.HTTPError {
    if err := t.templates.ExecuteTemplate(w, name, data); err != nil {
        return &echo.HTTPError{Error: err}
    }
    return nil
}

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/:uritext", func(c *echo.Context) *echo.HTTPError {

        rows, err := db.Query("SELECT title, content FROM gallery WHERE uri=$1", c.Param("uritext"))
        anotherquery, err := db.Query("SELECT id AS idnumber FROM gallery WHERE uri=$1", c.Param("uritext"))
        if err != nil {
            log.Fatal(err)
        }

        gallery := []Gallery{}

        for rows.Next() {
            g := Gallery{}
            err := rows.Scan(&g.Title, &g.Content)

            if err != nil {
                log.Fatal(err)
            }

            gallery = append(gallery, g)
        }

        for anotherquery.Next() {
            g := Gallery{}
            err := anotherquery.Scan(&g.Idnumber)

            if err != nil {
                log.Fatal(err)
            }

            gallery = append(gallery, g)
        }

        return c.Render(http.StatusOK, "onlytestingtpl", gallery)
    })

    e.Run(":4444")
}

Below is template public/views/testhere.html

{{define "onlytestingtpl"}}
<table>
    <tr>
        <th>Title</th>
        <th>Content</th>
    </tr>
    {{range.}}
    <tr>
        <td>{{.Title}}</td>
        <td>{{.Content}}</td>
    </tr>
    {{end}}
</table>

<h1>ID number:</h1>
{{range.}}
<h3>{{.Idnumber}}</h3>
{{end}}

{{end}}

I have feeling about the range in template but I have no idea since no error.

Answer 1

It looks right to me. You are running two separate queries:

rows, err := db.Query("SELECT title, content FROM gallery WHERE uri=$1", c.Param("uritext"))
anotherquery, err := db.Query("SELECT id AS idnumber FROM gallery WHERE uri=$1", c.Param("uritext"))

And then creating a slice from both:

gallery = append(gallery, g)
gallery = append(gallery, g)

So you have two rows:

{ "Nation", "Nation...", 0 }
{ "", "", 5 }

Is that what you wanted? If you want them merged you can just change your query to:

SELECT title, content, id as idnumber FROM gallery WHERE uri=$1

If you wanted two separate lists then maybe you should have two separate types:

type Gallery struct {
    Title, Content string
}
type IDNumber string

Build two separate lists and use a combined object for your render:

type Model struct {
    Galleries []Gallery
    IDNumbers []IDNumber
}
return c.Render(http.StatusOK, "onlytestingtpl", Model{
    Galleries: galleries,
    IDNumbers: idnumbers,
})

And your template ends up with:

{{range .Galleries}}
<tr>
    <td>{{.Title}}</td>
    <td>{{.Content}}</td>
</tr>
{{end}}