Use jOOQ to write vendor-agnostic SQL with JPA's native query or @Formula.

If you are traditionalJPAOccasionally applications using native queries orHibernate@Formula 或Spring Data@Query 注释,Embedded the vendor specific localSQL,你可以使用jOOQ的 The connection and parse data sourceBetween the dialect translation,Without having to go all out to usejOOQ--Although I think once you seejOOQ能为你做什么,这就是不可避免的.

现在,Let's design a to the table.

CREATE TABLE author (
  id INT NOT NULL,
  first_name TEXT,
  last_name TEXT NOT NULL,

  CONSTRAINT pk_author PRIMARY KEY (id)
);

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现在,You may want to use in the tableJPA的 [EntityManager.createNativeQuery()](https://jakarta.ee/specifications/persistence/3.0/apidocs/jakarta.persistence/jakarta/persistence/entitymanager#createNativeQuery(java.lang.String,java.lang.Class)),Map it to the entity.你可以使用jOOQ的DSL API,But if you are not prepared to move tojOOQ,Or do you want to use byDBAProvide the actualSQL,而不是jOOQ的DSL.

所以,在MariaDB中,You may want to write something like that.

List<Author> result =
em.createNativeQuery(""" select a.id, nvl(a.first_name, 'N/A') as first_name, a.last_name from t_author as a order by a.id """, Author.class)
  .getResultList();

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Which one of the defined entity is this.

@Entity
@Table(name = "author")
public class Author {
    @Id
    public int id;

    @Column(name = "first_name")
    public String firstName;

    @Column(name = "last_name")
    public String lastName;

    // Constructors, getters, setters, equals, hashCode, etc
}

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The above methods run very well,并且在MariaDBOf all the author,它实现了对Oracle的 [NVL()](https://mariadb.com/docs/reference/mdb/functions/NVL/)函数的支持.但是Oracle本身呢？查询在Oracle上失败了,因为.

ORA-00933:SQLWe do not have the right to end command

这是因为在Oracle中,你不能使用AS Keyword to don't watch,Only don't finished.当然,你可以去掉这个,但是,NVL() 呢？You want it inMySQL和SQL ServerWork on,But they will complain about.

MySQL

SQL错误[1305] [42000].FUNCTION test.nvl不存在

SQL服务器

SQL Error [195] [S0010]: 'nvl' Is not a recognized built-in function name.

现在,你有这些选择.

• 使用jOOQTo generate for youSQL字符串,使用DSL
• 使用JPQLRather than native queries（But to a large number of rewriting,因为JPQL比SQLThe function of much less）.
• 试试你的运气,Manually write the actual supplier has nothing to doSQL.
• 或者...

jOOQThe resolution of connection

你可以使用jOOQThe resolution of connection,It as your actual connection agent,在JDBCLevel to intercept eachSQL语句,To translate it into target language.

It's like your existingJDBCConnection 或DataSource Packaged in the following as simple.

DataSource originalDataSource = ...
DataSource parsingDataSource = DSL
    .using(originalDataSource, dialect)
    .parsingDataSource();

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就是这样!我的意思是,你可以在dialect After passing some additional configurationSettings ,But this is the simplest.新的DataSource ,Now you can run on all of these dialects of youSQL查询,例如,你可能会在你的DEBUG Log in to see this.

在MySQL上.

-- org.hibernate.SQL
   select a.id, nvl(a.first_name, 'N/A') as first_name, a.last_name 
   from t_author as a 
   order by a.id
-- org.jooq.impl.ParsingConnection Translating from:
   select a.id, nvl(a.first_name, 'N/A') as first_name, a.last_name
   from t_author as a 
   order by a.id
-- org.jooq.impl.ParsingConnection Translation cache miss: 
   select a.id, nvl(a.first_name, 'N/A') as first_name, a.last_name
   from t_author as a 
   order by a.id
-- org.jooq.impl.ParsingConnection Translating to: 
   select a.id, ifnull(a.first_name, 'N/A') as first_name, a.last_name
   from t_author as a 
   order by a.id

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在SQL Server上.

