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Posted to issues@calcite.apache.org by "Danny Chen (Jira)" <ji...@apache.org> on 2019/10/15 12:41:00 UTC
[jira] [Commented] (CALCITE-3414) Unify Expression'type cast and
conversion as a robust one
[ https://issues.apache.org/jira/browse/CALCITE-3414?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16951893#comment-16951893 ]
Danny Chen commented on CALCITE-3414:
-------------------------------------
I'm inclined to move the Types#castIfNecessary into Calcite core, and use the RexToLixTranslator#convert as the last fallback invocation. Then we should always use Types#castIfNecessary instead of RexToLixTranslator#convert.
> Unify Expression'type cast and conversion as a robust one
> ---------------------------------------------------------
>
> 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: 10m
> 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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