[GitHub] [beam] htyleo commented on a change in pull request #15746: [BEAM-13068] Add a SQL API in Beam Go SDK

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

htyleo commented on a change in pull request #15746:
URL: https://github.com/apache/beam/pull/15746#discussion_r731391933



##########
File path: sdks/go/pkg/beam/transforms/sql/sql.go
##########
@@ -0,0 +1,121 @@
+// 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 sql contains SQL transform APIs, allowing SQL queries to be used
+// in Beam Go pipelines.
+//
+// NOTE: This is an experimental feature. It currently only works when an
+// expansion service/handler is registered for SQL transform. The APIs are
+// subject to change without backward compatibility guarantees.
+package sql
+
+import (
+	"reflect"
+
+	"github.com/apache/beam/sdks/v2/go/pkg/beam"
+	"github.com/apache/beam/sdks/v2/go/pkg/beam/core/graph"
+	"github.com/apache/beam/sdks/v2/go/pkg/beam/core/typex"
+	"github.com/apache/beam/sdks/v2/go/pkg/beam/transforms/sql/sqlx"
+)
+
+// Option is the base type of all the SQL transform options.
+type Option func(*Options)
+
+// Options contain all the options for a SQL transform.
+type Options struct {
+	dialect       string
+	expansionAddr string
+	inputs        map[string]beam.PCollection
+	outType       beam.FullType
+	customs       []sqlx.Option
+}
+
+// Add adds a custom option.
+func (o *Options) Add(opt sqlx.Option) {
+	o.customs = append(o.customs, opt)
+}
+
+// Input adds a named PCollection input to the transform.
+func Input(name string, in beam.PCollection) Option {
+	return func(o *Options) {
+		o.inputs[name] = in
+	}
+}
+
+// OutputType specifies the output PCollection type of the transform.
+// It must match the SQL output schema.
+//
+// There is currently no default output type, so users must set this option.
+// In the future, Row, once implemented, may become the default output type.
+func OutputType(t reflect.Type) Option {
+	return func(o *Options) {
+		o.outType = typex.New(t)
+	}
+}
+
+// Dialect specifies the SQL dialect, e.g. use 'zetasql' for ZetaSQL.
+func Dialect(dialect string) Option {
+	return func(o *Options) {
+		o.dialect = dialect
+	}
+}
+
+// ExpansionAddr is the URL of the expansion service to use.
+func ExpansionAddr(addr string) Option {
+	return func(o *Options) {
+		o.expansionAddr = addr
+	}
+}
+
+// Transform creates a SQL-based transform over zero or more PCollections
+// and/or named data sources.
+//
+// PCollection inputs can be added using the sql.Input option. SQL queries can
+// also refer to external tables that can be resolved by the expansion service.
+//
+// The output PCollection type must be specified by the sql.OutputType option.
+//
+// Example:
+//
+//  in := beam.Create(s, 1, 2, 3)
+//  out := sql.Transform(s, "SELECT COUNT(*) FROM t",
+//      sql.Input("t", in),
+//      sql.OutputType(reflect.TypeOf(int64(0))))
+//  // `out` is a PCollection<int64> with a single element 3.
+func Transform(s beam.Scope, query string, opts ...Option) beam.PCollection {
+	options := &Options{
+		inputs: make(map[string]beam.PCollection),
+	}
+	for _, opt := range opts {
+		opt(options)
+	}
+	if options.outType == nil {
+		panic("output type must be specified for sql.Transform")
+	}
+
+	payload := beam.CrossLanguagePayload(&sqlx.ExpansionPayload{
+		Query:   query,
+		Dialect: options.dialect,
+		Options: options.customs,
+	})
+
+	expansionAddr := sqlx.DefaultExpansionAddr
+	if options.expansionAddr != "" {
+		expansionAddr = options.expansionAddr

Review comment:
       That's a great point, thanks! Done.




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