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Thread: uuid values as parameters

uuid values as parameters

From
vtkstef
Date:
Hi,

I have a simple table foo with a column guid of data type uuid

if I execute the following query

select  guid from foo where guid = '849b3d72-1400-44f1-
a965-1f4648475589'

the query returns fine

but if I parameterize the query as this

select guid from foo where guid = ?

and I set the the parameter using setString(1, '849b3d72-1400-44f1-
a965-1f4648475589')

the query bombs with the following:

 [Error Code: 0, SQL State: 42883]  ERROR: operator does not exist:
uuid = character varying

I understand I need to use setObject(), or that I could explicitly
cast it (select guid from foo where guid = ?::uuid)  but I don't
understand why harcoding a string works, and sending a string
parameter does not

Ciao
Stefano

Re: uuid values as parameters

From
Lew
Date:
On 08/19/2010 12:10 PM, vtkstef wrote:
> Hi,
>
> I have a simple table foo with a column guid of data type uuid
>
> if I execute the following query
>
> select  guid from foo where guid = '849b3d72-1400-44f1-
> a965-1f4648475589'
>
> the query returns fine
>
> but if I parameterize the query as this
>
> select guid from foo where guid = ?
>
> and I set the the parameter using setString(1, '849b3d72-1400-44f1-
> a965-1f4648475589')
>
> the query bombs with the following:
>
>   [Error Code: 0, SQL State: 42883]  ERROR: operator does not exist:
> uuid = character varying
>
> I understand I need to use setObject(), or that I could explicitly
> cast it (select guid from foo where guid = ?::uuid)  but I don't
> understand why harcoding a string works, and sending a string
> parameter does not

When you give the SQL parser a string literal, it knows that it might have to
convert to the column type, and at that can only do so for column types that
define a conversion for string literals.  When you give the parser a parameter
to a prepared statement, you are adding the feature of strong type safety.
You are actually depending on the parser to reject inputs of the wrong type.
For it to accept a string value for the parameter would be a violation of that
trust.

--
Lew

Re: uuid values as parameters

From
Florian Weimer
Date:
* Lew:

> When you give the SQL parser a string literal, it knows that it might
> have to convert to the column type, and at that can only do so for
> column types that define a conversion for string literals.  When you
> give the parser a parameter to a prepared statement, you are adding
> the feature of strong type safety. You are actually depending on the
> parser to reject inputs of the wrong type. For it to accept a string
> value for the parameter would be a violation of that trust.

You usually can work around that by adding a type cast, as in
"?::uuid".

To get behavior which more closely matches those of other PostgreSQL
bindings, add "?stringtype=unspecified" to the JDBC URL.

--
Florian Weimer                <fweimer@bfk.de>
BFK edv-consulting GmbH       http://www.bfk.de/
Kriegsstraße 100              tel: +49-721-96201-1
D-76133 Karlsruhe             fax: +49-721-96201-99