How can I implement a Singleton pattern for managing database connections in Go?

Singleton Pattern for Database Management

The singleton pattern ensures that a class has only one instance and provides a global point of access to that instance. In this context, it allows you to create a single connection to the database and access it from any part of your application.

To create a singleton database instance, you can follow these steps:

1. Create an interface that defines the database operations you want to perform.
2. Create an unexported type that implements the interface and contains your database connection.
3. Use a package init() function to initialize a global variable that implements the interface, using the unexported type.

Here's an example of how you can implement this in Go:

<code class="go">package dbprovider

import (
    "github.com/jinzhu/gorm"
    _ "github.com/jinzhu/gorm/dialects/sqlite"
    "log"
)

type DBManager interface {
    AddArticle(article *article.Article) error
    // Add other methods
}

type dbManager struct {
    db *gorm.DB
}

var dbManagerInstance DBManager

func init() {
    db, err := gorm.Open("sqlite3", "../articles.db")
    if err != nil {
        log.Fatal("Failed to init db:", err)
    }
    dbManagerInstance = &dbManager{db: db}
}</code>

To use the singleton database instance, you can call the following function:

<code class="go">func GetDBManager() DBManager {
    return dbManagerInstance
}</code>

This will return the shared database manager instance, which can be used to perform database operations.

Handling Exceptions

To handle exceptions from the GORM library, you can use the GetErrors() method. This method returns a slice of errors that occurred during the last database operation. If there are no errors, the slice will be empty.

In your AddArticle method, you can use this method to check for errors and return them appropriately:

<code class="go">func (mgr *dbManager) AddArticle(article *article.Article) (err error) {
    mgr.db.Create(article)
    if errs := mgr.db.GetErrors(); len(errs) > 0 {
        err = errs[0]
    }
    return
}</code>

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