flywayTest: 实验通过flyway达成：a依赖b，b依赖c，a、b、c的SQL脚本需要初始化到不同库里;a依赖b1,b2,a和b1,b2的SQL脚本都初始化到a的库里

此demo是为了实验： a依赖b,b依赖c这种情况下，b和c的初始化脚本能自动执行。这在把b和c当做插件来使用时很有用 
参考文章：https://blog.csdn.net/qianzhitu/article/details/110629847
### 情况一、/condition1： con1-a依赖con1-b，a和b的脚本需要初始化到一个库里（但大多情况应该都是情况二里的混合模式吧，至少按混合模式去支持总好过后面需要改）
>测试类：con1/a/src/test/java/org/example/a/Con1AAppTest.java

#### 1. 只需要con1-a和con1-b把脚本放在各种项目的同一个目录,即flyway.locations配置的目录
        PS：只是这1步骤并不会执行con1-b的脚本
#### 2. 在con1-b里添加FlywayConfig
```java
package org.example.b.config;

import org.flywaydb.core.Flyway;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.sql.DataSource;
@Configuration
public class FlywayConfig {
    @Bean(initMethod = "migrate")
    public Flyway bFlyway(DataSource dataSource ) {
        return Flyway.configure()
                .dataSource(dataSource)
                .load();
    }
}
```
#### 3.并且增在con1-b的resources目录下增加META-INF/spring.factories，这样引入con1-b项目就能自动装载FlywayConfig了，这样con1-b下的脚本也能执行到con1-a所配置的数据库中了
```markdown
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  org.example.b.config.FlywayConfig
```

#### 4.1. 重要说明：con1-b的脚本文件可千万别跟con1-a重复了，如果名字一毛一样了则最终只有con1-a的脚本执行了。至于脚本执行先后顺序根据实际情况控制脚本版本号大小即可，版本号越小的越先执行。

#### 4.2. 测试了有3个项目，执行顺序 con1-a版本为V1,V4,con1-b版本为V2,V3,V6,con1-c版本为V5,V7，因为它们3个项目的脚本路径是一致的，所以没问题。在下面的混合模式下（既有同数据源(>=3会出问题，<=2m没事)，也有不同数据源）

>PS:从spring boot2.7开始，慢慢不支持META-INF/spring.factories文件了
需要导入的自动配置类可以放在 /META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports文件中

### 情况二、/condition2： a依赖b，b依赖c，a、b、c的脚本需要初始化到不同库里;a依赖b1,b2,a和b1,b2的脚本都初始化到a的库里
>测试类：con2/a/src/test/java/org/example/a/Con2AAppTest.java
先说不同数据源的

#### 1.就是多数据源的配置了，b和c基本一样,以b举例 
（用其他多数据源方式的比如dynamic-datasource的除1.2基本也能参考）
##### 1.1自己的数据库配置前缀
```java
package org.example.b.config;

import org.springframework.boot.autoconfigure.jdbc.DataSourceProperties;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Configuration;
import org.springframework.stereotype.Component;

@Component
@ConfigurationProperties("spring.datasource.b")
public class BDataSourceProperties extends DataSourceProperties{

} 
```
为什么要定义一个类继承DataSourceProperties，看源码就知道DataSourceProperties已经定义了@ConfigurationProperties("spring.datasource")，这个标签不能覆盖，直接使用DataSourceProperties的话有前缀的配置值是set不进去的
##### 1.2定义自己的DataSource
```java
package org.example.b.config;

import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.jdbc.DataSourceBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.sql.DataSource;

@Configuration
public class BDataSourceConfig {

@Qualifier
    @Bean("bDataSource")
    public DataSource bDataSource(BDataSourceProperties properties){
        return DataSourceBuilder.create()
                .driverClassName(properties.getDriverClassName())
                .url(properties.getUrl())
                .username(properties.getUsername())
                .password(properties.getPassword())
                .build();
    }
}
```
##### 1.3把自己的DataSource赋给Flyway
```java
package org.example.b.config;

import org.flywaydb.core.Flyway;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.DependsOn;
import org.springframework.core.annotation.Order;

import javax.annotation.Resource;
import javax.sql.DataSource;

@Configuration
public class BFlywayConfig {
    @Resource(name = "bDataSource")
    private DataSource bDataSource;

@Bean(initMethod = "migrate",name = "bFlyway")
    public Flyway bFlyway() {
        System.out.println("bFlyway初始化");
        return Flyway.configure()
                .dataSource(bDataSource)
                .locations("classpath:db/migration/b")
                .load();
    }
}

