[jira] [Created] (ARROW-308) UnionListWriter.setPosition() should not call startList()

["Deneche A. Hakim (JIRA)" <ji...@apache.org>]

Deneche A. Hakim created ARROW-308:
--------------------------------------

             Summary: UnionListWriter.setPosition() should not call startList()
                 Key: ARROW-308
                 URL: https://issues.apache.org/jira/browse/ARROW-308
             Project: Apache Arrow
          Issue Type: Bug
          Components: Java - Vectors
            Reporter: Deneche A. Hakim
            Assignee: Deneche A. Hakim


UnionListWriter.setPosition() is implemented as follows:
{code}
  @Override
  public void setPosition(int index) {
    super.setPosition(index);
    startList();
  }
{code}

It works fine, but if you run the following code:
{code}
    MapVector parent = new MapVector("parent", allocator, null);
    ComplexWriter writer = new ComplexWriterImpl("root", parent);
    MapWriter rootWriter = writer.rootAsMap();

    rootWriter.start();
    rootWriter.bigInt("int").writeBigInt(0);
    rootWriter.list("list").startList();
    rootWriter.list("list").bigInt().writeBigInt(0);
    rootWriter.list("list").endList();
    rootWriter.end();

    rootWriter.setPosition(1);
    rootWriter.start();
    rootWriter.bigInt("int").writeBigInt(1);
    rootWriter.end();

    rootWriter.setPosition(2);
    rootWriter.bigInt("int").writeBigInt(2);
    rootWriter.start();
    rootWriter.list("list").startList();
    rootWriter.list("list").bigInt().writeBigInt(2);
    rootWriter.list("list").endList();
    rootWriter.end();
    writer.setValueCount(3);

    for (int i = 0; i < 3; i++) {
      parent.getReader().setPosition(i);
      System.out.printf("%d: %s%n", i, parent.getReader().readObject());
    }
{code}

You get:
{noformat}
0: {"root":{"int":0,"list":[0]}}
1: {"root":{"int":1,"list":[]}}
2: {"root":{"int":2,"list":[2]}}
{noformat}

Even though we didn't write anything in the 2nd row "list", it shows up as empty instead of null. I tracked the problem to UnionListWriter.setPosition() calling startList() which marks the row as not null even if we don't write anything to it.




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