XML XSD Schema - Enforce Unique Attribute Values in Schema
Lets say I have a schema that defines the following XML:
<Values>
<Add Key="Key1">Value 1</Add>
<Add Key="Key2">Value 2</Add>
<Add Key="Key3">Value 3</Add>
<Add Key="Key4">Value 4</Add>
</Values>
I would like, at a schema level, to be able to enforce that the values for the Key attribute are unique, i.e. the example above is valid, but the following example would be invalid:
<Values>
<Add Key="Key1">Value 1</Add>
<Add Key="Key2">Value 2</Add>
<Add Key="Key2">Value 3</Add>
<Add Key="Key3">Value 4</Add>
</Values>
Notice that there are two Add
elements with a Key
of Key2
For reference here is the simple schema:
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:element name="Values">
<xs:complexType>
<xs:sequence>
<xs:element name="Add" maxOccurs="unbounded">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="Key" type="xs:token" use="required"/>
开发者_运维技巧 </xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
I am under the impression that this is not possible at a schema level, however I am all ears.
@BatteryBackupUnit has the right idea, but the syntax is more like:
<xs:element name="Values">
<xs:complexType>
<xs:sequence>
<xs:element ref="Add" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:unique name="UniqueAddKey">
<xs:selector xpath="Add" />
<xs:field xpath="@Key" />
</xs:unique>
</xs:element>
More on Michael Kay's answer: If your schema (XSD) declares a namespace, you must include this in your selection.xpath. If you are using Microsoft Visual Studio 2010, you may find a namespace automatically declared.
<xs:schema id="MyData"
targetNamespace="http://tempuri.org/MyData.xsd"
elementFormDefault="qualified"
xmlns="http://tempuri.org/MyData.xsd"
xmlns:mstns="http://tempuri.org/MyData.xsd"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
>
...
<xs:unique name="UniqueAddKey">
<xs:selector xpath="mstns:Add" />
<xs:field xpath="@Key" />
</xs:unique>
</xs:schema>
you can achieve this by using xs:unique
<xs:element name="Instrument">
<xs:complexType>
<xs:all>
<xs:unique name="ModuleId">
<xs:selector xpath="./*" />
<xs:field xpath="@id" />
</xs:unique>
</xs:all>
</xs:complexType>
</xs:element>
The above example will enforce a unique attribute "id" for all Instrument Elements. there's also xs:key, which can be used to establish a Primary Key - Foreign Key relationship: http://www.datypic.com/books/defxmlschema/chapter17.html
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