MyBatis-Plus动态返回实体类示例详解-Java开发

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1. 自定义SqlSession

@Slf4j
public class GenericSqlSession extends DefaultSqlSession {
    private static final ThreadLocal<Class<?>> CTX = new ThreadLocal<>();
    private final Executor generalExecutor;
    public GenericSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
        super(configuration, executor, autoCommit);
        this.generalExecutor = executor;
    }
    @Override
    public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
        return doSelectList(statement, parameter, rowBounds);
    }
    protected <E> List<E> doSelectList(String statement, Object parameter, RowBounds rowBounds) {
        try {
            return generalExecutor.query(getCustomMappedStatement(statement),
                    ParamNameResolver.wrapToMapIfCollection(parameter, null), rowBounds, Executor.NO_RESULT_HANDLER);
        } catch (Exception e) {
            throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
        } finally {
            ErrorContext.instance().reset();
        }
    }
    protected MappedStatement getCustomMappedStatement(String statement) {
        var ms = getConfiguration().getMappedStatement(statement);
        var clazz = GenericSqlSession.get();
        if (ObjectUtil.isEmpty(clazz)) {
            return ms;
        } else {
            var resultMaps = ms.getResultMaps();
            var resultMap = resultMaps.get(0);
            var customMap = new ResultMap.Builder(getConfiguration(), resultMap.getId(),
                    clazz, resultMap.getResultMappings(), resultMap.getAutoMapping()).build();
            return new MappedStatement.Builder(getConfiguration(), ms.getId(), ms.getSqlSource(), ms.getSqlCommandType())
                    .resultMaps(Collections.singletonList(customMap))
                    .resource(ms.getResource())
                    .useCache(ms.isUseCache())
                    .build();
        }
    }
    public static void set(Class<?> clazz) {
        CTX.set(clazz);
    }
    public static Class<?> get() {
        return CTX.get();
    }
    public static void remove() {
        CTX.remove();
    }
}

2. 自定义SqlSessionFactory

public class GenericSqlSessionFactory extends DefaultSqlSessionFactory {
    public GenericSqlSessionFactory(Configuration configuration) {
        super(configuration);
    }
    @Override
    public SqlSession openSession(ExecutorType execType) {
        Transaction tx = null;
        try {
            final var environment = getConfiguration().getEnvironment();
            final var transactionFactory = getTransactionFactoryFromEnvironment(environment);
            tx = transactionFactory.newTransaction(environment.getDataSource(), null, false);
            final var executor = getConfiguration().newExecutor(tx, execType);
            return new GenericSqlSession(getConfiguration(), executor, false);
        } catch (Exception e) {
            // may have fetched a connection so let's call close()
            closeTransaction(tx);
            throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
        } finally {
            ErrorContext.instance().reset();
        }
    }
    private TransactionFactory getTransactionFactoryFromEnvironment(Environment environment) {
        if (environment == null || environment.getTransactionFactory() == null) {
            return new ManagedTransactionFactory();
        }
        return environment.getTransactionFactory();
    }
    private void closeTransaction(Transaction tx) {
        if (tx != null) {
            try {
                tx.close();
            } catch (SQLException ignore) {
                // Intentionally ignore. Prefer previous error.
            }
        }
    }
}

3. 自定义SqlSessionTemplate

@Component
public class GenericSqlSessionTemplate extends SqlSessionTemplate {
    public GenericSqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
        super(new GenericSqlSessionFactory(sqlSessionFactory.getConfiguration()));
    }
}

4. 自定义基础Mapper

public interface SuperMapper<T> extends BaseMapper<T> {
    /**
     * selectById
     *
     * @param clazz 自定义结果集class
     * @param id    id
     * @param <D>   D
     * @return D
     */
    @SuppressWarnings("unchecked")
    default <D> D selectById(Class<D> clazz, Serializable id) {
        try {
            GenericSqlSession.set(clazz);
            return (D) selectById(id);
        } finally {
            GenericSqlSession.remove();
        }
    }
}

5. 使用

继承自定义的基础Mapper

@Data
@TableName("tag")
public class TagPO implements Serializable {
    private static final long serialVersionUID = 1L;
    @TableId(type = IdType.AUTO)
    private Integer id;
    private String name;
}
public interface TagDAO extends SuperMapper<TagPO> {
}
@Component
@Slf4j
public class MybatisTest implements CommandLineRunner {
    @Autowired
    TagDAO tagDAO;
    @Override
    public void run(String... args) throws Exception {
        TagDTO id1 = tagDAO.selectById(TagDTO.class, 1);
        log.info("{}", id1);
        TagPO id2 = tagDAO.selectById(1);
        log.info("{}", id2);
    }
}

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