如何在 Spring Boot 应用程序中手动注册非标准化 SQL 函数？

Question

I'm using JPA query in my current spring-boot project. How can I add non-standardized SQL functions like GROUP_CONCAT ?

Prior, to my previous problem : How to show a column result in a one line comma separated list in JPA query

I found that GROUP_CONCAT is not a registered function in JPA query but could be accessed by registering it manually. I already tried following links but didn't work for me :

How to add non-standardized sql functions in Spring Boot application?

Registering a SQL function with JPA and Hibernate

https://thoughts-on-java.org/database-functions/

https://vladmihalcea.com/hibernate-sql-function-jpql-criteria-api-query/

1.

public class SqlFunctionsMetadataBuilderContributor
        implements MetadataBuilderContributor {

    @Override
    public void contribute(MetadataBuilder metadataBuilder) {
        metadataBuilder.applySqlFunction(
                "group_concat",
                new StandardSQLFunction(
                        "group_concat",
                        StandardBasicTypes.STRING
                )
        );
    }
}

2.

 public String render(Type firstArgumentType, List arguments, SessionFactoryImplementor factory)
            throws QueryException {
        if (arguments.size() < 1) {
            throw new QueryException(new IllegalArgumentException("group_concat should have at least one arg"));
        }

        StringBuilder builder = new StringBuilder();
        if (arguments.size() > 1 && arguments.get(0).equals("'distinct'")) {
            builder.append("distinct ");
            builder.append(arguments.get(1));
        } else {
            builder.append(arguments.get(0));
        }

        return "group_concat(" + builder.toString() + ")";
    }

3.

@Configuration
public class DataSource {
    @Bean
    public JpaVendorAdapter jpaVendorAdapter() {
        AbstractJpaVendorAdapter adapter = new HibernateJpaVendorAdapter();
        adapter.setShowSql(true);
        adapter.setDatabase(Database.MYSQL);
        // package to CustomMysqlDialect
        adapter.setDatabasePlatform("com.myprojet.admin.configuration.RegisterSqlFunction");
        adapter.setGenerateDdl(false);
        return adapter;
    }
}

    public RegisterSqlFunction() {
        super();

         registerFunction("group_concat, new StandardSQLFunction("group_concat", 
       StandardBasicTypes.STRING));
    }

I except using group_concat with JPA query.

Answer 1

You can find a fully functional example in my High-Performance Java Persistence GitHub repository .

In your case, you don't need to customize the JpaPlatform . That should be set to the HibernateJpaPlatform .

You can register the MetadataBuilderContributer either programaticallly via the application.properties configuration file:

hibernate.metadata_builder_contributor=com.vladmihalcea.book.hpjp.SqlFunctionsMetadataBuilderContributor

Answer 2

Create a class and add mySql Function you need to use in the overridden method:

public class SqlFunctionsMetadataBuilderContributor implements MetadataBuilderContributor{

 @Override
    public void contribute(MetadataBuilder metadataBuilder) {
        metadataBuilder.applySqlFunction(
            "group_concat",
            new StandardSQLFunction(
                "group_concat",
                StandardBasicTypes.STRING
            )
        );
    }
}

After that, provide your metadata_builder_contributor via application.properties:

spring.jpa.properties.hibernate.metadata_builder_contributor = qualifiedClassName

Answer 3

In case someone is having issues when registering this in a SpringBoot app this is the right way:

Create a class that implements: MetadataBuilderContributor interface.

package com.application.config;

public class SqlFunctionsMetadataBuilderContributor implements MetadataBuilderContributor {

  @Override
  public void contribute(MetadataBuilder metadataBuilder) {
    metadataBuilder.applySqlFunction(
        "STRING_AGG",
        new StandardSQLFunction(
            "STRING_AGG",
            StandardBasicTypes.STRING
        )
    );
  }
}

In your application .yml (or .properties) refer to the previously created class in the following properties path: spring.jpa.properties.hibernate.metadata_builder_contributor

  spring:      
    jpa:
      properties:
        hibernate:
          metadata_builder_contributor: com.application.config.SqlFunctionsMetadataBuilderContributor