mybatis_generator-gui生成代码的一些总结

有道地址： https://note.youdao.com/ynoteshare1/index.html?id=d7d96fe0d846cc6d8700dbe727d282fd&type=note
对springboot整合mybatis项目中的mapper.xml手写也可以从github上直接拉取mybatis_generator-gui在本地直接跑起来反向生成mappers mapper entity这三个部分，这里主要说明用工具自动生成代码中要注意的细节。

---

1. 首先看一下代码运行起来的ui
   1> 点击 数据库连接，会出现下面这张图，不用多说，填写自己要连接数据库的信息：
   

   (注意：连接服务器后不要急着双击打开，可以右键来编辑要连接的数据库)
   2> 生成具体代码需要填写的信息
   
   a> java实体类名：
   数据库用abs_copy这种明明规则，工具可以自己转化成AbsCopy，要不然就自己重新命名。
   b> 主键可以选填，但是填与不填将来在代码中会有如下代码不一样：
   加了主键：

     <insert id="insert" keyColumn="name" keyProperty="name" parameterType="com.szzt.csp.entity.AbsCopy" useGeneratedKeys="true">
    insert into abs_copy (age, `add`, nick
      )
    values (#{age,jdbcType=INTEGER}, #{add,jdbcType=VARCHAR}, #{nick,jdbcType=VARCHAR}
      )
   

```

不加主键:

  <insert id="insert" parameterType="com.szzt.csp.entity.AbsCopy">
 insert into abs_copy (`name`, age, `add`, 
   nick)
 values (#{name,jdbcType=VARCHAR}, #{age,jdbcType=INTEGER}, #{add,jdbcType=VARCHAR}, 
   #{nick,jdbcType=VARCHAR})
</insert>   

建议：设计表的时候有主键生成代码就写着，没有就不要乱加，以免后面在用mapper的时候出错。
c> 其他信息就如图所示找到自己的路径，注意勾选 使用example 来生成响应的分页信息，然后生成代码就可以了。

---

2. 生成的两个entity
   Abs 和 AbsExample:
   Abs.java比较简单，有

   set  get 方法
   public boolean equals(Object that){}
   public int hashCode(){}
   public String toString(){}
   

   几个方法也都常用。
   AbsExample.java的内容比较多，也是实际项目中用的比较多的一个：
   里面主要是 设置增删改查的变量，以及分页排序的参数

       protected String orderByClause;
   
    protected boolean distinct;
   
    protected List<Criteria> oredCriteria;
   
    private Integer limit;
   
    private Long offset;
     public AbsCopyExample() {
        oredCriteria = new ArrayList<Criteria>();
    }
   
    public void setOrderByClause(String orderByClause) {
        this.orderByClause = orderByClause;
    }
   
    public String getOrderByClause() {
        return orderByClause;
    }
   
    public void setDistinct(boolean distinct) {
        this.distinct = distinct;
    }
   
    public boolean isDistinct() {
        return distinct;
    }
   
    public List<Criteria> getOredCriteria() {
        return oredCriteria;
    }
   
    public void or(Criteria criteria) {
        oredCriteria.add(criteria);
    }
   
    public Criteria or() {
        Criteria criteria = createCriteriaInternal();
        oredCriteria.add(criteria);
        return criteria;
    }
   
    public Criteria createCriteria() {
        Criteria criteria = createCriteriaInternal();
        if (oredCriteria.size() == 0) {
            oredCriteria.add(criteria);
        }
        return criteria;
    }
   
    protected Criteria createCriteriaInternal() {
        Criteria criteria = new Criteria();
        return criteria;
    }
   
    public void clear() {
        oredCriteria.clear();
        orderByClause = null;
        distinct = false;
    }
   
    public void setLimit(Integer limit) {
        this.limit = limit;
    }
   
    public Integer getLimit() {
        return limit;
    }
   
    public void setOffset(Long offset) {
        this.offset = offset;
    }
   
    public Long getOffset() {
        return offset;
    }
   
    protected abstract static class GeneratedCriteria {
        protected List<Criterion> criteria;
   
        protected GeneratedCriteria() {
            super();
            criteria = new ArrayList<Criterion>();
        }
   
        public boolean isValid() {
            return criteria.size() > 0;
        }
   
        public List<Criterion> getAllCriteria() {
            return criteria;
        }
   
        public List<Criterion> getCriteria() {
            return criteria;
        }
   
        protected void addCriterion(String condition) {
            if (condition == null) {
                throw new RuntimeException("Value for condition cannot be null");
            }
            criteria.add(new Criterion(condition));
        }
   
        protected void addCriterion(String condition, Object value, String property) {
            if (value == null) {
                throw new RuntimeException("Value for " + property + " cannot be null");
            }
            criteria.add(new Criterion(condition, value));
        }
   
