MyBatis-Plus - 一篇带你玩转自定义 BaseMapper（一）-阿里云开发者社区

业务背景

在使用 @TableLogic (逻辑删)注解的基础上，提供一个全局方法，使得插入数据的时候，一旦发现有相同主键 Id 的记录就先删除再插入（系统搬家的时候遇到。因为系统搬家产生这个问题的场景：先导入搬家的数据，然后在目标系统删除该数据[假删除]，再次重复导入就会 SQL 物理主键冲突报错）~

解决方案

实现一个插入方法，在插入的时候，先删除该记录 Id 并且 del == 1（假删除标记），然后再插入！

实现思路

在玩 MP 的时候我们都知道 BaseMapper，那么优秀的框架一定会给我们扩展的机会，果真如此

1、【DBaseMapper】实现一个自定义 Mapper 继承 BaseMapper 来替代 BaseMapper 在 Dao 的继承上

import cn.hutool.core.util.StrUtil;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableLogic;
import com.baomidou.mybatisplus.core.conditions.Wrapper;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.baomidou.mybatisplus.core.toolkit.Constants;
import org.apache.ibatis.annotations.Param;
import java.lang.reflect.Field;
import java.util.Objects;
/**
 * @author Lux Sun
 * @date 2022/1/14
 */
public interface DBaseMapper<T> extends BaseMapper<T> {
    Integer IS_DEL = 1;
    /**
     * 插入一条记录(解决主键冲突)
     *
     * @param entity
     */
    default int insertWithPrimary(T entity) {
        // 主键 Id
        Field[] fields = entity.getClass().getDeclaredFields();
        // 删除条件
        QueryWrapper<T> qw = new QueryWrapper<>();
        String fieldName;
        for (Field field : fields) {
            fieldName = field.getName();
            // 装配逻辑删字段 == 1
            if (Objects.nonNull(field.getAnnotation(TableLogic.class))) {
                qw.eq(StrUtil.toUnderlineCase(fieldName), IS_DEL);
            }
            // 装配主键 Id
            else if (Objects.nonNull(field.getAnnotation(TableId.class))) {
                try {
                    field.setAccessible(true);
                    qw.eq(StrUtil.toUnderlineCase(fieldName), field.get(entity));
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            }
        }
        this.deletePhysically(qw);
        return this.insert(entity);
    }
    /**
     * 根据 entity 条件, 删除记录(物理删除)
     *
     * @param wrapper 实体对象封装操作类(可以为 null)
     */
    int deletePhysically(@Param(Constants.WRAPPER) Wrapper<T> wrapper);
}

2、因为插入的方法 BaseMapper 本身自带，但是没有一个方法可以在 @TableLogic 注解的基础上删除，等下给几段官方源码你就明白了，因为 MyBatis 只要识别出 POJO 有该注解，就会对一系列必要地方进行特判

