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https://issues.apache.org/jira/browse/CASSANDRA-11458?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15217662#comment-15217662
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Sam Tunnicliffe commented on CASSANDRA-11458:
---------------------------------------------
Custom expressions as implemented by CASSANDRA-10217 are intended for use by
custom indexes. Only a single custom expression is permitted per query and we
validate that the index referred to is a valid one, so when the query is
executed on each replica we know that an index lookup will be performed rather
than a simple read from the base table. So you would implement your custom
lookup code (in your case, the "type of "IN" query filter") in the {{Searcher}}
provided by your custom index implementation. What kind of lookup does your
custom index implementation perform and is it not possible to incorporate that
"IN" filtering into that?
As you've seen, {{isSatisfiedBy}} is used for performing additional filtering
of the results of a query (at that point, whether the results came from an
index lookup or from a direct read of the base table is immaterial). The fact
that the {{CustomExpression::isSatisfiedBy}} is even relevant is somewhat
incorrect as I'd expect the expression to be removed from the row filter by
your index's implementation of {{getPostIndexQueryFilter}}. It seems that maybe
what you really want is to be able to add a custom filter without necessitating
the use of a custom index. CASSANDRA-11295 provides a first version of that,
though in that first version the filters can only be added programmatically and
not via CQL, so this might not be enough for your use case. Perhaps you could
comment there if you have some thoughts on a suitable syntax for that.
As a general point, the best way to get feedback on your approach would be to
attach a patch for your prototype.
> Complete support for CustomExpression
> -------------------------------------
>
> Key: CASSANDRA-11458
> URL: https://issues.apache.org/jira/browse/CASSANDRA-11458
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Henry Manasseh
> Priority: Minor
> Attachments: Custom-expression-Change.png, addCustomIndexExpression
> change.png
>
>
> This is a proposal to complete the CustomExpression support first introduced
> as part of https://issues.apache.org/jira/browse/CASSANDRA-10217.
> The current support for custom expressions is partial. There is no clean way
> to implement queries making use of the "exp('index', 'value)" syntax due to
> the fact CustomExpression is declared as final and there is no way to for
> developers to cleanly plug-in their own expressions.
> https://github.com/apache/cassandra/blob/6e69c75900f3640195130085ad69daa1659184eb/src/java/org/apache/cassandra/db/filter/RowFilter.java#L869
> The proposal is to make CustomExpression not final so that developers can
> extend and create their own subclass and provide their own isSatisfiedBy
> operation (which currently always returns true).
> Introducing a new custom expression would be done as follows:
> 1. Developer would create a subclass of CustomExpression and override
> isSatisfiedBy method with their logic (public boolean
> isSatisfiedBy(CFMetaData metadata, DecoratedKey partitionKey, Row row))
> 2. This class would be packaged in a jar and copied to the cassandra lib
> directory along with a secondary index class which overrides
> Index.customExpressionValueType
> 2. Create the custom index with an option which identifies the
> CustomExpression subclass (custom_expression_class).
> CREATE CUSTOM INDEX ON keyspace.my_table(my_indexed_column) USING
> 'org.custom.MyCustomIndex'
> WITH OPTIONS = { 'custom_expression_class': 'org.custom.MyCustomExpression' };
> I have prototyped the change and works as designed. In my case I do a type of
> "IN" query filter which will simplify my client logic significantly.
> The default behavior of using the CustomExpression class would be maintained
> if the developer does not provide a custom class in the create index options.
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