On 18-08-2022 04:02, Adriano dos Santos Fernandes wrote:
How are client libraries (Jaybird, .NET Provider, Delphi ones)
describing its named parameters to their users?
I mean, given this SQL:
select *
from rdb$database
where :param = 1 or :param = '2'
We have here single name used in context with multiple types.
I suppose you transform this to:
select *
from rdb$database
where ? = 1 or ? = '2'
Which will map to two Firebird parameters with different types.
But for the user of the library, I suppose it's one parameter, correct?
And what type (and the deduction rules) this parameter will be described as?
JDBC doesn't define support for named parameters in
java.sql.PreparedStatement, only in java.sql.CallableStatement, which is
for calling stored procedures, and that support is optional, so Jaybird
doesn't have any support for named parameters.
So, if Firebird is going to implement real named parameters, Jaybird is
probably not going to support them, and in that case I would really love
if this is controlled through a DPB item so when disabled, use of a
named parameter results in an error (e.g. "named parameters in DSQL are
not enabled" or something). Maybe I can then allow users aware of named
parameters to enable it explicitly to map it them themselves, for
example if something like `column1 = :param1 and column2 = :param2 and
colum3 = :param1` results in two parameters (param1 = position 1, and
param2 = position 2), and setting by position still works.
The reason Jaybird probably is not going to support this, is because
most people don't use the JDBC API directly, but through things like
Hibernate, so adding vendor extensions to the JDBC API is pretty much
wasted effort because those libraries only use the JDBC API. I could add
such methods to the FirebirdPreparedStatement interface, but that would
then be a niche feature for people who do use JDBC, and are able to
unwrap to the FirebirdPreparedStatement interface (which is not always
possible when obtained from a connection pool).
In the Java world, named parameters are usually emulated by layers like
Hibernate, or Spring's NamedParameterJdbcTemplate, which will map names
to positional parameters, and set the values of those positional
parameters appropriately.
Mark
--
Mark Rotteveel
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