-- org.hibernate.SQL
   select a.id, nvl(a.first_name, 'N/A') as first_name, a.last_name 
   from t_author as a 
   order by a.id
-- org.jooq.impl.ParsingConnection Translating from:
   select a.id, nvl(a.first_name, 'N/A') as first_name, a.last_name
   from t_author as a 
   order by a.id
-- org.jooq.impl.ParsingConnection Translation cache miss: 
   select a.id, nvl(a.first_name, 'N/A') as first_name, a.last_name
   from t_author as a 
   order by a.id
-- org.jooq.impl.ParsingConnection] Translating to: 
   select a.id, coalesce(a.first_name, 'N/A') first_name, a.last_name 
   from author a 
   order by a.id

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Hibernate被jOOQ欺骗了!NVL The function of translated intoMySQL的 [IFNULL](https://dev.mysql.com/doc/refman/8.0/en/flow-control-functions.html#function_ifnull)或SQL Server [COALESCE](https://docs.microsoft.com/en-us/sql/t-sql/language-elements/coalesce-transact-sql?view=sql-server-ver15),并且从SQL ServerIn the query to deleteAS 关键字.这些只是简单的例子,你的实际SQLCould be much more complex.On the Internet to play the feature set,在这里.

另外, [Settings.cacheParsingConnectionLRUCacheSize](https://www.jooq.org/javadoc/latest/org.jooq/org/jooq/conf/Settings.html#cacheParsingConnectionLRUCacheSize)标志,默认为8192,We can ensure that the same query translation would not have been to,所以你不会在jOOQThe parser spend too much time.

@Formula也是,Is not only a local query

在Hibernate中,When you want to project the additional value,A quick victory,类似于SQL自己的计算列,在许多SQLDialects are,这就是@Formula 注释,It can be added to any entity in the,就像这样.Suppose you have the extra column.

ALTER TABLE author ADD year_of_birth INT;

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We may have the following revised entity.

@Entity
@Table(name = "author")
public class Author {
    @Id
    public int id;

    @Column(name = "first_name")
    public String firstName;

    @Column(name = "last_name")
    public String lastName;

    @Column(name = "year_of_birth")
    public Integer yearOfBirth;

    @Formula("year_of_birth between 1981 and 1996")
    public Boolean millenial;

    // Constructors, getters, setters, equals, hashCode, etc
}

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但不幸的是,There are still so manyRDBMSIn fact don't support Boolean type,而且@Formula Annotations are purely static,Do not allow the specific vendor's cover.If we want to manually override theSQL查询,To ensure that there is aSQL-92的、Has nothing to do with the manufacturer's localSQLFragments of all the dialects can be use？

Or we just insert againjOOQThe resolution of connection？Let's try using the latter.

Author author = em.find(Author.class, 1);

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MySQLThe logs contain.

-- org.hibernate.SQL
   select 
     jpaauthorw0_.id as id1_4_0_,
     jpaauthorw0_.first_name as first_na2_4_0_, 
     jpaauthorw0_.last_name as last_nam3_4_0_, 
     jpaauthorw0_.year_of_birth between 1981 and 1996 as formula1_0_ 
   from author jpaauthorw0_ 
   where jpaauthorw0_.id=?
-- org.jooq.impl.ParsingConnection Translating from: [...]
-- org.jooq.impl.ParsingConnection Translation cache miss: [...]
-- org.jooq.impl.ParsingConnection Translating to: 
   select 
     jpaauthorw0_.id as id1_4_0_, 
     jpaauthorw0_.first_name as first_na2_4_0_, 
     jpaauthorw0_.last_name as last_nam3_4_0_, 
     jpaauthorw0_.year_of_birth between 1981 and 1996 as formula1_0_ 
   from author as jpaauthorw0_ 
   where jpaauthorw0_.id = ?


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正如你所看到的,jOOQ重新添加了AS Keyword to aliasMySQL,Because we like clear alias,Also because it is aMySQL的默认值.Settings.renderOptionalAsKeywordForTableAliases

而SQL ServerThe logs contain.

