Catch UniqueConstraintViolationException inside insertIfNotExist

This is the most common case for the usage of this method.

See also https://github.com/nextcloud/server/issues/12369 and the linked tickets.

Signed-off-by: Morris Jobke <hey@morrisjobke.de>

lib/private/DB/Adapter.php

@@ -27,6 +27,8 @@
 
 namespace OC\DB;
 
+use Doctrine\DBAL\Exception\UniqueConstraintViolationException;
+
 /**
  * This handles the way we use to write queries, into something that can be
  * handled by the database abstraction layer.
@@ -79,7 +81,9 @@ class Adapter {
 	}
 
 	/**
-	 * Insert a row if the matching row does not exists.
+	 * Insert a row if the matching row does not exists. To accomplish proper race condition avoidance
+	 * it is needed that there is also a unique constraint on the values. Then this method will
+	 * catch the exception and return 0.
 	 *
 	 * @param string $table The table name (will replace *PREFIX* with the actual prefix)
 	 * @param array $input data that should be inserted into the table  (column name => value)
@@ -111,6 +115,14 @@ class Adapter {
 		$query = substr($query, 0, -5);
 		$query .= ' HAVING COUNT(*) = 0';
 
+		try {
 			return $this->conn->executeUpdate($query, $inserts);
+		} catch (UniqueConstraintViolationException $e) {
+			// if this is thrown then a concurrent insert happened between the insert and the sub-select in the insert, that should have avoided it
+			// it's fine to ignore this then
+			//
+			// more discussions about this can be found at https://github.com/nextcloud/server/pull/12315
+			return 0;
+		}
 	}
 }

lib/private/DB/AdapterSqlite.php

@@ -27,6 +27,8 @@
 
 namespace OC\DB;
 
+use Doctrine\DBAL\Exception\UniqueConstraintViolationException;
+
 class AdapterSqlite extends Adapter {
 
 	/**
@@ -50,7 +52,9 @@ class AdapterSqlite extends Adapter {
 	}
 
 	/**
-	 * Insert a row if the matching row does not exists.
+	 * Insert a row if the matching row does not exists. To accomplish proper race condition avoidance
+	 * it is needed that there is also a unique constraint on the values. Then this method will
+	 * catch the exception and return 0.
 	 *
 	 * @param string $table The table name (will replace *PREFIX* with the actual prefix)
 	 * @param array $input data that should be inserted into the table  (column name => value)
@@ -82,6 +86,14 @@ class AdapterSqlite extends Adapter {
 		$query = substr($query, 0, -5);
 		$query .= ')';
 
+		try {
 			return $this->conn->executeUpdate($query, $inserts);
+		} catch (UniqueConstraintViolationException $e) {
+			// if this is thrown then a concurrent insert happened between the insert and the sub-select in the insert, that should have avoided it
+			// it's fine to ignore this then
+			//
+			// more discussions about this can be found at https://github.com/nextcloud/server/pull/12315
+			return 0;
+		}
 	}
 }

lib/private/DB/Connection.php

@@ -240,7 +240,9 @@ class Connection extends ReconnectWrapper implements IDBConnection {
 	}
 
 	/**
-	 * Insert a row if the matching row does not exists.
+	 * Insert a row if the matching row does not exists. To accomplish proper race condition avoidance
+	 * it is needed that there is also a unique constraint on the values. Then this method will
+	 * catch the exception and return 0.
 	 *
 	 * @param string $table The table name (will replace *PREFIX* with the actual prefix)
 	 * @param array $input data that should be inserted into the table  (column name => value)

lib/public/IDBConnection.php

@@ -104,7 +104,9 @@ interface IDBConnection {
 	public function lastInsertId($table = null);
 
 	/**
-	 * Insert a row if the matching row does not exists.
+	 * Insert a row if the matching row does not exists. To accomplish proper race condition avoidance
+	 * it is needed that there is also a unique constraint on the values. Then this method will
+	 * catch the exception and return 0.
 	 *
 	 * @param string $table The table name (will replace *PREFIX* with the actual prefix)
 	 * @param array $input data that should be inserted into the table  (column name => value)