Handling Dynamic Errors In Go (Specifically database/sql Package) - string

Question

Using the database/sql package in go for things like sql.Exec will return dynamically generated, unreferenced errors such as
"Error 1062: Duplicate entry '192' for key 'id'"
The problem is that it can also return errors such as
"Error 1146: Table 'tbl' doesn't exist"
From the same call to sql.Exec
How can I tell the difference between these two errors without
String comparison, or
Pattern matching for error code
Or are those idiomatic viable solutions for this problem?

Answer 1

database/sql package does not solve this problem. It's driver specific. For example, for mysql you can use:
if mysqlError, ok := err.(*mysql.MySQLError); ok {
if mysqlError.Number == 1146 {
//handling
}
}
Also, you can find some error constant package, like mysqlerr from VividCortex, and use it:
if mysqlError, ok := err.(*mysql.MySQLError); ok {
if mysqlError.Number == mysqlerr.ER_NO_SUCH_TABLE {
//handling
}
}
It's not much better than pattern matching, but seems to be more idiomatic.

Answer 2

I think there's no idiomatic solution, but I wrote a simple function for getting the error number, so you can easily compare them.
In this solution I assume that the construction of the error message is always the same: "Error -some number here-: Error description".
If there's no number in the error or something went wrong it returns 0.
func ErrorCode(e error) int {
err := e.Error() //the description of the error
if len(err) < 6 { //if its too small return 0
return 0
}
i := 6 //Skip the part "Error "
for ; len(err) > i && unicode.IsDigit(rune(err[i])); i++ {
} // Raising i until we reach the end of err or we reach the end of error code
n, e := strconv.Atoi(string(err[6:i])) //convert it to int
if e != nil {
return 0 //something went wrong
}
return n //return the error code
}
Go playground link: http://play.golang.org/p/xqhVycsuyI