Function extractCorrelation

packages/db/src/query/builder/index.ts:1345–1375

* Checks if two eq() arguments form a parent-child correlation. * Returns the parent and child PropRefs if found, undefined otherwise.

(
  argA: BasicExpression,
  argB: BasicExpression,
  parentAliases: Array<string>,
  childAliases: Array<string>,
)

 * Returns the parent and child PropRefs if found, undefined otherwise.
 */
function extractCorrelation(
  argA: BasicExpression,
  argB: BasicExpression,
  parentAliases: Array<string>,
  childAliases: Array<string>,
): { parentRef: PropRef; childRef: PropRef } | undefined {
  if (argA.type === `ref` && argB.type === `ref`) {
    const aAlias = argA.path[0]
    const bAlias = argB.path[0]

    if (
      aAlias &&
      bAlias &&
      parentAliases.includes(aAlias) &&
      childAliases.includes(bAlias)
    ) {
      return { parentRef: argA, childRef: argB }
    }

    if (
      aAlias &&
      bAlias &&
      parentAliases.includes(bAlias) &&
      childAliases.includes(aAlias)
    ) {
      return { parentRef: argB, childRef: argA }
    }
  }

  return undefined
}

// Internal function to build a query from a callback
// used by liveQueryCollectionOptions.query