Serialization and Concatenating String Values

A common requirement for an XML based application is the ability to do some form of simple string building. For example, the following query outputs a set of elements whose values are built up as a string, depending on some other value that is passed is as part of an iteration:

declare @x xml
set @x=``

select @x.query(`
for $index in (1, 2, 3)
return

{ "Item" }{ $index }

`)

The result of this query is the following set of 3 nodes:

Item1
Item2
Item3

In this instance, we constructed the string value for the element by creating 2 separate text nodes - one containing the string literal "Item" and the other containing the iterator value. As part of XML serialization, consecutive text nodes in the XML infoset are merged into a single text node, thus providing us with our desired output. Alternatively, we could have used the XQuery concat() function:

declare @x xml
set @x=``

select @x.query(`
for $index in (1, 2, 3)
return

{ concat( "Item", $index cast as xs:string  ) }

`)

Notice that we had to add an explicit cast to the iterator value since the concat() function will only accept string values as it`s arguments.

A further option would be to build your string value as a sequence of atomic values:

declare @x xml
set @x=``

select @x.query(`
for $index in (1, 2, 3)
return

{ ( "Item", $index ) }

`)

But, there is a subtle difference in the output of this query which is as follows:

Item 1
Item 2
Item 3

Notice that there is a space between the "Item" string value and the iterator value. Sequences of items are serialized with a space between each of the entries!

So, if you need to build strings - use the concat() function explicitly or rely on the XML infoset serialization rules and build multiple, consecutive text nodes. Remember that sequences are serialized with a space between each item.

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