java 使用 Hibernate 映射 ArrayList
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Map ArrayList with Hibernate
提问by Martin Preusse
I just coded my first Hibernate examples.
我刚刚编写了我的第一个 Hibernate 示例。
The database connection works and I understand how I can map a String from a POJO to a database field:
数据库连接有效，我了解如何将字符串从 POJO 映射到数据库字段：
private String firstName;
And in the mapping file:
在映射文件中：
<property name="firstName" type="java.lang.String">
<column name="FIRSTNAME" />
</property>
But how can I map an ArrayList to the database? A simpl example from the mapping xml file would be appreciated.
但是如何将 ArrayList 映射到数据库？来自映射 xml 文件的简单示例将不胜感激。
Cheers
干杯
UPDATE
更新
I switched to List instead of ArrayList found an example. Now I map as follows:
我切换到 List 而不是 ArrayList 找到了一个例子。现在我映射如下：
<list name="test" inverse="false" table="CONTACT" lazy="true">
<key>
<column name="ID" />
</key>
<list-index></list-index>
<element type="java.lang.String">
<column name="TEST" />
</element>
</list>
Unfortunately, I get an exception that I do not understand:
不幸的是，我遇到了一个我不明白的异常：
Exception in thread "main" org.hibernate.MappingException: Foreign key (FK6382B0003257FF7F:CONTACT [ID])) must have same number of columns as the referenced primary key (CONTACT [ID,idx])
Any ideas?
有任何想法吗？
Cheers
干杯
回答by Vincent Ramdhanie
I notice that you are using XML to map your POJOs. You will find some information about that here.
我注意到您正在使用 XML 来映射您的 POJO。您将在此处找到一些相关信息。
for example:
例如：
<list name="myArrayListProperty" cascade="all">
<key column="parent_id"/>
<index column="idx"/>
<one-to-many class="WhatIsInTheList"/>
</list>
However, using annotations have some advantages. This linkwill explain how to map any collection using annotations.
但是，使用注释有一些优点。此链接将解释如何使用注释映射任何集合。
回答by Alberto Vazquez
You have a little error in the XML configuration:
您在 XML 配置中有一个小错误：
When you have a list the solution to map this list using a database is to link with a additional table, so instead of doing:
当您有一个列表时，使用数据库映射此列表的解决方案是链接一个附加表，而不是执行以下操作：
<list name="test" inverse="false" table="CONTACT" lazy="true">
<key>
<column name="ID" />
</key>
<list-index></list-index>
<element type="java.lang.String">
<column name="TEST" />
</element>
</list>
You should have to do map to a new data table that holds the list values:
您应该映射到包含列表值的新数据表：
<list name="test" inverse="false" table="CONTACT_test" lazy="true">
<key>
<column name="ID" />
</key>
<list-index></list-index>
<element type="java.lang.String">
<column name="TEST" />
</element>
</list>
Hibernate automatically creates the new table for you.
Hibernate 会自动为您创建新表。
回答by Bozho
See the collection mappingsection of the docs. There are multiple ways to map a list (one-to-many, many-to-many, a collection of elements). You can map it as a list or as a bag, so read the whole section.
请参阅文档的集合映射部分。有多种方法可以映射列表（一对多、多对多、元素集合）。您可以将其映射为列表或包，因此请阅读整个部分。