```
##### 1.4在的resources目录下增加META-INF/spring.factories
这样引入b项目就能自动装载FlywayConfig了
spring.factories:
```markdown
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
    org.example.b.config.BDataSourceProperties,\
    org.example.b.config.BDataSourceConfig,\
    org.example.b.config.BFlywayConfig
```
##### 1.5记得在DataSource上加@Primary，即项目A里
##### 1.6在主程序的配置加加a,b,c的数据源配置
```yaml
spring:
  datasource:
    type: com.zaxxer.hikari.HikariDataSource
    a:
      driver-class-name: com.mysql.jdbc.Driver
      url: jdbc:mysql://localhost:3306/flyway-a?useUnicode=true&characterEncoding=utf8&zeroDateTimeBehavior=convertToNull&useSSL=true&serverTimezone=GMT%2B8&rewriteBatchedStatements=true&allowPublicKeyRetrieval=true
      username: root
      password: root
    b:
      driver-class-name: com.mysql.jdbc.Driver
      url: jdbc:mysql://localhost:3306/flyway-b?useUnicode=true&characterEncoding=utf8&zeroDateTimeBehavior=convertToNull&useSSL=true&serverTimezone=GMT%2B8&rewriteBatchedStatements=true&allowPublicKeyRetrieval=true
      username: root
      password: root
    c:
      driver-class-name: com.mysql.jdbc.Driver
      url: jdbc:mysql://localhost:3306/flyway-c?useUnicode=true&characterEncoding=utf8&zeroDateTimeBehavior=convertToNull&useSSL=true&serverTimezone=GMT%2B8&rewriteBatchedStatements=true&allowPublicKeyRetrieval=true
      username: root
      password: root
```

>备注: 
1、所有的Flyway初始化里一定指定.locations("classpath:db/migration/xxx")，只是单纯配置yml还是会在初始化a时读到b的sql文件，导致flyway报异常，不能成功初始化 
2、还是要注意脚本的version不要重复，否则会报异常:
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'b2Flyway' defined in class path resource [org/example/b2/config/FlywayConfig.class]: Invocation of init method failed; nested exception is org.flywaydb.core.api.FlywayException: Found more than one migration with version 2
Offenders:
-> E:\wonders\myOwnProjects\flywayTest\con2\a\target\classes\db\migration\a\V2__init.sql (SQL)
-> E:\wonders\myOwnProjects\flywayTest\con2\b\target\classes\db\migration\b\V2__init.sql (SQL)

#### 2. b1、b2的情况跟condition1有2个特殊点导致最终实现上不太一样 
##### 特殊点.1 所有初始化Flyway时一定要指定自己的位置.locations("classpath:db/migration/xxx")，否则在b2里没有指定，那么在初始化完b2,去初始化b时会报如下的错
```markdown
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'b2Flyway' defined in class path resource [org/example/b2/config/FlywayConfig.class]: Invocation of init method failed; nested exception is org.flywaydb.core.api.FlywayException: Found more than one migration with version 2
Offenders:
-> E:\wonders\myOwnProjects\flywayTest\con2\b\target\classes\db\migration\b\V1__init.sql (SQL)
-> E:\wonders\myOwnProjects\flywayTest\con2\b\target\classes\db\migration\V1__init.sql (SQL)
```
实际上b下面没有db\migration\V1__init.sql 这个文件，因为在b2没有在初始化Flyway对象时没有指定locations导致b的flyway把locations有了2个路径（执行顺序先b2在b）

