How to Access a Database Connection from Within a Function in Golang?

Accessing the Database Connection from Within a Function in Golang

In Golang, database operations typically begin with opening a connection to the database. However, when working with functions that require database interactions, there's often a need to refer to the open connection.

Problem:

Consider the following scenario:

<code class="go">func main() {
    db, err := sql.Open("sqlite3", "./house.db")
    checkErr(err)

    addRow(Room{
        Name: "Bedroom",
        Size: 12.5,
        ...
    })
}</code>

In this example, the main function opens a database connection, represented by db. However, the addRow function cannot directly access db because it is defined outside of the main function.

Solution:

There are several ways to handle this situation:

Global Access:

Make the db variable global by declaring it outside of any function, for example:

<code class="go">var db *sql.DB

func main() {
    db, err := sql.Open("sqlite3", "./house.db")
    checkErr(err)

    addRow(Room{
        Name: "Bedroom",
        Size: 12.5,
        ...
    })
}</code>

This approach allows all functions within the same package to access the db variable. However, it's not recommended for long-running applications as global variables can lead to resource leaks and unexpected behavior.

Parameter Passing:

Pass the db variable as a parameter to the addRow function:

<code class="go">func addRow(db *sql.DB, row Room) error {
    stmt, err := db.Prepare("INSERT INTO Rooms (...)")
    ...
    return nil
}</code>

This method provides more control over the scope of the database connection and allows for better dependency injection.

Method of Struct:

Another option is to define addRow as a method of a struct that stores the database connection:

<code class="go">type Database struct {
    db *sql.DB
}

func (db *Database) AddRow(row Room) error {
    stmt, err := db.db.Prepare("INSERT INTO Rooms (...)")
    ...
    return nil
}</code>

This approach encapsulates the database connection and provides a more structured way of accessing it.

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