        protected void addCriterion(String condition, Object value1, Object value2, String property) {
            if (value1 == null || value2 == null) {
                throw new RuntimeException("Between values for " + property + " cannot be null");
            }
            criteria.add(new Criterion(condition, value1, value2));
        }
   
        public Criteria andNameIsNull() {
            addCriterion("`name` is null");
            return (Criteria) this;
        }
   
        public Criteria andNameIsNotNull() {
            addCriterion("`name` is not null");
            return (Criteria) this;
        }
   
        public Criteria andNameEqualTo(String value) {
            addCriterion("`name` =", value, "name");
            return (Criteria) this;
        }
   
        public Criteria andNameNotEqualTo(String value) {
            addCriterion("`name` <>", value, "name");
            return (Criteria) this;
        }
   
        public Criteria andNameGreaterThan(String value) {
            addCriterion("`name` >", value, "name");
            return (Criteria) this;
        }
   
        public Criteria andNameGreaterThanOrEqualTo(String value) {
            addCriterion("`name` >=", value, "name");
            return (Criteria) this;
        }
   
        public Criteria andNameLessThan(String value) {
            addCriterion("`name` <", value, "name");
            return (Criteria) this;
        }
   
        public Criteria andNameLessThanOrEqualTo(String value) {
            addCriterion("`name` <=", value, "name");
            return (Criteria) this;
        }
   
        public Criteria andNameLike(String value) {
            addCriterion("`name` like", value, "name");
            return (Criteria) this;
        }
   
        public Criteria andNameNotLike(String value) {
            addCriterion("`name` not like", value, "name");
            return (Criteria) this;
        }
   
        public Criteria andNameIn(List<String> values) {
            addCriterion("`name` in", values, "name");
            return (Criteria) this;
        }
   
        public Criteria andNameNotIn(List<String> values) {
            addCriterion("`name` not in", values, "name");
            return (Criteria) this;
        }
   
        public Criteria andNameBetween(String value1, String value2) {
            addCriterion("`name` between", value1, value2, "name");
            return (Criteria) this;
        }
   
        public Criteria andNameNotBetween(String value1, String value2) {
            addCriterion("`name` not between", value1, value2, "name");
            return (Criteria) this;
        }
   
        public Criteria andAgeIsNull() {
            addCriterion("age is null");
            return (Criteria) this;
        }
   
        public Criteria andAgeIsNotNull() {
            addCriterion("age is not null");
            return (Criteria) this;
        }
   
        public Criteria andAgeEqualTo(Integer value) {
            addCriterion("age =", value, "age");
            return (Criteria) this;
        }
   
        public Criteria andAgeNotEqualTo(Integer value) {
            addCriterion("age <>", value, "age");
            return (Criteria) this;
        }
   
        public Criteria andAgeGreaterThan(Integer value) {
            addCriterion("age >", value, "age");
            return (Criteria) this;
        }
   
        public Criteria andAgeGreaterThanOrEqualTo(Integer value) {
            addCriterion("age >=", value, "age");
            return (Criteria) this;
        }
   
        public Criteria andAgeLessThan(Integer value) {
            addCriterion("age <", value, "age");
            return (Criteria) this;
        }
   
        public Criteria andAgeLessThanOrEqualTo(Integer value) {
            addCriterion("age <=", value, "age");
            return (Criteria) this;
        }
   
        public Criteria andAgeIn(List<Integer> values) {
            addCriterion("age in", values, "age");
            return (Criteria) this;
        }
   
        public Criteria andAgeNotIn(List<Integer> values) {
            addCriterion("age not in", values, "age");
            return (Criteria) this;
        }
   
