MetadataFactory is still useful. It provides a way to access Metadata directly. If someone creates a new type of Metadata class, it can be accessed through AbstractRelNode.metadata(). This way you don’t need to update RelMetadataQuery interface to include the getter for this new meta. Although I don’t see this pattern being used often, but I do think it is still useful and shouldn’t be removed.
For your second point, I think you would still need a way to keep RelMetadataQuery object during a rule call. If you choose to create new instance, you will have to pass it around while applying the rule. That actually complicates things a lot. > On Oct 17, 2019, at 12:49 AM, XING JIN <jinxing.co...@gmail.com> wrote: > > 1. RelMetadataQuery covers the functionality of MetadataFactory, why should > we keep/maintain both of them ? shall we just deprecate MetadataFactory. I > see MetadataFactory is rarely used in current code. Also I > think MetadataFactory is not good place to offering customized metadata, > which will make user confused for the difference between RelMetadataQuery > and MetadataFactory. > >> Customized RelMetadataQuery with code generated meta handler for > customized metadata, also can provide convenient way to get metadata. > It makes sense for me. > > 2. If the natural lifespan of a RelMetadataQuery is a RelOptCall, shall we > deprecate RelOptCluster#getMetadataQuery ? If a user wants to get the > metadata but without a RelOptCall, he/she will need to create a new > instance of RelMetadataQuery. > > Xiening Dai <xndai....@gmail.com> 于2019年10月17日周四 上午2:27写道： > >> I have seen both patterns in current code base. In most places, for >> example SubQueryRemoveRule, AggregateUnionTrasposeRule >> SortJoinTransposeRule, etc., RelOptCluster.getMetadataQuery() is used. And >> there are a few other places where new RelMetadataQuery instance is >> created, which Haisheng attempts to fix. >> >> Currently RelOptCluster.invalidateMetadataQuery() is called at the end of >> RelOptRuleCall.transformTo(). So the lifespan of RelMetadataQuery is >> guaranteed to be within a RelOptCall. I think Haisheng’s fix is safe. >> >> >>> On Oct 16, 2019, at 1:53 AM, Danny Chan <yuzhao....@gmail.com> wrote: >>> >>> This is the reason I was struggling for the discussion. >>> >>> Best, >>> Danny Chan >>> 在 2019年10月16日 +0800 AM11:23，dev@calcite.apache.org，写道： >>>> >>>> RelMetadataQuery >> >>
