example_parentchild.po

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#, no-c-format
msgid ""
"To tighten things up a bit, we could create an <literal>addChild()</literal> "
"method of <literal>Parent</literal>."
msgstr ""
"为了让事情变得井井有条，可以为<literal>Parent</literal>加一个"
"<literal>addChild()</literal>方法。"

#. Tag: programlisting
#: example_parentchild.xml:141
#, no-c-format
msgid ""
"<![CDATA[public void addChild(Child c) {\n"
"    c.setParent(this);\n"
"    children.add(c);\n"
"}]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:143
#, no-c-format
msgid "Now, the code to add a <literal>Child</literal> looks like"
msgstr "现在，添加<literal>Child</literal>的代码就是这样"

#. Tag: programlisting
#: example_parentchild.xml:147
#, no-c-format
msgid ""
"<![CDATA[Parent p = (Parent) session.load(Parent.class, pid);\n"
"Child c = new Child();\n"
"p.addChild(c);\n"
"session.save(c);\n"
"session.flush();]]>"
msgstr ""

#. Tag: title
#: example_parentchild.xml:152
#, no-c-format
msgid "Cascading life cycle"
msgstr "级联生命周期（Cascading life cycle）"

#. Tag: para
#: example_parentchild.xml:154
#, no-c-format
msgid ""
"The explicit call to <literal>save()</literal> is still annoying. We will "
"address this by using cascades."
msgstr ""
"需要显式调用<literal>save()</literal>仍然很麻烦，我们可以用级联来解决这个问"
"题。"

#. Tag: programlisting
#: example_parentchild.xml:159
#, no-c-format
msgid ""
"<![CDATA[<set name=\"children\" inverse=\"true\" cascade=\"all\">\n"
"    <key column=\"parent_id\"/>\n"
"    <one-to-many class=\"Child\"/>\n"
"</set>]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:161
#, no-c-format
msgid "This simplifies the code above to"
msgstr "这样上面的代码可以简化为："

#. Tag: programlisting
#: example_parentchild.xml:165
#, no-c-format
msgid ""
"<![CDATA[Parent p = (Parent) session.load(Parent.class, pid);\n"
"Child c = new Child();\n"
"p.addChild(c);\n"
"session.flush();]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:167
#, no-c-format
msgid ""
"Similarly, we don't need to iterate over the children when saving or "
"deleting a <literal>Parent</literal>. The following removes <literal>p</"
"literal> and all its children from the database."
msgstr ""
"同样的，保存或删除<literal>Parent</literal>对象的时候并不需要遍历其子对象。 "
"下面的代码会删除对象<literal>p</literal>及其所有子对象对应的数据库记录。"

#. Tag: programlisting
#: example_parentchild.xml:172
#, no-c-format
msgid ""
"<![CDATA[Parent p = (Parent) session.load(Parent.class, pid);\n"
"session.delete(p);\n"
"session.flush();]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:174
#, no-c-format
msgid "However, this code"
msgstr "然而，这段代码"

#. Tag: programlisting
#: example_parentchild.xml:178
#, no-c-format
msgid ""
"<![CDATA[Parent p = (Parent) session.load(Parent.class, pid);\n"
"Child c = (Child) p.getChildren().iterator().next();\n"
"p.getChildren().remove(c);\n"
"c.setParent(null);\n"
"session.flush();]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:180
#, no-c-format
msgid ""
"will not remove <literal>c</literal> from the database; it will ony remove "
"the link to <literal>p</literal> (and cause a <literal>NOT NULL</literal> "
"constraint violation, in this case). You need to explicitly <literal>delete()"
"</literal> the <literal>Child</literal>."
msgstr ""
"不会从数据库删除<literal>c</literal>；它只会删除与<literal>p</literal>之间的"
"连接（并且会导致违反<literal>NOT NULL</literal>约束，在这个例子中）。你需要显"
"式调用<literal>delete()</literal>来删除<literal>Child</literal>。"

#. Tag: programlisting
#: example_parentchild.xml:186
#, no-c-format
msgid ""
"<![CDATA[Parent p = (Parent) session.load(Parent.class, pid);\n"
"Child c = (Child) p.getChildren().iterator().next();\n"
"p.getChildren().remove(c);\n"
"session.delete(c);\n"
"session.flush();]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:188
#, no-c-format
msgid ""
"Now, in our case, a <literal>Child</literal> can't really exist without its "
"parent. So if we remove a <literal>Child</literal> from the collection, we "
"really do want it to be deleted. For this, we must use <literal>cascade="
"\"all-delete-orphan\"</literal>."
msgstr ""
"在我们的例子中，如果没有父对象，子对象就不应该存在，如果将子对象从collection"
"中移除，实际上我们是想删除它。要实现这种要求，就必须使用<literal>cascade="
"\"all-delete-orphan\"</literal>。"

#. Tag: programlisting
#: example_parentchild.xml:194
#, no-c-format
msgid ""
"<![CDATA[<set name=\"children\" inverse=\"true\" cascade=\"all-delete-orphan"
"\">\n"
"    <key column=\"parent_id\"/>\n"
"    <one-to-many class=\"Child\"/>\n"
"</set>]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:196
#, no-c-format
msgid ""
"Note: even though the collection mapping specifies <literal>inverse=\"true"
"\"</literal>, cascades are still processed by iterating the collection "
"elements. So if you require that an object be saved, deleted or updated by "
"cascade, you must add it to the collection. It is not enough to simply call "
"<literal>setParent()</literal>."
msgstr ""
"注意：即使在collection一方的映射中指定<literal>inverse=\"true\"</literal>，级"
"联仍然是通过遍历collection中的元素来处理的。如果你想要通过级联进行子对象的插"
"入、删除、更新操作，就必须把它加到collection中，只调用<literal>setParent()</"
"literal>是不够的。"

