用gorm插入数据时，检查不存在相同的检查

I am using gorm. I want to insert value while not exist same value

just like the raw sql.

INSERT INTO student (firstname, lastname)
SELECT 'NEW FIRSTNAME', 'NEW LASTNAME'
FROM DUAL
WHERE NOT EXISTS(
    SELECT 1
    FROM table_name
    WHERE firstname = 'NEW FIRSTNAME' AND lastname = 'NEW LASTNAME'
)
LIMIT 1;

How to implement this function with gorm

type Student struct {
    Firstname string
    Lastname string
}

func insert()  {
    stu :=Student{"fir","la"}
    if res := DB.Create(&stu).Or("some condition"); res.Error != nil {
        logrus.Println(res.Error)

    }
}

when found same value i want a message or error message

FirstOrCreate

Get first matched record, or initalize a new one with given conditions (only works with struct, map conditions)

db.FirstOrCreate(&user, User{Name: "non_existing"})