SpringBoot——MyBatis-Plus源码分析及开发实践详解

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引言

  在上一家公司一直使用Spring Data JPA，它是对基于JPA的数据访问层的增强支持，底层使用Hibernate框架，支持使用原生SQL或JPQL查询语言。JPA是基于ORM的，它把代码和DB分离，即在代码和DB之间增加了新的一层，从而间接操作DB，大家可能觉得这个学习成本比较高，但其实也还好，都用不到xml文件等。
  而在新的公司，使用的是Mybatis，Mybatis面向DB基于SQL的模式，复杂的SQL需要通过mapper写xml文件来操作DB可能更直观友好，当Mybatis结合Mybatis-Plus就原地起飞了。本文主要总结使用Mybatis-Plus的一些实践经验及源码分析。

MyBatis-Plus 介绍

概述

  MyBatis-Plus是Mybatis的增强工具，可以简化开发，提高我们的开发效率。

特点

1. 无侵入：是Mybatis的增强工具，不做侵入式改变。
2. 丰富的lambda调用支持：通过Lambda表达式编写各类查询。
3. 强大的CRUD操作支持：内置Mapper和IService接口和各种操作方法。
4. 内置分页插件：基于 MyBatis 物理分页，开发者无需关心具体操作。
   … …

常用注解

@TableName

描述：表名注解，标识实体类。

@TableId

描述：主键注解

IdType类型

值	说明
AUTO	数据库ID自增
NONE	默认，无状态，该类型为未设置主键类型（注解里等于跟随全局，全局里约等于 INPUT）
INPUT	insert 前自行 set 主键值
ASSIGN_ID	分配 ID(主键类型为 Number(Long 和 Integer)或 String)(since 3.3.0),使用接口IdentifierGenerator的方法nextId(默认实现类为DefaultIdentifierGenerator雪花算法)
ASSIGN_UUID	分配 UUID,主键类型为 String(since 3.3.0),使用接口IdentifierGenerator的方法nextUUID(默认 default 方法)
ID_WORKER	分布式全局唯一 ID 长整型类型(please use ASSIGN_ID)
UUID	32 位 UUID 字符串(please use ASSIGN_UUID)
ID_WORKER_STR	分布式全局唯一 ID 字符串类型(please use ASSIGN_ID)

@TableField

描述：字段注解（非主键）
常用属性：

属性	类型 必须指定 默认值 描述
value	String 否 “” 数据库字段名
exist	boolean 否 true 是否为数据库表字段

MyBatis-Plus 源码分析

IService原生CURD接口

save

// 插入一条记录（选择字段，策略插入）
boolean save(T entity);
// 插入（批量）
boolean saveBatch(Collection<T> entityList);
// 根据插入批次数量，插入（批量）
boolean saveBatch(Collection<T> entityList, int batchSize);

saveorUpdate

// TableId 注解存在更新记录，是否插入一条记录或者更新记录
boolean saveOrUpdate(T entity);
// 根据updateWrapper尝试更新，否继续执行saveOrUpdate(T)方法
boolean saveOrUpdate(T entity, Wrapper<T> updateWrapper);
// 批量修改插入
boolean saveOrUpdateBatch(Collection<T> entityList);
// 根据插入批次数量，批量修改插入
boolean saveOrUpdateBatch(Collection<T> entityList, int batchSize);

remove

// 根据 entity 条件，删除记录
boolean remove(Wrapper<T> queryWrapper);
// 根据 ID 删除
boolean removeById(Serializable id);
// 根据 columnMap 条件，删除记录
boolean removeByMap(Map<String, Object> columnMap);
// 删除（根据ID 批量删除）
boolean removeByIds(Collection<? extends Serializable> idList);

update

// 根据 UpdateWrapper 条件，更新记录 需要设置sqlset
boolean update(Wrapper<T> updateWrapper);
// 根据 whereWrapper 条件，更新记录
boolean update(T updateEntity, Wrapper<T> whereWrapper);
// 根据 ID 选择修改
boolean updateById(T entity);
// 根据ID 批量更新
boolean updateBatchById(Collection<T> entityList);
// 根据插入批次数量，根据ID 批量更新
boolean updateBatchById(Collection<T> entityList, int batchSize);

