Mybatis-Plus的SQL语句组拼原理

逃离我推掉我的手 2022-04-01 12:28 146阅读 0赞

# 前言：记录查找自动组拼SQL语句的过程 #

**首先在Base****Mapper其中的一个方法下打个断点**

![20181230212352989.png][]

**在断点显示的值栏找到相关的SQL**

**发现SQL语句在MappedStatement对象中，而sqlSource存的就是相关的sql语句**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70 1][]

**然后在MappedStatement这个对象打断点，看看到底是哪个对象对它进行了操作 **

![20181230212757104.png][]

**发现是AutoSqlInjector创建了MappedStatement**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70 2][]

**在AutoSqlInjector对象找到与selectById相关的一个方法，打断点**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70 3][]

** SqlSource果然在这里创建出来了，createSqlSource就是具体过程，然后添加到MappedStatement对象中，此SQL完成组拼**

**在createSqlSource方法打下断点，进入具体的组拼过程**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70 4][]

**方法sqlSelectColumns就是具体的组拼方法，一直在此方法进行递归 **

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70 5][]

** 在此方法中，迭代器在不断迭代组拼**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70 6][]

**最后SQL全部完成组拼，存在集合对象中，就可以取出来了 **

### **总结：学会从逆推到顺推，学会怎样打断点是关键** ###

[20181230212352989.png]: /images/20220401/2dffdc90091241b98d94fc7916d50762.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70]: /images/20220401/6b6dfd87bbe14b789c82cc5a6adfd8d0.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70 1]: /images/20220401/cfa81973a8854d21ae7cc2e9dcbb9acc.png
[20181230212757104.png]: /images/20220401/47fa9f5eedeb4f62bc12507be36aa642.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70 2]: /images/20220401/4424cdc657df4159932e583d69637812.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70 3]: /images/20220401/9d55c062048547a1bdded5a7745437f5.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70 4]: /images/20220401/6ca360598449455a9995c8ed1a205f2e.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70 5]: /images/20220401/8d0b4ef9747944a08e1b08d0bd9e7418.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODgwMjA2MQ_size_16_color_FFFFFF_t_70 6]: /images/20220401/b46aed273f39484f80b0b9b2852708ac.png