Mybatis #foreach中相同的變量名導致值覆蓋的問題解決
使用Mybatis中執行如下查詢：
單元測試
@Testpublic void test1() { String resource = 'mybatis-config.xml'; InputStream inputStream = null; try {inputStream = Resources.getResourceAsStream(resource); } catch (IOException e) {e.printStackTrace(); } SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); try (SqlSession sqlSession = sqlSessionFactory.openSession()) {CommonMapper mapper = sqlSession.getMapper(CommonMapper.class);QueryCondition queryCondition = new QueryCondition();List<Integer> list = new ArrayList<>();list.add(1);list.add(2);list.add(3);queryCondition.setWidthList(list);System.out.println(mapper.findByCondition(queryCondition)); }}
XML
<select parameterType='cn.liupjie.pojo.QueryCondition' resultType='cn.liupjie.pojo.Test'> select * from test <where><if test='id != null'> and id = #{id,jdbcType=INTEGER}</if><if test='widthList != null and widthList.size > 0'> <foreach collection='widthList' open='and width in (' close=')' item='width' separator=','>#{width,jdbcType=INTEGER} </foreach></if><if test='width != null'> and width = #{width,jdbcType=INTEGER}</if> </where></select>
打印的SQL：DEBUG [main] - ==> Preparing: select * from test WHERE width in ( ? , ? , ? ) and width = ? DEBUG [main] - ==> Parameters: 1(Integer), 2(Integer), 3(Integer), 3(Integer)
Mybatis版本
<dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.1</version></dependency>
這是公司的老項目，在迭代的過程中遇到了此問題，以此記錄！PS: 此bug在mybatis-3.4.5版本中已經解決。并且Mybatis維護者也建議不要在item/index中使用重復的變量名。
//foreach標簽解析完成后，從bindings中移除item context.getBindings().remove(item); context.getBindings().remove(index);Mybatis流程源碼解析（長文警告，按需自?。┮弧@取SqlSessionFactory
入口，跟著build方法走
//獲取SqlSessionFactory， 解析完成后，將XML中的內容封裝到一個Configuration對象中，//使用此對象構造一個DefaultSqlSessionFactory對象，并返回SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
來到SqlSessionFactoryBuilder#build方法
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) { try { //獲取XMLConfigBuilder，在XMLConfigBuilder的構造方法中，會創建XPathParser對象 //在創建XPathParser對象時，會將mybatis-config.xml文件轉換成Document對象 XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties); //調用XMLConfigBuilder#parse方法開始解析Mybatis的配置文件 return build(parser.parse()); } catch (Exception e) { throw ExceptionFactory.wrapException('Error building SqlSession.', e); } finally { ErrorContext.instance().reset(); try { inputStream.close(); } catch (IOException e) { // Intentionally ignore. Prefer previous error. } }}
跟著parse方法走，來到XMLConfigBuilder#parseConfiguration方法
private void parseConfiguration(XNode root) { try { Properties settings = settingsAsPropertiess(root.evalNode('settings')); //issue #117 read properties first propertiesElement(root.evalNode('properties')); loadCustomVfs(settings); typeAliasesElement(root.evalNode('typeAliases')); pluginElement(root.evalNode('plugins')); objectFactoryElement(root.evalNode('objectFactory')); objectWrapperFactoryElement(root.evalNode('objectWrapperFactory')); reflectorFactoryElement(root.evalNode('reflectorFactory')); settingsElement(settings); // read it after objectFactory and objectWrapperFactory issue #631 environmentsElement(root.evalNode('environments')); databaseIdProviderElement(root.evalNode('databaseIdProvider')); typeHandlerElement(root.evalNode('typeHandlers')); //這里解析mapper mapperElement(root.evalNode('mappers')); } catch (Exception e) { throw new BuilderException('Error parsing SQL Mapper Configuration. Cause: ' + e, e); }}
來到mapperElement方法
//本次mappers配置：<mapper resource='xml/CommomMapper.xml'/>private void mapperElement(XNode parent) throws Exception { if (parent != null) { for (XNode child : parent.getChildren()) { if ('package'.equals(child.getName())) {String mapperPackage = child.getStringAttribute('name');configuration.addMappers(mapperPackage); } else {String resource = child.getStringAttribute('resource');String url = child.getStringAttribute('url');String mapperClass = child.getStringAttribute('class');if (resource != null && url == null && mapperClass == null) { //因此走這里，讀取xml文件，并開始解析 ErrorContext.instance().resource(resource); InputStream inputStream = Resources.getResourceAsStream(resource); //這里同上文創建XMLConfigBuilder對象一樣，在內部構造時，也將xml文件轉換為了一個Document對象 XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments()); //解析 mapperParser.parse();} else if (resource == null && url != null && mapperClass == null) { ErrorContext.instance().resource(url); InputStream inputStream = Resources.getUrlAsStream(url); XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments()); mapperParser.parse();} else if (resource == null && url == null && mapperClass != null) { Class<?> mapperInterface = Resources.classForName(mapperClass); configuration.addMapper(mapperInterface);} else { throw new BuilderException('A mapper element may only specify a url, resource or class, but not more than one.');} } } }}
