How to dynamically generate SQL query column names and values from arrays? - sql

Question

I have about 20 columns in one row and not all columns are required to be filled in when row created also i dont want to cardcode name of every column in SQL query and on http.post request on frontend. All values are from form. My code:
var colNames, values []string
for k, v := range formData {
colNames = append(colNames, k)
values = append(values, v)
}
Now i have 2 arrays: one with column names and second with values to be inserted. I want to do something like this:
db.Query("insert into views (?,?,?,?,?,?) values (?,?,?,?,?,?)", colNames..., values...)
or like this:
db.Query("insert into views " + colNames + " values" + values)
Any suggestions?
Thanks!

Answer 1

I assume your code examples are just pseudo code but I'll state the obvious just in case.
db.Query("insert into views (?,?,?,?,?,?) values (?,?,?,?,?,?)", colNames..., values...)
This is invalid Go since you can only "unpack" the last argument to a function, and also invalid MySQL since you cannot use placeholders (?) for column names.
db.Query("insert into views " + colNames + " values" + values)
This is also invalid Go since you cannot concatenate strings with slices.
You could fromat the slices into strings that look like this:
colNamesString := "(col1, col2, col3)"
valuesString := "(val1, val2, val3)"
and now your second code example becomes valid Go and would compile but don't do this. If you do this your app becomes vulnerable to SQL injection and that's something you definitely don't want.
Instead do something like this:
// this can be a package level global and you'll need
// one for each table. Keep in mind that Go maps that
// are only read from are safe for concurrent use.
var validColNames = map[string]bool{
"col1": true,
"col2": true,
"col3": true,
// ...
}
// ...
var colNames, values []string
var phs string // placeholders for values
for k, v := range formData {
// check that column is valid
if !validColNames[k] {
return ErrBadColName
}
colNames = append(colNames, k)
values = append(values, v)
phs += "?,"
}
if len(phs) > 0 {
phs = phs[:len(phs)-1] // drop the last comma
}
phs = "(" + phs + ")"
colNamesString := "(" + strings.Join(colNames, ",") + ")"
query := "insert into views " + colNamesString + phs
db.Query(query, values...)