JPA Criteria API calling SQL Server database exist function - sql-server

Question

I am building a query using the JPA's CriteriaBuilder to call the SQL Server exist function to find data based on an XML field and it is failing to run due to a The argument 1 of the XML data type method "exist" must be a string literal. error.
I traced the SQL generated and get the same error when I try the query in SQL Server Management Studio. I've simplified the SQL to the following for reference
declare #p1 int
set #p1=NULL
exec sp_prepexec #p1 output,
N'#P0 varchar(8000)',
N'select id, name from mytable where xmlfield.exist(#P0)=1 order by id desc',
'true()'
select #p1
The interesting thing is when I try the query by itself, it runs fine and returns the results.
select id, name from mytable where xmlfield.exist('true()')=1 order by id desc;
Any thoughts on why the generated parameterized SQL statement generated does not work?

Answer 1

As the error message states, the value passed into the "exist" function must be a string literal. The example given is trying to pass a variable into the function, but then when you're running the query by itself it works just fine because you're passing in a string literal.
For example...
DECLARE #xml XML = '';
DECLARE #P0 NVARCHAR(500) = 'true()';
SELECT #xml.exist(#P0) -- will not work
SELECT #xml.exist('true()') -- will work
For the longest time I thought this made these functions worthless because I didn't know you could use variables within the string literal. Here is an example:
DECLARE #xml XML = '<root><item id="1" /><item id="2"><test /></item></root>';
DECLARE #item_id INT;
SET #item_id = 1; -- "test" element does not exist
SELECT #xml.exist('/root/item[#id=sql:variable("#item_id")]/test')
SET #item_id = 2; -- "test" element does exist
SELECT #xml.exist('/root/item[#id=sql:variable("#item_id")]/test')