如何编程缩小XSD属性大小？咨询截取属性最后20字符的方法

Got it, let's break down how to handle those extra-long attributes in your XSD and map them to take only the last 20 characters. Here are the most practical approaches depending on your workflow:

1. Directly Use XPath substring() in Your Mapping Tool #

Most XML mapping tools (like Altova MapForce, Talend, Informatica, or even open-source options) support standard XPath functions, which is the easiest way to handle this during mapping.

To grab the last 20 characters of an attribute, use this formula:

substring(yourAttribute, string-length(yourAttribute) - 19)

• Why -19? XPath uses 1-based indexing, so if your attribute is 100 characters long, 100-19=81 starts the substring at the 81st character, giving you characters 81-100 (20 total).

Add a safety check for attributes shorter than 20 characters to avoid errors:

if(string-length(yourAttribute) >= 20) 
then substring(yourAttribute, string-length(yourAttribute) - 19) 
else yourAttribute

Example in a mapping context: If your source attribute is customerId on a user element, the expression would look like:

substring($source/user/@customerId, string-length($source/user/@customerId) - 19)

2. Preprocess XML with XSLT (Before Importing to Mapping Tool) #

If you need to standardize the XML data first (instead of handling it in the mapping tool), use an XSLT stylesheet to truncate the attributes upfront.

Here's a reusable XSLT 1.0 example that targets a specific attribute (e.g., longAttribute):

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <!-- Copy all content by default -->
  <xsl:template match="@*|node()">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()"/>
    </xsl:copy>
  </xsl:template>

  <!-- Truncate the target attribute -->
  <xsl:template match="@longAttribute">
    <xsl:attribute name="longAttribute">
      <xsl:choose>
        <xsl:when test="string-length(.) >= 20">
          <xsl:value-of select="substring(., string-length(.) - 19)"/>
        </xsl:when>
        <xsl:otherwise>
          <xsl:value-of select="."/>
        </xsl:otherwise>
      </xsl:choose>
    </xsl:attribute>
  </xsl:template>
</xsl:stylesheet>

Run this XSLT against your source XML to generate a new file with truncated attributes, then import this cleaned XML into your mapping tool.

3. Document the Rule in Your XSD (For Team/Clarity) #

XSD itself doesn't execute transformation logic, but you can add annotations to explicitly note the truncation requirement for anyone using the schema (including your mapping tool):

<xs:attribute name="longAttribute" type="xs:string">
  <xs:annotation>
    <xs:documentation>
      Mapping Rule: Truncate to the last 20 characters. Use XPath: 
      substring(., string-length(.) - 19) (keep full value if length < 20)
    </xs:documentation>
  </xs:annotation>
</xs:attribute>

This ensures consistency across your team and avoids missed steps during mapping.

Pro Tips #

• Test Edge Cases: Always validate with attributes that are exactly 20 characters long, 19 characters, and empty to ensure no unexpected behavior.
• XPath Version Compatibility: If your tool supports XPath 2.0+, you can simplify the safety check to:

  substring(yourAttribute, max(1, string-length(yourAttribute) - 19))
  

• Reusable Functions: Most mapping tools let you create custom functions (e.g., getLast20Chars($value)). Define this once and reuse it across all attributes that need truncation.

内容的提问来源于stack exchange，提问作者user1736665