example_parentchild.po

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msgid ""
msgstr ""
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"Report-Msgid-Bugs-To: http://bugs.kde.org\n"
"POT-Creation-Date: 2007-10-25 01:01+0000\n"
"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
"Language-Team: LANGUAGE <[e-mail]>\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"

#. Tag: title
#: example_parentchild.xml:5
#, no-c-format
msgid "Example: Parent/Child"
msgstr "示例：父子关系(Parent Child Relationships)"

#. Tag: para
#: example_parentchild.xml:7
#, no-c-format
msgid ""
"One of the very first things that new users try to do with Hibernate is to "
"model a parent / child type relationship. There are two different approaches "
"to this. For various reasons the most convenient approach, especially for "
"new users, is to model both <literal>Parent</literal> and <literal>Child</"
"literal> as entity classes with a <literal>&lt;one-to-many&gt;</literal> "
"association from <literal>Parent</literal> to <literal>Child</literal>. (The "
"alternative approach is to declare the <literal>Child</literal> as a "
"<literal>&lt;composite-element&gt;</literal>.) Now, it turns out that "
"default semantics of a one to many association (in Hibernate) are much less "
"close to the usual semantics of a parent / child relationship than those of "
"a composite element mapping. We will explain how to use a "
"<emphasis>bidirectional one to many association with cascades</emphasis> to "
"model a parent / child relationship efficiently and elegantly. It's not at "
"all difficult!"
msgstr ""
"刚刚接触Hibernate的人大多是从父子关系（parent / child type relationship）的建"
"模入手的。父子关系的建模有两种方法。由于种种原因，最方便的方法是把"
"<literal>Parent</literal>和<literal>Child</literal>都建模成实体类，并创建一个"
"从<literal>Parent</literal>指向<literal>Child</literal>的&lt;one-to-many&gt;"
"关联，对新手来说尤其如此。还有一种方法，就是将<literal>Child</literal>声明为"
"一个<literal>&lt;composite-element&gt;</literal>（组合元素）。 事实上在"
"Hibernate中one to many关联的默认语义远没有composite element贴近parent / child"
"关系的通常语义。下面我们会阐述如何使用<emphasis>带有级联的双向一对多关联"
"(bidirectional one to many association with cascades)</emphasis>去建立有效、"
"优美的parent / child关系。这一点也不难！"

#. Tag: title
#: example_parentchild.xml:21
#, no-c-format
msgid "A note about collections"
msgstr "关于collections需要注意的一点"

#. Tag: para
#: example_parentchild.xml:23
#, no-c-format
msgid ""
"Hibernate collections are considered to be a logical part of their owning "
"entity; never of the contained entities. This is a crucial distinction! It "
"has the following consequences:"
msgstr ""
"Hibernate collections被当作其所属实体而不是其包含实体的一个逻辑部分。这非常重"
"要！它主要体现为以下几点："

#. Tag: para
#: example_parentchild.xml:30
#, no-c-format
msgid ""
"When we remove / add an object from / to a collection, the version number of "
"the collection owner is incremented."
msgstr "当删除或增加collection中对象的时候，collection所属者的版本值会递增。"

#. Tag: para
#: example_parentchild.xml:36
#, no-c-format
msgid ""
"If an object that was removed from a collection is an instance of a value "
"type (eg, a composite element), that object will cease to be persistent and "
"its state will be completely removed from the database. Likewise, adding a "
"value type instance to the collection will cause its state to be immediately "
"persistent."
msgstr ""
"如果一个从collection中移除的对象是一个值类型(value type)的实例，比如"
"composite element，那么这个对象的持久化状态将会终止，其在数据库中对应的记录会"
"被删除。同样的，向collection增加一个value type的实例将会使之立即被持久化。"

#. Tag: para
#: example_parentchild.xml:44
#, no-c-format
msgid ""
"On the other hand, if an entity is removed from a collection (a one-to-many "
"or many-to-many association), it will not be deleted, by default. This "
"behaviour is completely consistent - a change to the internal state of "
"another entity should not cause the associated entity to vanish! Likewise, "
"adding an entity to a collection does not cause that entity to become "
"persistent, by default."
msgstr ""
"另一方面，如果从一对多或多对多关联的collection中移除一个实体，在缺省情况下这"
"个对象并不会被删除。这个行为是完全合乎逻辑的－－改变一个实体的内部状态不应该"
"使与它关联的实体消失掉！同样的，向collection增加一个实体不会使之被持久化。"

#. Tag: para
#: example_parentchild.xml:54
#, no-c-format
msgid ""
"Instead, the default behaviour is that adding an entity to a collection "
"merely creates a link between the two entities, while removing it removes "
"the link. This is very appropriate for all sorts of cases. Where it is not "
"appropriate at all is the case of a parent / child relationship, where the "
"life of the child is bound to the life cycle of the parent."
msgstr ""
"实际上，向Collection增加一个实体的缺省动作只是在两个实体之间创建一个连接而"
"已，同样移除的时候也只是删除连接。这种处理对于所有的情况都是合适的。对于父子"
"关系则是完全不适合的，在这种关系下，子对象的生存绑定于父对象的生存周期。"

#. Tag: title
#: example_parentchild.xml:64
#, no-c-format
msgid "Bidirectional one-to-many"
msgstr "双向的一对多关系(Bidirectional one-to-many)"

