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This patch implements the previously-unimplemented Select option of the Query and Scan operators. The most interesting use case of this option is Select=COUNT which means we should only count the items, without returning their actual content. But there are actually four different Select settings: COUNT, ALL_ATTRIBUTES, SPECIFIC_ATTRIBUTES, and ALL_PROJECTED_ATTRIBUTES. Five previously-failing tests now pass, and their xfail mark is removed: * test_query.py::test_query_select * test_scan.py::test_scan_select * test_query_filter.py::test_query_filter_and_select_count * test_filter_expression.py::test_filter_expression_and_select_count * test_gsi.py::test_gsi_query_select_1 These tests cover many different cases of successes and errors, including combination of Select and other options. E.g., combining Select=COUNT with filtering requires us to get the parts of the items needed for the filtering function - even if we don't need to return them to the user at the end. Because we do not yet support GSI/LSI projection (issue #5036), the support for ALL_PROJECTED_ATTRIBUTES is a bit simpler than it will need to be in the future, but we can only finish that after #5036 is done. Fixes #5058. The most intrusive part of this patch is a change from attrs_to_get - a map of top-level attributes that a read needs to fetch - to an optional<attrs_to_get>. This change is needed because we also need to support the case that we want to read no attributes (Select=COUNT), and attrs_to_get.empty() used to mean that we want to read *all* attributes, not no attributes. After this patch, an unset optional<attrs_to_get> means read *all* attributes, a set but empty attrs_to_get means read *no* attributes, and a set and non-empty attrs_to_get means read those specific attributes. Signed-off-by: Nadav Har'El <nyh@scylladb.com> Message-Id: <20220405113700.9768-2-nyh@scylladb.com>
Scylla Developer Documentation
This documentation targets developers who are interested in contributing to Scylla codebase.
Contents
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