装饰器模式与模板方法模式实现MyBatis-Plus QueryWrapper 扩展

pom

<dependency><groupId>com.github.yulichang</groupId><artifactId>mybatis-plus-join-boot-starter</artifactId> <!-- MyBatis 联表查询 -->
</dependency>

MPJLambdaWrapperX

/*** 拓展 MyBatis Plus Join QueryWrapper 类，主要增加如下功能：* <p>* 1. 拼接条件的方法，增加 xxxIfPresent 方法，用于判断值不存在的时候，不要拼接到条件中。** @param <T> 数据类型*/
public class MPJLambdaWrapperX<T> extends MPJLambdaWrapper<T> {public MPJLambdaWrapperX<T> likeIfPresent(SFunction<T, ?> column, String val) {MPJWrappers.lambdaJoin().like(column, val);if (StringUtils.hasText(val)) {return (MPJLambdaWrapperX<T>) super.like(column, val);}return this;}public MPJLambdaWrapperX<T> inIfPresent(SFunction<T, ?> column, Collection<?> values) {if (ObjectUtil.isAllNotEmpty(values) && !ArrayUtil.isEmpty(values)) {return (MPJLambdaWrapperX<T>) super.in(column, values);}return this;}public MPJLambdaWrapperX<T> inIfPresent(SFunction<T, ?> column, Object... values) {if (ObjectUtil.isAllNotEmpty(values) && !ArrayUtil.isEmpty(values)) {return (MPJLambdaWrapperX<T>) super.in(column, values);}return this;}public MPJLambdaWrapperX<T> eqIfPresent(SFunction<T, ?> column, Object val) {if (ObjectUtil.isNotEmpty(val)) {return (MPJLambdaWrapperX<T>) super.eq(column, val);}return this;}public MPJLambdaWrapperX<T> neIfPresent(SFunction<T, ?> column, Object val) {if (ObjectUtil.isNotEmpty(val)) {return (MPJLambdaWrapperX<T>) super.ne(column, val);}return this;}public MPJLambdaWrapperX<T> gtIfPresent(SFunction<T, ?> column, Object val) {if (val != null) {return (MPJLambdaWrapperX<T>) super.gt(column, val);}return this;}public MPJLambdaWrapperX<T> geIfPresent(SFunction<T, ?> column, Object val) {if (val != null) {return (MPJLambdaWrapperX<T>) super.ge(column, val);}return this;}public MPJLambdaWrapperX<T> ltIfPresent(SFunction<T, ?> column, Object val) {if (val != null) {return (MPJLambdaWrapperX<T>) super.lt(column, val);}return this;}public MPJLambdaWrapperX<T> leIfPresent(SFunction<T, ?> column, Object val) {if (val != null) {return (MPJLambdaWrapperX<T>) super.le(column, val);}return this;}public MPJLambdaWrapperX<T> betweenIfPresent(SFunction<T, ?> column, Object val1, Object val2) {if (val1 != null && val2 != null) {return (MPJLambdaWrapperX<T>) super.between(column, val1, val2);}if (val1 != null) {return (MPJLambdaWrapperX<T>) ge(column, val1);}if (val2 != null) {return (MPJLambdaWrapperX<T>) le(column, val2);}return this;}public MPJLambdaWrapperX<T> betweenIfPresent(SFunction<T, ?> column, Object[] values) {Object val1 = ArrayUtils.get(values, 0);Object val2 = ArrayUtils.get(values, 1);return betweenIfPresent(column, val1, val2);}// ========== 重写父类方法，方便链式调用 ==========@Overridepublic <X> MPJLambdaWrapperX<T> eq(boolean condition, SFunction<X, ?> column, Object val) {super.eq(condition, column, val);return this;}@Overridepublic <X> MPJLambdaWrapperX<T> eq(SFunction<X, ?> column, Object val) {super.eq(column, val);return this;}@Overridepublic <X> MPJLambdaWrapperX<T> orderByDesc(SFunction<X, ?> column) {//noinspection uncheckedsuper.orderByDesc(true, column);return this;}@Overridepublic MPJLambdaWrapperX<T> last(String lastSql) {super.last(lastSql);return this;}@Overridepublic <X> MPJLambdaWrapperX<T> in(SFunction<X, ?> column, Collection<?> coll) {super.in(column, coll);return this;}@Overridepublic MPJLambdaWrapperX<T> selectAll(Class<?> clazz) {super.selectAll(clazz);return this;}@Overridepublic MPJLambdaWrapperX<T> selectAll(Class<?> clazz, String prefix) {super.selectAll(clazz, prefix);return this;}@Overridepublic <S> MPJLambdaWrapperX<T> selectAs(SFunction<S, ?