#. Tag: para
#: example_parentchild.xml:66
#, no-c-format
msgid ""
"Suppose we start with a simple <literal>&lt;one-to-many&gt;</literal> "
"association from <literal>Parent</literal> to <literal>Child</literal>."
msgstr "假设我们要实现一个简单的从Parent到Child的&lt;one-to-many&gt;关联。"

#. Tag: programlisting
#: example_parentchild.xml:71
#, no-c-format
msgid ""
"<![CDATA[<set name=\"children\">\n"
"    <key column=\"parent_id\"/>\n"
"    <one-to-many class=\"Child\"/>\n"
"</set>]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:73
#, no-c-format
msgid "If we were to execute the following code"
msgstr "如果我们运行下面的代码"

#. Tag: programlisting
#: example_parentchild.xml:77
#, no-c-format
msgid ""
"<![CDATA[Parent p = .....;\n"
"Child c = new Child();\n"
"p.getChildren().add(c);\n"
"session.save(c);\n"
"session.flush();]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:79
#, no-c-format
msgid "Hibernate would issue two SQL statements:"
msgstr "Hibernate会产生两条SQL语句："

#. Tag: para
#: example_parentchild.xml:85
#, no-c-format
msgid ""
"an <literal>INSERT</literal> to create the record for <literal>c</literal>"
msgstr "一条<literal>INSERT</literal>语句，为<literal>c</literal>创建一条记录"

#. Tag: para
#: example_parentchild.xml:88
#, no-c-format
msgid ""
"an <literal>UPDATE</literal> to create the link from <literal>p</literal> to "
"<literal>c</literal>"
msgstr ""
"一条<literal>UPDATE</literal>语句，创建从<literal>p</literal>到<literal>c</"
"literal>的连接"

#. Tag: para
#: example_parentchild.xml:95
#, no-c-format
msgid ""
"This is not only inefficient, but also violates any <literal>NOT NULL</"
"literal> constraint on the <literal>parent_id</literal> column. We can fix "
"the nullability constraint violation by specifying <literal>not-null=\"true"
"\"</literal> in the collection mapping:"
msgstr ""
"这样做不仅效率低，而且违反了列<literal>parent_id</literal>非空的限制。我们可"
"以通过在集合类映射上指定<literal>not-null=\"true\"</literal>来解决违反非空约"
"束的问题："

#. Tag: programlisting
#: example_parentchild.xml:101
#, no-c-format
msgid ""
"<![CDATA[<set name=\"children\">\n"
"    <key column=\"parent_id\" not-null=\"true\"/>\n"
"    <one-to-many class=\"Child\"/>\n"
"</set>]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:103
#, no-c-format
msgid "However, this is not the recommended solution."
msgstr "然而，这并非是推荐的解决方法。"

#. Tag: para
#: example_parentchild.xml:106
#, no-c-format
msgid ""
"The underlying cause of this behaviour is that the link (the foreign key "
"<literal>parent_id</literal>) from <literal>p</literal> to <literal>c</"
"literal> is not considered part of the state of the <literal>Child</literal> "
"object and is therefore not created in the <literal>INSERT</literal>. So the "
"solution is to make the link part of the <literal>Child</literal> mapping."
msgstr ""
"这种现象的根本原因是从<literal>p</literal>到<literal>c</literal>的连接（外键"
"parent_id）没有被当作<literal>Child</literal>对象状态的一部分，因而没有在"
"INSERT语句中被创建。因此解决的办法就是把这个连接添加到Child的映射中。"

#. Tag: programlisting
#: example_parentchild.xml:113
#, no-c-format
msgid ""
"<![CDATA[<many-to-one name=\"parent\" column=\"parent_id\" not-null=\"true\"/"
">]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:115
#, no-c-format
msgid ""
"(We also need to add the <literal>parent</literal> property to the "
"<literal>Child</literal> class.)"
msgstr ""
"（我们还需要为类<literal>Child</literal>添加<literal>parent</literal>属性）"

#. Tag: para
#: example_parentchild.xml:119
#, no-c-format
msgid ""
"Now that the <literal>Child</literal> entity is managing the state of the "
"link, we tell the collection not to update the link. We use the "
"<literal>inverse</literal> attribute."
msgstr ""
"现在实体<literal>Child</literal>在管理连接的状态，为了使collection不更新连"
"接，我们使用<literal>inverse</literal>属性。"

#. Tag: programlisting
#: example_parentchild.xml:124
#, no-c-format
msgid ""
"<![CDATA[<set name=\"children\" inverse=\"true\">\n"
"    <key column=\"parent_id\"/>\n"
"    <one-to-many class=\"Child\"/>\n"
"</set>]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:126
#, no-c-format
msgid "The following code would be used to add a new <literal>Child</literal>"
msgstr "下面的代码是用来添加一个新的<literal>Child</literal>"

#. Tag: programlisting
#: example_parentchild.xml:130
#, no-c-format
msgid ""
"<![CDATA[Parent p = (Parent) session.load(Parent.class, pid);\n"
"Child c = new Child();\n"
"c.setParent(p);\n"
"p.getChildren().add(c);\n"
"session.save(c);\n"
"session.flush();]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:132
#, no-c-format
msgid "And now, only one SQL <literal>INSERT</literal> would be issued!"
msgstr "现在，只会有一条<literal>INSERT</literal>语句被执行！"

#. Tag: para
#: example_parentchild.xml:136