get

// 根据 ID 查询
T getById(Serializable id);
// 根据 Wrapper，查询一条记录。结果集，如果是多个会抛出异常，随机取一条加上限制条件 wrapper.last("LIMIT 1")
T getOne(Wrapper<T> queryWrapper);
// 根据 Wrapper，查询一条记录
T getOne(Wrapper<T> queryWrapper, boolean throwEx);
// 根据 Wrapper，查询一条记录
Map<String, Object> getMap(Wrapper<T> queryWrapper);
// 根据 Wrapper，查询一条记录
<V> V getObj(Wrapper<T> queryWrapper, Function<? super Object, V> mapper);

list

// 查询所有
List<T> list();
// 查询列表
List<T> list(Wrapper<T> queryWrapper);
// 查询（根据ID 批量查询）
Collection<T> listByIds(Collection<? extends Serializable> idList);
// 查询（根据 columnMap 条件）
Collection<T> listByMap(Map<String, Object> columnMap);
// 查询所有列表
List<Map<String, Object>> listMaps();
// 查询列表
List<Map<String, Object>> listMaps(Wrapper<T> queryWrapper);
// 查询全部记录
List<Object> listObjs();
// 查询全部记录
<V> List<V> listObjs(Function<? super Object, V> mapper);
// 根据 Wrapper 条件，查询全部记录
List<Object> listObjs(Wrapper<T> queryWrapper);
// 根据 Wrapper 条件，查询全部记录
<V> List<V> listObjs(Wrapper<T> queryWrapper, Function<? super Object, V> mapper);

page

// 无条件分页查询
IPage<T> page(IPage<T> page);
// 条件分页查询
IPage<T> page(IPage<T> page, Wrapper<T> queryWrapper);
// 无条件分页查询
IPage<Map<String, Object>> pageMaps(IPage<T> page);
// 条件分页查询
IPage<Map<String, Object>> pageMaps(IPage<T> page, Wrapper<T> queryWrapper);

Mapper原生CURD接口

insert

int insert(T entity);

delete

    int deleteById(Serializable id);

    int deleteById(T entity);

    int deleteByMap(@Param("cm") Map<String, Object> columnMap);

    int delete(@Param("ew") Wrapper<T> queryWrapper);

    int deleteBatchIds(@Param("coll") Collection<? extends Serializable> idList);

update

    int updateById(@Param("et") T entity);

    int update(@Param("et") T entity, @Param("ew") Wrapper<T> updateWrapper);

select

    T selectById(Serializable id);

    List<T> selectBatchIds(@Param("coll") Collection<? extends Serializable> idList);

    List<T> selectByMap(@Param("cm") Map<String, Object> columnMap);

    default T selectOne(@Param("ew") Wrapper<T> queryWrapper) {
        List<T> ts = this.selectList(queryWrapper);
        if (CollectionUtils.isNotEmpty(ts)) {
            if (ts.size() != 1) {
                throw ExceptionUtils.mpe("One record is expected, but the query result is multiple records", new Object[0]);
            } else {
                return ts.get(0);
            }
        } else {
            return null;
        }
    }

    Long selectCount(@Param("ew") Wrapper<T> queryWrapper);

    List<T> selectList(@Param("ew") Wrapper<T> queryWrapper);

    List<Map<String, Object>> selectMaps(@Param("ew") Wrapper<T> queryWrapper);

    List<Object> selectObjs(@Param("ew") Wrapper<T> queryWrapper);

page

    <P extends IPage<T>> P selectPage(P page, @Param("ew") Wrapper<T> queryWrapper);

    <P extends IPage<Map<String, Object>>> P selectMapsPage(P page, @Param("ew") Wrapper<T> queryWrapper);

自动分页

原理

1. 分页拦截器PaginationInnerInterceptor对所有查询请求进行拦截，beforeQuery查询时，首先判断参数中是否包含IPage类型参数。
2. 若包含IPage类型参数，则根据传参值进行分页查询，否则，不分页。

PaginationInnerInterceptor源码

位置：mybatis-plus-extension-3.4.3.4.jar#PaginationInnerInterceptor

public class PaginationInnerInterceptor implements InnerInterceptor {
    public void beforeQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
    	//判断并寻找IPage参数
        IPage<?> page = (IPage)ParameterUtils.findPage(parameter).orElse((Object)null);
        //参数中包含IPage类型参数，则执行分页
        if (null != page) {
            boolean addOrdered = false;
            String buildSql = boundSql.getSql();
            List<OrderItem> orders = page.orders();
            if (CollectionUtils.isNotEmpty(orders)) {
                addOrdered = true;
                buildSql = this.concatOrderBy(buildSql, orders);
            }
			//根据page参数，组装分页查询sql
            Long _limit = page.maxLimit() != null ? page.maxLimit() : this.maxLimit;
            //无需分页
            if (page.getSize() < 0L && null == _limit) {
                if (addOrdered) {
                    PluginUtils.mpBoundSql(boundSql).sql(buildSql);
                }

