XSD中的可选键 [英] Optional key in XSD
问题描述
我已经在根元素上创建了key/keyref，以便基于指定的元素创建文档范围内的唯一性.
I've created a key/keyref on the root element in order to create document-wide uniqueness based on the specified element.
因此，通过.//foo/@name，在foo的所有实例中每次出现的@name都必须是唯一的.对于.//bar/@name同样.这似乎工作正常.这些分别由.//foo-ref/@name-ref和.//bar-ref/@name-ref引用，它们也在根节点上定义.
Therefore, via .//foo/@name every occurrence of @name across all instances of foo must be unique; likewise for .//bar/@name. This seems to be working fine. These are referenced by .//foo-ref/@name-ref and .//bar-ref/@name-ref respectively, also defined at the root node.
但是，我已经收集到一个不能创建 optional 密钥的功能，这带来了一些问题.从语义上来说，根据符合条件的文档的性质，在foo或bar的每个单个实例上都不需要密钥. foo-ref/@name-ref的实例显然需要针对现有的foo/@name，但是对于foo没有@name来说在语义上不是无效的.
However, I've gathered that one cannot create an optional key, and this is presenting a bit of a problem. Semantically, by the nature of the conforming documents, a key is not required on every single instance of foo or bar. The instances of foo-ref/@name-ref would obviously need to target an existing foo/@name, but it isn't semantically invalid for a foo to be without a @name.
有什么解决方法吗?我不喜欢消费者必须为每个单个元素定义键的想法，而合理的情况是只有少数几个键需要它们.
Is there any work-around for this? I don't like the idea of consumers having to define a key for every single element, when reasonably only a handful will need them.
这是示例架构(，我当然没有部署某些foobar架构，但是结构相同；这只是我一直在尝试的测试架构)
Here's the example schema (of course, I'm not deploying some foobar schema, but the structure is identical; this is just a testing schema I've been toying with)
<xs:schema elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:complexType name="ref">
<xs:attribute name="name-ref" type="xs:string" use="required" />
</xs:complexType>
<xs:complexType name="obj">
<xs:attribute name="name" type="xs:string" use="optional" />
</xs:complexType>
<xs:complexType name="foo">
<xs:complexContent>
<xs:extension base="obj">
<xs:sequence>
<xs:choice maxOccurs="unbounded">
<xs:element name="foo" type="foo" />
<xs:element name="bar" type="bar" />
<xs:element name="foo-ref" type="foo-ref" />
<xs:element name="bar-ref" type="bar-ref" />
</xs:choice>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="foo-ref">
<xs:complexContent>
<xs:extension base="ref" />
</xs:complexContent>
</xs:complexType>
<xs:complexType name="bar">
<xs:complexContent>
<xs:extension base="obj">
<xs:sequence>
<xs:choice maxOccurs="unbounded">
<xs:element name="bar" type="bar" />
<xs:element name="qux" type="qux" />
<xs:element name="bar-ref" type="bar-ref" />
</xs:choice>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="bar-ref">
<xs:complexContent>
<xs:extension base="ref" />
</xs:complexContent>
</xs:complexType>
<xs:complexType name="qux">
<xs:simpleContent>
<xs:extension base="xs:string" />
</xs:simpleContent>
</xs:complexType>
<xs:element name="root">
<xs:complexType>
<xs:sequence>
<xs:element name="foo" type="foo" maxOccurs="unbounded" />
</xs:sequence>
</xs:complexType>
<xs:key name="foo">
<xs:selector xpath=".//foo" />
<xs:field xpath="@name" />
</xs:key>
<xs:key name="bar">
<xs:selector xpath=".//bar" />
<xs:field xpath="@name" />
</xs:key>
<xs:keyref name="foo-ref" refer="foo">
<xs:selector xpath=".//foo-ref" />
<xs:field xpath="@name-ref" />
</xs:keyref>
<xs:keyref name="bar-ref" refer="bar">
<xs:selector xpath=".//bar-ref" />
<xs:field xpath="@name-ref" />
</xs:keyref>
</xs:element>
</xs:schema>
附录
只需感谢@PetruGardea，就可以对我的修订进行跟进.那么unique可以被keyref引用，谁知道呢? (显然不是我)
Addendum
Just following up with my revisions thanks to @PetruGardea. So unique can be referenced by a keyref, who knew? (not me apparently)
<xs:element name="root">
<xs:complexType>
<xs:sequence>
<xs:element name="foo" type="foo" maxOccurs="unbounded" />
</xs:sequence>
</xs:complexType>
<xs:keyref name="foo-ref" refer="foo">
<xs:selector xpath=".//foo-ref" />
<xs:field xpath="@name-ref" />
</xs:keyref>
<xs:keyref name="bar-ref" refer="bar">
<xs:selector xpath=".//bar-ref" />
<xs:field xpath="@name-ref" />
</xs:keyref>
<!--
the use of xs:unique here, in lieu of xs:key allows for
nullable "keys", retaining referential integrity with the
above defined keyrefs. awesome possum.
-->
<xs:unique name="foo">
<xs:selector xpath=".//foo" />
<xs:field xpath="@name" />
</xs:unique>
<xs:unique name="bar">
<xs:selector xpath=".//bar" />
<xs:field xpath="@name" />
</xs:unique>
</xs:element>
推荐答案
使用 xsd:unique ;与键不同，它的匹配值是唯一的或nil(nil或不存在).
Use xsd:unique; unlike a key, its matched value is either unique or nil (nil or not present).
示例:
<?xml version="1.0" encoding="utf-8" ?>
<!-- XML Schema generated by QTAssistant/XSD Module (http://www.paschidev.com) -->
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:element name="root">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="uk" maxOccurs="unbounded">
<xsd:complexType>
<xsd:attribute name="name" type="xsd:string"/>
</xsd:complexType>
</xsd:element>
<xsd:element name="fk" maxOccurs="unbounded">
<xsd:complexType>
<xsd:attribute name="name" type="xsd:string"/>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:unique name="uq">
<xsd:selector xpath="uk"/>
<xsd:field xpath="@name"/>
</xsd:unique>
<xsd:keyref name="fk" refer="uq">
<xsd:selector xpath="fk"/>
<xsd:field xpath="@name"/>
</xsd:keyref>
</xsd:element>
</xsd:schema>
样本(有效)XML:
<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<!-- Sample XML generated by QTAssistant (http://www.paschidev.com) -->
<root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<uk name="name1"/>
<uk />
<fk/>
<fk name="name1"/>
</root>
这篇关于XSD中的可选键的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
