How to use Spring's BackendIdConverter? - spring

Question

I have an entity named VendorProductMapping with embedded primary key. Hence I want to use BackendIdConverter to convert the embedded primary key to string and vice-versa.
I followed a few posts on stackoverflow and learnt that I need to use BackendIdConverter.
I created the following class:
public class VendorProductMappingIdConverter implements BackendIdConverter {
#Override
public Serializable fromRequestId(String id, Class<?> entityType) {
--
}
#Override
public String toRequestId(Serializable source, Class<?> entityType) {
--
}
#Override
public boolean supports(Class<?> type) {
--
}
}
The very first line gives me an error saying
Cannot resolve symbol 'BackendIdConverter'
Do I explicitly need to create a BackendIdConverter interface ?
Here is my pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.5.4</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>UI</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>UI</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<!-- <dependency>-->
<!-- <groupId>org.springframework.boot</groupId>-->
<!-- <artifactId>spring-boot-starter-validation</artifactId>-->
<!-- </dependency>-->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
EDIT:
Now that I've written a converter class, how do I use this ?
I need to send the primary key of VendorProductMapping class (i.e, VendorProductMappingPk) may be in an anchor tag. The error I see is
Failed to convert value of type 'java.lang.String' to required type 'com.example.UI.entity.VendorProductMappingPk'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'com.example.UI.entity.VendorProductMappingPk': no matching editors or conversion strategy found

Answer 1

BackendIdConverter is part of Spring Boot Data REST, so try adding the following dependency. However, I am not sure this is what you need for your case.
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-rest</artifactId>
</dependency>
I would say you need a JPA converter to achieve this:
#Converter
public class PersonNameConverter implements AttributeConverter<YourEmbeddedPrimaryKeyClass, String> {
#Override
public String convertToDatabaseColumn(YourEmbeddedPrimaryKeyClass id) {
// your conversion to String logic
}
#Override
public YourEmbeddedPrimaryKeyClass convertToEntityAttribute(String id) {
// your conversion to YourEmbeddedPrimaryKeyClass logic
}
}
Then you can configure this converter in your model:
#Entity
#IdClass(PK.class)
public class YourClass {
#Id
private YourEmbeddedPrimaryKeyClass id;
...
}
public class PK implements Serializable {
#Column(name = "MY_ID_FIELD")
#Convert(converter = IdConverter.class)
private YourEmbeddedPrimaryKeyClass id;
}
You can check additional details at https://www.baeldung.com/jpa-attribute-converters.