mybatis-plus 属性为空时判断问题

mybatis-plus 属性为空时判断问题

最近在做项目时,发现前端调用查询接口，发现接口返回数据不对。我通过日志发现前端查询字段值为空时，竟然被当作一个条件，因为后端采用的mybatis-plus，通过官网我找到了一个配置

mybatis-plus:
  global-config:
    db-config:
      select-strategy: not_empty

然后再测试一遍发现好使了。
我决定看一下mybatis-plus的底层时怎么实现的。
mybatis-plus 为我们提供了许多默认的方法，通过继承BaseMapper就可以实现,无需配置xml，具体的方法可以参考mybatis-plus的官方网站：
mybatis-plus

   mybatis 在启动的时候,会根据mapper方法，生成一个MappedStatement，一个mapper的方法会对应一个MappedStatement.

public final class MappedStatement {

  private String resource;
  private Configuration configuration;
  private String id;
  private Integer fetchSize;
  private Integer timeout;
  private StatementType statementType;
  private ResultSetType resultSetType;
  private SqlSource sqlSource;
  private Cache cache;
  private ParameterMap parameterMap;
  private List resultMaps;
  private boolean flushCacheRequired;
  private boolean useCache;
  private boolean resultOrdered;
  private SqlCommandType sqlCommandType;
  private KeyGenerator keyGenerator;
  private String[] keyProperties;
  private String[] keyColumns;
  private boolean hasNestedResultMaps;
  private String databaseId;
  private Log statementLog;
  private LanguageDriver lang;
  private String[] resultSets;

由此可以想到，mybatis-plus 启动的时候会生成一些默认的方法的 MappedStatement我们先看MybatisConfiguration 的addMapper 方法

    @Override
    public  void addMapper(Class type) {
        mybatisMapperRegistry.addMapper(type);
    }

跳转到MybatisMapperRegistry 类中

 @Override
    public  void addMapper(Class type) {
        if (type.isInterface()) {
            if (hasMapper(type)) {
                // TODO 如果之前注入 直接返回
                return;
                // TODO 这里就不抛异常了
//                throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
            }
            boolean loadCompleted = false;
            try {
                // TODO 这里也换成 MybatisMapperProxyFactory 而不是 MapperProxyFactory
                knownMappers.put(type, new MybatisMapperProxyFactory<>(type));
                // It's important that the type is added before the parser is run
                // otherwise the binding may automatically be attempted by the
                // mapper parser. If the type is already known, it won't try.
                // TODO 这里也换成 MybatisMapperAnnotationBuilder 而不是 MapperAnnotationBuilder
                MybatisMapperAnnotationBuilder parser = new MybatisMapperAnnotationBuilder(config, type);
                parser.parse();
                loadCompleted = true;
            } finally {
                if (!loadCompleted) {
                    knownMappers.remove(type);
                }
            }
        }
    }

重点看 parser.parse() 我们在点进去看

 @Override
    public void parse() {
        String resource = type.toString();
        if (!configuration.isResourceLoaded(resource)) {
            loadXmlResource();
            configuration.addLoadedResource(resource);
            final String typeName = type.getName();
            assistant.setCurrentNamespace(typeName);
            parseCache();
            parseCacheRef();
            SqlParserHelper.initSqlParserInfoCache(type);
            Method[] methods = type.getMethods();
            for (Method method : methods) {
                try {
                    // issue #237
                    if (!method.isBridge()) {
                        parseStatement(method);
                        SqlParserHelper.initSqlParserInfoCache(typeName, method);
                    }
                } catch (IncompleteElementException e) {
                    // TODO 使用 MybatisMethodResolver 而不是 MethodResolver
                    configuration.addIncompleteMethod(new MybatisMethodResolver(this, method));
                }
            }
            // TODO 注入 CURD 动态 SQL , 放在在最后, because 可能会有人会用注解重写sql
            if (GlobalConfigUtils.isSupperMapperChildren(configuration, type)) {
                GlobalConfigUtils.getSqlInjector(configuration).inspectInject(assistant, type);
            }
        }
        parsePendingMethods();
    }

我们看inspectInject方法:

@Override
    public void inspectInject(MapperBuilderAssistant builderAssistant, Class mapperClass) {
        Class modelClass = extractModelClass(mapperClass);
        if (modelClass != null) {
            String className = mapperClass.toString();
            Set mapperRegistryCache = GlobalConfigUtils.getMapperRegistryCache(builderAssistant.getConfiguration());
            if (!mapperRegistryCache.contains(className)) {
                List methodList = this.getMethodList(mapperClass);
                if (CollectionUtils.isNotEmpty(methodList)) {
                	//包装一个实体类
                    TableInfo tableInfo = TableInfoHelper.initTableInfo(builderAssistant, modelClass);
                    // 循环注入自定义方法
                    methodList.forEach(m -> m.inject(builderAssistant, mapperClass, modelClass, tableInfo));
                } else {
                    logger.debug(mapperClass.toString() + ", No effective injection method was found.");
                }
                mapperRegistryCache.add(className);
            }
        }
    }

