Function createFilterFunction

packages/db/src/collection/change-events.ts:189–220

(
  whereCallback: (row: SingleRowRefProxy<T>) => any,
)

 * @returns A function that takes an item and returns true if it matches the filter
 */
export function createFilterFunction<T extends object>(
  whereCallback: (row: SingleRowRefProxy<T>) => any,
): (item: T) => boolean {
  return (item: T): boolean => {
    try {
      // First try the RefProxy approach for query builder functions
      const singleRowRefProxy = createSingleRowRefProxy<T>()
      const whereExpression = whereCallback(singleRowRefProxy)
      const expression = toExpression(whereExpression)
      const evaluator = compileSingleRowExpression(expression)
      const result = evaluator(item as Record<string, unknown>)
      // WHERE clauses should always evaluate to boolean predicates (Kevin's feedback)
      return toBooleanPredicate(result)
    } catch {
      // If RefProxy approach fails (e.g., arithmetic operations), fall back to direct evaluation
      try {
        // Create a simple proxy that returns actual values for arithmetic operations
        const simpleProxy = new Proxy(item as any, {
          get(target, prop) {
            return target[prop]
          },
        }) as SingleRowRefProxy<T>

        const result = whereCallback(simpleProxy)
        return toBooleanPredicate(result)
      } catch {
        // If both approaches fail, exclude the item
        return false
      }
    }
  }
}

/**
 * Creates a filter function from a pre-compiled expression