Query methods with isTrue/isFalse predicates do not work with Oracle

[cedric-schaller]

Query methods in repositories such as findByAvailableIsTrue() are converted to SQL statements with where parts like ("SOME_TABLE"."AVAILABLE" = TRUE). This is fine for many databases, but Oracle has no boolean type and people typically use the type NUMBER(1) instead. In such a case, the predicate should correctly translate to ("SOME_TABLE"."AVAILABLE" = 1).

The reason for this erroneous translation is located in org.springframework.data.relational.core.sql.render.ExpressionVisitor, which in our case calls the toString() method of the org.springframework.data.relational.core.sql.BooleanLiteral to compute the value of the expression (TRUE), despite the fact that the documentation of the toString() method of the org.springframework.data.relational.core.sql.Segment interface (which BooleanLiteral implements) explicitly states that

While it might work in the context of a specific dialect, you should not that the toString() representation works across multiple databases. (sic)

A possible solution would be to extend org.springframework.data.relational.core.dialect.Dialect with a

BooleanComparison booleanComparison()

method that would then be implemented in OracleDialect.

[schauder]

Related: #908

[schauder]

Do you use the latest version of Spring Data JDBC(2.3)?
This seems indeed to be fixed with #908.
If it isn't please provide a reproducer.

Thanks for pointing the typo in the docs.

[cedric-schaller]

After testing the whole thing again with Spring Boot 2.6.0 (which came out on Thursday), I can confirm that the problem is fixed with Spring Data JDBC 2.3. @schauder Thanks for the hint!