How can I query and return only id array by GORM?

When using GORM for database operations, if you only want to query and return an array of values for a specific field (e.g., the id field), you can use the Pluck method. The Pluck method allows you to select a specific column from the model and collect the results into a slice. Here is a specific example:

Assume you have a model named User that represents the users table in the database, which contains multiple fields, one of which is ID.

go
type User struct {
    ID    uint
    Name  string
    Email string
}

// Initialize GORM connection
db, err := gorm.Open(sqlite.Open("test.db"), &gorm.Config{})
if err != nil {
    panic("failed to connect database")
}

// Use Pluck method to query all users' IDs
var ids []uint
result := db.Model(&User{}).Pluck("ID", &ids)
if result.Error != nil {
    // Handle potential errors
    fmt.Println("Query error: ", result.Error)
}

fmt.Println("User ID list: ", ids)

In the above code:

1. Defines a User struct containing ID, Name, and Email fields.
2. Connects to an SQLite database (though it can be other databases like MySQL or PostgreSQL).
3. Uses the Pluck method to select only the ID column from the User model and store these IDs in the ids slice.

This method is particularly suitable when retrieving values of specific fields without loading the full model data, effectively reducing data transfer and improving performance.