            } else {
                this.handlerLimit(page, _limit);
                IDialect dialect = this.findIDialect(executor);
                Configuration configuration = ms.getConfiguration();
                //构建分页sql
                DialectModel model = dialect.buildPaginationSql(buildSql, page.offset(), page.getSize());
                MPBoundSql mpBoundSql = PluginUtils.mpBoundSql(boundSql);
                List<ParameterMapping> mappings = mpBoundSql.parameterMappings();
                Map<String, Object> additionalParameter = mpBoundSql.additionalParameters();
                model.consumers(mappings, configuration, additionalParameter);
                mpBoundSql.sql(model.getDialectSql());
                mpBoundSql.parameterMappings(mappings);
            }
        }
    }
}

ParameterUtils

位置：mybatis-plus-core-3.4.3.4.jar#ParameterUtils

public class ParameterUtils {
    private ParameterUtils() {
    }

    public static Optional<IPage> findPage(Object parameterObject) {
        if (parameterObject != null) {
        	//若多个参数，转为map对象，任意一个value包含IPage类型对象，则返回IPage对象
            if (parameterObject instanceof Map) {
                Map<?, ?> parameterMap = (Map)parameterObject;
                Iterator var2 = parameterMap.entrySet().iterator();

                while(var2.hasNext()) {
                    Entry entry = (Entry)var2.next();
                    if (entry.getValue() != null && entry.getValue() instanceof IPage) {
                        return Optional.of((IPage)entry.getValue());
                    }
                }
            } else if (parameterObject instanceof IPage) {
            	//单个参数，若类型为IPage，则返回IPage对象
                return Optional.of((IPage)parameterObject);
            }
        }
		//参数中无IPage类型参数，则返回空
        return Optional.empty();
    }
}

public class MySqlDialect implements IDialect {
    public MySqlDialect() {
    }

    public DialectModel buildPaginationSql(String originalSql, long offset, long limit) {
    	//拼接构建分页sql
        StringBuilder sql = (new StringBuilder(originalSql)).append(" LIMIT ").append("?");
        if (offset != 0L) {
            sql.append(",").append("?");
            return (new DialectModel(sql.toString(), offset, limit)).setConsumerChain();
        } else {
            return (new DialectModel(sql.toString(), limit)).setConsumer(true);
        }
    }
}

lambda函数

Compare接口源码

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com.baomidou.mybatisplus.core.conditions.interfaces;

import java.io.Serializable;
import java.util.Map;
import java.util.function.BiPredicate;

public interface Compare<Children, R> extends Serializable {
    default <V> Children allEq(Map<R, V> params) {
        return this.allEq(params, true);
    }

    default <V> Children allEq(Map<R, V> params, boolean null2IsNull) {
        return this.allEq(true, params, null2IsNull);
    }

    <V> Children allEq(boolean condition, Map<R, V> params, boolean null2IsNull);

    default <V> Children allEq(BiPredicate<R, V> filter, Map<R, V> params) {
        return this.allEq(filter, params, true);
    }

    default <V> Children allEq(BiPredicate<R, V> filter, Map<R, V> params, boolean null2IsNull) {
        return this.allEq(true, filter, params, null2IsNull);
    }

    <V> Children allEq(boolean condition, BiPredicate<R, V> filter, Map<R, V> params, boolean null2IsNull);

    default Children eq(R column, Object val) {
        return this.eq(true, column, val);
    }

    Children eq(boolean condition, R column, Object val);

    default Children ne(R column, Object val) {
        return this.ne(true, column, val);
    }

    Children ne(boolean condition, R column, Object val);

    default Children gt(R column, Object val) {
        return this.gt(true, column, val);
    }

    Children gt(boolean condition, R column, Object val);

    default Children ge(R column, Object val) {
        return this.ge(true, column, val);
    }

    Children ge(boolean condition, R column, Object val);

    default Children lt(R column, Object val) {
        return this.lt(true, column, val);
    }

