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From dsbos <...@git.apache.org>
Subject [GitHub] drill pull request: DRILL-2288: Fix ScanBatch violation of IterOut...
Date Tue, 03 Nov 2015 21:23:11 GMT
Github user dsbos commented on a diff in the pull request:

    https://github.com/apache/drill/pull/228#discussion_r43808779
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/vector/complex/fn/JsonReader.java
---
    @@ -93,13 +93,15 @@ public void ensureAtLeastOneField(ComplexWriter writer) {
         if (!atLeastOneWrite) {
           // if we had no columns, create one empty one so we can return some data for count
purposes.
           SchemaPath sp = columns.get(0);
    -      PathSegment root = sp.getRootSegment();
    +      PathSegment fieldPath = sp.getRootSegment();
           BaseWriter.MapWriter fieldWriter = writer.rootAsMap();
    -      while (root.getChild() != null && !root.getChild().isArray()) {
    -        fieldWriter = fieldWriter.map(root.getNameSegment().getPath());
    -        root = root.getChild();
    +      while (fieldPath.getChild() != null && ! fieldPath.getChild().isArray())
{
    +        fieldWriter = fieldWriter.map(fieldPath.getNameSegment().getPath());
    +        fieldPath = fieldPath.getChild();
    +      }
    +      if (fieldWriter.isEmptyMap()) {
    --- End diff --
    
    Recall that ensureAtLeastOneField used to create that dummy NullableIntVector field/column
(so that the schema didn't end up with zero fields/columns) _regardless_ of whether it needed
to (i.e., even if the schema already had a column or columns from a previous JsonRecordReader
for the same ScanBatch).  
    
    Under the failure conditions, that blind vector setting frequently replaced a NullableVarCharVector
with that NullableIntVector, causing either explicit "schema change not supported" user-targeted
errors or internal errors about the mismatch between the NullableIntVector and the expectation
of a NullableVarCharVector.
    
    The additional check prevents ensureAtLeastOneField from overriding a column in an existing
non-empty schema and causing those schema changes.



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