        public Criteria andAgeBetween(Integer value1, Integer value2) {
            addCriterion("age between", value1, value2, "age");
            return (Criteria) this;
        }
   
        public Criteria andAgeNotBetween(Integer value1, Integer value2) {
            addCriterion("age not between", value1, value2, "age");
            return (Criteria) this;
        }
   
        public Criteria andAddIsNull() {
            addCriterion("`add` is null");
            return (Criteria) this;
        }
   
        public Criteria andAddIsNotNull() {
            addCriterion("`add` is not null");
            return (Criteria) this;
        }
   
        public Criteria andAddEqualTo(String value) {
            addCriterion("`add` =", value, "add");
            return (Criteria) this;
        }
   
        public Criteria andAddNotEqualTo(String value) {
            addCriterion("`add` <>", value, "add");
            return (Criteria) this;
        }
   
        public Criteria andAddGreaterThan(String value) {
            addCriterion("`add` >", value, "add");
            return (Criteria) this;
        }
   
        public Criteria andAddGreaterThanOrEqualTo(String value) {
            addCriterion("`add` >=", value, "add");
            return (Criteria) this;
        }
   
        public Criteria andAddLessThan(String value) {
            addCriterion("`add` <", value, "add");
            return (Criteria) this;
        }
   
        public Criteria andAddLessThanOrEqualTo(String value) {
            addCriterion("`add` <=", value, "add");
            return (Criteria) this;
        }
   
        public Criteria andAddLike(String value) {
            addCriterion("`add` like", value, "add");
            return (Criteria) this;
        }
   
        public Criteria andAddNotLike(String value) {
            addCriterion("`add` not like", value, "add");
            return (Criteria) this;
        }
   
        public Criteria andAddIn(List<String> values) {
            addCriterion("`add` in", values, "add");
            return (Criteria) this;
        }
   
        public Criteria andAddNotIn(List<String> values) {
            addCriterion("`add` not in", values, "add");
            return (Criteria) this;
        }
   
        public Criteria andAddBetween(String value1, String value2) {
            addCriterion("`add` between", value1, value2, "add");
            return (Criteria) this;
        }
   
        public Criteria andAddNotBetween(String value1, String value2) {
            addCriterion("`add` not between", value1, value2, "add");
            return (Criteria) this;
        }
   
        public Criteria andNickIsNull() {
            addCriterion("nick is null");
            return (Criteria) this;
        }
   
        public Criteria andNickIsNotNull() {
            addCriterion("nick is not null");
            return (Criteria) this;
        }
   
        public Criteria andNickEqualTo(String value) {
            addCriterion("nick =", value, "nick");
            return (Criteria) this;
        }
   
        public Criteria andNickNotEqualTo(String value) {
            addCriterion("nick <>", value, "nick");
            return (Criteria) this;
        }
   
        public Criteria andNickGreaterThan(String value) {
            addCriterion("nick >", value, "nick");
            return (Criteria) this;
        }
   
        public Criteria andNickGreaterThanOrEqualTo(String value) {
            addCriterion("nick >=", value, "nick");
            return (Criteria) this;
        }
   
        public Criteria andNickLessThan(String value) {
            addCriterion("nick <", value, "nick");
            return (Criteria) this;
        }
   
        public Criteria andNickLessThanOrEqualTo(String value) {
            addCriterion("nick <=", value, "nick");
            return (Criteria) this;
        }
   
        public Criteria andNickLike(String value) {
            addCriterion("nick like", value, "nick");
            return (Criteria) this;
        }
   
        public Criteria andNickNotLike(String value) {
            addCriterion("nick not like", value, "nick");
            return (Criteria) this;
        }
   
