fix(transfer): reseed Oracle identity columns after copying explicit ids

crates/dbx-core/src/data/transfer.rs

@@ -2858,6 +2858,50 @@ fn generate_postgres_sequence_sync_sql(columns: &[db::ColumnInfo], table: &str,
         .collect()
 }
 
+/// `ALTER TABLE ... MODIFY <column> GENERATED BY DEFAULT AS IDENTITY (START WITH LIMIT VALUE)`
+/// statements for Oracle targets.
+///
+/// Oracle accepts explicit values in a `GENERATED BY DEFAULT AS IDENTITY` column but
+/// does not advance its sequence, so the first auto-generated insert after copying
+/// explicit ids can collide with a copied value. `START WITH LIMIT VALUE` makes Oracle
+/// lock the table and move the sequence past the maximum value in the column.
+///
+/// The filter mirrors the identity emission in
+/// `generate_create_table_ddl_with_column_quoting` (primary key, explicit
+/// auto-increment, integer-like mapped type), so the ALTER only targets a column the
+/// generated DDL created as an identity column.
+fn oracle_identity_reseed_statements(
+    columns: &[db::ColumnInfo],
+    table: &str,
+    schema: &str,
+    source_schema: &str,
+    source_db: &DatabaseType,
+    quote_target_column_names: bool,
+) -> Vec<String> {
+    let full_table = qualified_table(table, schema, &DatabaseType::Oracle, None);
+    columns
+        .iter()
+        .filter(|column| {
+            column.is_primary_key
+                && column_is_auto_increment(column)
+                && type_looks_integer(&postgres_column_type_sql(
+                    column,
+                    source_schema,
+                    schema,
+                    source_db,
+                    &DatabaseType::Oracle,
+                ))
+        })
+        .map(|column| {
+            let quoted_column =
+                transfer_column_identifier(&column.name, &DatabaseType::Oracle, quote_target_column_names);
+            format!(
+                "ALTER TABLE {full_table} MODIFY {quoted_column} GENERATED BY DEFAULT AS IDENTITY (START WITH LIMIT VALUE)"
+            )
+        })
+        .collect()
+}
+
 /// Explicit identity values do not advance Xugu's backing sequence. Resolve the
 /// sequence through SERIAL_ID rather than relying on its generated name, which
 /// belongs to SYSDBA even when the table lives in another schema.
@@ -12257,6 +12301,30 @@ where
         }
     }
 
+    // Oracle accepts explicit ids in a `GENERATED BY DEFAULT AS IDENTITY` column but
+    // does not advance the sequence, so move it past the copied values. Only for
+    // tables this run created — `START WITH LIMIT VALUE` requires the identity column
+    // the generated DDL just created, and a preexisting target may not have one.
+    // OceanBase Oracle and DM8 stay out until their behavior is verified.
+    if *target_db_type == DatabaseType::Oracle
+        && request.create_table
+        && !target_table_preexisting
+        && total_transferred > 0
+    {
+        for statement in oracle_identity_reseed_statements(
+            &columns,
+            &target_table,
+            &request.target_schema,
+            &request.source_schema,
+            source_db_type,
+            request.quote_target_column_names,
+        ) {
+            execute_on_pool(state, target_pool_key, &statement)
+                .await
+                .map_err(|e| format!("Failed to reseed the Oracle identity column for {target_table}: {e}"))?;
+        }
+    }
+
     if should_restore_postgres_table_schema {
         restore_postgres_table_schema_objects(
             state,
@@ -19024,6 +19092,31 @@ PARTITION p_old VALUES LESS THAN (TO_DAYS('2026-01-01')))";
         );
     }
 
+    #[test]
+    fn oracle_identity_reseed_targets_generated_identity_columns() {
+        let columns = vec![
+            db::ColumnInfo {
+                is_primary_key: true,
+                extra: Some("auto_increment".to_string()),
+                ..test_column("id", "int")
+            },
+            // Not a key on the source: the generated DDL keeps it a plain column.
+            db::ColumnInfo { extra: Some("auto_increment".to_string()), ..test_column("ticket", "int") },
+            // Plain integer primary key without an explicit auto-increment stays plain.
+            db::ColumnInfo { is_primary_key: true, ..test_column("tenant", "int") },
+        ];
+
+        let statements =
+            oracle_identity_reseed_statements(&columns, "users", "SALES", "source", &DatabaseType::Mysql, true);
+
+        assert_eq!(
+            statements,
+            vec![
+                "ALTER TABLE \"SALES\".\"users\" MODIFY \"id\" GENERATED BY DEFAULT AS IDENTITY (START WITH LIMIT VALUE)".to_string()
+            ]
+        );
+    }
+
     #[test]
     fn postgres_sequence_sync_sql_casts_text_and_numeric_columns_to_bigint() {
         let sql = generate_postgres_sequence_sync_sql(