Configure the association between tables and tables in the. Hbm.xml mapping file in the Hibernate framework

The association relationship in 1.Hibernate can be divided into:

One-way relationship: Only one table points to another table.

Bidirectional relationship: Tables and tables can be pointed to each other.

2. Depending on the associated table, it can be divided into:

1 to 1 relations

1 to multiple relationships

Multi-Many-to-many relationships

For example: 1 customers can correspond to multiple orders, is 1 to many of the relationship.

(1) 1 pairs of multiple associations :

One -way Many-to-many 1: Using <many-to-one/> mapping, a foreign key column is added to the database.

Use the following code in a multiport. hbm.xml file:

<many-to-one name= "Multi-terminal entity class corresponding to property name" column= "foreign key column name" class= "Association class name (corresponding foreign key class name)"/>

one-way 1 to many: Using <many-to-one/> Mapping, foreign key columns are added in the database

Use the following code in the 1-port. hbm.xml File:

<set name= "1-Port corresponding property name" >
	<key column = "Foreign key column name"/>
	<one-to-many name= "Association class name"/>
</set>

bidirectional 1 to many: Use <set&gt at 1 end, use <many-to-one/&gt in multiport, and generally use this association in actual development

(2) 1 to 1 association : 4 Types (primary table: Table with foreign keys; foreign key table: Table with foreign key)

based on the foreign Key one-way association : a special one-way 1 relationship, multi-terminal is also 1

Use the following code in the corresponding entity class. hbm.xml file in the primary table:

<many-to-one name= "Property name" column= "foreign key column name" class= "Association table name" unique= "true" cascade= "all"/>

Unique= "true": 1 to 1, default to False for 1.

Cascade= "All": represents an operation on the associated object while the current entity object is being manipulated.

Bidirectional Association based on foreign key :

Foreign keys can be placed on either side, at the end of the foreign key to the use of <many-to-one/>, the property unique property value to see True, the external key corresponding to the other end of the set <one-to-one/> based on the primary key one-way association :

Define a primary key generation policy in the primary table corresponding to the entity class. Hbm.xml mapping File:

<!--foreign: represents generating primary key with associated entity-->
 <generator class= "foreign" >
            <param name= "Property" > Association property name </param> </generator> in current class
 

and set the <one-to-one/> association in the main table corresponding entity class. hbm.xml file:

<one-to-one name= "Property name" class= "Association class name (foreign key class name)" Constrained= "true"/>

Constrained= ' true ': The primary key of the datasheet that represents the current entity mapping is also used as a foreign key association to specify the data table for the entity class mapping.

Bidirectional Association based on primary key :

Both ends use <one-to-one/>, where the primary key generation policy for one end must be generated by the associated entity:

<generator class= "foreign" >
	<param name= "Property" > Associated attribute name in current class </param> </generator
>