// sortByValue fetches values and sort UIDList.
func sortByValue(attr string, ul *task.List, scalar types.Scalar, desc bool) error {
values := make([]types.Value, len(ul.Uids))
for i, uid := range ul.Uids {
val, err := fetchValue(uid, attr, scalar)
if err != nil {
return err
}
values[i] = val
}
return scalar.Sort(values, ul, desc)
}
// getPostingValue looks up key, gets the value, converts it. If any error is
// encountered, we return nil. This is used in some filtering where we do not
// want to waste time creating errors.
func getPostingValue(key []byte, scalarType types.Scalar) *types.Value {
pl, decr := posting.GetOrCreate(key)
defer decr()
valBytes, vType, err := pl.Value()
if bytes.Equal(valBytes, nil) {
return nil
}
val := types.ValueForType(types.TypeID(vType))
if val == nil {
return nil
}
if err := val.UnmarshalBinary(valBytes); err != nil {
return nil
}
// Convert to schema type.
sv, err := scalarType.Convert(val)
if err != nil {
return nil
}
return &sv
}
// fetchValue gets the value for a given UID.
func fetchValue(uid uint64, attr string, scalar types.Scalar) (types.Value, error) {
pl, decr := posting.GetOrCreate(x.DataKey(attr, uid))
defer decr()
valBytes, vType, err := pl.Value()
if err != nil {
return nil, err
}
val := types.ValueForType(types.TypeID(vType))
if val == nil {
return nil, x.Errorf("Invalid type: %v", vType)
}
err = val.UnmarshalBinary(valBytes)
if err != nil {
return nil, err
}
schemaVal, err := scalar.Convert(val)
if err != nil {
return nil, err
}
return schemaVal, nil
}