一、背景描述

Springboot项目集成了Mybatis-plus，最近在做一个导出功能，我的详情里面可能会有上好几千条数据，后面的导出需要将详情中的数据导出来，单页查询（pageSize < 500时）很正常，需求是把详情中所有数据全部导出，但是每次导出的时候只能导出500条数据，估计是源码里加了默认限制。

二、问题原因

查看源码：

@Setter
@Accessors(chain = true)
@Intercepts({@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})})
public class PaginationInterceptor extends AbstractSqlParserHandler implements Interceptor {

    protected static final Log logger = LogFactory.getLog(PaginationInterceptor.class);
    /**
     * COUNT SQL 解析
     */
    private ISqlParser countSqlParser;
    /**
     * 溢出总页数，设置第一页
     */
    private boolean overflow = false;
    /**
     * 单页限制 500 条，小于 0 如 -1 不受限制
     */
    private long limit = 500L;
    /**
     * 方言类型
     */
    private String dialectType;
    /**
     * 方言实现类<br>
     * 注意！实现 com.baomidou.mybatisplus.extension.plugins.pagination.dialects.IDialect 接口的子类
     */
    private String dialectClazz;

    /**
     * 查询SQL拼接Order By
     *
     * @param originalSql 需要拼接的SQL
     * @param page        page对象
     * @return ignore
     */
    public static String concatOrderBy(String originalSql, IPage<?> page) {
        if (CollectionUtils.isNotEmpty(page.orders())) {
            try {
                List<OrderItem> orderList = page.orders();
                Select selectStatement = (Select) CCJSqlParserUtil.parse(originalSql);
                if (selectStatement.getSelectBody() instanceof PlainSelect) {
                    PlainSelect plainSelect = (PlainSelect) selectStatement.getSelectBody();
                    List<OrderByElement> orderByElements = plainSelect.getOrderByElements();
                    List<OrderByElement> orderByElementsReturn = addOrderByElements(orderList, orderByElements);
                    plainSelect.setOrderByElements(orderByElementsReturn);
                    return plainSelect.toString();
                } else if (selectStatement.getSelectBody() instanceof SetOperationList) {
                    SetOperationList setOperationList = (SetOperationList) selectStatement.getSelectBody();
                    List<OrderByElement> orderByElements = setOperationList.getOrderByElements();
                    List<OrderByElement> orderByElementsReturn = addOrderByElements(orderList, orderByElements);
                    setOperationList.setOrderByElements(orderByElementsReturn);
                    return setOperationList.toString();
                } else if (selectStatement.getSelectBody() instanceof WithItem) {
                    // todo: don't known how to resole
                    return originalSql;
                } else {
                    return originalSql;
                }

            } catch (JSQLParserException e) {
                logger.warn("failed to concat orderBy from IPage, exception=" + e.getMessage());
            }
        }
        return originalSql;
    }

MyBatis-Plus低版本的PaginationInterceptor，定义了默认limit为500。当size超出limit时设置size为limit的值，即当size大于500时，就默认使用 size = 500。

三、解决方案

关于这个问题的解决方案：配置分页插件时重新设置limit的值，源码中有提示 paginationInterceptor.setLimit(-1)表示不受限制：

/**
 * 分页插件配置类
 */
@EnableTransactionManagement(proxyTargetClass = true)
@Configuration
public class MybatisPlusConfig {
    /**
     * 分页插件
     *
     * @return
     */
    @Bean
    public PaginationInterceptor paginationInterceptor() {
        PaginationInterceptor paginationInterceptor = new PaginationInterceptor();
        paginationInterceptor.setLimit(-1);
        return paginationInterceptor;
    }
}