I have created /app/models/todo-item.go file that looks like this:
package models
import (
"github.com/revel/revel"
)
type TodoItem struct {
Id int64 `db:"id" json:"id"`
Name string `db:"name" json:"name"`
}
func (b *TodoItem) Validate(v *revel.Validation) {
v.Check(b.Name,
revel.ValidRequired(),
revel.ValidMaxSize(25))
}
In src/RevelApp/app/controllers/init.go, I have this (PS, I am using GorpController to interact with MySQL):
func defineTodoItemTable(dbm *gorp.DbMap){
// set "id" as primary key and autoincrement
t := dbm.AddTable(models.TodoItem{}).SetKeys(true, "id")
t.ColMap("name").SetMaxSize(25)
}
I am getting an error :
The Go code src/RevelApp/app/controllers/init.go does not compile: undefined: models
I have tried importing ."RevelApp/app/models" then doing away with models in models.TodoItem{} (as describer here: Revel with Gorm "undefined: Page") and I get the error : App failed to start up
revel/harness: app timed out.
That link is the only one I could find related to this issue. Am I missing something?
EDIT: $GOPATH:
/home/me/Source/go
models location:
/home/me/Source/go/src/RevelApp/app/models
How I am importing models package:
import (
."RevelApp/app/models"
"github.com/revel/revel"
"github.com/coopernurse/gorp"
"database/sql"
_ "github.com/go-sql-driver/mysql"
"fmt"
"strings"
)
You have imported your models using the dot (.) import qualifier. From the language spec:
If an explicit period (.) appears instead of a name, all the package's exported identifiers will be declared in the current file's file block and can be accessed without a qualifier.
This means you don't need to use models.TodoItem .. you can simply use TodoItem.
That said .. I would suggest avoiding this and removing the dot from the import statement:
import (
"RevelApp/app/models"
"github.com/revel/revel"
"github.com/coopernurse/gorp"
"database/sql"
_ "github.com/go-sql-driver/mysql"
"fmt"
"strings"
)
Why? It stops your local file scope becoming crowded and allows you to see where each object actually resides.
For completeness (and you're probably wondering what its for since the dot is similar), that underscore (_) before the mysql package statement basically says "import this package .. but I don't need to use anything in it directly". This fires the packages init function allowing it to register itself with the database/sql packages routines. Which is why when you use the sql.DB type it is eventually routed to the MySql package code.
Related
I took the example from Gorm's docs of how to create a unique index, which seems to be be simply adding a ,unique to the column tag when declaring a model. But when I tried to run it, it would always output the following message in the console:
(/Users/[...]/main.go:16)
[2021-06-26 13:59:20] near "unique": syntax error
While it seemed bizarre that an example directly from their docs would fail, I tried running that code in isolation, and it indeed worked fine on its own. Then, adding on more and more code from my app, it seemed to start outputting that message once Gin-Gonic was introduced and gin.Default() was called. I don't know if this is only because Go won't output the error by default, or there is some sort of a clash going on. But either way, I have also never had Gorm actually create the unique index; syntax error or not.
The minimum reproducible code is as follows, though it behaves rather inconsistently, running without any error about 1 out of 5 times:
package main
import (
"github.com/jinzhu/gorm"
_ "github.com/jinzhu/gorm/dialects/sqlite"
"github.com/gin-gonic/gin"
)
type User struct {
gorm.Model
Name string `gorm:"size:40;index:idx_name,unique"`
}
func main() {
db, _ := gorm.Open("sqlite3", "test.db")
db.AutoMigrate(&User{})
r := gin.Default()
r.Run(":8082")
}
How would I go about fixing this; Both getting rid of the inconsistent error, and having the unique index actually being created?
If relevant, I'm running this on a Mac.
You took an example from the gorm.io but you didn't use the right packages imports.
See here the installation here: https://gorm.io/docs/#Install
You are using imports from v1 (http://v1.gorm.io/docs/) and coding with examples from the latest version. (http://gorm.io/docs/)
Look the import and the database drive initialization in the code below:
package main
import (
"github.com/gin-gonic/gin"
"gorm.io/driver/sqlite"
"gorm.io/gorm"
)
type User struct {
gorm.Model
Name string `gorm:"size:40;index:idx_name,unique"`
}
func main() {
db, _ := gorm.Open(sqlite.Open("gorm.db"), &gorm.Config{})
db.AutoMigrate(&User{})
r := gin.Default()
r.Run("localhost:8082")
}
I want to export a function from my package so that I can use it without typing a package name before it, how to do that?
import "mypackage"
func main() {
mypackage.myfunc() <-- that's what I have already
myfunc() <-- that's what I need
}
You can use one of the followings:
import (
. "mypackage" // without a name
mp "my/other/package" // rename
_ "my/totally/diffrent/package" // import a package solely for its side-effects (initialization)
)
Obviously, this pattern is not recommended since it can cause name conflicts with other packages.
