How do I insert a row into an SQLite database using swift? - sql

Question

I have a SQLITE3 database with two tables, main and activities. I am trying to insert a row into the main table just to check it works, using the sql command on terminal I am able to insert, but not through swift. The database is connected and allows me to read from the database using swift but not write to it.
let insertStatementString = "INSERT INTO main (DATE) VALUES (?);"
func insert() {
var insertStatement: OpaquePointer?
//1
if sqlite3_prepare_v2(mySQLDB,insertStatementString, -1, &insertStatement, nil) == SQLITE_OK {
let date: NSString = "14071999"
sqlite3_bind_text(insertStatement,1,date.utf8String, -1, nil)
if sqlite3_step(insertStatement) == SQLITE_DONE {
print("\nSuccessfully inserted row")
} else
{ print("\nCould not insert a row")
}
}
else
{ print("\nInsert statement not prepared")
}
sqlite3_finalize(insertStatement)
}
When the program reaches 'if sqlite3_step(insertStatement) == SQLITE_DONE' it then skips to 'Could not insert row'.
Can anyone see why this is going wrong?

Answer 1

If your insert failed, you should print the error message, sqlite3_errmsg, which will tell you precisely what went wrong.
FWIW, your code worked for me, so it’s probably something not included in your question, for example how you opened the database and/or how the table was defined. Possible problems include:
inserting into a read-only database (e.g., opened database in the bundle which is read-only, explicitly opened with sqlite3_open_v2 in read-only mode, etc.);
your bind statement failed (you really should check for success there, too);
having a unique key on this column and already having this value somewhere; or
having other required (NOT NULL) columns that were not supplied.
Regardless, logging the error message will remove any ambiguity.
E.g.
func insert() {
var insertStatement: OpaquePointer?
guard sqlite3_prepare_v2(mySQLDB, insertStatementString, -1, &insertStatement, nil) == SQLITE_OK else {
printError(with: "INSERT statement not prepared")
return
}
defer { sqlite3_finalize(insertStatement) }
let date = "14071999"
guard sqlite3_bind_text(insertStatement, 1, date.cString(using: .utf8), -1, SQLITE_TRANSIENT) == SQLITE_OK else {
printError(with: "Bind for INSERT failed")
return
}
guard sqlite3_step(insertStatement) == SQLITE_DONE else {
printError(with: "Could not insert a row")
return
}
print("Successfully inserted row")
}
func printError(with message: String) {
let errmsg = sqlite3_errmsg(mySQLDB).flatMap { String(cString: $0) } ?? "Unknown error"
print(message, errmsg)
}
Where
internal let SQLITE_TRANSIENT = unsafeBitCast(-1, to: sqlite3_destructor_type.self)
While I structured this with guard statements, even if you stay with your if pattern, make sure you only sqlite3_finalize if the prepare statement succeeded. There’s no point in finalizing if the prepare failed.
It’s also prudent to use SQLITE_TRANSIENT for bound parameters.