[nhibernate-issues] [JIRA] Commented: (NH-628) HQL functions mapping

[NHibernate J. <mik...@us...>]

     [ http://jira.nhibernate.org/browse/NH-628?page=comments#action_14164 ]
     
Ayende Rahien commented on NH-628:
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The result seems like it fails to understand the meaning of distinct in the query. (not a different parameter).
I would say tha tthis is not good.

> HQL functions mapping
> ---------------------
>
>          Key: NH-628
>          URL: http://jira.nhibernate.org/browse/NH-628
>      Project: NHibernate
>         Type: Improvement
>   Components: Data Providers
>     Versions: 1.2.0.Beta1
>     Reporter: Fabio Maulo
>     Assignee: Fabio Maulo
>  Attachments: NH628CastFunction.patch, NH628First.patch, NH628Next1.patch, NH628Next2.patch
>
> For columns types we have RegisterColumnType in the dialect to registr the supported types for a specific dialect.
> With RegisterColumnType we can map a DbType with a equivalent specific dialect type although it isn't directly supported (a DbType.Guid can be mapped to a CHAR(38)).
> Functions haven't mapping so if i write "from Person p where lenght(p.Name) > 10" i can't sure that work with all, or many, dialect. If the "lenght" function is not supported by an specific dialect i don't recive a NHibernate excetion directly with the message "lenght is not supported by XYZ dialect".
> I think that he would be useful to have a collection of "basic" HQL function that can be specialized for a specific
> dialect.
> For example NHb can have in it's HQLfunctionList:
> -a function named "hblenstr" that recive a parameter type NHibernateUtil.String (or a property with type NHibernateUtil.String) and return a NHibernateUtil.Int32.
> -a function named "hbNullToInt" that recive two parameter; the first is a NHibernateUtil.Int16 or NHibernateUtil.Int32 or NHibernateUtil.Int64 (or a property...); the 2th is a constant of type NHibernateUtil.Int16 .. etc.
> Heach dialect can have an overload of RegisterFunction( string hbFunctionName, dialectFunctionName ).
> For the two function in the example we can have:
> for Oracle9Dialect
> RegisterFunction("hblenstr","length");
> RegisterFunction("hbNullToInt","nvl");
> for MsSql2000Dialect
> RegisterFunction("hblenstr","length");
> for FirebirdDialect (or a specific FirebirdDialect with extended UDFs ;) )
> RegisterFunction("hblenstr","strlen");
> RegisterFunction("hbNullToInt","invl");
> Now we can write an HQL like this "from Person p where hblenstr(p.Name) > 10" and NHb can substitue "hblenstr" with apropiate dialect function (before substitution can control that the hblenstr revive de apropiate param type etc.).
> This posible implementation don't have problems if an hbXYZ function have the same name of specific dialect function (i think the probability is very low but there are no problems).
> The actual implementation of RegisterFunction don't need any adjustment because all continue to work.
> Finally:
> -If a dialect use actual implementation of RegisterFunction and a developer use this function in a HQL he can't be sure that all work fine when he need to change de hibernate.cfg.xml to change the dialect.
> -If a dialect was implemented with RegisterFunction( string hbFunctionName, dialectFunctionName ) mapping and a developer use the hbXYZ function in a HQL he can have an hight probability that all work fine.
> Bye.
> Fabio.

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