如何将指定字符串转换为XML？解决未声明前缀解析错误

Hey there! The error you're hitting (Msg 9459, Level 16, State 1) happens because your XML string uses the rd: prefix for the TypeName element, but you haven't declared what that rd namespace actually refers to. XML parsers strictly require all prefixed elements to have a corresponding namespace definition.

Here's how to fix your code: #

You need to add the xmlns:rd attribute to your root <Field> element to define the namespace. The most common namespace for rd (used in SQL Server Reporting Services scenarios) is http://schemas.microsoft.com/SQLServer/reporting/reportdesigner, so we'll use that in the corrected example:

DECLARE @Cname NVARCHAR(100) = 'YourTargetColumnName'; -- Replace with your actual column name
DECLARE @string NVARCHAR(MAX);
DECLARE @xmlstring XML;

-- Updated string with namespace declaration for the 'rd' prefix
SET @string = '<Field xmlns:rd="http://schemas.microsoft.com/SQLServer/reporting/reportdesigner"> 
    <Field Name="'+@Cname+'"> 
        <DataField>'+@Cname+'</DataField> 
        <rd:TypeName>System.String</rd:TypeName> 
    </Field>
</Field>';

-- Now convert to XML without parsing errors
SET @xmlstring = CONVERT(XML, @string);

-- Optional: Check the resulting XML
SELECT @xmlstring;

Why this works: #

The xmlns:rd="..." attribute tells the XML parser that any element starting with rd: belongs to the specified namespace URI. This meets the XML specification's requirement for prefixed elements, so the CONVERT(XML, ...) function will parse the string successfully.

If you're using a custom namespace for rd, just swap out the URI in the xmlns:rd attribute with your actual namespace value.

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