Adding custom converter to Projection

[martashorak]

Hi,
in previous versions it was possible to register custom converter for proxy projections via shared instance:
https://github.com/spring-projects/spring-data-commons/blob/2.3.x/src/main/java/org/springframework/data/projection/ProxyProjectionFactory.java#L64

However in most recent version (2.4.x) it is not possible anymore as new instance is used instead of shared one. What is the correct way to register custom converter?

spring-data-commons/src/main/java/org/springframework/data/projection/ProxyProjectionFactory.java

Line 53 in fa7ddcb

final static GenericConversionService CONVERSION_SERVICE = new DefaultConversionService();

Thank you
Martin

[mp911de]

We never intended to allow converter registration in the first place. They kind-of worked by accident.

Can you help us understand your use-case, why you want to register a converter and what conversion you try to make work?

[martashorak]

We never intended to allow converter registration in the first place. They kind-of worked by accident.

Can you help us understand your use-case, why you want to register a converter and what conversion you try to make work?

I see, i was following example from stack overflow and it is connected to native query which is also my case:
https://stackoverflow.com/questions/58417190/spring-data-jpa-custom-type-conversion-in-interface-based-projection

Here you can try simple failing test for it:
https://github.com/martashorak/spring-data-projection-test/blob/master/src/test/java/com/example/demoprojection/ProjectionConverterTest.java
If you change version of parent pom to 2.3.9.RELEASE it is passing

[joshiste]

@mp911de We have projections with custom value types for Ids (mostly wrapping String or UUID) this has stopped working:

 interface ObjectPagePosition {
        Integer getRowNumber();

        Boolean getDraft();

        TeamId getTeamId(); // Custom Value Type
    }

[markoknez]

Is there any news on this topic? We are facing the same issue

[asiaon123]

Also facing this issue, in my case, i want to convert string like 2024-05 to YearMonth

interface:

YearMonth getDate();

repo:

@Query("SELECT DATE_FORMAT(createdAt, '%Y-%m') AS date, COUNT(1) AS count FROM ArticleView GROUP BY date")
List<ArticleViewCountMonth> countByMonth();

[da-z]

Hi. In Spring Boot 2.x we are using enums in interface projections and the conversions seem to be done automatically without custom converters. When we switched to Spring Boot 3.x (3.5.4 in the example below), we are getting this kind of exception:

java.lang.UnsupportedOperationException: Cannot project java.lang.Character to acme.SomeEnum; Target type is not an interface and no matching Converter found
	at org.springframework.data.projection.ProjectingMethodInterceptor.potentiallyConvertResult(ProjectingMethodInterceptor.java:114)
	at org.springframework.data.projection.ProjectingMethodInterceptor.invoke(ProjectingMethodInterceptor.java:84)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:184)
	at org.springframework.data.projection.ProxyProjectionFactory$TargetAwareMethodInterceptor.invoke(ProxyProjectionFactory.java:253)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:184)
	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:223)

Reading https://docs.spring.io/spring-data/relational/reference/commons/custom-conversions.html I created a custom Converter from java.lang.Character to acme.SomeEnum however the documentation does not give exact code example on how to register it, and I am having trouble to do so, after many various attempts.

Can someone please guide me?