As a part of my research I have stumbled across need for a script to generate an XSD (XML Schema Document) directly from XML. This is great if you write XML files regularly but havent had time to generate a schema. Plus, if you need to validate XML, this gives you a free, easy to use tool without having to download the Windows SDK. Here is the script. Ill try to walk through it to explain the process,
$file = C:PowershellProjectsPowerShell and XML ypes_xsd.xml
$xsd = C:PowershellProjectsPowerShell and XML ypes_xsd.xsd
# Remove existing XSD
if(Test-Path $xsd)
{
Remove-Item -Path $xsd
}
# Read xml file
$reader = [System.Xml.XmlReader]::Create($file)
# Instntiate XmlSchemaSet and XmlSchemaInference to process new XSD
$schemaSet = New-Object System.Xml.Schema.XmlSchemaSet
$schema = New-Object System.Xml.Schema.XmlSchemaInference
# Infer schemaSet from XML document in $reader
$schemaSet = $schema.InferSchema($reader);
# Create new output file
$file = New-Object System.IO.FileStream($xsd, [IO.FileMode]::CreateNew)
# Create XmlTextWriter with UTF8 Encoding to write to file
$xwriter = New-Object System.Xml.XmlTextWriter($file, [Text.Encoding]::UTF8)
# Set formatting to indented
$xwriter.Formatting = [System.Xml.Formatting]::Indented
# Parse SchemaSet objects
$schemaSet.Schemas() |
ForEach-Object {
[System.Xml.Schema.XmlSchema] $_.Write($xwriter)
}
$xwriter.Close()
$reader.Close()
The first couple of lines are purely set up. The .xml and .xsd file paths, then, I remove the .xsd file if it already exists. Since this is just a proof of theory script, youd obviously handle this differently in production grade scripts/functions. Here are the main steps:
- I create a [System.Xml.XmlReader]::Create($file) to parse the file specified in the variable.
- With the XML document mapped into the $reader object, I then instantiate two new objects:
- System.Xml.Schema.XmlSchemaSet and
- System.Xml.Schema.XmlSchemaInference.
- Once I have these two objects, I infer the schema, $schema.InferSchema($reader), and, store the inferred XmlSchemaSets in the System.Xml.Schema.XmlSchemaSet object, $schemaSet.
- I then create a FileStream object, $file = New-Object System.IO.FileStream($xsd, [IO.FileMode]::CreateNew), to prevent the underlying .xml file from getting locked by the reader.
- To parse the file, I need an Xml object, so, I create one: New-Object System.Xml.XmlTextWriter($file, [Text.Encoding]::UTF8).
- To ensure my output file is reasonably well-formed, I then set the $xwriters output formatting to Indented, [System.Xml.Formatting]::Indented.
- Since an XmlSchemaSet object may contain multiple XmlSchemaSets, I call the $schemaSets Schemas() method enumeration to a ForEach-Object loop and send each Schema to the $xwriter.
- Lastly, to close the stream, I call the appropriate .Close() methods on the two wrappers:
- $xwriter.Close()
- $reader.Close()
I know this is a bit cryptic, but, this is a pretty .NET heavy script. Its a step in the direction of the developer. Nonetheless, being able to parse your own XML files and generate .xsd files gives you a lot of power, and, considering its power PowerShell, makes it very automation-friendly.
Using this script I was able to read a file with the following XML,
<?xml version="1.0"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Dont forget me this weekend!</body>
</note>
And it generated this XSD
<?xml version="1.0" encoding="utf-8"?>
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" >
<xs:element name="note">
<xs:complexType>
<xs:sequence>
<xs:element name="to" type="xs:string" />
<xs:element name="from" type="xs:string" />
<xs:element name="heading" type="xs:string" />
<xs:element name="body" type="xs:string" />
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
I know there are probably 500 ways this could be improved upon, so, feel free to leave comments...so long as they dont talk about your web hosting company in South Korea. Hint: Spammers, thats directed at you.
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