[GitHub] [beam] robertwb commented on a change in pull request #17101: PayloadBuilder for ExternalPythonTransform

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

robertwb commented on a change in pull request #17101:
URL: https://github.com/apache/beam/pull/17101#discussion_r827542787



##########
File path: runners/core-construction-java/src/main/java/org/apache/beam/runners/core/construction/PayloadBuilder.java
##########
@@ -0,0 +1,79 @@
+package org.apache.beam.runners.core.construction;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import org.apache.beam.sdk.schemas.JavaFieldSchema;
+import org.apache.beam.sdk.schemas.NoSuchSchemaException;
+import org.apache.beam.sdk.schemas.Schema;
+import org.apache.beam.sdk.schemas.SchemaRegistry;
+import org.apache.beam.sdk.values.Row;
+
+
+// TODO: Move to sdks/java/extensions/python/src/main/java/org/apache/beam/sdk/extensions/python/
+//  when https://github.com/apache/beam/pull/17035 is in.
+// TODO: Add unit tests.
+public class PayloadBuilder {
+
+  private Schema schema;
+  private static final SchemaRegistry SCHEMA_REGISTRY = SchemaRegistry.createDefault();
+  private List<Object> args;
+  private Map<String, Object> kwargs;
+
+  private PayloadBuilder(Schema schema) {
+    this.schema = schema;
+    args = new ArrayList<>();
+    kwargs = new HashMap<>();
+  }
+
+  static PayloadBuilder fromSchema(Schema schema) {
+    return new PayloadBuilder(schema);
+  }
+
+  static PayloadBuilder fromType(Class<?> type) {
+    try {
+      return fromSchema(SCHEMA_REGISTRY.getSchema(type));
+    } catch (NoSuchSchemaException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  static PayloadBuilder fromJavaPojo(Object pojo) {

Review comment:
       Ideally, one could just do 
   
   ```
     row = PayloadBuilder.fromJavaPojo(pojo)
   ```
   
   rather than
   
   ```
     row = PayloadBuilder.fromJavaPojo(pojo).withArg(pojo.someArg).withArg(pojo.anotherArg).buildArgs()
   ```
   
   (and making sure that `someArg` and `anotherArg` were properly ordered). 
   
   I think perhaps we should structure this in terms of what a Pipeline author should write, e.g.
   
   ```
   PythonTransform.named("apache_beam.some.Transform").withArgs("foo", 3, ...)
   PythonTransform.named("apache_beam.some.Transform")
       .withKeywordArg("stringArg", "value")
       .withKeywordArg("intArg", 100)
       .withKeywordArgs(mapOfStringToObjectInferringTypes)
       .withKeywordArgs(rowOrMaybeEvenRegisteredPojo);
   ```




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