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https://issues.apache.org/jira/browse/BEAM-9615?focusedWorklogId=536836&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-536836
]
ASF GitHub Bot logged work on BEAM-9615:
----------------------------------------
Author: ASF GitHub Bot
Created on: 16/Jan/21 17:23
Start Date: 16/Jan/21 17:23
Worklog Time Spent: 10m
Work Description: lostluck commented on a change in pull request #13760:
URL: https://github.com/apache/beam/pull/13760#discussion_r558971442
##########
File path: sdks/go/pkg/beam/example_schema_test.go
##########
@@ -0,0 +1,254 @@
+// Licensed to the Apache Software Foundation (ASF) under one or more
+// contributor license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright ownership.
+// The ASF licenses this file to You under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance with
+// the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package beam_test
+
+import (
+ "bytes"
+ "fmt"
+ "io"
+ "reflect"
+
+ "github.com/apache/beam/sdks/go/pkg/beam"
+ "github.com/apache/beam/sdks/go/pkg/beam/core/graph/coder"
+ "github.com/google/go-cmp/cmp"
+)
+
+// RegisterSchemaProvider must be called before beam.Init, and conventionally
in a package init block.
+func init() {
+ beam.RegisterSchemaProvider(reflect.TypeOf((*Alphabet)(nil)).Elem(),
&AlphabetProvider{})
+ // TODO(BEAM-9615): Registerying a self encoding type causes a cycle.
Needs resolving.
+ // beam.RegisterType(reflect.TypeOf((*Cyrillic)(nil)))
+ beam.RegisterType(reflect.TypeOf((*Latin)(nil)))
+ beam.RegisterType(reflect.TypeOf((*Ελληνικά)(nil)))
+}
+
+type Alphabet interface {
+ alphabet() string
+}
+
+type Cyrillic struct {
+ A, B int
+}
+
+func (*Cyrillic) alphabet() string {
+ return "Cyrillic"
+}
+
+type Latin struct {
+ // Unexported fields are not serializable by beam schemas by default
+ // so we need to handle this ourselves.
+ c uint64
+ d *float32
+}
+
+func (*Latin) alphabet() string {
+ return "Latin"
+}
+
+type Ελληνικά struct {
+ q string
+ G func() string
+}
+
+func (*Ελληνικά) alphabet() string {
+ return "Ελληνικά"
+}
+
+// AlphabetProvider provides encodings for types that implement the Alphabet
interface.
+type AlphabetProvider struct {
+ enc *coder.RowEncoderBuilder
+ dec *coder.RowDecoderBuilder
+}
+
+var (
+ typeCyrillic = reflect.TypeOf((*Cyrillic)(nil))
+ typeLatin = reflect.TypeOf((*Latin)(nil))
+ typeΕλληνικά = reflect.TypeOf((*Ελληνικά)(nil))
+)
+
+func (p *AlphabetProvider) FromLogicalType(rt reflect.Type) (reflect.Type,
error) {
+ // FromLogicalType produces schema representative types, which match
the encoders
+ // and decoders that this function generates for this type.
+ // While this example uses statically assigned schema representative
types, it's
+ // possible to generate the returned reflect.Type dynamically instead,
using the
+ // reflect package.
+ switch rt {
+ // The Cyrillic type is able to be encoded by default, so we simply use
it directly
+ // as it's own representative type.
+ case typeCyrillic:
+ return typeCyrillic, nil
+ case typeLatin:
+ // The Latin type only has unexported fields, so we need to
make the equivalent
+ // have exported fields.
+ return reflect.TypeOf((*struct {
+ C uint64
+ D *float32
+ })(nil)).Elem(), nil
+ case typeΕλληνικά:
+ return reflect.TypeOf((*struct{ Q string })(nil)).Elem(), nil
+ }
+ return nil, fmt.Errorf("Unknown Alphabet: %v", rt)
+}
+
+// BuildEncoder returns beam schema encoder functions for types with the
Alphabet interface.
+func (p *AlphabetProvider) BuildEncoder(rt reflect.Type) (func(interface{},
io.Writer) error, error) {
+ switch rt {
+ case typeCyrillic:
+ if p.enc == nil {
+ p.enc = &coder.RowEncoderBuilder{}
+ }
+ // Since Cyrillic is by default encodable, defer to the
standard schema row decoder for the type.
+ return p.enc.Build(rt)
+ case typeLatin:
+ return func(iface interface{}, w io.Writer) error {
+ v := iface.(*Latin)
+ // Beam Schema Rows have a header that indicates which
fields if any, are nil.
+ if err := coder.WriteRowHeader(2, func(i int) bool {
+ if i == 1 {
+ return v.d == nil
+ }
+ return false
+ }, w); err != nil {
+ return err
+ }
+ // Afterwards, each field is encoded using the
appropriate helper.
