To change Entity data to snake case json…

@Configuration
public class JacksonConfiguration {
    @Bean
    public Jackson2ObjectMapperBuilder jackson2ObjectMapperBuilder() {
        return new Jackson2ObjectMapperBuilder().propertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);
    }
}

Or add

spring.jackson.property-naming-strategy=SNAKE_CASE

DSL Method

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