如何确保数据完整性时，使用表每子类

Question

我在Grails中使用表每个子类策略，方法是将超类中静态mapping字段的tablePerHierarchy属性设置为false。这样，Grails为我的超类创建一个表，为我的每个子类创建一个额外的表。

然而，虽然父类和子类记录共享相同的ID(主键)，但没有外键约束来保持它们的一致性，即有可能删除父类记录，使子类记录处于无效状态。我想知道是否有一个设置/属性使GORM以某种方式解决这个问题，例如通过约束。还是我唯一的选择是手动添加外键?

---

例如，给定以下域类作为超类:

class Product {
    String productCode
    static mapping = {
        tablePerHierarchy false
    }
}

和以下域类作为子类:

class Book extends Product {
    String isbn
}

这导致创建两个表，Product表和Book表。当创建Book(例如，通过脚手架页面)时，将一条记录插入到每个表中，它们之间的唯一联系是每个表的ID值是相同的。具体来说，数据可能如下所示:

PRODUCT
Id      Version     ProductCode
1       1           BLAH-02X1
BOOK
Id      ISBN
1       123-4-56-7891011-1

因为没有在数据库级别为这些表定义正式的关系，所以有可能删除其中一条记录而留下另一条记录，从而导致无效数据。显然，我可以使用SQL在两个ID字段上手动创建一个外键约束，但我希望让Grails来处理这个问题。这可能吗?

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使用Grails 2.2.1

Answer 1

解决!

下面的解决方案为我解决了这个问题。将下面的类添加到src/java(这个类不能用Groovy编写)

package org.example;
import org.codehaus.groovy.grails.orm.hibernate.cfg.GrailsAnnotationConfiguration;
import org.hibernate.MappingException;
import org.hibernate.mapping.JoinedSubclass;
import org.hibernate.mapping.PersistentClass;
import org.hibernate.mapping.RootClass;
import java.util.Iterator;
public class TablePerSubclassConfiguration extends GrailsAnnotationConfiguration {
    private static final long serialVersionUID = 1;
    private boolean alreadyProcessed = false;
    @Override
    protected void secondPassCompile() throws MappingException {
        super.secondPassCompile();
        if (alreadyProcessed) {
            return;
        }
        for (PersistentClass persistentClass : classes.values()) {
            if (persistentClass instanceof RootClass) {
                RootClass rootClass = (RootClass) persistentClass;
                if (rootClass.hasSubclasses()) {
                    Iterator subclasses = rootClass.getSubclassIterator();
                    while (subclasses.hasNext()) {
                        Object subclass = subclasses.next();
                        // This test ensures that foreign keys will only be created for subclasses that are
                        // mapped using "table per subclass"
                        if (subclass instanceof JoinedSubclass) {
                            JoinedSubclass joinedSubclass = (JoinedSubclass) subclass;
                            joinedSubclass.createForeignKey();
                        }
                    }
                }
            }
        }
        alreadyProcessed = true;
    }
}

然后在DataSource.groovy中将其设置为配置类

dataSource {
    configClass = 'org.example.TablePerSubclassConfiguration'
    pooled = true
    driverClassName = "org.h2.Driver"
    username = "sa"
    password = ""
    dbCreate = "update"
    url = "jdbc:h2:mem:testDb;MVCC=TRUE;LOCK_TIMEOUT=10000"
}

更新

我已经向Grails提交了这个问题的pull request。这个修复包含在Grails 2.3.8或2.3.9中(不记得是哪个了)。

Answer 2

Hibernate确保每个子类对应一个表的情况下数据的完整性。在每个子类对应一个表的情况下，子类与超类保持主键关联。看看每个子类的Hibernate表。下面是您的测试用例:

---

class Product {
    String productCode
    static mapping = {
        tablePerHierarchy false
    }
}
class Book extends Product{
    String isbn
}
//Test Case
def testTablePerSubclass{
    def product = new Product(productCode: 'XYZ456')
    product.save(flush: true, failOnError: true)
    def book = new Book(isbn: '123456123', productCode: 'ABC123')
    book.save(flush: true, failOnError: true)
    assert Book.list().size() == 1 //One Book
    assert Book.list()*.id == [2] //Book id
    assert Product.list().size() == 2 //One Product, one Book (2 Products)
    assert Product.list()*.id == [1, 2] //Product id, Book Id
    //Grab the product (book) to delete
    def productToDelete = Product.get(book.id)
    productToDelete.delete(flush: true)
    assert Book.list().isEmpty() //Book deleted from Book table as well
    assert Product.list().size() == 1 //One Product remaining in Product table
    assert Product.list()*.id == [1] //Remaining Product Id
}

在DataSource.groovy中保持logSql为true，以查看相应的sql被执行。

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Log Sql Output:-
Hibernate: insert into product (id, version, product_code) values (null, ?, ?)
Hibernate: insert into product (id, version, product_code) values (null, ?, ?)
Hibernate: insert into book (isbn, id) values (?, ?)
Hibernate: select this_.id as id0_0_, this_1_.version as version0_0_, this_1_.product_code as product3_0_0_, this_.isbn as isbn1_0_ from book this_ inner join product this_1_ on this_.id=this_1_.id
[com.example.Book : 2]
Hibernate: select this_.id as id0_0_, this_.version as version0_0_, this_.product_code as product3_0_0_, this_1_.isbn as isbn1_0_, case when this_1_.id is not null then 1 when this_.id is not null then 0 end as clazz_0_ from product this_ left outer join book this_1_ on this_.id=this_1_.id
[com.example.Product : 1, com.example.Book : 2]
Hibernate: delete from book where id=?
Hibernate: delete from product where id=? and version=?
Hibernate: select this_.id as id0_0_, this_1_.version as version0_0_, this_1_.product_code as product3_0_0_, this_.isbn as isbn1_0_ from book this_ inner join product this_1_ on this_.id=this_1_.id
[]
Hibernate: select this_.id as id0_0_, this_.version as version0_0_, this_.product_code as product3_0_0_, this_1_.isbn as isbn1_0_, case when this_1_.id is not null then 1 when this_.id is not null then 0 end as clazz_0_ from product this_ left outer join book this_1_ on this_.id=this_1_.id
[com.example.Product : 1]

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使用Grails 2.2.2