Add ON DELETE CASCADE to domain/range columns of association tables.

microrm/src/schema/build.rs

@@ -42,7 +42,7 @@ impl TableInfo {
         });
         let fkeys = self.columns.iter().filter_map(|col| {
             Some(format!(
-                ", foreign key(`{}`) references {}",
+                ", foreign key(`{}`) references {} on delete cascade",
                 col.name,
                 col.fkey.as_ref()?
             ))