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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-3652) Derby does not follow the SQL Standard when trying to map SQL routines to Java methods.
Date Thu, 01 May 2008 17:46:55 GMT

     [ https://issues.apache.org/jira/browse/DERBY-3652?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Rick Hillegas updated DERBY-3652:
---------------------------------

    Attachment: derby-3652-01-aa-mixTypesOnFirstPass.diff

Attaching derby-3652-01-aa-mixTypesOnFirstPass.diff. This makes a one line change to ClassInspector,
which lets the attached problem case run correctly. I have not run regression tests yet. If
this turns out to be the solution, we will need to add some more regression test cases.

The changed line (in the method resolver) used to remove methods from consideration which
had wrapper arguments rather than primitive arguments. According to the header comment on
resolveMethod(), those methods were supposed to be considered during a second pass through
the methods--but this check in the first pass effectively excluded these methods from later
consideration. This logic is very tricky and not very well documented. I have changed a boolean
argument from false to true. The meaning of this argument is "consider matching wrappers as
well as primitives". If I make this change, then the argument could actually be removed because
the affected method would then always be called with the argument set to true. This change,
however small, makes me uneasy. I will write some more tests to see if this change breaks
anything obvious. However, it would be great if this tricky code could be explained by someone
who has been through it before.

> Derby does not follow the SQL Standard when trying to map SQL routines to Java methods.
> ---------------------------------------------------------------------------------------
>
>                 Key: DERBY-3652
>                 URL: https://issues.apache.org/jira/browse/DERBY-3652
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.5.0.0
>            Reporter: Rick Hillegas
>         Attachments: derby-3652-01-aa-mixTypesOnFirstPass.diff, SignatureMapping.html,
SignatureProblems.java, signatureProblems.sql
>
>
> I have only tested this in the 10.5 trunk. However, I suspect that this affects all previous
releases of Derby as well.
> In resolving method signatures for function/procedure invocations, the SQL standard makes
the following definitions in part 13, section 4.5 (parameter mapping). These definitions,
in turn, refer to tables B-1 and B-3 in JDBC 3.0 Specification, Final Release, October 2001
([JDBC]).
>     * Simply mappable - This refers to the correspondence of SQL and Java types described
in [JDBC] table B-1. This is the table which defines the mapping of SQL types to Java primitives.
>     * Object mappable - This refers to the correspondence of SQL and Java types described
in [JDBC] table B-3. This is the table which defines the mapping of SQL types to Java wrapper
objects.
>     * Output mappable - For OUT and INOUT parameters, this refers to a single element
array whose cell is simply mappable or object mappable. E.g. Integer[] or float[].
>     * Mappable - This means simply, object, or output mappable.
>     * Result set mappable - This means a single element array whose cell is a type which
implements either java.sql.ResultSet or sqlj.runtime.ResultSetIterator.
> Putting all of this together, section 4.5 continues:
>     "A Java method with M parameters is mappable (to SQL) if and only if, for some N,
0 (zero) <= N <= M, the data types of the first N parameters are mappable, the last
M - N parameters are result set mappable, and the result type is either simply mappable, object
mappable, or void."
> Section 8.6 gives more detailed rules, but they are hard to follow. According to section
8.6, when resolving a routine invocation, Derby should expect to find one and only one static
mappable method with the expected external name (Java class + method name).
> I believe that this is a fair description of the rules. This, at least, is what some
other databases appear to do. See, for instance, http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.help.ase_15.0.java/html/java/java126.htm
and http://www.service-architecture.com/database/articles/mapping_sql_and_java_data_types.html
> We do not have a regression test which verifies that Derby applies the SQL standard resolution
rules. There may be several divergences from the standard. This JIRA is a place to track those
discrepancies. Here is one that I have noticed:
> The following SQL signature
> ( a int ) returns int
> should be mappable to any of the following Java signatures
> public static int f( int a )
> public static int f( Integer a )
> public static Integer f( int a )
> public static Integer f( Integer a )
> However, I observe that Derby is only able to resolve the first and third signatures
(the ones with primitive arguments). I will attach a test case showing this problem.
> I will also attach an html table summarizing the simply and object mappable rules.

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