-- org.hibernate.SQL 
   select 
     jpaauthorw0_.id as id1_4_0_, 
     jpaauthorw0_.first_name as first_na2_4_0_, 
     jpaauthorw0_.last_name as last_nam3_4_0_, 
     jpaauthorw0_.year_of_birth between 1981 and 1996 as formula1_0_ 
   from author jpaauthorw0_ 
   where jpaauthorw0_.id=?
-- org.jooq.impl.ParsingConnection Translating from: [...]
-- org.jooq.impl.ParsingConnection Translation cache miss: [...]
-- org.jooq.impl.ParsingConnection Translating to: 
   select
     jpaauthorw0_.id id1_4_0_, 
     jpaauthorw0_.first_name first_na2_4_0_, 
     jpaauthorw0_.last_name last_nam3_4_0_, 
     case 
       when jpaauthorw0_.year_of_birth between 1981 and 1996 
         then 1 
       when not (jpaauthorw0_.year_of_birth between 1981 and 1996) 
         then 0 
     end formula1_0_ 
   from author jpaauthorw0_ 
   where jpaauthorw0_.id = ?

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一个NULL-safeBOOLEAN 类型的模拟（因为如果YEAR_OF_BIRTH 是NULL （即UNKNOWN ）,那么MILLENIAL 也必须是NULL ,即UNKNOWN ）.

Spring Data @Query注解

在JPAIntegration of localSQL的另一种情况是Spring Data JPA的 [@Query](https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#jpa.query-methods.at-query)注解,特别是当与@Query(nativeQuery = true) .就像Hibernate的@Formula ,This annotation is static at compile time,There is no way to cover the value of the local query at runtime,Maybe it's just in each dialect points was carried out on the repository type.

But why go through the trouble.Always the same thing.只要用jOOQThe connection or parse the data source to repairDataSource ,就可以了.

结论

即使你不使用jOOQ的DSL API,You can also in your existing based onJDBC、R2DBC、JPA、MyBatisApplications such as in a variety of ways fromjOOQ中获利,Method is the hookjOOQ解析连接,And your vendor specific input dialect translation into any number of dialects can be configured to output.

如果jOOQThe parser can't handle a feature,你有可能使用ParseListener SPI来解决这个限制,例如,When you want to support a hypothesis ofLOGICAL_XOR 谓词时（MySQL原生支持）.

Query query = configuration
    .derive(ParseListener.onParseCondition(ctx -> {
        if (ctx.parseFunctionNameIf("LOGICAL_XOR")) {
            ctx.parse('(');
            Condition c1 = ctx.parseCondition();
            ctx.parse(',');
            Condition c2 = ctx.parseCondition();
            ctx.parse(')');

            return CustomCondition.of(c -> {
                switch (c.family()) {
                    case MARIADB:
                    case MYSQL:
                        c.visit(condition("{0} xor {1}", c1, c2));
                        break;
                    default:
                        c.visit(c1.andNot(c2).or(c2.andNot(c1)));
                        break;
            });
        }

        // Let the parser take over if we don't know the token
        return null;
    })
    .dsl()
    .parser()
    .parseQuery(
        "select * from t where logical_xor(t.a = 1, t.b = 2)"
    );
  
System.out.println(DSL.using(SQLDialect.MYSQL).render(query));
System.out.println(DSL.using(SQLDialect.ORACLE).render(query));

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The program will print out.

-- MYSQL:
select * 
from t
where (t.a = 1 xor t.b = 2);

-- ORACLE:
select * 
from t 
where (t.a = 1 and not (t.b = 2)) or (t.b = 2 and not (t.a = 1));

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因此,无论是否使用jOOQ的DSL,都可以通过使用jOOQWill you supply application specificSQL从一个RDBMS迁移到另一个RDBMS,Or in an application to support multipleRDBMSProduct and profit.

题外话.查询转换

This is not the subject of this post,But once you makejOOQAnalyses the each of youSQL语句,你也可以用jOOQ来转换这些SQL,And tampering with expression trees,For example, by implementing the client row-level security.这种可能性是无穷无尽的.