    Children lt(boolean condition, R column, Object val);

    default Children le(R column, Object val) {
        return this.le(true, column, val);
    }

    Children le(boolean condition, R column, Object val);

    default Children between(R column, Object val1, Object val2) {
        return this.between(true, column, val1, val2);
    }

    Children between(boolean condition, R column, Object val1, Object val2);

    default Children notBetween(R column, Object val1, Object val2) {
        return this.notBetween(true, column, val1, val2);
    }

    Children notBetween(boolean condition, R column, Object val1, Object val2);

    default Children like(R column, Object val) {
        return this.like(true, column, val);
    }

    Children like(boolean condition, R column, Object val);

    default Children notLike(R column, Object val) {
        return this.notLike(true, column, val);
    }

    Children notLike(boolean condition, R column, Object val);

    default Children likeLeft(R column, Object val) {
        return this.likeLeft(true, column, val);
    }

    Children likeLeft(boolean condition, R column, Object val);

    default Children likeRight(R column, Object val) {
        return this.likeRight(true, column, val);
    }

    Children likeRight(boolean condition, R column, Object val);
}

Func接口源码

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com.baomidou.mybatisplus.core.conditions.interfaces;

import java.io.Serializable;
import java.util.Collection;
import java.util.List;
import java.util.function.Consumer;

public interface Func<Children, R> extends Serializable {
    default Children isNull(R column) {
        return this.isNull(true, column);
    }

    Children isNull(boolean condition, R column);

    default Children isNotNull(R column) {
        return this.isNotNull(true, column);
    }

    Children isNotNull(boolean condition, R column);

    default Children in(R column, Collection<?> coll) {
        return this.in(true, column, coll);
    }

    Children in(boolean condition, R column, Collection<?> coll);

    default Children in(R column, Object... values) {
        return this.in(true, column, values);
    }

    Children in(boolean condition, R column, Object... values);

    default Children notIn(R column, Collection<?> coll) {
        return this.notIn(true, column, coll);
    }

    Children notIn(boolean condition, R column, Collection<?> coll);

    default Children notIn(R column, Object... value) {
        return this.notIn(true, column, value);
    }

    Children notIn(boolean condition, R column, Object... values);

    default Children inSql(R column, String inValue) {
        return this.inSql(true, column, inValue);
    }

    Children inSql(boolean condition, R column, String inValue);

    Children gtSql(boolean condition, R column, String inValue);

    default Children gtSql(R column, String inValue) {
        return this.gtSql(true, column, inValue);
    }

    Children geSql(boolean condition, R column, String inValue);

    default Children geSql(R column, String inValue) {
        return this.geSql(true, column, inValue);
    }

    Children ltSql(boolean condition, R column, String inValue);

    default Children ltSql(R column, String inValue) {
        return this.ltSql(true, column, inValue);
    }

    Children leSql(boolean condition, R column, String inValue);

    default Children leSql(R column, String inValue) {
        return this.leSql(true, column, inValue);
    }

    default Children notInSql(R column, String inValue) {
        return this.notInSql(true, column, inValue);
    }

    Children notInSql(boolean condition, R column, String inValue);

    Children groupBy(boolean condition, R column);

    default Children groupBy(R column) {
        return this.groupBy(true, column);
    }

    Children groupBy(boolean condition, List<R> columns);

    default Children groupBy(List<R> columns) {
        return this.groupBy(true, columns);
    }

    /** @deprecated */
    @Deprecated
    default Children groupBy(R column, R... columns) {
        return this.groupBy(true, column, columns);
    }

    /** @deprecated */
    @Deprecated
    Children groupBy(boolean condition, R column, R... columns);

    default Children orderByAsc(boolean condition, R column) {
        return this.orderBy(condition, true, column);
    }

    default Children orderByAsc(R column) {
        return this.orderByAsc(true, column);
    }

    default Children orderByAsc(boolean condition, List<R> columns) {
        return this.orderBy(condition, true, columns);
    }

    default Children orderByAsc(List<R> columns) {
        return this.orderByAsc(true, columns);
    }

    /** @deprecated */
    @Deprecated
    default Children orderByAsc(R column, R... columns) {
        return this.orderByAsc(true, column, columns);
    }

