Function getActiveAndLazySources

packages/db/src/query/compiler/joins.ts:662–686

* Returns the active and lazy collections for a join clause. * The active collection is the one that we need to fully iterate over * and it can be the main source (i.e. left collection) or the joined source (i.e. right collection). * The lazy collection is the one that we should join-in lazily ba

(
  joinType: JoinClause[`type`],
  leftCollection: Collection,
  rightCollection: Collection,
)

 * @returns The active and lazy collections. They are undefined if we need to loop over both collections (i.e. both are active)
 */
function getActiveAndLazySources(
  joinType: JoinClause[`type`],
  leftCollection: Collection,
  rightCollection: Collection,
):
  | { activeSource: `main` | `joined`; lazySource: Collection }
  | { activeSource: undefined; lazySource: undefined } {
  // Self-joins can now be optimized since we track lazy loading by source alias
  // rather than collection ID. Each alias has its own subscription and lazy state.

  switch (joinType) {
    case `left`:
      return { activeSource: `main`, lazySource: rightCollection }
    case `right`:
      return { activeSource: `joined`, lazySource: leftCollection }
    case `inner`:
      // The smallest collection should be the active collection
      // and the biggest collection should be lazy
      return leftCollection.size < rightCollection.size
        ? { activeSource: `main`, lazySource: rightCollection }
        : { activeSource: `joined`, lazySource: leftCollection }
    default:
      return { activeSource: undefined, lazySource: undefined }
  }
}