#. Tag: title
#: example_parentchild.xml:206
#, no-c-format
msgid "Cascades and <literal>unsaved-value</literal>"
msgstr ""
"级联与<literal>未保存值</literal>（Cascades and <literal>unsaved-value</"
"literal>）"

#. Tag: para
#: example_parentchild.xml:208
#, no-c-format
msgid ""
"Suppose we loaded up a <literal>Parent</literal> in one <literal>Session</"
"literal>, made some changes in a UI action and wish to persist these changes "
"in a new session by calling <literal>update()</literal>. The "
"<literal>Parent</literal> will contain a collection of childen and, since "
"cascading update is enabled, Hibernate needs to know which children are "
"newly instantiated and which represent existing rows in the database. Lets "
"assume that both <literal>Parent</literal> and <literal>Child</literal> have "
"genenerated identifier properties of type <literal>Long</literal>. Hibernate "
"will use the identifier and version/timestamp property value to determine "
"which of the children are new. (See <xref linkend=\"objectstate-saveorupdate"
"\"/>.) <emphasis>In Hibernate3, it is no longer necessary to specify an "
"<literal>unsaved-value</literal> explicitly.</emphasis>"
msgstr ""
"假设我们从<literal>Session</literal>中装入了一个<literal>Parent</literal>对"
"象，用户界面对其进行了修改，然后希望在一个新的Session里面调用<literal>update"
"()</literal>来保存这些修改。对象<literal>Parent</literal>包含了子对象的集合，"
"由于打开了级联更新，Hibernate需要知道哪些Child对象是新实例化的，哪些代表数据"
"库中已经存在的记录。我们假设<literal>Parent</literal>和<literal>Child</"
"literal>对象的标识属性都是自动生成的，类型为<literal>java.lang.Long</"
"literal>。Hibernate会使用标识属性的值，和version 或 timestamp 属性，来判断哪"
"些子对象是新的。(参见<xref linkend=\"objectstate-saveorupdate\"/>.) "
"<emphasis>在 Hibernate3 中,显式指定<literal>unsaved-value</literal>不再是必须"
"的了。</emphasis>"

#. Tag: para
#: example_parentchild.xml:220
#, no-c-format
msgid ""
"The following code will update <literal>parent</literal> and <literal>child</"
"literal> and insert <literal>newChild</literal>."
msgstr ""
"下面的代码会更新<literal>parent</literal>和<literal>child</literal>对象，并且"
"插入<literal>newChild</literal>对象。"

#. Tag: programlisting
#: example_parentchild.xml:225
#, no-c-format
msgid ""
"<![CDATA[//parent and child were both loaded in a previous session\n"
"parent.addChild(child);\n"
"Child newChild = new Child();\n"
"parent.addChild(newChild);\n"
"session.update(parent);\n"
"session.flush();]]>"
msgstr ""

#. Tag: para
#: example_parentchild.xml:227
#, no-c-format
msgid ""
"Well, that's all very well for the case of a generated identifier, but what "
"about assigned identifiers and composite identifiers? This is more "
"difficult, since Hibernate can't use the identifier property to distinguish "
"between a newly instantiated object (with an identifier assigned by the "
"user) and an object loaded in a previous session. In this case, Hibernate "
"will either use the timestamp or version property, or will actually query "
"the second-level cache or, worst case, the database, to see if the row "
"exists."
msgstr ""
"这对于自动生成标识的情况是非常好的，但是自分配的标识和复合标识怎么办呢？这是"
"有点麻烦，因为Hibernate没有办法区分新实例化的对象（标识被用户指定了）和前一个"
"Session装入的对象。在这种情况下，Hibernate会使用timestamp或version属性，或者"
"查询第二级缓存，或者最坏的情况，查询数据库，来确认是否此行存在。"

#. Tag: title
#: example_parentchild.xml:260
#, no-c-format
msgid "Conclusion"
msgstr "结论"

#. Tag: para
#: example_parentchild.xml:262
#, no-c-format
msgid ""
"There is quite a bit to digest here and it might look confusing first time "
"around. However, in practice, it all works out very nicely. Most Hibernate "
"applications use the parent / child pattern in many places."
msgstr ""
"这里有不少东西需要融会贯通，可能会让新手感到迷惑。但是在实践中它们都工作地非"
"常好。大部分Hibernate应用程序都会经常用到父子对象模式。"

#. Tag: para
#: example_parentchild.xml:267
#, no-c-format
msgid ""
"We mentioned an alternative in the first paragraph. None of the above issues "
"exist in the case of <literal>&lt;composite-element&gt;</literal> mappings, "
"which have exactly the semantics of a parent / child relationship. "
"Unfortunately, there are two big limitations to composite element classes: "
"composite elements may not own collections, and they should not be the child "
"of any entity other than the unique parent."
msgstr ""
"在第一段中我们曾经提到另一个方案。上面的这些问题都不会出现在<literal>&lt;"
"composite-element&gt;</literal>映射中，它准确地表达了父子关系的语义。很不幸复"
"合元素还有两个重大限制:复合元素不能拥有collections，并且，除了用于惟一的父对"
"象外，它们不能再作为其它任何实体的子对象。"