    /** @deprecated */
    @Deprecated
    default Children orderByAsc(boolean condition, R column, R... columns) {
        return this.orderBy(condition, true, column, columns);
    }

    default Children orderByDesc(boolean condition, R column) {
        return this.orderBy(condition, false, column);
    }

    default Children orderByDesc(R column) {
        return this.orderByDesc(true, column);
    }

    default Children orderByDesc(boolean condition, List<R> columns) {
        return this.orderBy(condition, false, columns);
    }

    default Children orderByDesc(List<R> columns) {
        return this.orderByDesc(true, columns);
    }

    /** @deprecated */
    @Deprecated
    default Children orderByDesc(R column, R... columns) {
        return this.orderByDesc(true, column, columns);
    }

    /** @deprecated */
    @Deprecated
    default Children orderByDesc(boolean condition, R column, R... columns) {
        return this.orderBy(condition, false, column, columns);
    }

    Children orderBy(boolean condition, boolean isAsc, R column);

    Children orderBy(boolean condition, boolean isAsc, List<R> columns);

    /** @deprecated */
    @Deprecated
    Children orderBy(boolean condition, boolean isAsc, R column, R... columns);

    default Children having(String sqlHaving, Object... params) {
        return this.having(true, sqlHaving, params);
    }

    Children having(boolean condition, String sqlHaving, Object... params);

    default Children func(Consumer<Children> consumer) {
        return this.func(true, consumer);
    }

    Children func(boolean condition, Consumer<Children> consumer);
}

Join接口源码

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com.baomidou.mybatisplus.core.conditions.interfaces;

import java.io.Serializable;

public interface Join<Children> extends Serializable {
    default Children or() {
        return this.or(true);
    }

    Children or(boolean condition);

    default Children apply(String applySql, Object... values) {
        return this.apply(true, applySql, values);
    }

    Children apply(boolean condition, String applySql, Object... values);

    default Children last(String lastSql) {
        return this.last(true, lastSql);
    }

    Children last(boolean condition, String lastSql);

    default Children comment(String comment) {
        return this.comment(true, comment);
    }

    Children comment(boolean condition, String comment);

    default Children first(String firstSql) {
        return this.first(true, firstSql);
    }

    Children first(boolean condition, String firstSql);

    default Children exists(String existsSql, Object... values) {
        return this.exists(true, existsSql, values);
    }

    Children exists(boolean condition, String existsSql, Object... values);

    default Children notExists(String existsSql, Object... values) {
        return this.notExists(true, existsSql, values);
    }

    Children notExists(boolean condition, String existsSql, Object... values);
}

Nested接口源码

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com.baomidou.mybatisplus.core.conditions.interfaces;

import java.io.Serializable;
import java.util.function.Consumer;

public interface Nested<Param, Children> extends Serializable {
    default Children and(Consumer<Param> consumer) {
        return this.and(true, consumer);
    }

    Children and(boolean condition, Consumer<Param> consumer);

    default Children or(Consumer<Param> consumer) {
        return this.or(true, consumer);
    }

    Children or(boolean condition, Consumer<Param> consumer);

    default Children nested(Consumer<Param> consumer) {
        return this.nested(true, consumer);
    }

    Children nested(boolean condition, Consumer<Param> consumer);

    default Children not(Consumer<Param> consumer) {
        return this.not(true, consumer);
    }