TableInfo.java

该类可以简单理解为和你的 POJO 有着千丝万缕的关系，言外之意你在 POJO 里的属性配置啥的都会在该类里更详细的体现出来

package com.baomidou.mybatisplus.core.metadata;
import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.KeySequence;
import com.baomidou.mybatisplus.core.MybatisConfiguration;
import com.baomidou.mybatisplus.core.toolkit.*;
import com.baomidou.mybatisplus.core.toolkit.sql.SqlScriptUtils;
import lombok.AccessLevel;
import lombok.Data;
import lombok.Getter;
import lombok.Setter;
import lombok.experimental.Accessors;
import org.apache.ibatis.mapping.ResultFlag;
import org.apache.ibatis.mapping.ResultMap;
import org.apache.ibatis.mapping.ResultMapping;
import org.apache.ibatis.session.Configuration;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Objects;
import java.util.function.Predicate;
import static java.util.stream.Collectors.joining;
/**
 * 数据库表反射信息
 *
 * @author hubin
 * @since 2016-01-23
 */
@Data
@Setter(AccessLevel.PACKAGE)
@Accessors(chain = true)
public class TableInfo implements Constants {
    /**
     * 是否开启逻辑删除
     */
    @Setter(AccessLevel.NONE)
    private boolean logicDelete;
    /**
     * 设置逻辑删除
     */
    void setLogicDelete(boolean logicDelete) {
        if (logicDelete) {
            this.logicDelete = true;
        }
    }
    /**
     * 获取逻辑删除字段的 sql 脚本
     *
     * @param startWithAnd 是否以 and 开头
     * @param deleteValue  是否需要的是逻辑删除值
     * @return sql 脚本
     */
    public String getLogicDeleteSql(boolean startWithAnd, boolean deleteValue) {
        if (logicDelete) {
            TableFieldInfo field = fieldList.stream().filter(TableFieldInfo::isLogicDelete).findFirst()
                .orElseThrow(() -> ExceptionUtils.mpe("can't find the logicFiled from table {%s}", tableName));
            String logicDeleteSql = formatLogicDeleteSql(field, deleteValue);
            if (startWithAnd) {
                logicDeleteSql = " AND " + logicDeleteSql;
            }
            return logicDeleteSql;
        }
        return EMPTY;
    }
    // 省略其他代码...
}

Delete.java
因为我们参考的是该方法的代码来进行编码彻底删除的逻辑，所以我们先看下原先该方法的模样

/*
 * Copyright (c) 2011-2020, baomidou (jobob@qq.com).
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * <p>
 * https://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.baomidou.mybatisplus.core.injector.methods;
import com.baomidou.mybatisplus.core.enums.SqlMethod;
import com.baomidou.mybatisplus.core.injector.AbstractMethod;
import com.baomidou.mybatisplus.core.metadata.TableInfo;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.SqlSource;
/**
 * 根据 entity 条件删除记录
 *
 * @author hubin
 * @since 2018-04-06
 */
public class Delete extends AbstractMethod {
    @Override
    public MappedStatement injectMappedStatement(Class<?> mapperClass, Class<?> modelClass, TableInfo tableInfo) {
        String sql;
        SqlMethod sqlMethod = SqlMethod.LOGIC_DELETE;
        // 使用 logicDelete 进行判断
        if (tableInfo.isLogicDelete()) {
            sql = String.format(sqlMethod.getSql(), tableInfo.getTableName(), sqlLogicSet(tableInfo),
                sqlWhereEntityWrapper(true, tableInfo),
                sqlComment());
            SqlSource sqlSource = languageDriver.createSqlSource(configuration, sql, modelClass);
            return addUpdateMappedStatement(mapperClass, modelClass, getMethod(sqlMethod), sqlSource);
        } else {
            sqlMethod = SqlMethod.DELETE;
            sql = String.format(sqlMethod.getSql(), tableInfo.getTableName(),
                sqlWhereEntityWrapper(true, tableInfo),
                sqlComment());
            SqlSource sqlSource = languageDriver.createSqlSource(configuration, sql, modelClass);
            return this.addDeleteMappedStatement(mapperClass, getMethod(sqlMethod), sqlSource);
        }
    }
}

