删除对象时使用Hibernate违反MS-SQL中的UNIQUE KEY约束

Question

The application we have used MySQL until today and everything was fine. Now we need to use MSSQL.

A lot of our unit tests are now failing. A sample is as follows:

Caused by: java.sql.BatchUpdateException: 
Violation of UNIQUE KEY constraint 'UQ__field_ty__5068257C6DE5E37D'. 
Cannot insert duplicate key in object 'dbo.field_type_mapping'. 
The duplicate key value is (<NULL>, -11).

As I said, this test is successful when using MySQL.

The table field_type_mapping has a constraint:

/****** Object:  Index [UQ__field_ty__5068257C6DE5E37D]
ALTER TABLE [dbo].[field_type_mapping] ADD UNIQUE NONCLUSTERED 
(
    [mapping_entity_id] ASC,
    [field_type_id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO

The test is as follows and the exception is thrown at the last line of this test:

Invoice document = documentDao.get(5000);
assertEquals("Document should have exactly one reference field!", 1, document.getFieldTypeMappings().size());
assertEquals("Document should have exactly one item!", 1, document.getDocumentItems().size());

Set<InvoiceItem> items = document.getDocumentItems();
InvoiceItem item = items.iterator().next();
assertEquals("Document's item should have no reference field!", 0, item.getFieldTypeMappings().size());

ReferenceFieldType referenceFieldType = referenceFieldTypeDao.get(-11L);
FieldTypeMapping documentFieldType = new FieldTypeMapping();
documentFieldType.setFieldType(referenceFieldType);
documentFieldType.setFieldValue("a value");
document.addFieldTypeMapping(documentFieldType);

FieldTypeMapping documentItemFieldType = new FieldTypeMapping();
documentItemFieldType.setFieldType(referenceFieldType);
documentItemFieldType.setFieldValue("another value");
item.addFieldTypeMapping(documentItemFieldType);
documentDao.save(document);
flush();

document = documentDao.get(id);
assertEquals("Reference object for document not added!", 2, document.getFieldTypeMappings().size());
items = document.getDocumentItems();
item = items.iterator().next();
assertEquals("Reference object for document item not added!", 1, item.getFieldTypeMappings().size());

document.addFieldTypeMapping(documentFieldType);
item.addFieldTypeMapping(documentItemFieldType);
documentDao.save(document);
flush();

document = documentDao.get(id);
assertEquals("Number of reference object should not have changed for document!", 2, document.getFieldTypeMappings().size());
items = document.getDocumentItems();
item = items.iterator().next();
assertEquals("Number of reference object should not have changed for document' item!", 1, item.getFieldTypeMappings().size());

document.getFieldTypeMappings().remove(documentFieldType);
item.getFieldTypeMappings().remove(documentItemFieldType);
documentDao.save(document);
flush();  // Exception is thrown at this point..

My understanding is something is wrong with:

item.getFieldTypeMappings().remove(documentItemFieldType);

as the exception is mentioning id -11 ?

The hibernate code for removal is as follows:

@OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
@Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE,
        org.hibernate.annotations.CascadeType.DETACH,
        org.hibernate.annotations.CascadeType.LOCK})
@JoinColumn(name = "mapping_entity_id")
@XmlTransient
@Fetch(FetchMode.SELECT)
public Set<FieldTypeMapping> getFieldTypeMappings() {
    return fieldTypeMappings;
}

As I am pretty novice with this I do not even understand what might be wrong. How can I fix this issue? Is this an issue with hibernate and how it handles the queries? I also want to mention that all the db is created with hibernate as well, no manual sql execution and db creation is made.

Answer 1

You usually need the ability to have a null FK when you may not know the value at the time of entering the data, especially whilst you know other values to be entered.

To allow nulls in an FK generally all you have to do is allow nulls on the field that has the FK. The null value is separate from the idea of it being an FK. - This is what I believe you need to do.

Whether it is unique or not unique relates to whether the table has a one-one or a one-many relationship to the parent table.