6

我在我的项目中使用 mybatis 执行 sql 查询。我需要在执行之前拦截 sql 查询以动态应用一些更改。我读过这样的@Interseptors：

@Intercepts({@Signature(type= Executor.class, method = "query", args = {...})})
public class ExamplePlugin implements Interceptor {
  public Object intercept(Invocation invocation) throws Throwable {
    return invocation.proceed();
  }
  public Object plugin(Object target) {
    return Plugin.wrap(target, this);
  }
  public void setProperties(Properties properties) {
  }
}

它确实拦截了执行，但是由于相应的字段不可写，因此无法更改 sql 查询。我应该手动构建整个对象的新实例来替换 sql 查询吗？拦截查询执行以动态更改它的正确位置在哪里？感谢。

4

3 回答 3

8

我希望它会帮助你：

@Intercepts( { @Signature(type = Executor.class, method = "query", args = {
        MappedStatement.class, Object.class, RowBounds.class,
        ResultHandler.class
    })
})
public class SelectCountSqlInterceptor2 implements Interceptor
{
    public static String COUNT = "_count";
    private static int MAPPED_STATEMENT_INDEX = 0;
    private static int PARAMETER_INDEX = 1;
    @Override
    public Object intercept(Invocation invocation) throws Throwable
    {
        processCountSql(invocation.getArgs());
        return invocation.proceed();
    }
    @SuppressWarnings("rawtypes")
    private void processCountSql(final Object[] queryArgs)
    {
        if (queryArgs[PARAMETER_INDEX] instanceof Map)
        {
            Map parameter = (Map) queryArgs[PARAMETER_INDEX];
            if (parameter.containsKey(COUNT))
            {
                MappedStatement ms = (MappedStatement) queryArgs[MAPPED_STATEMENT_INDEX];
                BoundSql boundSql = ms.getBoundSql(parameter);
                String sql = ms.getBoundSql(parameter).getSql().trim();
                BoundSql newBoundSql = new BoundSql(ms.getConfiguration(),
                                                    getCountSQL(sql), boundSql.getParameterMappings(),
                                                    boundSql.getParameterObject());
                MappedStatement newMs = copyFromMappedStatement(ms,
                                        new OffsetLimitInterceptor.BoundSqlSqlSource(newBoundSql));
                queryArgs[MAPPED_STATEMENT_INDEX] = newMs;
            }
        }
    }
    // see: MapperBuilderAssistant
    @SuppressWarnings({ "unchecked", "rawtypes" })
    private MappedStatement copyFromMappedStatement(MappedStatement ms,
            SqlSource newSqlSource)
    {
        Builder builder = new MappedStatement.Builder(ms.getConfiguration(), ms
                .getId(), newSqlSource, ms.getSqlCommandType());
        builder.resource(ms.getResource());
        builder.fetchSize(ms.getFetchSize());
        builder.statementType(ms.getStatementType());
        builder.keyGenerator(ms.getKeyGenerator());
        // setStatementTimeout()
        builder.timeout(ms.getTimeout());
        // setParameterMap()
        builder.parameterMap(ms.getParameterMap());
        // setStatementResultMap()
        List<ResultMap> resultMaps = new ArrayList<ResultMap>();
        String id = "-inline";
        if (ms.getResultMaps() != null)
        {
            id = ms.getResultMaps().get(0).getId() + "-inline";
        }
        ResultMap resultMap = new ResultMap.Builder(null, id, Long.class,
                new ArrayList()).build();
        resultMaps.add(resultMap);
        builder.resultMaps(resultMaps);
        builder.resultSetType(ms.getResultSetType());
        // setStatementCache()
        builder.cache(ms.getCache());
        builder.flushCacheRequired(ms.isFlushCacheRequired());
        builder.useCache(ms.isUseCache());
        return builder.build();
    }
    private String getCountSQL(String sql)
    {
        String lowerCaseSQL = sql.toLowerCase().replace("\n", " ").replace("\t", " ");
        int index = lowerCaseSQL.indexOf(" order ");
        if (index != -1)
        {
            sql = sql.substring(0, index);
        }
        return "SELECT COUNT(*) from ( select 1 as col_c " + sql.substring(lowerCaseSQL.indexOf(" from "))  + " )   cnt";
    }
    @Override
    public Object plugin(Object target)
    {
        return Plugin.wrap(target, this);
    }
    @Override
    public void setProperties(Properties properties)
    {
    }
}
于 2013-07-23T02:21:15.647 回答
0

您可以考虑使用字符串模板库（例如 Velocity、Handlebars、Mustache）来帮助您

迄今为止，甚至还有 MyBatis-Velocity ( http://mybatis.github.io/velocity-scripting/ ) 可以帮助您为 sql 编写脚本。

于 2013-06-01T14:12:09.777 回答
0

根据您要进行的更改，您可能希望使用mybatis 3的动态 sql功能

于 2013-06-08T20:43:47.007 回答