AbstractMethod.java - sqlWhereEntityWrapper 函数中的 TableInfo.getLogicDeleteSql 函数

sqlWhereEntityWrapper 该函数是实现对 SQL 语句 WHERE 的生成，所以会涉及到 “DEL = ?” 的逻辑

package com.baomidou.mybatisplus.core.injector;
import com.baomidou.mybatisplus.core.metadata.TableFieldInfo;
import com.baomidou.mybatisplus.core.metadata.TableInfo;
import com.baomidou.mybatisplus.core.toolkit.Constants;
import com.baomidou.mybatisplus.core.toolkit.StringPool;
import com.baomidou.mybatisplus.core.toolkit.sql.SqlScriptUtils;
import org.apache.ibatis.builder.MapperBuilderAssistant;
import org.apache.ibatis.executor.keygen.KeyGenerator;
import org.apache.ibatis.executor.keygen.NoKeyGenerator;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.logging.LogFactory;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.SqlCommandType;
import org.apache.ibatis.mapping.SqlSource;
import org.apache.ibatis.mapping.StatementType;
import org.apache.ibatis.scripting.LanguageDriver;
import org.apache.ibatis.session.Configuration;
import java.util.List;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Stream;
import static java.util.stream.Collectors.joining;
/**
 * 抽象的注入方法类
 *
 * @author hubin
 * @since 2018-04-06
 */
public abstract class AbstractMethod implements Constants {
    /**
     * EntityWrapper方式获取select where
     *
     * @param newLine 是否提到下一行
     * @param table   表信息
     * @return String
     */
    protected String sqlWhereEntityWrapper(boolean newLine, TableInfo table) {
        if (table.isLogicDelete()) {
            String sqlScript = table.getAllSqlWhere(true, true, WRAPPER_ENTITY_DOT);
            sqlScript = SqlScriptUtils.convertIf(sqlScript, String.format("%s != null", WRAPPER_ENTITY),
                true);
            // 关键代码点
            sqlScript += (NEWLINE + table.getLogicDeleteSql(true, false) + NEWLINE);
            String normalSqlScript = SqlScriptUtils.convertIf(String.format("AND ${%s}", WRAPPER_SQLSEGMENT),
                String.format("%s != null and %s != '' and %s", WRAPPER_SQLSEGMENT, WRAPPER_SQLSEGMENT,
                    WRAPPER_NONEMPTYOFNORMAL), true);
            normalSqlScript += NEWLINE;
            normalSqlScript += SqlScriptUtils.convertIf(String.format(" ${%s}", WRAPPER_SQLSEGMENT),
                String.format("%s != null and %s != '' and %s", WRAPPER_SQLSEGMENT, WRAPPER_SQLSEGMENT,
                    WRAPPER_EMPTYOFNORMAL), true);
            sqlScript += normalSqlScript;
            sqlScript = SqlScriptUtils.convertChoose(String.format("%s != null", WRAPPER), sqlScript,
                table.getLogicDeleteSql(false, false));
            sqlScript = SqlScriptUtils.convertWhere(sqlScript);
            return newLine ? NEWLINE + sqlScript : sqlScript;
        } else {
            String sqlScript = table.getAllSqlWhere(false, true, WRAPPER_ENTITY_DOT);
            sqlScript = SqlScriptUtils.convertIf(sqlScript, String.format("%s != null", WRAPPER_ENTITY), true);
            sqlScript += NEWLINE;
            sqlScript += SqlScriptUtils.convertIf(String.format(SqlScriptUtils.convertIf(" AND", String.format("%s and %s", WRAPPER_NONEMPTYOFENTITY, WRAPPER_NONEMPTYOFNORMAL), false) + " ${%s}", WRAPPER_SQLSEGMENT),
                String.format("%s != null and %s != '' and %s", WRAPPER_SQLSEGMENT, WRAPPER_SQLSEGMENT,
                    WRAPPER_NONEMPTYOFWHERE), true);
            sqlScript = SqlScriptUtils.convertWhere(sqlScript) + NEWLINE;
            sqlScript += SqlScriptUtils.convertIf(String.format(" ${%s}", WRAPPER_SQLSEGMENT),
                String.format("%s != null and %s != '' and %s", WRAPPER_SQLSEGMENT, WRAPPER_SQLSEGMENT,
                    WRAPPER_EMPTYOFWHERE), true);
            sqlScript = SqlScriptUtils.convertIf(sqlScript, String.format("%s != null", WRAPPER), true);
            return newLine ? NEWLINE + sqlScript : sqlScript;
        }
    }
    // 省略其他代码...
}

Ps：以上几段框架中的代码都能说明 @TableLogic 注解的重要性，但同样是我们的要解决的难点，废话不多说了，看下面我们的解决方案

MyBatis-Plus - 一篇带你玩转自定义 BaseMapper（一）

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