> column, String alias) {super.selectAs(column, alias);return this;}@Overridepublic <E> MPJLambdaWrapperX<T> selectAs(String column, SFunction<E, ?> alias) {super.selectAs(column, alias);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectAs(SFunction<S, ?> column, SFunction<X, ?> alias) {super.selectAs(column, alias);return this;}@Overridepublic <E, X> MPJLambdaWrapperX<T> selectAs(String index, SFunction<E, ?> column, SFunction<X, ?> alias) {super.selectAs(index, column, alias);return this;}@Overridepublic <E> MPJLambdaWrapperX<T> selectAsClass(Class<E> source, Class<?> tag) {super.selectAsClass(source, tag);return this;}@Overridepublic <E, F> MPJLambdaWrapperX<T> selectSub(Class<E> clazz, Consumer<MPJLambdaWrapper<E>> consumer, SFunction<F, ?> alias) {super.selectSub(clazz, consumer, alias);return this;}@Overridepublic <E, F> MPJLambdaWrapperX<T> selectSub(Class<E> clazz, String st, Consumer<MPJLambdaWrapper<E>> consumer, SFunction<F, ?> alias) {super.selectSub(clazz, st, consumer, alias);return this;}@Overridepublic <S> MPJLambdaWrapperX<T> selectCount(SFunction<S, ?> column) {super.selectCount(column);return this;}@Overridepublic MPJLambdaWrapperX<T> selectCount(Object column, String alias) {super.selectCount(column, alias);return this;}@Overridepublic <X> MPJLambdaWrapperX<T> selectCount(Object column, SFunction<X, ?> alias) {super.selectCount(column, alias);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectCount(SFunction<S, ?> column, String alias) {super.selectCount(column, alias);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectCount(SFunction<S, ?> column, SFunction<X, ?> alias) {super.selectCount(column, alias);return this;}@Overridepublic <S> MPJLambdaWrapperX<T> selectSum(SFunction<S, ?> column) {super.selectSum(column);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectSum(SFunction<S, ?> column, String alias) {super.selectSum(column, alias);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectSum(SFunction<S, ?> column, SFunction<X, ?> alias) {super.selectSum(column, alias);return this;}@Overridepublic <S> MPJLambdaWrapperX<T> selectMax(SFunction<S, ?> column) {super.selectMax(column);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectMax(SFunction<S, ?> column, String alias) {super.selectMax(column, alias);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectMax(SFunction<S, ?> column, SFunction<X, ?> alias) {super.selectMax(column, alias);return this;}@Overridepublic <S> MPJLambdaWrapperX<T> selectMin(SFunction<S, ?> column) {super.selectMin(column);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectMin(SFunction<S, ?> column, String alias) {super.selectMin(column, alias);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectMin(SFunction<S, ?> column, SFunction<X, ?> alias) {super.selectMin(column, alias);return this;}@Overridepublic <S> MPJLambdaWrapperX<T> selectAvg(SFunction<S, ?> column) {super.selectAvg(column);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectAvg(SFunction<S, ?> column, String alias) {super.selectAvg(column, alias);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectAvg(SFunction<S, ?> column, SFunction<X, ?> alias) {super.selectAvg(column, alias);return this;}@Overridepublic <S> MPJLambdaWrapperX<T> selectLen(SFunction<S, ?> column) {super.selectLen(column);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectLen(SFunction<S, ?> column, String alias) {super.selectLen(column, alias);return this;}@Overridepublic <S, X> MPJLambdaWrapperX<T> selectLen(SFunction<S, ?> column, SFunction<X, ?> alias) {super.selectLen(column, alias);return this;}}

