JPA配置不生成外键

JPA配置不生成外键

通过查看源码发现创建外键的SQL语句是通过Dialect的StandardForeignKeyExporter对象来生成的，而JPA(hibernate)允许我们自定义Dialect的解析器(DialectResolver)。因此我们可以先配置自定义的DialectResolver，解析Dialect的方法直接抄StandardDialectResolver里面的代码，在获取到正确的Dialect后，我们再通过cglib动态生成代理类，拦截其中的getForeignKeyExporter方法，给他返回一个自定义的StandardForeignKeyExporter类，将getSqlCreateStrings方法的返回值直接改为Exporter.NO_COMMANDS，这样就获取不到创建外键的SQL语句。

1. MyInterceptor.java (作用：cglib方法拦截器，拦截类的方法)

public class MyInterceptor implements MethodInterceptor {
    @Override
    public Object intercept(Object object, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        
        //直接返回Exporter.NO_COMMANDS
        if(method.getName().equals("getForeignKeyExporter")){
            return new StandardForeignKeyExporter((Dialect) object){
                @Override
                public String[] getSqlCreateStrings(ForeignKey foreignKey, Metadata metadata) {
                    return Exporter.NO_COMMANDS;
                }

                @Override
                public String[] getSqlDropStrings(ForeignKey foreignKey, Metadata metadata) {
                    return Exporter.NO_COMMANDS;
                }
            };
        }
        return methodProxy.invokeSuper(object, objects);
    }
}

2. MyStandardDialectResolver.java (自定义DialectResolver)

import org.hibernate.dialect.Database;
import org.hibernate.dialect.Dialect;
import org.hibernate.engine.jdbc.dialect.spi.DialectResolutionInfo;
import org.hibernate.engine.jdbc.dialect.spi.DialectResolver;
import org.springframework.cglib.proxy.Enhancer;

/**
 * 自定义方言解析器
 *
 * @Author: yx
 * @Date: 2021/12/10
 **/
public class MyStandardDialectResolver implements DialectResolver {
    @Override
    public Dialect resolveDialect(DialectResolutionInfo info) {
        for ( Database database : Database.values() ) {
            Dialect dialect = database.resolveDialect( info );
            if ( dialect != null ) {
                MyInterceptor myInterceptor = new MyInterceptor();
                Enhancer enhancer = new Enhancer();
                enhancer.setSuperclass(dialect.getClass());  // 设置超类，cglib是通过继承来实现的
                enhancer.setCallback(myInterceptor);
                return (Dialect) enhancer.create();
            }
        }

        return null;
    }
}

3. 在application.yml(或者properties)配置自定义DialectResolver

spring:
  jpa:
    show-sql: true
    open-in-view: true
    hibernate:
      ddl-auto: update
    properties:
      hibernate:
        enable_lazy_load_no_trans: true
        # 配置自定义DialectResolver
        dialect_resolvers: com.acrabsoft.web.develop.base.util.MyStandardDialectResolver
        format_sql: true