[GitHub] [arrow] xxlaykxx opened a new issue, #36375: Added creating MapWriter in ComplexWriter.

["xxlaykxx (via GitHub)" <gi...@apache.org>]

xxlaykxx opened a new issue, #36375:
URL: https://github.com/apache/arrow/issues/36375

   ### Describe the enhancement requested
   
   Add new method rootAsMap() to ComplexWriter and implement it in ComplexWriterImpl for supporting Map type. Because currently it's possible to create MapWriter but like a part of list or struct.
   Previously in dremio side:
   
   When i trying to return map like @output ComplexWrite
   with this code:
   
   ```
   org.apache.arrow.vector.complex.writer.BaseWriter.MapWriter mapWriter = out.rootAsList().map(false);
   
   mapWriter.startMap();
   for (java.util.Map.Entry<java.lang.Integer, java.lang.Integer> element : map.entrySet()) {
   mapWriter.startEntry();
   mapWriter.key().integer().writeInt((Integer) element.getKey());
   mapWriter.value().integer().writeInt((Integer) element.getValue());
   mapWriter.endEntry();
   }
   mapWriter.endMap();
   ```
   It use UnionMapWriter and generate schema like:
   `EXPR$0: Map(false)<$data$: Union(Sparse, [1, 39])<struct: Struct<key: Int(32, true) not null, value: Int(32, true) not null> not null, map: Map(false)<entries: Struct<key: Int(32, true) not null, value: Int(32, true)> not null>>>`
   But in OutputDerivation impl class where i should create output Complete type
   
   ```
   List children = Arrays.asList( CompleteType.INT.toField("key", false), CompleteType.INT.toField("value", false));
   return new CompleteType(CompleteType.MAP.getType(), CompleteType.struct(children).toField(MapVector.DATA_VECTOR_NAME, false));
   ```
   (This is only one valid case, because MapVector.initializeChildrenFromFields())
   return
   EXPR$0::map<key::int32, value::int32> I found a place where it start using union - PromotableWriter.promoteToUnion.
   And in the end i have
   
   SCHEMA_CHANGE ERROR: Schema changed during projection. Schema was
   schema(EXPR$0::map<key::int32, value::int32>)
   but then changed to
   schema(EXPR$0::map<struct::struct<key::int32, value::int32>, map::map<key::int32, value::int32>>)
   
   ### Component(s)
   
   Java


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[GitHub] [arrow] lidavidm closed issue #36375: [Java] Added creating MapWriter in ComplexWriter.

["lidavidm (via GitHub)" <gi...@apache.org>]

lidavidm closed issue #36375: [Java] Added creating MapWriter in ComplexWriter.
URL: https://github.com/apache/arrow/issues/36375


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