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use crate::{Client, Error, Transaction};
/// The isolation level of a database transaction.
#[derive(Debug, Copy, Clone)]
#[non_exhaustive]
pub enum IsolationLevel {
/// Equivalent to `ReadCommitted`.
ReadUncommitted,
/// An individual statement in the transaction will see rows committed before it began.
ReadCommitted,
/// All statements in the transaction will see the same view of rows committed before the first query in the
/// transaction.
RepeatableRead,
/// The reads and writes in this transaction must be able to be committed as an atomic "unit" with respect to reads
/// and writes of all other concurrent serializable transactions without interleaving.
Serializable,
}
/// A builder for database transactions.
pub struct TransactionBuilder<'a> {
client: &'a mut Client,
isolation_level: Option<IsolationLevel>,
read_only: Option<bool>,
deferrable: Option<bool>,
}
impl<'a> TransactionBuilder<'a> {
pub(crate) fn new(client: &'a mut Client) -> TransactionBuilder<'a> {
TransactionBuilder {
client,
isolation_level: None,
read_only: None,
deferrable: None,
}
}
/// Sets the isolation level of the transaction.
pub fn isolation_level(mut self, isolation_level: IsolationLevel) -> Self {
self.isolation_level = Some(isolation_level);
self
}
/// Sets the access mode of the transaction.
pub fn read_only(mut self, read_only: bool) -> Self {
self.read_only = Some(read_only);
self
}
/// Sets the deferrability of the transaction.
///
/// If the transaction is also serializable and read only, creation of the transaction may block, but when it
/// completes the transaction is able to run with less overhead and a guarantee that it will not be aborted due to
/// serialization failure.
pub fn deferrable(mut self, deferrable: bool) -> Self {
self.deferrable = Some(deferrable);
self
}
/// Begins the transaction.
///
/// The transaction will roll back by default - use the `commit` method to commit it.
pub async fn start(self) -> Result<Transaction<'a>, Error> {
let mut query = "START TRANSACTION".to_string();
let mut first = true;
if let Some(level) = self.isolation_level {
first = false;
query.push_str(" ISOLATION LEVEL ");
let level = match level {
IsolationLevel::ReadUncommitted => "READ UNCOMMITTED",
IsolationLevel::ReadCommitted => "READ COMMITTED",
IsolationLevel::RepeatableRead => "REPEATABLE READ",
IsolationLevel::Serializable => "SERIALIZABLE",
};
query.push_str(level);
}
if let Some(read_only) = self.read_only {
if !first {
query.push(',');
}
first = false;
let s = if read_only {
" READ ONLY"
} else {
" READ WRITE"
};
query.push_str(s);
}
if let Some(deferrable) = self.deferrable {
if !first {
query.push(',');
}
let s = if deferrable {
" DEFERRABLE"
} else {
" NOT DEFERRABLE"
};
query.push_str(s);
}
struct RollbackIfNotDone<'me> {
client: &'me Client,
done: bool,
}
impl Drop for RollbackIfNotDone<'_> {
fn drop(&mut self) {
if self.done {
return;
}
self.client.__private_api_rollback(None);
}
}
// This is done as `Future` created by this method can be dropped after
// `RequestMessages` is synchronously send to the `Connection` by
// `batch_execute()`, but before `Responses` is asynchronously polled to
// completion. In that case `Transaction` won't be created and thus
// won't be rolled back.
{
let mut cleaner = RollbackIfNotDone {
client: self.client,
done: false,
};
self.client.batch_execute(&query).await?;
cleaner.done = true;
}
Ok(Transaction::new(self.client))
}
}