How to Pass Arguments to Gin Router Handlers in Golang?

Passing Arguments to Router Handlers in Golang with Gin

When developing RESTful APIs in Golang using the Gin web framework, you may encounter the need to pass arguments to your route handlers. This is useful for reusing resources, such as database connections, across routes.

There are two common approaches to passing arguments to route handlers:

1. Global Variables: A simple option is to store the argument as a global variable. However, this approach can lead to code inconsistencies and is not ideal for larger projects.
2. Closures: A cleaner solution is to use closures. A closure allows you to pass an additional variable to a route handler while satisfying Gin's gin.HandlerFunc interface.

Here's an example using a closure:

// SomeHandler returns a `func(*gin.Context)` to satisfy Gin's router methods
// db is an example argument that you want to pass down to the handler
func SomeHandler(db *sql.DB) gin.HandlerFunc {
    fn := func(c *gin.Context) {
        // Your handler code goes in here
        // You now have access to the db variable

        // Example request handling
        rows, err := db.Query(...)

        c.String(200, results)
    }

    return gin.HandlerFunc(fn)
}

func main() {
    db, err := sql.Open(...)
    // Handle error

    router := gin.Default()
    router.GET("/test", SomeHandler(db))
    router.Run(":8080")
}

In this scenario, the SomeHandler function creates a closure that wraps the actual route handler. The closure captures the db variable, allowing the handler to access it.

Remember that this technique can be applied to any type of argument you need to pass to your route handlers.

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