框架层能否增加查询数量的限制？

[mwjmwj]

问题：
在使用mybatis查询数据时，如果sql编写不得当，会出现全表扫数据，数据很多的话

容易出现内存溢出的问题，能否在 statementid层 对查询的总数做一个可配置的校验

解决思路：
例如：

<select id="query" resultType="java.util.HashMap" maxCountSize="10000"> （也可做成读上下文动态配置，可实时修改）

使用的位置：

org.apache.ibatis.executor.resultset.DefaultResultSetHandler

private void handleRowValuesForSimpleResultMap(ResultSetWrapper rsw, ResultMap resultMap,
    ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping) throws SQLException {
    DefaultResultContext<Object> resultContext = new DefaultResultContext<>();
    ResultSet resultSet = rsw.getResultSet();
    skipRows(resultSet, rowBounds);
    int queryIndex = 0;
    while (shouldProcessMoreRows(resultContext, rowBounds) && !resultSet.isClosed() && resultSet.next()) {
        queryIndex++;
        if (queryIndex > 当前sql语句配置的最大值) {
                    // 弹出报错，不然继续解析最终会导致oom
            throw new RuntimeException("query Size has large greate 10000!");
        }
        ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(resultSet, resultMap, null);
        Object rowValue = getRowValue(rsw, discriminatedResultMap, null);
        storeObject(resultHandler, resultContext, rowValue, parentMapping, resultSet);
    }

}

[harawata]

Hello @mwjmwj ,

No. MyBatis does not provide such feature.

Checking the result size after retrieving ResultSet isn't efficient.
JDBC provides java.sql.Statement#setMaxRows(), but its efficiency depends on the db/driver implementation.
The best way is to limit the number of returned rows in SQL using FETCH NEXT x ROWS ONLY or LIMIT x.
See this answer: https://stackoverflow.com/a/61140502/1261766

If you expect an exception, for some reason, you may have to get an extra row and check the result size. e.g.

select * from some_table fetch next 10001 rows only

List results = yourMapper.select();
if (results.size() > 10000) {
  throw new RuntimeException("query Size has large greate 10000!");
}

[quaff]

@mwjmwj You should use Cursor or Stream (not supported yet), and set proper fetchSize, and append useCursorFetch=true to JDBC url if you are using MySQL.