LambdaQueryWrapperX

/*** 拓展 MyBatis Plus QueryWrapper 类，主要增加如下功能：* <p>* 1. 拼接条件的方法，增加 xxxIfPresent 方法，用于判断值不存在的时候，不要拼接到条件中。** @param <T> 数据类型*/
public class LambdaQueryWrapperX<T> extends LambdaQueryWrapper<T> {public LambdaQueryWrapperX<T> likeIfPresent(SFunction<T, ?> column, String val) {if (StringUtils.hasText(val)) {return (LambdaQueryWrapperX<T>) super.like(column, val);}return this;}public LambdaQueryWrapperX<T> inIfPresent(SFunction<T, ?> column, Collection<?> values) {if (ObjectUtil.isAllNotEmpty(values) && !ArrayUtil.isEmpty(values)) {return (LambdaQueryWrapperX<T>) super.in(column, values);}return this;}public LambdaQueryWrapperX<T> inIfPresent(SFunction<T, ?> column, Object... values) {if (ObjectUtil.isAllNotEmpty(values) && !ArrayUtil.isEmpty(values)) {return (LambdaQueryWrapperX<T>) super.in(column, values);}return this;}public LambdaQueryWrapperX<T> eqIfPresent(SFunction<T, ?> column, Object val) {if (ObjectUtil.isNotEmpty(val)) {return (LambdaQueryWrapperX<T>) super.eq(column, val);}return this;}public LambdaQueryWrapperX<T> neIfPresent(SFunction<T, ?> column, Object val) {if (ObjectUtil.isNotEmpty(val)) {return (LambdaQueryWrapperX<T>) super.ne(column, val);}return this;}public LambdaQueryWrapperX<T> gtIfPresent(SFunction<T, ?> column, Object val) {if (val != null) {return (LambdaQueryWrapperX<T>) super.gt(column, val);}return this;}public LambdaQueryWrapperX<T> geIfPresent(SFunction<T, ?> column, Object val) {if (val != null) {return (LambdaQueryWrapperX<T>) super.ge(column, val);}return this;}public LambdaQueryWrapperX<T> ltIfPresent(SFunction<T, ?> column, Object val) {if (val != null) {return (LambdaQueryWrapperX<T>) super.lt(column, val);}return this;}public LambdaQueryWrapperX<T> leIfPresent(SFunction<T, ?> column, Object val) {if (val != null) {return (LambdaQueryWrapperX<T>) super.le(column, val);}return this;}public LambdaQueryWrapperX<T> betweenIfPresent(SFunction<T, ?> column, Object val1, Object val2) {if (val1 != null && val2 != null) {return (LambdaQueryWrapperX<T>) super.between(column, val1, val2);}if (val1 != null) {return (LambdaQueryWrapperX<T>) ge(column, val1);}if (val2 != null) {return (LambdaQueryWrapperX<T>) le(column, val2);}return this;}public LambdaQueryWrapperX<T> betweenIfPresent(SFunction<T, ?> column, Object[] values) {Object val1 = ArrayUtils.get(values, 0);Object val2 = ArrayUtils.get(values, 1);return betweenIfPresent(column, val1, val2);}// ========== 重写父类方法，方便链式调用 ==========@Overridepublic LambdaQueryWrapperX<T> eq(boolean condition, SFunction<T, ?> column, Object val) {super.eq(condition, column, val);return this;}@Overridepublic LambdaQueryWrapperX<T> eq(SFunction<T, ?> column, Object val) {super.eq(column, val);return this;}@Overridepublic LambdaQueryWrapperX<T> orderByDesc(SFunction<T, ?> column) {super.orderByDesc(true, column);return this;}@Overridepublic LambdaQueryWrapperX<T> last(String lastSql) {super.last(lastSql);return this;}@Overridepublic LambdaQueryWrapperX<T> in(SFunction<T, ?> column, Collection<?> coll) {super.in(column, coll);return this;}
}

