Function old_value 

pub fn old_value<C: Column>(col: C) -> old_value<C>

Available on crate feature mariadb_backend only.

Refer to the pre-modification value of col in a Mariadb RETURNING clause.

This corresponds to the SQL RETURNING OLD_VALUE(col) syntax introduced in Mariadb 13.0.

Requires Mariadb 13.0 or newer

Diesel emits OLD_VALUE(col) in the SQL it sends to the database. Earlier versions of Mariadb will reject the query at execution time.

Statement compatibility

old_value(col) is valid inside the RETURNING clause of:

• an UPDATE statement, as a whole RETURNING item that loads into the same Rust types as col (since every returned row necessarily came from a pre-existing row).

Use of old_value(col) in INSERT or DELETE RETURNING is rejected at compile time, because it is invalid there. (Note that ON CONFLICT DO NOTHING never returns untouched rows.)

On MariaDB 13.0, old_value of a view column that is an expression or a constant crashes the server (MDEV-40125). MariaDB 13.1.1 returns the right value.

Example

let was_and_now = diesel::update(users.find(1))
    .set(name.eq("Updated"))
    .returning((old_value(name), name))
    .get_result::<(String, String)>(connection);
assert_eq!(Ok(("Sean".to_string(), "Updated".to_string())), was_and_now);