XMLMapperBuilder類，負責解析SQL語句所在XML中的內容
//parse方法public void parse() { if (!configuration.isResourceLoaded(resource)) { //解析mapper標簽 configurationElement(parser.evalNode('/mapper')); configuration.addLoadedResource(resource); bindMapperForNamespace(); } parsePendingResultMaps(); parsePendingChacheRefs(); parsePendingStatements();}//configurationElement方法private void configurationElement(XNode context) { try { String namespace = context.getStringAttribute('namespace'); if (namespace == null || namespace.equals('')) { throw new BuilderException('Mapper’s namespace cannot be empty'); } builderAssistant.setCurrentNamespace(namespace); cacheRefElement(context.evalNode('cache-ref')); cacheElement(context.evalNode('cache')); parameterMapElement(context.evalNodes('/mapper/parameterMap')); resultMapElements(context.evalNodes('/mapper/resultMap')); sqlElement(context.evalNodes('/mapper/sql')); //解析各種類型的SQL語句：select|insert|update|delete buildStatementFromContext(context.evalNodes('select|insert|update|delete')); } catch (Exception e) { throw new BuilderException('Error parsing Mapper XML. Cause: ' + e, e); }}private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) { for (XNode context : list) { //創建XMLStatementBuilder對象 final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId); try { //解析 statementParser.parseStatementNode(); } catch (IncompleteElementException e) { configuration.addIncompleteStatement(statementParser); } }}
XMLStatementBuilder負責解析單個select|insert|update|delete節點
public void parseStatementNode() { String id = context.getStringAttribute('id'); String databaseId = context.getStringAttribute('databaseId'); //判斷databaseId是否匹配，將namespace+’.’+id拼接，判斷是否已經存在此id if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) { return; } Integer fetchSize = context.getIntAttribute('fetchSize'); Integer timeout = context.getIntAttribute('timeout'); String parameterMap = context.getStringAttribute('parameterMap'); //獲取參數類型 String parameterType = context.getStringAttribute('parameterType'); //獲取參數類型的class對象 Class<?> parameterTypeClass = resolveClass(parameterType); String resultMap = context.getStringAttribute('resultMap'); String resultType = context.getStringAttribute('resultType'); String lang = context.getStringAttribute('lang'); LanguageDriver langDriver = getLanguageDriver(lang); //獲取resultType的class對象 Class<?> resultTypeClass = resolveClass(resultType); String resultSetType = context.getStringAttribute('resultSetType'); StatementType statementType = StatementType.valueOf(context.getStringAttribute('statementType', StatementType.PREPARED.toString())); ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType); //獲取select|insert|update|delete類型 String nodeName = context.getNode().getNodeName(); SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH)); boolean isSelect = sqlCommandType == SqlCommandType.SELECT; boolean flushCache = context.getBooleanAttribute('flushCache', !isSelect); boolean useCache = context.getBooleanAttribute('useCache', isSelect); boolean resultOrdered = context.getBooleanAttribute('resultOrdered', false); // Include Fragments before parsing XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant); includeParser.applyIncludes(context.getNode()); // Parse selectKey after includes and remove them. processSelectKeyNodes(id, parameterTypeClass, langDriver); // Parse the SQL (pre: <selectKey> and <include> were parsed and removed) //獲取SqlSource對象，langDriver為默認的XMLLanguageDriver，在new Configuration時設置 //若sql中包含元素節點或$，則返回DynamicSqlSource，否則返回RawSqlSource SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass); String resultSets = context.getStringAttribute('resultSets'); String keyProperty = context.getStringAttribute('keyProperty'); String keyColumn = context.getStringAttribute('keyColumn'); KeyGenerator keyGenerator; String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX; keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true); if (configuration.hasKeyGenerator(keyStatementId)) { keyGenerator = configuration.getKeyGenerator(keyStatementId); } else { keyGenerator = context.getBooleanAttribute('useGeneratedKeys',configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))? new Jdbc3KeyGenerator() : new NoKeyGenerator(); } builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType, fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass, resultSetTypeEnum, flushCache, useCache, resultOrdered, keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);}二、獲取SqlSession
由上文可知，此處的SqlSessionFactory使用的是DefaultSqlSessionFactory
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) { Transaction tx = null; try { final Environment environment = configuration.getEnvironment(); final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment); tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit); //創建執行器，默認是SimpleExecutor //如果在配置文件中開啟了緩存（默認開啟），則是CachingExecutor final Executor executor = configuration.newExecutor(tx, execType); //返回DefaultSqlSession對象 return new DefaultSqlSession(configuration, executor, autoCommit); } catch (Exception e) { closeTransaction(tx); // may have fetched a connection so lets call close() throw ExceptionFactory.wrapException('Error opening session. Cause: ' + e, e); } finally { ErrorContext.instance().reset(); }}
這里獲取到了一個DefaultSqlSession對象
三、執行SQL獲取CommonMapper的對象，這里CommonMapper是一個接口，因此是一個代理對象，代理類是MapperProxy
org.apache.ibatis.binding.MapperProxy@72cde7cc
執行Query方法，來到MapperProxy的invoke方法
@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable { if (Object.class.equals(method.getDeclaringClass())) { try { return method.invoke(this, args); } catch (Throwable t) { throw ExceptionUtil.unwrapThrowable(t); } } //緩存 final MapperMethod mapperMethod = cachedMapperMethod(method); //執行操作：select|insert|update|delete return mapperMethod.execute(sqlSession, args);}
執行操作時，根據SELECT操作，以及返回值類型（反射方法獲?。┐_定executeForMany方法
caseSELECT: if (method.returnsVoid() && method.hasResultHandler()) { executeWithResultHandler(sqlSession, args); result = null; } else if (method.returnsMany()) { result = executeForMany(sqlSession, args); } else if (method.returnsMap()) { result = executeForMap(sqlSession, args); } else if (method.returnsCursor()) { result = executeForCursor(sqlSession, args); } else { Object param = method.convertArgsToSqlCommandParam(args); result = sqlSession.selectOne(command.getName(), param); } break;
來到executeForMany方法中，就可以看到執行查詢的操作，由于這里沒有進行分頁查詢，因此走else
if (method.hasRowBounds()) { RowBounds rowBounds = method.extractRowBounds(args); result = sqlSession.<E>selectList(command.getName(), param, rowBounds);} else { result = sqlSession.<E>selectList(command.getName(), param);}
來到DefaultSqlSession#selectList方法中
@Overridepublic <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) { try { //根據key（namespace+'.'+id）來獲取MappedStatement對象 //MappedStatement對象中封裝了解析好的SQL信息 MappedStatement ms = configuration.getMappedStatement(statement); //通過CachingExecutor#query執行查詢 return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER); } catch (Exception e) { throw ExceptionFactory.wrapException('Error querying database. Cause: ' + e, e); } finally { ErrorContext.instance().reset(); }}
CachingExecutor#query
@Overridepublic <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException { //解析SQL為可執行的SQL BoundSql boundSql = ms.getBoundSql(parameter); //獲取緩存的key CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql); //執行查詢 return query(ms, parameter, rowBounds, resultHandler, key, boundSql);}
MappedStatement#getBoundSql
public BoundSql getBoundSql(Object parameterObject) { //解析SQL BoundSql boundSql = sqlSource.getBoundSql(parameterObject); List<ParameterMapping> parameterMappings = boundSql.getParameterMappings(); if (parameterMappings == null || parameterMappings.isEmpty()) { boundSql = new BoundSql(configuration, boundSql.getSql(), parameterMap.getParameterMappings(), parameterObject); } //檢查是否有嵌套的ResultMap // check for nested result maps in parameter mappings (issue #30) for (ParameterMapping pm : boundSql.getParameterMappings()) { String rmId = pm.getResultMapId(); if (rmId != null) { ResultMap rm = configuration.getResultMap(rmId); if (rm != null) {hasNestedResultMaps |= rm.hasNestedResultMaps(); } } } return boundSql;}
