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From Francois Eyl <f...@smaeur.com>
Subject Re: EJBQL and parameters
Date Thu, 09 Apr 2009 08:26:27 GMT
I already use a lot of SelectQuery and even some SQLTemplate.

My problem with SelectQuery is the fact that it fetches all columns
information for a table and so, can be expensive for specific needs where I
need high performances (here only need ids, so only 1 column to return
rather than 25 -> more efficient on remote connection). SelectQuery is very
easy and friendly but limited to existing relationships, good point with
EJBQL is the fact that you can select which column(s) you want to fetch and
even merge your query with Expressions, so its object oriented, easy and
powerful. But can be a nightmare to maintain when column/table's name
change.

Well, it seems there is no magic solution to my issue even if your
sugestions are appreciated :) Will check the JPA 1.0 spec just in case...

Thanks again for your thoughts,
Francois


2009/4/8 Robert Zeigler <robert.zeigler@roxanemy.com>

> Two thoughts.
> 1) You're not doing anything that /requires/ EJBQLQuery. So, if you're
> /really/ interested in using the cayenne-provided constants, switch to
> SelectQuery.
>    SelectQuery q = new SelectQuery(UserSchedule.class);//<-- see? Type
> safety... :)
>    Expression e =
> ExpressionFactory.matchExp(UserSchedule.USER_ID_PROPERTY,theUserIdValue);
>    q.setQualifier(e);
>    UserSchedule us = (UserSchedule)
> DataObjectUtils.objectForQuery(objectContext,q);
>
>    us.getSku();
>
> 2) Externalize your query.
>     This doesn't save you from having to change column names, but at least
> your query is external to the code, so
>      a) You can reuse it other places (so fewer places to change)
>      b) All queries in one place, if you externalize them all, so you don't
> have to hunt through your code to find them.
>      c) You can fix your query without a recompile.
>
>
> 3) Use SQLTemplate.  SQLTemplate let's you script anything, including table
> and column names.  BUT, you'll be writing direct sql, so you'll have to use
> the database names rather than the object names.
>
>
> Note that EJBQLQuery parsing follows (or is supposed to follow) the JPA 1.0
> spec.  So if you can find reference in the spec that says that parameters
> can be used anywhere (including column names), then you should file a
> feature request.
>
> Robert
>
>
> On Apr 8, 2009, at 4/89:08 AM , Francois Eyl wrote:
>
>  oh, sorry it's my bad. I did a typing mistake I wanted to type :
>> query.setParameter("SKDID", UserSchedule.SCHEDULE_ID_PROPERTY);
>>
>> Robert, you right, I'm trying to use paramters to specify Columns and so
>> use
>> available constants coming from Cayenne. This way, even if columns name
>> change, nothing to change into the query. But, parameters sounds work only
>> for values :(
>>
>> No working solution please ?
>>
>> Thanks,
>> Francois
>>
>> 2009/4/8 Robert Zeigler <robert.zeigler@roxanemy.com>
>>
>>  Hm. I've never thought about specifying the columns and table via
>>> parameters.
>>> Event supposing that this works (not convinced it does/will), do you
>>> actually have a property named 1 in the UserSchedule entity
>>> (select us.:SKDID...setParameter("SKDID",1) => select us.1)?
>>>
>>> Try specifying the entity and property names directly.  Parameters are
>>> generally used for parameterized values, like:
>>>
>>> EJQLQuery query = new EJBQLQuery("select us.sku from UserSchedule us
>>> where
>>> us.userId=:id");
>>> query.setParameter("id",1);
>>>
>>> Robert
>>>
>>>
>>> On Apr 8, 2009, at 4/84:48 AM , Francois Eyl wrote:
>>>
>>> Howdy guys,
>>>
>>>>
>>>> I'm trying to use EJBQL query and parameters, but I can't get it to
>>>> work.
>>>> Is
>>>> there something special for ?
>>>> Bellow is a quick sample of what I'm doing :
>>>>
>>>>             String queryString = "SELECT us.:SKDID FROM :USCHED us WHERE
>>>> us.:UID=1";
>>>>             EJBQLQuery query = new EJBQLQuery(queryString);
>>>>
>>>>             query.setParameter("SKDID", 1);
>>>>             query.setParameter("USCHED",
>>>> UserSchedule.class.getSimpleName());
>>>>             query.setParameter("UID", UserSchedule.USER_ID_PROPERTY);
>>>>
>>>>             try {
>>>>                ctx.getContext().performQuery(query);
>>>>             } catch (CayenneRuntimeException e) {
>>>>                 System.err.println(e.getMessage());
>>>>             }
>>>>
>>>> I'm getting the following message : "[v.3.0M5 Dec 09 2008 00:42:23]
>>>> Error
>>>> parsing EJB QL statement".
>>>>
>>>> Can somebody tell me where I'm wrong ?
>>>>
>>>> Thanks,
>>>> Francois.
>>>>
>>>>
>>>
>>>
>

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