Method WriteTo

factstore/simplecolumn.go:240–309

WriteTo writes contents of a fact store to the writer. It only calls the ListPredicates and GetFacts methods on the store. Flushing or closing the writer is is the caller's responsibility.

(store ReadOnlyFactStore, w io.Writer)

// calls the ListPredicates and GetFacts methods on the store.
// Flushing or closing the writer is is the caller's responsibility.
func (sc SimpleColumn) WriteTo(store ReadOnlyFactStore, w io.Writer) error {
	preds := store.ListPredicates()
	if len(preds) > maxNumPreds {
		return ErrTooManyPreds
	}
	if sc.Deterministic {
		sort.Slice(preds, func(i, j int) bool {
			a := preds[i]
			b := preds[j]
			return a.Arity < b.Arity || a.Arity == b.Arity && a.Symbol < b.Symbol
		})
	}
	predFactCount := make([]int, len(preds))
	for i, p := range preds {
		if p.Arity > maxArity {
			return fmt.Errorf("pred %v: %w", p, ErrUnsupportedArity)
		}
		var numFacts int
		if err := store.GetFacts(ast.NewQuery(p), func(a ast.Atom) error {
			numFacts++
			return nil
		}); err != nil {
			return err
		}
		if numFacts > maxFactsPerPredicate {
			return fmt.Errorf("pred %v: %w", p, ErrTooManyFacts)
		}
		predFactCount[i] = numFacts
	}
	if err := sc.writeHeader(preds, predFactCount, w); err != nil {
		return err
	}
	// for each predicate p with arity > 0:
	for _, p := range preds {
		if p.Arity == 0 {
			continue
		}
		var facts []ast.Atom
		if err := store.GetFacts(ast.NewQuery(p), func(a ast.Atom) error {
			facts = append(facts, a)
			return nil
		}); err != nil {
			return err
		}
		if sc.Deterministic {
			sort.Slice(facts, func(i, j int) bool {
				h1, h2 := facts[i].Hash(), facts[j].Hash()
				if h1 == h2 {
					return facts[i].String() < facts[j].String()
				}
				return h1 < h2
			})
		}
		for i := 0; i < p.Arity; i++ {
			for _, f := range facts {
				if len(f.Args) != p.Arity {
					return fmt.Errorf("malformed fact: %v predicate arity %d: %w", f, p.Arity, ErrWrongArgument)
				}