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Specifying Explicit Conversion Functions in XPath Queries (SQLXML 4.0)

  • Artikkeli

The following examples show how explicit conversion functions are specified in XPath queries. The XPath queries in these examples are specified against the mapping schema contained in SampleSchema1.xml. For information about this sample schema, see Sample Annotated XSD Schema for XPath Examples (SQLXML 4.0).

Examples

A. Use the number() explicit conversion function

The number() function converts an argument to a number.

Assuming the value of ContactID is nonnumeric, the following query converts ContactID to a number and compares it with the value 4. The query then returns all <Employee> element children of the context node with the ContactID attribute that has a numeric value of 4:

/child::Contact[number(attribute::ContactID)= 4]

A shortcut to the attribute axis (@) can be specified, and because the child axis is the default, it can be omitted from the query:

/Contact[number(@ContactID) = 4]

In relational terms, the query returns an employee with a ContactID of 4.

To test the XPath query against the mapping schema

  1. Copy the sample schema code and paste it into a text file. Save the file as SampleSchema1.xml.

  2. Create the following template (ExplicitConversionA.xml) and save it in the directory where SampleSchema1.xml was saved.

    <ROOT xmlns:sql="urn:schemas-microsoft-com:xml-sql">
  <sql:xpath-query mapping-schema="SampleSchema1.xml">
    /Contact[number(@ContactID)=4]
  </sql:xpath-query>
</ROOT>

    The directory path specified for the mapping schema (SampleSchema1.xml) is relative to the directory where the template is saved. An absolute path also can be specified, for example:

    mapping-schema="C:\MyDir\SampleSchema1.xml"

  3. Create and use the SQLXML 4.0 Test Script (Sqlxml4test.vbs) to execute the template.

    For more information, see Using ADO to Execute SQLXML 4.0 Queries.

The result set for this template execution is:

<ROOT xmlns:sql="urn:schemas-microsoft-com:xml-sql">
  <Contact ContactID="4" LastName="Acevedo" FirstName="Humberto" Title="Sr." /> 
</ROOT>

B. Use the string() explicit conversion function

The string() function converts an argument to a string.

The following query converts ContactID to a string and compares it with the string value "4". The query returns all <Employee> element children of the context node with a ContactID with a string value of "4":

/child::Contact[string(attribute::ContactID)="4"]

A shortcut to the attribute axis (@) can be specified, and because the child axis is the default, it can be omitted from the query:

/Contact[string(@ContactID)="4"]

Functionally, this query returns the same results as the previous example query, though the evaluation is done against a string value and not the numeric value (that is, the number 4).

To test the XPath query against the mapping schema

  1. Copy the sample schema code and paste it into a text file. Save the file as SampleSchema1.xml.

  2. Create the following template (ExplicitConversionB.xml) and save it in the directory where SampleSchema1.xml was saved.

    <ROOT xmlns:sql="urn:schemas-microsoft-com:xml-sql">
  <sql:xpath-query mapping-schema="SampleSchema1.xml">
    Contact[string(@ContactID)="4"]
  </sql:xpath-query>
</ROOT>

    The directory path specified for the mapping schema (SampleSchema1.xml) is relative to the directory where the template is saved. An absolute path also can be specified, for example:

    mapping-schema="C:\MyDir\SampleSchema1.xml"

  3. Create and use the SQLXML 4.0 Test Script (Sqlxml4test.vbs) to execute the template.

    For more information, see Using ADO to Execute SQLXML 4.0 Queries.

Here is the result set of the template execution:

<ROOT xmlns:sql="urn:schemas-microsoft-com:xml-sql">
  <Contact ContactID="4" LastName="Acevedo" FirstName="Humberto" Title="Sr." /> 
</ROOT>