Currently the `routes` table has these two columns: `source_type` and `source_id`. The `source_type` column can either be `Namespace`, or `Project`. Because there are two columns this means you need to use both when filtering routes. For example: ```sql SELECT * FROM routes WHERE source_type = 'Project' AND source_id = 13083 ``` Combining such a query with other conditions and JOINs can lead to less than ideal query plan. Another problem is that we're storing string values in `source_type`, with no limitation on the length. This means we're wasting both disk and index space. We need to adjust the `routes` table so these two columns are replaced with the following columns: * `namespace_id` for namespace routes * `project_id` for project routes This allows changing the above query to: ```sql SELECT * FROM routes WHERE project_id = 13083 ``` This also optimizes index and disk usage because we can now store integer values, instead of string values. Finally, this allows us to set up foreign keys. This ensures a route can not point to orphaned data, and routes are removed automatically when their source object is removed (if desired). This does mean that we need to add 1 column per source type. This however is still _much_ better than the existing setup. Besides, it's unlikely we'll add many more over time (I don't see us using more than a handful of source types). cc @dzaporozhets @smcgivern @rspeicher @DouweM