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https://issues.apache.org/jira/browse/DRILL-7359?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16972136#comment-16972136
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ASF GitHub Bot commented on DRILL-7359:
---------------------------------------
paul-rogers commented on issue #1870: DRILL-7359: Add support for DICT type in
RowSet Framework
URL: https://github.com/apache/drill/pull/1870#issuecomment-552769421
The schema builder issue has been nagging at me. I observed above that the
current way of handling nested types is getting too complex, with all the
special cases and "resumeFoo" methods.
The current design was originally designed to build a `BatchSchema` with
`MaterializedField`s,. Those classes require a top-down construction. (That is
also why the final `build()` method returns a `BatchSchema` and why we must
call `buildSchema()` to get a `TupleMetadata`.)
It turns out that the `SchemaMetadata` classes *do not* have the same
constraints. They can actually be built bottom-up. It never occurred to me to
clean up the old-style of building when we repurposed `SchemaBuilder` to build
metadata objects.
So, since we can change the structure, we could borrow a technique from, I
think, certain JSON builders. Rather than having the schema builder create the
nested type builder, ask the user to do so explicitly:
```
TupleMetadata schema = new SchemaBuilder()
.addMap(new MapBuilder("myMap")
.add("name", MinorType.VARCHAR)
.addMap(new MapBuilder("nested")
.add("id", MinorType.INT)
.build())
.build())
.add("last", MinorType.INT)
.build();
```
Adopting this model as additional benefits. It is currently a bit awkward to
create a bare `ColumnMetadata`. We could create helper methods to create each
kind of column schema. Something like:
```
foo = SchemaBuilder.column("foo", MinorType.INT, DataMode.REQUIRED);
bar = SchemaBuilder.dict("bar", MinorType.VARCHAR)
.value(SchemaBuilder.map(...))
.build();
```
Lots of things we can play with.
Given all of this, my advice for the `DICT` type is to figure out something
that works with the structure we already have. Then, as a separate PR, we can
clean up the `SchemaBuilder` to make it easier to use for the many complex
types we now support. That way, you don't have to solve the schema builder
problem in this PR.
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> Add support for DICT type in RowSet Framework
> ---------------------------------------------
>
> Key: DRILL-7359
> URL: https://issues.apache.org/jira/browse/DRILL-7359
> Project: Apache Drill
> Issue Type: New Feature
> Reporter: Bohdan Kazydub
> Assignee: Bohdan Kazydub
> Priority: Major
> Fix For: 1.17.0
>
>
> Add support for new DICT data type (see DRILL-7096) in RowSet Framework
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