        public Criteria andNickIn(List<String> values) {
            addCriterion("nick in", values, "nick");
            return (Criteria) this;
        }
   
        public Criteria andNickNotIn(List<String> values) {
            addCriterion("nick not in", values, "nick");
            return (Criteria) this;
        }
   
        public Criteria andNickBetween(String value1, String value2) {
            addCriterion("nick between", value1, value2, "nick");
            return (Criteria) this;
        }
   
        public Criteria andNickNotBetween(String value1, String value2) {
            addCriterion("nick not between", value1, value2, "nick");
            return (Criteria) this;
        }
    }
   
    /**
     */
    public static class Criteria extends GeneratedCriteria {
   
        protected Criteria() {
            super();
        }
    }
   
    public static class Criterion {
        private String condition;
   
        private Object value;
   
        private Object secondValue;
   
        private boolean noValue;
   
        private boolean singleValue;
   
        private boolean betweenValue;
   
        private boolean listValue;
   
        private String typeHandler;
   
        public String getCondition() {
            return condition;
        }
   
        public Object getValue() {
            return value;
        }
   
        public Object getSecondValue() {
            return secondValue;
        }
   
        public boolean isNoValue() {
            return noValue;
        }
   
        public boolean isSingleValue() {
            return singleValue;
        }
   
        public boolean isBetweenValue() {
            return betweenValue;
        }
   
        public boolean isListValue() {
            return listValue;
        }
   
        public String getTypeHandler() {
            return typeHandler;
        }
   
        protected Criterion(String condition) {
            super();
            this.condition = condition;
            this.typeHandler = null;
            this.noValue = true;
        }
   
        protected Criterion(String condition, Object value, String typeHandler) {
            super();
            this.condition = condition;
            this.value = value;
            this.typeHandler = typeHandler;
            if (value instanceof List<?>) {
                this.listValue = true;
            } else {
                this.singleValue = true;
            }
        }
   
        protected Criterion(String condition, Object value) {
            this(condition, value, null);
        }
   
        protected Criterion(String condition, Object value, Object secondValue, String typeHandler) {
            super();
            this.condition = condition;
            this.value = value;
            this.secondValue = secondValue;
            this.typeHandler = typeHandler;
            this.betweenValue = true;
        }
   
        protected Criterion(String condition, Object value, Object secondValue) {
            this(condition, value, secondValue, null);
        }
    }
   

   代码中比较绕的是用or连接两个查询条件，还有就是熟练运用那些大于 小于 不等于 null notnull等

3. 代码中insert 和 insertSelective的区别：
   详见： https://blog.csdn.net/Com_ma/article/details/91463928

4. 生成的mapper
   每次代码会生成 MyBatisBaseDao 和 自己的mapper， 自己的mapper extends MyBatisBaseDao ， 自己在自己的mapper中可以用@SELECT标签写自己的sql，
   MyBatisBaseDao中定义了一些通用的接口：

   public interface MyBatisBaseDao<Model, PK extends Serializable, E> {
    long countByExample(E example);
   
    int deleteByExample(E example);
   
    int deleteByPrimaryKey(PK id);
   
    int insert(Model record);
   
    int insertSelective(Model record);
   
    List<Model> selectByExample(E example);
   
    Model selectByPrimaryKey(PK id);
   
    int updateByExampleSelective(@Param("record") Model record, @Param("example") E example);
   
    int updateByExample(@Param("record") Model record, @Param("example") E example);
   
    int updateByPrimaryKeySelective(Model record);
   
    int updateByPrimaryKey(Model record);
   }
   

   当然也可以在MyBatisBaseDao中写sql。

   总结 ：
   工具生成的distinct自己感觉是假的，想要sql中用distinct，还是自己动手写sql比较合适，用工具生成的代码就这些，个人觉的就能完成基本的增删改查，对于业务逻辑稍微复杂的还要借助mapper.xml 或者自己独立封装sql。