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https://issues.apache.org/jira/browse/CASSANDRA-7396?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Robert Stupp updated CASSANDRA-7396:
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Status: Patch Available (was: In Progress)
[Branch|https://github.com/apache/cassandra/compare/trunk...snazy:7396-coll-slice]
[utests|http://cassci.datastax.com/view/Dev/view/snazy/job/snazy-7396-coll-slice-testall/lastSuccessfulBuild/]
[dtests|http://cassci.datastax.com/view/Dev/view/snazy/job/snazy-7396-coll-slice-dtest/lastSuccessfulBuild/]
It allows single element and slice selections on sets, maps and lists - both
frozen and non-frozen ones.
Syntax for single element selections is {{collection_column\[element_term\]}}.
Syntax for slice selections is {{collection_column\[from_term..to_term\]}}.
Either {{from_term}} or {{to_term}} can be omitted to make either one unbounded.
All kinds of terms are allowed - including bind markers and function calls.
Single element and slice selections can also be passed to functions/aggregates.
The resulting type of any element or slice selection is the same as the
collection type. For example, {{set_column\[element\]}} will return a set (not
a boolean).
Non-frozen collections (complex data) except lists are treated special. It uses
{{ColumnFilter}} to filter only those values, that are within the bounds of the
slice(s).
{{CollectionSerializer.serializeForNativeProtocol}} (moved from
{{CollectionType}}) now takes additional parameters to prevent superfluous
serialization - this works for non-frozen lists, too.
{{CollectionSerializer.reserializeForNativeProtocol}} performs similar work for
frozen types.
{{SelectStatement}} tries to use one {{ColumnFilter}} instance for all
executions of a (prepared) statement. In case the terms for the element/slice
sub-selection are dynamic ones (bound parameters, function calls), a new
{{ColumnFilter}} needs to be created for each execution in order to benefit
from its select/slice capabilities.
The new class {{SelectionRestriction}} is used as a descriptor of column
element/slice/full selections. Each individual selection has its own
{{SelectionRestriction}} instance.
{{Term.Raw}} got a new function {{isConstant}}, which is needed to determine
whether a {{SelectionRestriction}} refers to a constant/literal value.
Some {{Selector}} methods now take {{QueryOptions}} instead of {{int
protocolVersion}}, which is needed to resolve bound variables and functions for
element/slice bounds.
{{Selection}} now distinguishes between {{ByteBuffer}}s and
{{ComplexColumnData}}. The {{ComplexColumnData}} is used to use the “raw” cells
for collection select/slice before these get serialized. That
{{ComplexColumnData}} is then passed to {{CollectionSerializer}}.
One maybe annoying thing in the syntax is the use of two dots to separate slice
bounds. Given a {{map<int,text>}} and doing a slice selection like {{SELECT
col\[1..5\]}} will result in a parser failure, because it interprets {{1.}} as
the start of a floating point literal and then complains about the 2nd dot.
Workaround is to put a space between ({{SELECT col\[1 .. 5\]}}). I thought
about using {{:}} as a separator, but that is the start of a bind parameter.
{{-}} is already “occupied” by negative numeric values. {{;}} is the end of a
statement. Using a keyword like {{TO}} makes unbounded slice queried look a bit
awkward ({{SELECT col\[ TO 5\]}} or {{SELECT col\[5 TO \]}}.
> Allow selecting Map key, List index
> -----------------------------------
>
> Key: CASSANDRA-7396
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7396
> Project: Cassandra
> Issue Type: New Feature
> Components: CQL
> Reporter: Jonathan Ellis
> Assignee: Robert Stupp
> Labels: cql
> Fix For: 3.x
>
> Attachments: 7396_unit_tests.txt
>
>
> Allow "SELECT map['key]" and "SELECT list[index]." (Selecting a UDT subfield
> is already supported.)
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