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use crate::{
execute::execute_with_parameters,
handles::{self, Statement, StatementImpl},
parameter_collection::ParameterCollection,
CursorImpl, Error, Preallocated, Prepared,
};
use std::thread::panicking;
use widestring::{U16Str, U16String};
impl<'conn> Drop for Connection<'conn> {
fn drop(&mut self) {
match self.connection.disconnect() {
Ok(()) => (),
Err(Error::Diagnostics(record)) if record.is_invalid_state_transaction() => {
// Invalid transaction state. Let's rollback the current transaction and try again.
if let Err(e) = self.connection.rollback() {
// Avoid panicking, if we already have a panic. We don't want to mask the original
// error.
if !panicking() {
panic!(
"Unexpected error rolling back transaction (In order to recover \
from invalid transaction state during disconnect): {:?}",
e
)
}
}
// Transaction is rolled back. Now let's try again to disconnect.
if let Err(e) = self.connection.disconnect() {
// Avoid panicking, if we already have a panic. We don't want to mask the original
// error.
if !panicking() {
panic!("Unexpected error disconnecting): {:?}", e)
}
}
}
Err(e) => {
// Avoid panicking, if we already have a panic. We don't want to mask the original
// error.
if !panicking() {
panic!("Unexpected error disconnecting: {:?}", e)
}
}
}
}
}
/// The connection handle references storage of all information about the connection to the data
/// source, including status, transaction state, and error information.
pub struct Connection<'c> {
connection: handles::Connection<'c>,
}
impl<'c> Connection<'c> {
pub(crate) fn new(connection: handles::Connection<'c>) -> Self {
Self { connection }
}
/// Executes an sql statement using a wide string. See [`Self::execute`].
pub fn execute_utf16(
&self,
query: &U16Str,
params: impl ParameterCollection,
) -> Result<Option<CursorImpl<StatementImpl>>, Error> {
let lazy_statement = move || self.connection.allocate_statement();
execute_with_parameters(lazy_statement, Some(query), params)
}
/// Executes an SQL statement. This is the fastest way to submit an SQL statement for one-time
/// execution.
///
/// # Parameters
///
/// * `query`: The text representation of the SQL statement. E.g. "SELECT * FROM my_table;".
/// * `params`: `?` may be used as a placeholder in the statement text. You can use `()` to
/// represent no parameters. See the [`crate::parameter`] module level documentation for more
/// information on how to pass parameters.
///
/// # Return
///
/// Returns `Some` if a cursor is created. If `None` is returned no cursor has been created (
/// e.g. the query came back empty). Note that an empty query may also create a cursor with zero
/// rows.
///
/// # Example
///
/// ```no_run
/// use odbc_api::Environment;
///
/// // I herby solemnly swear that this is the only ODBC environment in the entire process, thus
/// // making this call safe.
/// let env = unsafe {
/// Environment::new()?
/// };
///
/// let mut conn = env.connect("YourDatabase", "SA", "<YourStrong@Passw0rd>")?;
/// if let Some(cursor) = conn.execute("SELECT year, name FROM Birthdays;", ())? {
/// // Use cursor to process query results.
/// }
/// # Ok::<(), odbc_api::Error>(())
/// ```
pub fn execute(
&self,
query: &str,
params: impl ParameterCollection,
) -> Result<Option<CursorImpl<StatementImpl>>, Error> {
let query = U16String::from_str(query);
self.execute_utf16(&query, params)
}
/// Prepares an SQL statement. This is recommended for repeated execution of similar queries.
///
/// # Parameters
///
/// * `query`: The text representation of the SQL statement. E.g. "SELECT * FROM my_table;". `?`
/// may be used as a placeholder in the statement text, to be replaced with parameters during
/// execution.
pub fn prepare_utf16(&self, query: &U16Str) -> Result<Prepared, Error> {
let mut stmt = self.connection.allocate_statement()?;
stmt.prepare(query)?;
Ok(Prepared::new(stmt))
}
/// Prepares an SQL statement. This is recommended for repeated execution of similar queries.
///
/// # Parameters
///
/// * `query`: The text representation of the SQL statement. E.g. "SELECT * FROM my_table;". `?`
/// may be used as a placeholder in the statement text, to be replaced with parameters during
/// execution.
pub fn prepare(&self, query: &str) -> Result<Prepared, Error> {
let query = U16String::from_str(query);
self.prepare_utf16(&query)
}
/// Allocates an SQL statement handle. This is recommended if you want to sequentially execute
/// different queries over the same connection, as you avoid the overhead of allocating a
/// statement handle for each query.
