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。

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。

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

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

生成的mapper
每次代码会生成 MyBatisBaseDao 和自己的mapper，自己的mapper extends MyBatisBaseDao<Merchant, Long, MerchantExample> ，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。

mybatis_generator-gui生成代码的一些总结

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