Re: [hibernate-dev] Why does implicit join translate to inner join?

Hi Lukas, I think it is based on JPA 2.1 spec, 4.4.4 Path Expressions , "Path expression navigability is composed using “inner join” semantics." On 22 February 2018 at 08:09, Lukas Eder <lukas.eder(a)gmail.com&gt; wrote: > Hello, > > Vlad Mihalcea [1] was so kind to point me to this mailing list with my > question about implicit joins. The user guide [2] states that: > > "Implicit joins are always treated as inner joins." > > To me, this seems wrong, semantically, if implicit joins follow optional > (nullable) foreign key relationships. Let's assume that customers have > optional addresses. When we write > > SELECT c.firstName, c.lastName, c.address.city.country.code > FROM customer c > > The resulting query will INNER JOIN the customer / address / city / > country > tables, filtering out customers with no address, or addresses with no > cities, or cities with no countries (let's ignore the modelling aspect). > In > fact, I got a CROSS JOIN with join predicate in the WHERE clause, but that > doesn't really change anything. Hence the SELECT clause applies a filter, > which is rather surprising. To me, this seems simply wrong just like it > would be wrong for Stream.map() to apply any filters. > > However, I'm sure there must have been good reasons to default to this > behaviour, even in the presence of optional foreign keys. > > Does anyone know what those reasons are? > Cheers, > Lukas > > [1]: https://twitter.com/vlad_mihalcea/status/965927462684196864 > [2]: http://docs.jboss.org/hibernate/orm/5.2/userguide/ > html_single/Hibernate_User_Guide.html#hql-implicit-join > _______________________________________________ > hibernate-dev mailing list > hibernate-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/hibernate-dev >