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https://issues.apache.org/jira/browse/CAY-2816?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Nikita Timofeev closed CAY-2816.
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Resolution: Fixed
https://github.com/apache/cayenne/pull/603
> (NOT) EXIST usability - provide simple expression syntax
> --------------------------------------------------------
>
> Key: CAY-2816
> URL: https://issues.apache.org/jira/browse/CAY-2816
> Project: Cayenne
> Issue Type: Improvement
> Reporter: Andrus Adamchik
> Assignee: Nikita Timofeev
> Priority: Major
> Fix For: 5.0-M1
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> h2. Background
> Currently, the syntax for (NOT) EXISTS requires two queries and an explicit
> correlation expression:
> https://cayenne.apache.org/docs/4.2/cayenne-guide/#subqueries
> https://twitter.com/ApacheCayenne/status/1562702875327082496
> This is great for a general case, but often the "enclosing" expression is
> simply a relationship from top query root to subquery root. So the syntax can
> be drastically simplifed, replacing sub ObjectSelect with a simple
> expression. So this:
> {noformat}
> ObjectSelect<Painting> subQuery = ObjectSelect.query(Painting.class)
> .where(Painting.ARTIST.eq(Artist.ARTIST_ID_PK_PROPERTY.enclosing()));
> long count = ObjectSelect.query(Artist.class)
> .where(ExpressionFactory.notExists(subQuery))
> .selectCount(context);
> {noformat}
> becomes this:
> {noformat}
> long count = ObjectSelect.query(Artist.class)
> .where(ExpressionFactory.notExists(Artist.PAINTINGS))
> .selectCount(context);
> {noformat}
> or even better, this:
> {noformat}
> long count = ObjectSelect.query(Artist.class)
> .where(Artist.PAINTINGS.notExists())
> .selectCount(context);
> {noformat}
> h2. Task Scope
> _(TODO: break to subtasks?)_
> * Implement "ExpressionFactory.exists(Exp)" and
> "ExpressionFactory.notExists(Exp)". The trick would be to check all paths
> within the Exp and build the corresponding correlation expressions for the
> subquery. It may potentially resolve to multiple subqueries (if multiple
> relationships are specified), or no subqueries (for conditions based on the
> root query attributes: 'not exists name = "A"' would become 'not (name =
> "A")' in SQL)
> * Implement parseable exp syntax "exists <exp>" and "not exists <exp>"
> * Implement "exp.exists()" and "exp.notExists()" for fluent syntax
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