QueryWrapperX

/*** 拓展 MyBatis Plus QueryWrapper 类，主要增加如下功能：** 1. 拼接条件的方法，增加 xxxIfPresent 方法，用于判断值不存在的时候，不要拼接到条件中。** @param <T> 数据类型*/
public class QueryWrapperX<T> extends QueryWrapper<T> {public QueryWrapperX<T> likeIfPresent(String column, String val) {if (StringUtils.hasText(val)) {return (QueryWrapperX<T>) super.like(column, val);}return this;}public QueryWrapperX<T> inIfPresent(String column, Collection<?> values) {if (!CollectionUtils.isEmpty(values)) {return (QueryWrapperX<T>) super.in(column, values);}return this;}public QueryWrapperX<T> inIfPresent(String column, Object... values) {if (!ArrayUtils.isEmpty(values)) {return (QueryWrapperX<T>) super.in(column, values);}return this;}public QueryWrapperX<T> eqIfPresent(String column, Object val) {if (val != null) {return (QueryWrapperX<T>) super.eq(column, val);}return this;}public QueryWrapperX<T> neIfPresent(String column, Object val) {if (val != null) {return (QueryWrapperX<T>) super.ne(column, val);}return this;}public QueryWrapperX<T> gtIfPresent(String column, Object val) {if (val != null) {return (QueryWrapperX<T>) super.gt(column, val);}return this;}public QueryWrapperX<T> geIfPresent(String column, Object val) {if (val != null) {return (QueryWrapperX<T>) super.ge(column, val);}return this;}public QueryWrapperX<T> ltIfPresent(String column, Object val) {if (val != null) {return (QueryWrapperX<T>) super.lt(column, val);}return this;}public QueryWrapperX<T> leIfPresent(String column, Object val) {if (val != null) {return (QueryWrapperX<T>) super.le(column, val);}return this;}public QueryWrapperX<T> betweenIfPresent(String column, Object val1, Object val2) {if (val1 != null && val2 != null) {return (QueryWrapperX<T>) super.between(column, val1, val2);}if (val1 != null) {return (QueryWrapperX<T>) ge(column, val1);}if (val2 != null) {return (QueryWrapperX<T>) le(column, val2);}return this;}public QueryWrapperX<T> betweenIfPresent(String column, Object[] values) {if (values!= null && values.length != 0 && values[0] != null && values[1] != null) {return (QueryWrapperX<T>) super.between(column, values[0], values[1]);}if (values!= null && values.length != 0 && values[0] != null) {return (QueryWrapperX<T>) ge(column, values[0]);}if (values!= null && values.length != 0 && values[1] != null) {return (QueryWrapperX<T>) le(column, values[1]);}return this;}// ========== 重写父类方法，方便链式调用 ==========@Overridepublic QueryWrapperX<T> eq(boolean condition, String column, Object val) {super.eq(condition, column, val);return this;}@Overridepublic QueryWrapperX<T> eq(String column, Object val) {super.eq(column, val);return this;}@Overridepublic QueryWrapperX<T> orderByDesc(String column) {super.orderByDesc(true, column);return this;}@Overridepublic QueryWrapperX<T> last(String lastSql) {super.last(lastSql);return this;}@Overridepublic QueryWrapperX<T> in(String column, Collection<?> coll) {super.in(column, coll);return this;}
}

一、核心作用

1. 联表查询支持

• 避免空值条件拼接：自动跳过值为空的查询条件，防止生成 WHERE column = null 的低效 SQL
• MyBatis-Plus Join 扩展：提供基于 Lambda 的联表查询能力，弥补 MyBatis Plus 原生不支持联表的缺陷。
• 类型安全：通过 SFunction<T, ?> 泛型 Lambda 表达式引用实体字段，避免硬编码字段名。

2. 链式 API 设计

// 示例：联表查询用户和部门信息
new MPJLambdaWrapper<UserDO>().selectAll(UserDO.class).select(DepartmentDO::getName, "deptName").leftJoin(DepartmentDO.class, DepartmentDO::getId, UserDO::getDeptId).eq(UserDO::getStatus, 0);