    Children not(boolean condition, Consumer<Param> consumer);
}

常用函数总结

函数名	说明	示例与对应sql
eq	等于=	eq(“id”, 1) 即 id = 1
ne	不等于<>	ne(“id”, 1) 即 id <> 1
gt	大于>	gt(“id”, 1) 即 id > 1
ge	大于等于>=	ge(“id”,1) 即 id >= 1
lt	小于<	lt(“id”,1) 即 id < 1
le	小于等于<=	le("id,1) 即 id <= 1
between	BETWEEN 值1 AND 值2	between(“id”, 1, 3) 即 id BETWEEN 1 AND 3
notBetween	NOT BETWEEN 值1 AND 值2	notBetween(“id”, 1, 3) 即 id NOT BETWEEN 1 AND 3
like	LIKE ‘%值%’	like(“name”, "小”) 即 name LIKE ‘%小%’
notLike	NOT LIKE ‘%值%’	notLike(“name”, "小”) 即 name NOT LIKE ‘%小%’
likeLeft	LIKE ‘%值’	likeLeft(“name”, "小”) 即 name LIKE ‘%小’
likeRight	LIKE ‘值%’	likeRight(“name”, "小”) 即 name LIKE ‘小%’
isNull	字段 IS NULL	isNull(“name”) 即 name IS NULL
isNotNull	字段 IS NOT NULL	isNotNull(“name”) 即 name IS NOT NULL
in	字段 IN (值1, 值2, … …)	in(“id”, {1,2,3,4,5}) 即 id IN (1,2,3,4,5)
notIn	字段 NOT IN (值1, 值2, … …)	notIn(“id”, {1,2,3,4,5}) 即 id NOT IN (1,2,3,4,5)
inSql	字段 IN (sql语句)	inSql(“id”, “select id from tab_01 where id > 10”) 即 id IN (select id from tab_01 where id > 10)
notInSql	字段 NOT IN (sql语句)	notInSql(“id”, “select id from tab_01 where id > 10”) 即 id NOT IN (select id from tab_01 where id > 10)
groupBy	GROUP BY 字段1, 字段2, … …	groupBy(“id”, “name”) 即 GROUP BY id, name
orderBy	ORDER BY 字段1, 字段2, … …	orderBy(true, false, “id”, “name”) 即 ORDER BY id ASC, name DESC
orderByAsc	ORDER BY 字段1, 字段2, … … ASC	orderByAsc(“id”, “name”) 即 ORDER BY id ASC, name ASC
orderByDesc	ORDER BY 字段1, 字段2, … … DESC	orderByDesc(“id”, “name”) 即 ORDER BY id DESC, name DESC
having	HAVING(sql语句)	having(“count(number) > {0}”, 20) 即 HAVING COUNT(number) > 20
or	OR	eq(“id”, 2).or().eq(“name”, “小红”) 即 id = 2 OR name = “小红”
and	AND	and(query -> query.eq(“id”, 2).ne(“name”, "小红”)) 即 AND (id = 2 AND name <> “小红”
apply	拼接sql语句	apply("date_format(df, ‘%Y-%m-%d’) = {0}, “2023-04-25”) 即 date_format(df, ‘%Y-%m-%d’) = ‘2023-04-25’)
last	拼接sql到最后	last(“limit”, 10) 即 xxx limit 10
exists	EXISTS (sql语句)	exists("select id from tab_01 where name = “小红”) 即 EXISTS ("select id from tab_01 where name = “小红”)
notExists	NOT EXISTS (sql语句)	notExists("select id from tab_01 where name = “小红”) 即 NOT EXISTS ("select id from tab_01 where name = “小红”)
nested	不带AND或OR的嵌套	nested(query -> query.eq(“id”, 2).ne(“name”, "小红”)) 即 (id = 2 AND name <> “小红”

MyBatis-Plus 代码实践

依赖

      com.baomidou
      mybatis-plus-boot-starter

分页插件配置

@Configuration
public class MybatisPlusConfig {
    /**
     * mybatis-plus 拦截器
     */
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        //新增内置分页拦截器，并设置数据库类型为mysql
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }
}

IDEA插件MyBatisPlus

1. 【preferences】—>【Plugins】—>【Marketplace】
2. 搜索并安装MyBatisPlus插件，可以通过该插件进行Mapper层与xml之间的映射跳转。
   

类模板

entity类

@Data
@TableName("demo_entity")
@ApiModel(value = "demo表")
public class DemoEntity {

    /**
     * id
     */
    @TableId(type = IdType.ASSIGN_ID)
    private Long id;

    /**
     * 名称
     */
    private String name;

    /**
     * 编码
     */
    private String code;
	
	/**
     * 是否删除
     */
    private Integer deleted;
}

mapper类

@Mapper
public interface DemoEntityMapper extends BaseMapper<DemoEntity> {
... ...
}

service接口类

public interface DemoEntityService extends IService<DemoEntity> {
... ...
}

service实现类

@Slf4j
@Service
public class DemoEntityServiceImpl extends ServiceImpl<DemoEntityMapper, DemoEntity> implements DemoEntityService{
	/**
 	* mapper
 	*/
	@Autowired
	private DemoEntityMapper demoEntityMapper;
	
	... ...
}

lambda表达式

LambdaQueryWrapper查询

... ...
Long id = 1000L;
List<Long> userId = new ArrayList<>();
userId.add(100000L);
userId.add(100001L);
LambdaQueryWrapper<DemoEntity> lambdaQueryWrapper = new LambdaQueryWrapper();
lambdaQueryWrapper.eq(DemoEntity::getId, id)
                    .in(DemoEntity::getUserId, userId);
List<DemoEntity> entityList = demoEntityMapper.selectList(lambdaQueryWrapper);
... ...