##### 特殊点.2 因为b1,b2要跟a初始化到同一个库，a的flyway只是在.locations("classpath:db/migration/a")是不够的，得 .locations("classpath:db/migration/a","classpath:db/migration/b1","classpath:db/migration/b2")这样才行，否则会报错 
```markdown
Invocation of init method failed; nested exception is org.flywaydb.core.api.FlywayException: Validate failed: Detected applied migration not resolved locally: 1
```
而且实际情况a、b1、b2的脚本版本号可能会交叉执行，意味着3个bean初始化都需要声明指定3个项目的脚本路径。 
所以最终的实现是加入了一个公共依赖模块common-flyway，它提供一个全局注册各项目自己脚本路径的方法，最终在启动项目即a去初始化Flyway即可。
##### 2.1 common-fly
###### 2.1.1
```java
package org.example.common.flyway;

public interface FlywayMigrate {
    /**
     * 实际执行
     * @return
     */
    public int migrate();
}
```
###### 2.1.2
```java
package org.example.common.flyway.config;

import org.example.common.flyway.FlywayMigrate;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;
import javax.annotation.Resource;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

@Configuration("flywayInitHelper")
public class FlywayInitHelper  implements InitializingBean {
     @Resource
     private FlywayMigrate flywayMigrate;

private static List<String> locations = new ArrayList<>();
 public static void addLocations(String... location){
 locations.addAll(Arrays.asList(location));
 }

public static  String[] getLocations(){
          String[] array = new String[locations.size()];
          locations.toArray(array);
          for (String location: array ) {
               System.out.println("location:"+location);
          }
          return array;
     }
     @PostConstruct
     public void init(){
          System.out.println("中转工初始化...");
     }

@Override
     public void afterPropertiesSet() throws Exception {
          flywayMigrate.migrate();
     }
}
```
###### 2.1.3 common-flyway/src/main/resources/META-INF/spring.factories
##### 2.2 b1或b2
###### 2.2.1
```java
package org.example.b1.config;

import org.example.common.flyway.config.FlywayInitHelper;
import org.springframework.boot.autoconfigure.AutoConfigureBefore;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;

@Configuration
@AutoConfigureBefore({FlywayInitHelper.class})
public class B1FlywayConfig {

@PostConstruct
    public void addLocations() {
        System.out.println("添加con2-b1的locations");
        FlywayInitHelper.addLocations("classpath:db/migration/b1");
    }
}
```
###### 2.2.2 con2/b1/src/main/resources/META-INF/spring.factories
```
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  org.example.b1.config.B1FlywayConfig
```
###### 2.2.3 sql脚本
```
b1
└── src
    └──resources
        └──db
            └──migration
                    └──b1
                        ├──V1-init.sql
                        └──V4-init.sql
b2
    └── src
        └──resources
            └──db
                └──migration
                    └──b2
                        └──V2-init.sql
a
└── src
    └──resources
        └──db
            └──migration
                    └──a
                        ├──V3-init.sql
                        └──V5-init.sql
```
##### 2.3 a
###### 2.3.1
```java
package org.example.a.config;

import org.example.common.flyway.FlywayMigrate;
import org.example.common.flyway.config.FlywayInitHelper;
import org.flywaydb.core.Flyway;
import org.springframework.stereotype.Component;
import javax.annotation.Resource;
import javax.sql.DataSource;

@Component
public class AFlywayConfig  implements FlywayMigrate {
    @Resource(name = "aDataSource")
    private DataSource aDataSource;

private Flyway flyway;

@Override
    public int migrate() {
        System.out.println("aFlyway执行脚本");
        FlywayInitHelper.addLocations("classpath:db/migration/a");
        flyway = Flyway.configure().dataSource(aDataSource)
                .locations(FlywayInitHelper.getLocations()).load();
        return flyway.migrate();
    }
}
```
###### 2.3.2
应该注意到了为了解耦和执行顺序保持[b1.addLocations,b2.addLocations,a.addLocations任意],FlywayInitHelper,flyway.migrate();在AFlywayConfig里并没有@Bean去返回Flyway，实际spring用的是flyway自己根据配置文件初始化的。
所以一定要保证b1,b2,a的脚本目录在flyway.locations配置的子目录下。否则会发生脚本都初始化成功了，但是FlywayInitHelper会异常。因为flyway的校验会报异常。

##### 最后记录一下踩的坑，虽然不是最终方案，记录一下不可行方案备忘：
##### 坑1：后初始化Flyway的地方先获取到已经初始化的flyway对象们获取它们的locations，但是容易导致bean循环依赖。而且也没办法做到a,b1,b2版本的交叉执行，控制3个项目bean初始化的顺序也是问题，@order不起作用，使用 @DependsOn、@AutoConfigureAfter 或 @AutoConfigureBefore违背了即插即拔的初衷
##### 坑2：让a、b1、b2各自维护自己的版本记录表，但是控制脚本顺序，locations、version还是有影响，费劲也搞不好

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