Hibernate one-to-many and two-way association mapping method and its advantages and disadvantages (to be continued)

The basic principle of a one-to-many correlation mapping and a multi-pair association map implementation is the same, with one end of a foreign key pointing at one end of the foreign key, and the main difference being the difference between the maintenance side.
The difference between them is that they maintain different relationships:

A one-to-many association mapping refers to the data at the end of the load at the same time

Many-to-one association mappings are data that loads one end of the data at the same time

A one-way-to-multi-association mapping maintains relationships at one end, with the following drawbacks:

You must save one end before you can save a side, so when you save a side of the many one side does not know whether there is the corresponding data at the end, so you can only set the maintenance of the relationship field to NULL, if non-empty will not be saved. Because the relationship is maintained at one end, an extra UPDATE statement is issued to maintain the foreign key relationship at one end of the save.

The following example illustrates the mapping method for configuring one-to-many unidirectional and bidirectional associations:

Refer to one end and multi-terminal class structure reference this article: Hibernate configuration of a one-to-many association map and its cascade deletion issues

Configuration of a one-to-many bidirectional association map (refer to the article provided above):

Mapping with <key> tags at one end of the collection:

<set name= "Quesion" inverse= "true" cascade= "delete" ><key column= "Question_type_name"/><one-to-many class= "Question"/></set>

Add a foreign key to the private Questiontype questiontype at one end; Mapping with <many-to-one> Tags:

<many-to-one name= "Questiontype" column= "Question_type_name"/>

A one-to-many bi-directional association mapping generally lets many one end maintain relationships, so it is necessary to set the inverse property to true, which means that this segment does not maintain relationships and is handed over to the other side for maintenance. You can also use the SET CASCADE to cascade operations, such as the Cascade Delete setting for the previous article: cascade= "Delete", which represents deleting all data at one end of the associated multi-side.

One-to-many unidirectional association mappings:

A one-to-many-way association mapping of many end question does not need to join the foreign key private Questiontype questiontype; You only need to map the <key> tag at one end of the collection, and the mapping code is as follows:

<set name= "Quesion" inverse= "true" cascade= "delete" ><key column= "Question_type_name"/><one-to-many class= "Question"/></set>

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Keywords: Hibernate, one-to-many

Further information reference: http://blog.csdn.net/liangoo7/article/details/8070166

Hibernate one-to-many and two-way association mapping method and its advantages and disadvantages (to be continued)