由上文，此次語句由于SQL中包含元素節點，因此是DynamicSqlSource。由此來到DynamicSqlSource#getBoundSql。rootSqlNode.apply(context);這段代碼便是在執行SQL解析。
@Overridepublic BoundSql getBoundSql(Object parameterObject) { DynamicContext context = new DynamicContext(configuration, parameterObject); //執行SQL解析 rootSqlNode.apply(context); SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration); Class<?> parameterType = parameterObject == null ? Object.class : parameterObject.getClass(); SqlSource sqlSource = sqlSourceParser.parse(context.getSql(), parameterType, context.getBindings()); BoundSql boundSql = sqlSource.getBoundSql(parameterObject); for (Map.Entry<String, Object> entry : context.getBindings().entrySet()) { boundSql.setAdditionalParameter(entry.getKey(), entry.getValue()); } return boundSql;}
打上斷點，跟著解析流程，來到解析foreach標簽的代碼，ForEachSqlNode#apply
@Overridepublic boolean apply(DynamicContext context) { Map<String, Object> bindings = context.getBindings(); final Iterable<?> iterable = evaluator.evaluateIterable(collectionExpression, bindings); if (!iterable.iterator().hasNext()) { return true; } boolean first = true; //解析open屬性 applyOpen(context); int i = 0; for (Object o : iterable) { DynamicContext oldContext = context; if (first) { context = new PrefixedContext(context, ''); } else if (separator != null) { context = new PrefixedContext(context, separator); } else {context = new PrefixedContext(context, ''); } int uniqueNumber = context.getUniqueNumber(); // Issue #709 //集合中的元素是Integer，走else if (o instanceof Map.Entry) { @SuppressWarnings('unchecked') Map.Entry<Object, Object> mapEntry = (Map.Entry<Object, Object>) o; applyIndex(context, mapEntry.getKey(), uniqueNumber); applyItem(context, mapEntry.getValue(), uniqueNumber); } else { //使用index屬性 applyIndex(context, i, uniqueNumber); //使用item屬性 applyItem(context, o, uniqueNumber); } //當foreach中使用#號時，會將變量替換為占位符（類似__frch_width_0）（StaticTextSqlNode） //當使用$符號時，會將值直接拼接到SQL中（TextSqlNode） contents.apply(new FilteredDynamicContext(configuration, context, index, item, uniqueNumber)); if (first) { first = !((PrefixedContext) context).isPrefixApplied(); } context = oldContext; i++; } applyClose(context); return true;}private void applyItem(DynamicContext context, Object o, int i) { if (item != null) {//在參數映射中綁定item屬性值與集合值的關系//第一次：（width:1）//第二次：（width:2）//第三次：（width:3）context.bind(item, o);//在參數映射中綁定處理后的item屬性值與集合值的關系//第一次：（__frch_width_0:1）//第二次：（__frch_width_1:2）//第三次：（__frch_width_2:3）context.bind(itemizeItem(item, i), o); } }
到這里，結果就清晰了，在解析foreach標簽時，每次循環都會將item屬性值與參數集合中的值進行綁定，到最后就會保留（width:3）的映射關系，而在解析完foreach標簽后，會解析最后一個if標簽，此時在判斷if標簽是否成立時，答案是true，因此最終拼接出來一個錯誤的SQL。
在3.4.5版本中，代碼中增加了context.getBindings().remove(item);在foreach標簽解析完成后移除bindings中的參數映射。以下是源碼：
@Overridepublic boolean apply(DynamicContext context) { Map<String, Object> bindings = context.getBindings(); final Iterable<?> iterable = evaluator.evaluateIterable(collectionExpression, bindings); if (!iterable.iterator().hasNext()) { return true; } boolean first = true; applyOpen(context); int i = 0; for (Object o : iterable) { DynamicContext oldContext = context; if (first || separator == null) { context = new PrefixedContext(context, ''); } else { context = new PrefixedContext(context, separator); } int uniqueNumber = context.getUniqueNumber(); // Issue #709 if (o instanceof Map.Entry) { @SuppressWarnings('unchecked') Map.Entry<Object, Object> mapEntry = (Map.Entry<Object, Object>) o; applyIndex(context, mapEntry.getKey(), uniqueNumber); applyItem(context, mapEntry.getValue(), uniqueNumber); } else { applyIndex(context, i, uniqueNumber); applyItem(context, o, uniqueNumber); } contents.apply(new FilteredDynamicContext(configuration, context, index, item, uniqueNumber)); if (first) { first = !((PrefixedContext) context).isPrefixApplied(); } context = oldContext; i++; } applyClose(context); //foreach標簽解析完成后，從bindings中移除item context.getBindings().remove(item); context.getBindings().remove(index); return true;}
到此這篇關于Mybatis #foreach中相同的變量名導致值覆蓋的問題解決的文章就介紹到這了,更多相關Mybatis #foreach相同變量名覆蓋內容請搜索好吧啦網以前的文章或繼續瀏覽下面的相關文章希望大家以后多多支持好吧啦網！
相關文章：
網公網安備