// processClause retrieves the triples for the provided triple given the
// information available.
func (p *queryPlan) processClause(ctx context.Context, cls *semantic.GraphClause, lo *storage.LookupOptions) (bool, error) {
// This method decides how to process the clause based on the current
// list of bindings solved and data available.
if cls.Specificity() == 3 {
t, err := triple.New(cls.S, cls.P, cls.O)
if err != nil {
return false, err
}
b, tbl, err := simpleExist(ctx, p.grfs, cls, t)
if err != nil {
return false, err
}
if err := p.tbl.AppendTable(tbl); err != nil {
return b, err
}
return b, nil
}
exist, total := 0, 0
for _, b := range cls.Bindings() {
total++
if p.tbl.HasBinding(b) {
exist++
}
}
if exist == 0 {
// Data is new.
tbl, err := simpleFetch(ctx, p.grfs, cls, lo, p.chanSize)
if err != nil {
return false, err
}
if len(p.tbl.Bindings()) > 0 {
return false, p.tbl.DotProduct(tbl)
}
return false, p.tbl.AppendTable(tbl)
}
if exist > 0 && exist < total {
// Data is partially bound, retrieve data either extends the row with the
// new bindings or filters it out if now new bindings are available.
return false, p.specifyClauseWithTable(ctx, cls, lo)
}
if exist > 0 && exist == total {
// Since all bindings in the clause are already solved, the clause becomes a
// fully specified triple. If the triple does not exist the row will be
// deleted.
return false, p.filterOnExistence(ctx, cls, lo)
}
// Something is wrong with the code.
return false, fmt.Errorf("queryPlan.processClause(%v) should have never failed to resolve the clause", cls)
}
