Tag: Console Application

Setting up Go in VS Code

Firstly, I need to equip Visual Studio Code with the Go language support by installing Go extension in the IDE. Installing the extension helps us to do day-to-day job, such as, code navigating, code editing, code testing and debugging in an easy and efficient manner.

There are many cool features I like in the extension.

Firstly, it’s the convenience of F12 Code Navigation. With Go extension, in Go code I can easily view the source code of the type definition with just F12 or Alt+F12 on it. This is similar to my C# coding experience on Visual Studio too. To show all references of the type, I can simply use Shift+F12.

Secondly, for every file save, the extension will build, vet, and lint. Build (go build) builds the command or the package. Vet (go vet) examines Go source code and reports suspicious constructs, such as Printf calls whose arguments do not align with the format string. A linter is a tool giving coding style feedback and suggestions. By default, this extension uses the official golint as a linter.

After I have installed the Go extension, I proceed to start coding. The app that I am going to build in this learning journey is a YouTube video player app. So, let’s get started!

Storing Connection String in Environment

I will start with building a console application connecting to Azure PostgreSQL. To do that, I will connect to the database as follows.

package main;

const (
     // Initialize connection constants.
     HOST     = "...postgres.database.azure.com"
     DATABASE = "..."
     USER     = "..."
     PASSWORD = "..."
)

...

function main() {
    var connectionString = fmt.Sprintf("host=%s port=5432 user=%s password=%s dbname=%s sslmode=require", HOST, USER, PASSWORD, DATABASE) 
    ...
}

The code above is quite straight-forward. However, it does have a problem. The configuration to connect to database is hard-coded in the code. This will thus reduce the code maintainability. Also, it is extremely bad to have password appearing in the code in plain text. To store such sensitive data, we need to store them as Environment variables, as recommended by the article Best Practice for Configuration File in Your Code.

In Powershell, there are two ways of setting Environment variable. The first one is a temporarily variable that lasts only as long as the Powershell session. The command is as follows.

> $env:CONNECTION_STRING = '...'

If what you are looking for is a permanent one, you can do as follows.

> [environment]::SetEnvironmentVariable("CONNECTION_STRING", "...", "User")

After setting the connection string in environment variable, we then can edit the earlier code to be something shorter as follows.

package main;

…

function main() {
    var connectionString = fmt.Sprintf(os.Getenv("CONNECTION_STRING")) 

     …
}

Connecting to Database

After that, we can initialize the connection object.

package main

...
 
func checkError(err error) {
    if err != nil {
        log.Fatal(err)
        panic(err)
    }
} 

func main() {
    var connectionString = ...

    // Initialize connection string.
    db, err := sql.Open("postgres", connectionString)
    checkError(err)

    err = db.Ping()
    checkError(err)
    fmt.Println("Successfully created connection to database") 

    ...
}

The Ping() function verifies a connection to the database is alive and it will establish a connection if necessary. After that, we can use the database handler db to do CRUD operations, as demonstrated below.

Insert Data into Table

sqlStatement := "INSERT INTO table (column1) VALUES ($1);"
_, err = db.Exec(sqlStatement, "New Value")
checkError(err)

Read Data from Table

var id int
var column1 string

sqlStatement := "SELECT * from table;"
rows, err := db.Query(sqlStatement)
checkError(err)

defer rows.Close()

for rows.Next() {
    switch err := rows.Scan(&id, &column1); err {
    case sql.ErrNoRows:
       fmt.Println("No rows were returned")
    case nil:
       fmt.Printf("Data row = (%d, %s)\n", id, column1)
    default:
       checkError(err)
    }
}

Update Data in Database

sqlStatement := "UPDATE table SET column1 = $1 WHERE id = $2;"
_, err = db.Exec(sqlStatement, "New Value 2", 1)
checkError(err)

Delete Data from Database

sqlStatement := "DELETE FROM table WHERE id = $1;"
_, err = db.Exec(sqlStatement, 1)
checkError(err)

A YouTube Playlist Console App

With the codes above, we then can create a simple table to store our YouTube video URLs as a playlist, as shown in the following screenshot.

To make the program to play the video on a browser, we then can make use of the code written by hyg (黄勇刚) which is to open a web page on the default browser of the machine, as shown below.

func openbrowser(url string) {
    var err error

    switch runtime.GOOS {
    case "linux":
        err = exec.Command("xdg-open", url).Start()
    case "windows":
        err = exec.Command("rundll32", "url.dll,FileProtocolHandler", url).Start()
    case "darwin":
        err = exec.Command("open", url).Start()
    default:
        err = fmt.Errorf("unsupported platform")
    }

    if err != nil {
        checkError(err)
    }

}

Playing YouTube video via console is cool, isn’t it? Next, we will see how we can make it to be web application so that we can have a better UI/UX.

To be continued in next article…

References

1. Quickstart: Create an Azure Database for PostgreSQL server in the Azure portal;
2. Azure Database for PostgreSQL: Use Go language to connect and query data;
3. [StackOverflow] List all environment variables from command line;
4. Azure Database for PostgreSQL Server firewall rules;
5. PostgreSQL – CREATE Database;
6. [StackOverflow] How to switch databases in psql?;
7. [StackOverflow] How to read input from console line?;
8. [StackOverflow] Convert string to integer type in Go?;
9. [StackOverflow] Reading an integer from standard input;
10. [StackOverflow] How to exit from PostgreSQL command line utility: psql.