mybatis generator 自动生成的拼装sql分析

0.使用的场景
1.自己的实现: 一个简单的实现例子

2.成熟的解决方案: mybatis generator

3.源码分析

• java example

  点击查看代码

      public class JobLogExample {
    protected String orderByClause;
  
    protected boolean distinct;
  
    protected List<Criteria> oredCriteria;
  
    public JobLogExample() {
        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;
    }
  
    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 andIdIsNull() {
            addCriterion("id is null");
            return (Criteria) this;
        }
  
        public Criteria andIdIsNotNull() {
            addCriterion("id is not null");
            return (Criteria) this;
        }
  
        public Criteria andIdEqualTo(Long value) {
            addCriterion("id =", value, "id");
            return (Criteria) this;
        }
  
        public Criteria andIdNotEqualTo(Long value) {
            addCriterion("id <>", value, "id");
            return (Criteria) this;
        }
  
        public Criteria andIdGreaterThan(Long value) {
            addCriterion("id >", value, "id");
            return (Criteria) this;
        }
  
        public Criteria andIdGreaterThanOrEqualTo(Long value) {
            addCriterion("id >=", value, "id");
            return (Criteria) this;
        }
  
        public Criteria andIdLessThan(Long value) {
            addCriterion("id <", value, "id");
            return (Criteria) this;
        }
  
        public Criteria andIdLessThanOrEqualTo(Long value) {
            addCriterion("id <=", value, "id");
            return (Criteria) this;
        }
  
        public Criteria andIdIn(List<Long> values) {
            addCriterion("id in", values, "id");
            return (Criteria) this;
        }
  
        public Criteria andIdNotIn(List<Long> values) {
            addCriterion("id not in", values, "id");
            return (Criteria) this;
        }
  
        public Criteria andIdBetween(Long value1, Long value2) {
            addCriterion("id between", value1, value2, "id");
            return (Criteria) this;
        }
  
        public Criteria andIdNotBetween(Long value1, Long value2) {
            addCriterion("id not between", value1, value2, "id");
            return (Criteria) this;
        }
  
        public Criteria andCreateTimeIsNull() {
            addCriterion("create_time is null");
            return (Criteria) this;
        }
  
        public Criteria andCreateTimeIsNotNull() {
            addCriterion("create_time is not null");
            return (Criteria) this;
        }
  
        public Criteria andCreateTimeEqualTo(Date value) {
            addCriterion("create_time =", value, "createTime");
            return (Criteria) this;
        }
  
        public Criteria andCreateTimeNotEqualTo(Date value) {
            addCriterion("create_time <>", value, "createTime");
            return (Criteria) this;
        }
  
        public Criteria andCreateTimeGreaterThan(Date value) {
            addCriterion("create_time >", value, "createTime");
            return (Criteria) this;
        }
  
        public Criteria andCreateTimeGreaterThanOrEqualTo(Date value) {
            addCriterion("create_time >=", value, "createTime");
            return (Criteria) this;
        }
  
        public Criteria andCreateTimeLessThan(Date value) {
            addCriterion("create_time <", value, "createTime");
            return (Criteria) this;
        }
  
        public Criteria andCreateTimeLessThanOrEqualTo(Date value) {
            addCriterion("create_time <=", value, "createTime");
            return (Criteria) this;
        }
  
        public Criteria andCreateTimeIn(List<Date> values) {
            addCriterion("create_time in", values, "createTime");
            return (Criteria) this;
        }
  
        public Criteria andCreateTimeNotIn(List<Date> values) {
            addCriterion("create_time not in", values, "createTime");
            return (Criteria) this;
        }
  
        public Criteria andCreateTimeBetween(Date value1, Date value2) {
            addCriterion("create_time between", value1, value2, "createTime");
            return (Criteria) this;
        }
  
        public Criteria andCreateTimeNotBetween(Date value1, Date value2) {
            addCriterion("create_time not between", value1, value2, "createTime");
            return (Criteria) this;
        }
  }
  

}

```
</details>

• java mapper

  List<JobLog> selectByExample(JobLogExample example);
  
  int updateByExampleSelective(@Param("record") JobLogrecord, @Param("example") JobLogExample example);
  

• mybatis xml

  Example_Where_Clause

  <sql id="">
      <where>
        <foreach collection="oredCriteria" item="criteria" separator="or">
          <if test="criteria.valid">
            <trim prefix="(" prefixOverrides="and" suffix=")">
              <foreach collection="criteria.criteria" item="criterion">
                <choose>
                  <when test="criterion.noValue">
                    and ${criterion.condition}
                  </when>
                  <when test="criterion.singleValue">
                    and ${criterion.condition} #{criterion.value}
                  </when>
                  <when test="criterion.betweenValue">
                    and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                  </when>
                  <when test="criterion.listValue">
                    and ${criterion.condition}
                    <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                      #{listItem}
                    </foreach>
                  </when>
                </choose>
              </foreach>
            </trim>
          </if>
        </foreach>
      </where>
    </sql>
  

  Update_By_Example_Where_Clause

  <sql id="Update_By_Example_Where_Clause">
      <where>
        <foreach collection="example.oredCriteria" item="criteria" separator="or">
          <if test="criteria.valid">
            <trim prefix="(" prefixOverrides="and" suffix=")">
              <foreach collection="criteria.criteria" item="criterion">
                <choose>
                  <when test="criterion.noValue">
                    and ${criterion.condition}
                  </when>
                  <when test="criterion.singleValue">
                    and ${criterion.condition} #{criterion.value}
                  </when>
                  <when test="criterion.betweenValue">
                    and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                  </when>
                  <when test="criterion.listValue">
                    and ${criterion.condition}
                    <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                      #{listItem}
                    </foreach>
                  </when>
                </choose>
              </foreach>
            </trim>
          </if>
        </foreach>
      </where>
    </sql>
  

4.常见的问题