golang sqldatabase行。

Question

does rows.Next go to the end of the list and not let you go back to the beginning? I want to run a query that checks if there is data for a specific object in a database. If there is that object, I want to update it. If it's not there, i want to insert a new row. So I do this:

    rows, err := db.Query(query)
    if err != nil {
        Error.Printf("error querying: %v", err)
    }

    if !rows.Next() {
        // insert new data
    }

that works on it's own like i expect. BUT if I do this instead and at more logic to the end of the snippet:

    rows, err := db.Query(query)
    if err != nil {
        Error.Printf("error querying: %v", err)
    }

    if !rows.Next() {
        // insert new data
    }
    for rows.Next() {
        fmt.Println("-----")
        // do update
    }

My for rows.Next() never gets entered. If I move the for rows.Next() block above the if !rows.Next() block, it does work as expected. So is there something that happens when you call Next() that you have to do to read from the query again? Thanks in advance.

Answer 1

You probably want something like this:

rows, err := db.Query(query)
if err != nil {
    Error.Printf("error querying: %v", err)
}
shouldinsert := true
for rows.Next() {
    shouldinsert = false
    fmt.Println("-----")
    // do update
}
if shouldinsert {
    // insert new data
}