然后再看 m.inject方法:

  /**
     * 注入自定义方法
     */
    public void inject(MapperBuilderAssistant builderAssistant, Class mapperClass, Class modelClass, TableInfo tableInfo) {
        this.configuration = builderAssistant.getConfiguration();
        this.builderAssistant = builderAssistant;
        this.languageDriver = configuration.getDefaultScriptingLanguageInstance();
        /* 注入自定义方法 */
        injectMappedStatement(mapperClass, modelClass, tableInfo);
    }

终于看到增加MappedStatement了,injectMappedStatement有很多实现类

因为是查询 我们看selectList

@Override
    public MappedStatement injectMappedStatement(Class mapperClass, Class modelClass, TableInfo tableInfo) {
        SqlMethod sqlMethod = SqlMethod.SELECT_LIST;
        String sql = String.format(sqlMethod.getSql(), sqlSelectColumns(tableInfo, true),
            tableInfo.getTableName(), sqlWhereEntityWrapper(true, tableInfo),
            sqlComment());
        SqlSource sqlSource = languageDriver.createSqlSource(configuration, sql, modelClass);
        return this.addSelectMappedStatementForTable(mapperClass, sqlMethod.getMethod(), sqlSource, tableInfo);
    }

因为是查询条件，我们看sqlWhereEntityWrapper 方法 此方法会封装一些sql的条件语句:，最后来到TableFieldInfo的getSqlWhere方法:

 public String getSqlWhere(final String prefix) {
        final String newPrefix = prefix == null ? EMPTY : prefix;
        // 默认:  AND column=#{prefix + el}
        String sqlScript = " AND " + String.format(condition, column, newPrefix + el);
        // 查询的时候只判非空
        return convertIf(sqlScript, newPrefix + property, whereStrategy);
    }

然后进入convertIf方法:

private String convertIf(final String sqlScript, final String property, final FieldStrategy fieldStrategy) {
        if (fieldStrategy == FieldStrategy.NEVER) {
            return null;
        }
        if (fieldStrategy == FieldStrategy.IGNORED) {
            return sqlScript;
        }
        if (fieldStrategy == FieldStrategy.NOT_EMPTY && isCharSequence) {
            return SqlScriptUtils.convertIf(sqlScript, String.format("%s != null and %s != ''", property, property),
                false);
        }
        return SqlScriptUtils.convertIf(sqlScript, String.format("%s != null", property), false);
    }

通过代码可以看到生成的sql条件对空判断和策略有关，那我们就去找TableFieldInfo创建的时候是怎么赋值的，我们回到AbstractSqlInjector中

@Override
    public void inspectInject(MapperBuilderAssistant builderAssistant, Class mapperClass) {
        Class modelClass = extractModelClass(mapperClass);
        if (modelClass != null) {
            String className = mapperClass.toString();
            Set mapperRegistryCache = GlobalConfigUtils.getMapperRegistryCache(builderAssistant.getConfiguration());
            if (!mapperRegistryCache.contains(className)) {
                List methodList = this.getMethodList(mapperClass);
                if (CollectionUtils.isNotEmpty(methodList)) {
                    TableInfo tableInfo = TableInfoHelper.initTableInfo(builderAssistant, modelClass);
                    // 循环注入自定义方法
                    methodList.forEach(m -> m.inject(builderAssistant, mapperClass, modelClass, tableInfo));
                } else {
                    logger.debug(mapperClass.toString() + ", No effective injection method was found.");
                }
                mapperRegistryCache.add(className);
            }
        }
    }

TableFieldInfo 是TableInfo的属性，我们看initTableInfo方法:

   /* 初始化字段相关 */
        initTableFields(clazz, globalConfig, tableInfo);

此方法就是创建TableFieldInfo:

   /* 无 @TableField 注解的字段初始化 */
            fieldList.add(new TableFieldInfo(dbConfig, tableInfo, field));

然后看TableFieldInfo的构造方法:

 public TableFieldInfo(GlobalConfig.DbConfig dbConfig, TableInfo tableInfo, Field field) {
        this.version = field.getAnnotation(Version.class) != null;
        this.property = field.getName();
        this.propertyType = field.getType();
        this.isCharSequence = StringUtils.isCharSequence(this.propertyType);
        this.el = this.property;
        this.insertStrategy = dbConfig.getInsertStrategy();
        this.updateStrategy = dbConfig.getUpdateStrategy();
        this.whereStrategy = dbConfig.getSelectStrategy();
        tableInfo.setLogicDelete(this.initLogicDelete(dbConfig, field));

可以看到this.whereStrategy = dbConfig.getSelectStrategy();
就是说这个策略可以配置来改变