///
/// Should you want to repeatedly execute the same query with different parameters try
/// [`Self::prepare`] instead.
///
/// # Example
///
/// ```
/// use odbc_api::{Connection, Error};
/// use std::io::{self, stdin, Read};
///
/// fn interactive(conn: &Connection) -> io::Result<()>{
/// let mut statement = conn.preallocate().unwrap();
/// let mut query = String::new();
/// stdin().read_line(&mut query)?;
/// while !query.is_empty() {
/// match statement.execute(&query, ()) {
/// Err(e) => println!("{}", e),
/// Ok(None) => println!("No results set generated."),
/// Ok(Some(cursor)) => {
/// // ...print cursor contents...
/// },
/// }
/// stdin().read_line(&mut query)?;
/// }
/// Ok(())
/// }
/// ```
pub fn preallocate(&self) -> Result<Preallocated, Error> {
let stmt = self.connection.allocate_statement()?;
Ok(Preallocated::new(stmt))
}
/// Specify the transaction mode. By default, ODBC transactions are in auto-commit mode.
/// Switching from manual-commit mode to auto-commit mode automatically commits any open
/// transaction on the connection. There is no open or begin transaction method. Each statement
/// execution automatically starts a new transaction or adds to the existing one.
///
/// In manual commit mode you can use [`Connection::commit`] or [`Connection::rollback`]. Keep
/// in mind, that even `SELECT` statements can open new transactions. This library will rollback
/// open transactions if a connection goes out of SCOPE. This however will log an error, since
/// the transaction state is only discovered during a failed disconnect. It is preferable that
/// the appliacation makes sure all transactions are closed if in manual commit mode.
pub fn set_autocommit(&self, enabled: bool) -> Result<(), Error> {
self.connection.set_autocommit(enabled)
}
/// To commit a transaction in manual-commit mode.
pub fn commit(&self) -> Result<(), Error> {
self.connection.commit()
}
/// To rollback a transaction in manual-commit mode.
pub fn rollback(&self) -> Result<(), Error> {
self.connection.rollback()
}
/// Allows sending this connection to different threads. This Connection will still be only be
/// used by one thread at a time, but it may be a different thread each time.
///
/// # Example
///
/// ```no_run
/// use std::thread;
/// use lazy_static::lazy_static;
/// use odbc_api::Environment;
/// lazy_static! {
/// static ref ENV: Environment = unsafe { Environment::new().unwrap() };
/// }
/// const MSSQL: &str =
/// "Driver={ODBC Driver 17 for SQL Server};\
/// Server=localhost;\
/// UID=SA;\
/// PWD=<YourStrong@Passw0rd>;\
/// ";
///
/// let conn = ENV.connect_with_connection_string("MSSQL").unwrap();
/// let conn = unsafe { conn.promote_to_send() };
/// let handle = thread::spawn(move || {
/// if let Some(cursor) = conn.execute("SELECT title FROM Movies ORDER BY year",())? {
/// // Use cursor to process results
/// }
/// Ok::<(), odbc_api::Error>(())
/// });
/// handle.join().unwrap()?;
/// # Ok::<(), odbc_api::Error>(())
/// ```
///
/// # Safety
///
/// According to the ODBC standard this should be safe. By calling this function you express your
/// trust in the implementation of the ODBC driver your application is using.
///
/// See: <https://docs.microsoft.com/en-us/sql/odbc/reference/develop-app/multithreading?view=sql-server-ver15>
///
/// This function may be removed in future versions of this crate and connections would be
/// `Send` and `Sync` out of the Box. This will require sufficient testing in which a wide
/// variety of database drivers prove to be thread safe. For now this API tries to error on the
/// side of caution, and leaves the amount of trust you want to put in the driver implementation
/// to the user. I have seen this go wrong in the past, but time certainly improved the
/// situation. At one point this will be cargo cult and Connection can be `Send` and `Sync` by
/// default (hopefully).
///
/// Note to users of `unixodbc`: You may configure the threading level to make unixodbc
/// synchronize access to the driver (and therby making them thread safe if they are not
/// thread safe by themself. This may however hurt your performancy if the driver would actually
/// be able to perform operations in parallel.
///
/// See: <https://stackoverflow.com/questions/4207458/using-unixodbc-in-a-multithreaded-concurrent-setting>
pub unsafe fn promote_to_send(self) -> force_send_sync::Send<Self> {
force_send_sync::Send::new(self)
}
}