+ if err := coder.EncodeVarUint64(v.c, w); err != nil {
+ return err
+ }
+ // Nil fields have nothing written for them other than
the header.
+ if v.d != nil {
+ if err := coder.EncodeDouble(float64(*v.d), w);
err != nil {
+ return err
+ }
+ }
+ return nil
+ }, nil
+ case typeΕλληνικά:
+ return func(iface interface{}, w io.Writer) error {
+ // Since the representation for Ελληνικά never has nil
fields
+ // we can use the simple header helper.
+ if err := coder.WriteSimpleRowHeader(1, w); err != nil {
+ return err
+ }
+ v := iface.(*Ελληνικά)
+ if err := coder.EncodeStringUTF8(v.q, w); err != nil {
+ return fmt.Errorf("decoding string field A:
%v", err)
+ }
+ return nil
+ }, nil
+ }
+ return nil, fmt.Errorf("Unknown Alphabet: %v", rt)
+}
+
+// BuildDecoder returns beam schema decoder functions for types with the
Alphabet interface.
+func (p *AlphabetProvider) BuildDecoder(rt reflect.Type) (func(io.Reader)
(interface{}, error), error) {
+ switch rt {
+ case typeCyrillic:
+ if p.dec == nil {
+ p.dec = &coder.RowDecoderBuilder{}
+ }
+ // Since Cyrillic is by default encodable, defer to the
standard schema row decoder for the type.
+ return p.dec.Build(rt)
+ case typeLatin:
+ return func(r io.Reader) (interface{}, error) {
+ // Since the d field can be nil, we use the header get
the nil bits.
+ n, nils, err := coder.ReadRowHeader(r)
+ if err != nil {
+ return nil, err
+ }
+ // Header returns the number of fields, so we check if
it has what we
+ // expect. This allows schemas to evolve if necessary.
+ if n != 2 {
+ return nil, fmt.Errorf("expected 2 fields, but
got %v", n)
+ }
+ c, err := coder.DecodeVarUint64(r)
+ if err != nil {
+ return nil, err
+ }
+ // Check if the field is nil before trying to decode a
value for it.
+ var d *float32
+ if !coder.IsFieldNil(nils, 1) {
+ f, err := coder.DecodeDouble(r)
+ if err != nil {
+ return nil, err
+ }
+ f32 := float32(f)
+ d = &f32
+ }
+ return &Latin{
+ c: c,
+ d: d,
+ }, nil
+ }, nil
+ case typeΕλληνικά:
+ return func(r io.Reader) (interface{}, error) {
+ // Since the representation for Ελληνικά never has nil
fields
+ // we can use the simple header helper. Returns an
error if
+ // something unexpected occurs.
+ if err := coder.ReadSimpleRowHeader(1, r); err != nil {
+ return nil, err
+ }
+ q, err := coder.DecodeStringUTF8(r)
+ if err != nil {
+ return nil, fmt.Errorf("decoding string field
A: %v", err)
+ }
+ return &Ελληνικά{
+ q: q,
+ }, nil
+ }, nil
+ }
+ return nil, nil
+}
+
+// Schema providers work on fields of schema encoded types.
+type translation struct {
+ C *Cyrillic
+ L *Latin
+ E *Ελληνικά
+}
+
+func ExampleRegisterSchemaProvider() {
Review comment:
This is a whole file example, which appears in the Go Doc and is
executed as part of the tests. It's required that the file is named _test.go so
that it's not part of the main package compilation.
See https://blog.golang.org/examples for details.
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Issue Time Tracking
-------------------
Worklog Id: (was: 536836)
Time Spent: 20h 50m (was: 20h 40m)
> [Go SDK] Beam Schemas
> ---------------------
>
> Key: BEAM-9615
> URL: https://issues.apache.org/jira/browse/BEAM-9615
> Project: Beam
> Issue Type: New Feature
> Components: sdk-go
> Reporter: Robert Burke
> Assignee: Robert Burke
> Priority: P2
> Time Spent: 20h 50m
> Remaining Estimate: 0h
>
> Schema support is required for advanced cross language features in Beam, and
> has the opportunity to replace the current default JSON encoding of elements.
> Some quick notes, though a better fleshed out doc with details will be
> forthcoming:
> * All base coders should be implemented, and listed as coder capabilities. I
> think only stringutf8 is missing presently.
> * Should support fairly arbitrary user types, seamlessly. That is, users
> should be able to rely on it "just working" if their type is compatible.
> * Should support schema metadata tagging.
> In particular, one breaking shift in the default will be to explicitly fail
> pipelines if elements have unexported fields, when no other custom coder has
> been added. This has been a source of errors/dropped data/keys and a simply
> warning at construction time won't cut it. However, we could provide a manual
> "use beam schemas, but ignore unexported fields" registration as a work
> around.
> Edit: Doc is now at https://s.apache.org/beam-go-schemas
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