二、扩展点

1. 条件空值安全（核心增强）

通过 xxxIfPresent 方法实现 空值自动跳过，避免无效条件拼接。

方法	作用	示例代码
eqIfPresent	值非空时添加 eq 条件	wrapper.eqIfPresent(UserDO::getName, name)
inIfPresent	集合非空时添加 in 条件	wrapper.inIfPresent(UserDO::getRoleIds, roleIds)
betweenIfPresent	区间值有效时添加 between 条件	wrapper.betweenIfPresent(UserDO::getCreateTime, start, end)

2. 链式调用增强

重写父类方法（如 eq, select）返回子类类型，保持链式调用连贯性：

public MPJLambdaWrapperX<T> eq(SFunction<X, ?> column, Object val) {super.eq(column, val);return this; // 返回 MPJLambdaWrapperX 类型而非父类
}
@Override
public LambdaQueryWrapperX<T> eq(SFunction<T, ?> column, Object val) {super.eq(column, val);return this;
}

3. 智能区间处理

betweenIfPresent 方法支持 单边区间 自动转换：

// 当 val2 为空时，转换为 ge 条件
wrapper.betweenIfPresent(UserDO::getCreateTime, startTime, null);
// 生成 SQL：WHERE create_time >= startTime

三、设计模式分析

1. 装饰器模式（Decorator Pattern）

• 表现：MPJLambdaWrapperX 在 MPJLambdaWrapper 基础上增强功能（如空值安全），而非直接修改父类。
• 优势：符合开闭原则，MyBatis-Plus Join 升级时只需调整父类引用。

2. 模板方法模式（Template Method Pattern）

• 表现：xxxIfPresent 方法封装了空值判断逻辑，子类只需调用父类条件方法。

public MPJLambdaWrapperX<T> eqIfPresent(SFunction<T, ?> column, Object val) {if (ObjectUtil.isNotEmpty(val)) {return (MPJLambdaWrapperX<T>) super.eq(column, val); // 调用父类方法}return this;
}public LambdaQueryWrapperX<T> eqIfPresent(SFunction<T, ?> column, Object val) {if (ObjectUtil.isNotEmpty(val)) {return (LambdaQueryWrapperX<T>) super.eq(column, val); // 调用父类方法}return this;
}

四、典型使用场景

1. 动态查询条件构建

public List<UserDO> getUsers(String name, Integer status, LocalDateTime startTime) {return joinMapper.selectJoinList(new MPJLambdaWrapperX<UserDO>().eqIfPresent(UserDO::getName, name)       // name 为空时不拼接.eqIfPresent(UserDO::getStatus, status)   // status 为空时不拼接.geIfPresent(UserDO::getCreateTime, startTime).leftJoin(DepartmentDO.class, ...));
}

2. 复杂联表查询

wrapper.selectAll(UserDO.class).selectAs(DepartmentDO::getName, UserRespVO::getDeptName).leftJoin(DepartmentDO.class, DepartmentDO::getId, UserDO::getDeptId).inIfPresent(UserDO::getRoleIds, roleIds);

3. 区间查询优化

// 处理可能不完整的区间参数
wrapper.betweenIfPresent(UserDO::getCreateTime, params.getStartTime(), params.getEndTime());

五、与原生 MyBatis Plus 对比

特性	MyBatis Plus QueryWrapper	QueryWrapperX	MPJLambdaWrapperX	MyBatis Plus LambdaQueryWrapper	LambdaQueryWrapperX
联表支持	不支持	不支持	支持 LEFT/INNER JOIN	不支持	不支持
字段引用	字符串字段名（如 “name”）	字符串字段名（如 “name”）	Lambda 表达式（如 UserDO::getName）	Lambda 表达式（如 UserDO::getName）	Lambda 表达式（如 UserDO::getName）
空值处理	需手动判空	内置 xxxIfPresent 方法	内置 xxxIfPresent 方法自动处理	内置 xxxIfPresent 方法自动处理	内置 xxxIfPresent 方法自动处理
类型安全	容易拼写错误	容易拼写错误	编译期检查字段是否存在	编译期检查字段是否存在	编译期检查字段是否存在