allow explicit transactions in mysql

Author: lovasoa

CHANGELOG.md

@@ -19,6 +19,7 @@
     insert into t values ($invalid_value); -- if this statement fails, ...
     insert into t values (42); -- this next statement should not be executed
     ```
+- Fix `error returned from database: 1295 (HY000): This command is not supported in the prepared statement protocol yet` when trying to use transactions with MySQL. `START TRANSACTION` now works as expected in MySQL.
 
 ## 0.31.0 (2024-11-24)
 

src/webserver/database/execute_queries.rs

@@ -320,7 +320,12 @@ async fn bind_parameters<'a, 'b>(
             Some(Cow::Borrowed(v)) => arguments.add(v),
         }
     }
-    Ok(StatementWithParams { sql, arguments })
+    let has_arguments = !stmt.params.is_empty();
+    Ok(StatementWithParams {
+        sql,
+        arguments,
+        has_arguments,
+    })
 }
 
 async fn apply_delayed_functions(
@@ -404,6 +409,7 @@ fn apply_json_columns(item: &mut DbItem, json_columns: &[String]) {
 pub struct StatementWithParams<'a> {
     sql: &'a str,
     arguments: AnyArguments<'a>,
+    has_arguments: bool,
 }
 
 impl<'q> sqlx::Execute<'q, Any> for StatementWithParams<'q> {
@@ -416,7 +422,11 @@ impl<'q> sqlx::Execute<'q, Any> for StatementWithParams<'q> {
     }
 
     fn take_arguments(&mut self) -> Option<<Any as sqlx::database::HasArguments<'q>>::Arguments> {
-        Some(std::mem::take(&mut self.arguments))
+        if self.has_arguments {
+            Some(std::mem::take(&mut self.arguments))
+        } else {
+            None
+        }
     }
 
     fn persistent(&self) -> bool {

tests/failed_transaction_mysql.sql

@@ -0,0 +1,10 @@
+START TRANSACTION; -- mysql syntax
+CREATE TEMPORARY TABLE IF NOT EXISTS t(f VARCHAR(255) NOT NULL); -- mysql does not remove temporary tables on rollback
+INSERT INTO t(f) SELECT 'bad value' where $x is null;
+SELECT 'debug' as component, f from t;
+INSERT INTO t(f) VALUES ($x); -- this will fail if $x is null. And the transaction should be rolled back, so 'bad value' should not be in the table
+COMMIT;
+
+select 'text' as component, $x as contents
+where not exists (select 1 from t where f = 'bad value');
+

tests/index.rs

@@ -476,18 +476,25 @@ async fn test_transaction_error() -> actix_web::Result<()> {
     // But then, when we request again with a parameter, we should not see any side
     // effect coming from the first transaction, and it should succeed
     let data = make_app_data().await;
-    let req = get_request_to_with_data("/tests/failed_transaction.sql", data.clone())
+    let path = match data.db.to_string().to_lowercase().as_str() {
+        "mysql" => "/tests/failed_transaction_mysql.sql",
+        _ => "/tests/failed_transaction.sql",
+    };
+    let req = get_request_to_with_data(path, data.clone())
         .await?
         .to_srv_request();
     let resp = main_handler(req).await?;
     let body = test::read_body(resp).await;
-    let body_str = String::from_utf8(body.to_vec()).unwrap().to_ascii_lowercase();
+    let body_str = String::from_utf8(body.to_vec())
+        .unwrap()
+        .to_ascii_lowercase();
     assert!(
         body_str.contains("error") && body_str.contains("null"),
         "{body_str}\nexpected to contain: constraint failed"
     );
     // Now query again, with ?x=1447
-    let req = get_request_to_with_data("/tests/failed_transaction.sql?x=1447", data)
+    let path_with_param = path.to_string() + "?x=1447";
+    let req = get_request_to_with_data(&path_with_param, data.clone())
         .await?
         .to_srv_request();
     let resp = main_handler(req).await?;