Check out the dot imports bulletin
Here is an example of my code:
package main
import (
"./bio"
)
func main() {
bio.PeptideEncoding(genome, codonTable)
}
Is it possible to use functions from my paxkage (bio) without specifying package name:
func main() {
PeptideEncoding(genome, codonTable)
}
?
You could use as an import declaration like:
. "./bio"
If an explicit period (.) appears instead of a name, all the package's exported identifiers declared in that package's package block will be declared in the importing source file's file block and must be accessed without a qualifier.
That is what a testing framework like govey does:
package package_name
import (
"testing"
. "github.com/smartystreets/goconvey/convey"
)
func TestIntegerStuff(t *testing.T) {
Convey("Given some integer with a starting value", t, func() {
x := 1
Convey("When the integer is incremented", func() {
x++
Convey("The value should be greater by one", func() {
So(x, ShouldEqual, 2)
})
})
})
}
You don't need to use convey.So(), or convey.Convey() because of the import starting with a '.'.
Don't abuse it though, since, as twotwotwo comments, The style guide discourages it outside of tests.
Except for this one case, do not use import . in your programs.
It makes the programs much harder to read because it is unclear whether a name like Quux is a top-level identifier in the current package or in an imported package.
That is why I mentioned a testing framework using this technique.
As commented by Simon Whitehead, using relative import is not generally considered as the best practice (see for instance "Go language package structure").
You should also import the package via the GOPATH instead of relatively, as show in "Import and not used error".
I have created a library by the name libfastget which is in the src with my program as
src
|-libfastget
| |-libfastget.go
|
|-MainProgram
|-main.go
and the libfastget exports a funtion fastget as follows
package libfastget
import (
"fmt"
"io"
)
func fastget(urlPtr *string, nPtr *int, outFilePtr *string) download {
.....
return dl
}
When I use the library in my main program
package main
import (
"fmt"
"net/http"
"os"
"libfastget"
"path/filepath"
"strings"
"flag"
"time"
)
func uploadFunc(w http.ResponseWriter, r *http.Request) {
n:=libfastget.fastget(url,4,filename)
}
}
I get the following error upon trying to build with go build
# FServe
./main.go:94: cannot refer to unexported name libfastget.fastget
./main.go:94: undefined: libfastget.fastget
The strange thing is that the library file libfastget.a is present in the pkg folder.
you would need to make your function exportable with an uppercase for its name:
func Fastget(...
Used as:
n:=libfastget.Fastget(url,4,filename)
The spec mentions: "Exported identifiers":
An identifier may be exported to permit access to it from another package. An identifier is exported if both:
the first character of the identifier's name is a Unicode upper case letter (Unicode class "Lu"); and
the identifier is declared in the package block or it is a field name or method name.
All other identifiers are not exported.
to export a function into another package the function identifier must start with a capital letter.
I recently started learning GO Lang (2 days back)
And what I found was you need to setup a workspace folder to make the local packages import into other projects or main.go files. I'm using VS Code editor. Please correct me if Im wrong, but this setup works fine for me.
Inside your bash_profile OR .zshrc file add below lines, update the GOPATH as per your folder path.
export GOPATH=~/projects/GO_PROJECTS
export PATH=$PATH:$GOPATH/bin:$PATH
and this is my sayHello.go file, please note to be able to export a function the func name should start with a CapitalCase SayHello
package utils
import "fmt"
func SayHello() {
fmt.Println("Hello, Ajinkya")
}
and now I am able to import utils package into main.go file
package main
import (
"go_proj1/utils"
)
func main() {
utils.SayHello()
}
set the current directory as GOPATH
or you can use local import as follows
move your main.go to the ../ directory to the libfastget.go.
i mean the files looks like:
src
|-libfastget
| |-libfastget.go
|
|-main.go
import "./libfastget"
I'm trying to write an application to pull status from a database, but I seem to be getting stuck on a really basic principle of the language. I have the program written, but it doesn't compile due to the error use of package time not in selector.
A really basic example (from play.golang.org's own test environment)
package main
import (
"fmt"
"time"
)
func main() {
s_str := time.Now()
fmt.Println( printT(s_str) )
}
func printT(t time) time {
return t.Add(100)
}
Unfortunately, I've found documentation and helpdocs online a bit wanting. My understanding is that the import statement should include the library for the entire program like in C++ correct?
You have to prefix the imported types or variables with the name you gave to the package in the import (here you use the default name, that is "time"). That's what you did for the function Now but you have to do it also for the types.
So the type isn't time but time.Time (that is : the type Time that is declared in the package you import with the name "time").
Change your function to
func printT(t time.Time) time.Time {
return t.Add(100)
}
And for your second question : No, the import statement doesn't include the library for the entire program but only for the current file.