[GitHub] [beam] lostluck commented on a change in pull request #12471: [BEAM-9615] Add initial Schema to Go conversions.

[GitBox <gi...@apache.org>]

lostluck commented on a change in pull request #12471:
URL: https://github.com/apache/beam/pull/12471#discussion_r466572230



##########
File path: sdks/go/pkg/beam/core/runtime/graphx/schema/schema.go
##########
@@ -0,0 +1,245 @@
+// 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 schema contains utility functions for relating Go types and Beam Schemas.
+//
+// Not all Go types can be converted to schemas. This is Go is more expressive than
+// Beam schemas. Just as not all Go types can be serialized, similarly,
+// not all Beam Schemas will have a conversion to Go types, until the correct
+// mechanism exists in the SDK to handle them.
+//
+// While efforts will be made to have conversions be reversable, this will not
+// be possible in all instances. Eg. Go arrays as fields will be converted to
+// Beam Arrays, but a Beam Array type will map by default to a Go slice.
+package schema
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+
+	"github.com/apache/beam/sdks/go/pkg/beam/core/util/reflectx"
+	"github.com/apache/beam/sdks/go/pkg/beam/internal/errors"
+	pipepb "github.com/apache/beam/sdks/go/pkg/beam/model/pipeline_v1"
+)
+
+// FromType returns a Beam Schema of the passed in type.
+// Returns an error if the type cannot be converted to a Schema.
+func FromType(ot reflect.Type) (*pipepb.Schema, error) {
+	t := ot // keep the original type for errors.
+	// The top level schema for a pointer to struct and the struct is the same.
+	if t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+	if t.Kind() != reflect.Struct {
+		return nil, errors.Errorf("cannot convert %v to schema. FromType only converts structs to schemas", ot)
+	}
+	return structToSchema(t), nil
+}
+
+func structToSchema(t reflect.Type) *pipepb.Schema {
+	fields := make([]*pipepb.Field, 0, t.NumField())
+	for i := 0; i < t.NumField(); i++ {
+		fields = append(fields, structFieldToField(t.Field(i)))
+	}
+	return &pipepb.Schema{
+		Fields: fields,
+	}
+}
+
+func structFieldToField(sf reflect.StructField) *pipepb.Field {
+	name := sf.Name
+	if tag := sf.Tag.Get("beam"); tag != "" {
+		name, _ = parseTag(tag)
+	}
+	ftype := reflectTypeToFieldType(sf.Type)
+
+	return &pipepb.Field{
+		Name: name,
+		Type: ftype,
+	}
+}
+
+func reflectTypeToFieldType(ot reflect.Type) *pipepb.FieldType {
+	var isPtr bool
+	t := ot
+	if t.Kind() == reflect.Ptr {
+		isPtr = true
+		t = t.Elem()
+	}
+	switch t.Kind() {
+	case reflect.Map:
+		kt := reflectTypeToFieldType(t.Key())
+		vt := reflectTypeToFieldType(t.Elem())
+		return &pipepb.FieldType{
+			Nullable: isPtr,
+			TypeInfo: &pipepb.FieldType_MapType{
+				MapType: &pipepb.MapType{
+					KeyType:   kt,
+					ValueType: vt,
+				},
+			},
+		}
+	case reflect.Struct:
+		sch := structToSchema(t)
+		return &pipepb.FieldType{
+			Nullable: isPtr,
+			TypeInfo: &pipepb.FieldType_RowType{
+				RowType: &pipepb.RowType{
+					Schema: sch,
+				},
+			},
+		}
+	case reflect.Slice, reflect.Array:
+		// Special handling for []byte
+		if t == reflectx.ByteSlice {
+			return &pipepb.FieldType{
+				Nullable: isPtr,
+				TypeInfo: &pipepb.FieldType_AtomicType{
+					AtomicType: pipepb.AtomicType_BYTES,
+				},
+			}
+		}
+		vt := reflectTypeToFieldType(t.Elem())
+		return &pipepb.FieldType{
+			Nullable: isPtr,
+			TypeInfo: &pipepb.FieldType_ArrayType{
+				ArrayType: &pipepb.ArrayType{
+					ElementType: vt,
+				},
+			},
+		}
+	case reflect.Interface, reflect.Chan, reflect.UnsafePointer, reflect.Complex128, reflect.Complex64, reflect.Int:
+		panic(fmt.Sprintf("Unsupported type to convert to schema: %v", ot))
+	default: // must be an atomic type
+		enum := reflectTypeToAtomicType(t)
+		return &pipepb.FieldType{
+			Nullable: isPtr,
+			TypeInfo: &pipepb.FieldType_AtomicType{
+				AtomicType: enum,
+			},
+		}
+	}
+}
+
+func reflectTypeToAtomicType(rt reflect.Type) pipepb.AtomicType {
+	switch rt {
+	case reflectx.Uint8:
+		return pipepb.AtomicType_BYTE
+	case reflectx.Int16:
+		return pipepb.AtomicType_INT16
+	case reflectx.Int32:
+		return pipepb.AtomicType_INT32
+	case reflectx.Int64, reflectx.Int:
+		return pipepb.AtomicType_INT64
+	case reflectx.Float32:
+		return pipepb.AtomicType_FLOAT
+	case reflectx.Float64:
+		return pipepb.AtomicType_DOUBLE
+	case reflectx.String:
+		return pipepb.AtomicType_STRING
+	case reflectx.Bool:
+		return pipepb.AtomicType_BOOLEAN
+	case reflectx.ByteSlice:
+		return pipepb.AtomicType_BYTES
+	default:
+		panic(fmt.Sprintf("non atomic reflect type: %v", rt))
+	}
+}
+
+// ToType returns a Go type of the passed in Schema.
+// Types returned by ToType are always of Struct kind.
+// Returns an error if the Schema cannot be converted to a type.
+func ToType(s *pipepb.Schema) (reflect.Type, error) {
+	fields := make([]reflect.StructField, 0, len(s.GetFields()))
+	for _, sf := range s.GetFields() {
+		rf := fieldToStructField(sf)
+		fields = append(fields, rf)
+	}
+	return reflect.StructOf(fields), nil
+}
+
+func fieldToStructField(sf *pipepb.Field) reflect.StructField {
+	name := sf.GetName()
+	return reflect.StructField{
+		Name: strings.ToUpper(name[:1]) + name[1:], // Go field name must be capitalized for export and encoding.
+		Type: fieldTypeToReflectType(sf.GetType()),
+		Tag:  reflect.StructTag(fmt.Sprintf("beam:\"%s\"", name)),
+	}
+}
+
+var atomicTypeToReflectType = map[pipepb.AtomicType]reflect.Type{

Review comment:
       Honestly, when I first wrote it, it complained that reflect.Type couldn't be used as a key, but I do that all the time so... very strange.




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