QueryWrapper查询

... ...
Long id = 1000L;
List<Long> userId = new ArrayList<>();
userId.add(100000L);
userId.add(100001L);
QueryWrapper<DemoEntity> queryWrapper = Wrappers.query();
queryWrapper.lambda()
	//and筛选  
	.and(wrapper -> wrapper.in(DemoEntity::getUserId, userId)
	//or条件
	.or()
	.eq(DemoEntity::getId, id);
... ...

lambdaUpdate更新

... ...
Long id = 1000L;
this.lambdaUpdate()
    .eq(DemoEntity::getId, id)
    .set(DemoEntity::getUserId, 10000002L)
    //更新
    .update();
... ...

Mapper结合xml文件查询

根据基本数据类型查询

mapper方法

@Mapper
public interface DemoEntityMapper extends BaseMapper<DemoEntity> {
... ...
	/**
 	* 根据id进行查询
 	* @param id
 	* @return
 	*/
	public DemoVO getById(int id);
... ...
}

DemoEntityMapper.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.ljy.demo.mapper.DemoEntityMapper">
	<select id="getById" parameterType="int" resultType="com.ljy.demo.vo.DemoVO">
        SELECT * FROM demo_entity WHERE id=#{id}
    </select>
</mapper>

根据多个参数查询

mapper方法

@Mapper
public interface DemoEntityMapper extends BaseMapper<DemoEntity> {
... ...
	/**
 	* 根据name和code进行查询
 	* @param name
 	* @param code
 	* @return
 	*/
	public List<DemoVO> getByNameOrCode(String name, String code);
... ...
}

DemoEntityMapper.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.ljy.demo.mapper.DemoEntityMapper">
	<select id="getByNameOrCode" resultType="com.ljy.demo.vo.DemoVO">
        SELECT * FROM demo_entity WHERE name=#{0} OR code=#{1}
    </select>
</mapper>

根据对象参数查询

mapper方法

@Mapper
public interface DemoEntityMapper extends BaseMapper<DemoEntity> {
... ...
	/**
 	* 根据dto的不同入参进行查询
 	* @param demoDTO
 	* @return
 	*/
	public List<DemoVO> listDemo(@Param("dto") DemoDTO demoDTO);
... ...
}

DemoEntityMapper.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.ljy.demo.mapper.DemoEntityMapper">

    <sql id="List_demo">
        select de.id,
               de.name,
               de.code
        from demo_entity de
    </sql>

    <select id="listDemo" resultType="com.ljy.demo.vo.DemoVO">
        <include refid="List_demo"/>

        <where>
            <if test="dto.id != null" >
            	 <!--id不为空，则精准查询-->
                and de.id = #{dto.id}
            </if>
            <if test="dto.name != null and dto.name != ''">
                <!--名称不为空，则模糊查询-->
                and de.name like concat('%',#{dto.name},'%')
            </if>
            <!--未删除-->
            and de.deleted = 0
        </where>
        group by de.id
        order by de.name desc
    </select>
</mapper>

分页查询

mapper方法

@Mapper
public interface DemoEntityMapper extends BaseMapper<DemoEntity> {
... ...
	/**
 	* 分页查询
 	* @param page
 	* @param demoDTO
 	* @return
 	*/
	IPage<DemoVO> pageListDemo(@Param("page") IPage<DemoVO> page, @Param("dto") DemoDTO demoDTO);
... ...
}

DemoEntityMapper.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.ljy.demo.mapper.DemoEntityMapper">

    <sql id="List_demo">
        select de.id,
               de.name,
               de.code
        from demo_entity de
    </sql>
	<!--名称保持一致-->
    <select id="pageListDemo" resultType="com.ljy.demo.vo.DemoVO">
        <include refid="List_demo"/>
        <where>
            <if test="dto.name != null and dto.name != ''">
                <!--名称不为空，则模糊查询-->
                and de.name like concat('%',#{dto.name},'%')
            </if>
            <!--未删除-->
            and de.deleted = 0
        </where>
        group by de.id
        order by de.name desc
    </select>
</mapper>

调用代码

...
//构造分页
Page<DemoVO> page = new Page<>(2, 10);
//page 查询
IPage<DemoVO> iPage = demoEntityMapper.pageListDemo(page, demoDTO);
...