CODEWITHSUNDEEP
postgresqlgo
connectwithpalaniappan
connectwithpalaniappan

Reputation: 973

Error "value of type []uint8 is not assignable to type []string" when scanning a DB row

I am using postgresql as my backend database.

Tried to scan a field languagespoken which is an array of text

var user userprofile
row := core.db.QueryRow(
    "SELECT languagespoken FROM \"user\" WHERE id = $1",
    userId,
)

err := row.Scan(&user.Languages)

if err != nil {
    return user, err
}

My structure looks like this

type userprofile struct {
    Languages []string `json:languages`
}

But getting the error

2014/06/30 15:27:17 PANIC: reflect.Set: **value of type []uint8 is not assignable to type []string**
/usr/lib/go/src/pkg/reflect/value.go:2198 (0x56c152)
    Value.assignTo: panic(context + ": value of type " + v.typ.String() + " is not assignable to type " + dst.String())
/usr/lib/go/src/pkg/reflect/value.go:1385 (0x56966b)
    Value.Set: x = x.assignTo("reflect.Set", v.typ, target)
/usr/lib/go/src/pkg/database/sql/convert.go:215 (0x492d70)
    convertAssign: dv.Set(sv)
/usr/lib/go/src/pkg/database/sql/sql.go:1562 (0x49c0e5)
    (*Rows).Scan: err := convertAssign(dest[i], sv)
/usr/lib/go/src/pkg/database/sql/sql.go:1630 (0x49c560)
    (*Row).Scan: err := r.rows.Scan(dest...)
/home/ceresti/source/gocode/src/ceresti.kilnhg.com/ceresti/server/app/databaseapi.go:144 (0x402478)
    (*coreStruct).GetUserProfile: err := row.Scan(&user.Languages)
/home/ceresti/source/gocode/src/ceresti.kilnhg.com/ceresti/server/app/restfulapi.go:327 (0x40a63c)
    Getuserprofile: userprofileStruct, err := core.GetUserProfile(userId)
/usr/lib/go/src/pkg/runtime/asm_amd64.s:340 (0x4309c2)

Please let me know how to resolve this issue.

Upvotes: 3

Views: 6869

Answers (2)

weberc2
weberc2

Reputation: 7898

Not all sql databases specify array types (e.g., sqlite3). Go doesn't support any sql implementations directly, but it supplies an implementation-agnostic interface (in the generic sense of the word) for which third-party drivers may be written. Go doesn't impose any limitations on which types its drivers may support, so if a type doesn't cooperate, it's probably the fault of the driver.

TL;DR: Try getting it as a string

// if `string` doesn't work, try `[]uint8` or `[]byte` and then convert
// that output to a string if necessary
var languages string
if err := row.Scan(&languages); err != nil {
    // handle error
}

// depending on how the string is encoded, this may or may not work
// Update: since you say your list is encoded in the form:
// `{elem1, elem2, elem3}`, we'll simply ignore the first and last
// characters and split on ", "
user.Languages = strings.Split(languages[1:len(languages)-1], ", ")

Upvotes: 5

andlabs
andlabs

Reputation: 11578

It appears you're trying to scan the entire result set of that database query in one shot. You can't do that; you need to read each row, one at a time, into a byte slice, then convert the byte slice into a string.

Since you're serializing into a []string, saving the byte slice each time is not a priority. In this case, you can use sql.RawBytes instead of []byte, which will reuse the same memory.

// error checking elided
var row sql.RawBytes
myRow.Scan(&row) // note the pointer!
str := string(row)

Upvotes: 2

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