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https://issues.apache.org/jira/browse/CALCITE-3414?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Danny Chen updated CALCITE-3414:
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Summary: [CALCITE-3414] In calcite-core, use RexToLixTranslator.convert for
type conversion code generation uniformly (was: Unify Expression'type cast and
conversion as a robust one)
> [CALCITE-3414] In calcite-core, use RexToLixTranslator.convert for type
> conversion code generation uniformly
> ------------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-3414
> URL: https://issues.apache.org/jira/browse/CALCITE-3414
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.21.0
> Reporter: Feng Zhu
> Assignee: Feng Zhu
> Priority: Major
> Labels: pull-request-available
> Attachments: RexToLixTranslator.png, TypeConversion.txt, Types.png
>
> Time Spent: 1h
> Remaining Estimate: 0h
>
> Current now, there are two functions in calcite that can be used to
> cast/convert Expression to a specific Type.
> *_Types.castIfNecessary_* and _*RexToLixTranslator.convert*_.
> We make a deep investigation on their implementations and demonstrate them as
> below.
> {color:#ff0000}
> !RexToLixTranslator.png!{color}
> {color:#ff0000}
> *RexToLixTranslator.convert*{color}
> !Types.png!
> {color:#ff0000}
> *Types.castIfNecessary*{color}
> It can be seen that:
> (1) They have a lot of overlaps;
> (2) *_RexToLixTranslator.cast_* can cover more cases with tools like
> _SqlFunctions_ and etc.
> (3) Both of them have limitations and may generate incorrect code, which is
> listed in attachment(TypeConversion.txt).
> Multiple choices usually bring confusion to developers and resulting to the
> misuse of them.
> For example, CALCITE-3245 exposes that Types.castIfNecessary cannot cast the
> Expression to BigDecimal.class.
> Fixing the issue in *_Types.castIfNecessary_* directly seems to be not a
> good idea.
> On one hand, it is not convenient to call _SqlFunctions_ in linq4j. One the
> other hand, it will brings duplicate with _*RexToLixTranslator.cast*_.
> However, due to some unique logic in _*Types.castIfNecessary*_, we cannot
> replace it as _*RexToLixTranslator.cast*_ neither.
> Therefore, it is a good idea to integrate implementations into
> RexToLixTranslator.cast.
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