Method fillVars

query/query.go:1806–1876

fillVars reads the value corresponding to a variable from the map mp and stores it inside SubGraph. This value is then later used for execution of the SubGraph.

(mp map[string]varValue)

// fillVars reads the value corresponding to a variable from the map mp and stores it inside
// SubGraph. This value is then later used for execution of the SubGraph.
func (sg *SubGraph) fillVars(mp map[string]varValue) error {
	if sg.Params.Alias == "shortest" {
		if err := sg.fillShortestPathVars(mp); err != nil {
			return err
		}
	}

	var lists []*pb.List
	// Go through all the variables in NeedsVar and see if we have a value for them in the map. If
	// we do, then we store that value in the appropriate variable inside SubGraph.
	for _, v := range sg.Params.NeedsVar {
		l, ok := mp[v.Name]
		if !ok {
			continue
		}
		switch {
		case (v.Typ == dql.AnyVar || v.Typ == dql.ListVar) && l.strList != nil:
			// This is for the case when we use expand(val(x)) with a value variable.
			// We populate the list of values into ExpandPreds and use that for the expand query
			// later.
			// TODO: If we support value vars for list type then this needn't be true
			sg.ExpandPreds = l.strList

		case (v.Typ == dql.UidVar && sg.SrcFunc != nil && sg.SrcFunc.Name == "uid_in"):
			srcFuncArgs := sg.SrcFunc.Args[:0]

			for _, uid := range l.Uids.GetUids() {
				// We use base 10 here because the uid parser expects the uid to be in base 10.
				arg := dql.Arg{Value: strconv.FormatUint(uid, 10)}
				srcFuncArgs = append(srcFuncArgs, arg)
			}
			sg.SrcFunc.Args = srcFuncArgs

		case (v.Typ == dql.AnyVar || v.Typ == dql.UidVar) && l.Uids != nil:
			lists = append(lists, l.Uids)

		case (v.Typ == dql.AnyVar || v.Typ == dql.ValueVar):
			// This should happen only once.
			// TODO: This allows only one value var per subgraph, change it later
			sg.Params.UidToVal = l.Vals

		case (v.Typ == dql.AnyVar || v.Typ == dql.UidVar) && l.Vals.Len() != 0:
			// Derive the UID list from value var.
			uids := make([]uint64, 0, l.Vals.Len())
			l.Vals.Iterate(func(uid uint64, _ types.Val) error {
				uids = append(uids, uid)
				return nil
			})
			sort.Slice(uids, func(i, j int) bool { return uids[i] < uids[j] })
			lists = append(lists, &pb.List{Uids: uids})

		case l.Vals.Len() != 0 || l.Uids != nil:
			return errors.Errorf("Wrong variable type encountered for var(%v) %v.", v.Name, v.Typ)

		default:
			glog.V(3).Infof("Warning: reached default case in fillVars for var: %v", v.Name)
		}
	}