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From "Gentry, Michael \(Contractor\)" <michael_gen...@fanniemae.com>
Subject RE: Query Examples Needed � Expression.fromString() syntax?
Date Thu, 25 May 2006 13:34:40 GMT
If by a composite data structure you mean joins across multiple tables, yes, Cayenne will handle
that automatically for you based on your definitions of the relationships in the modeler.
 It'll include all the tables needed and construct the joins as part of the where clause.

I use the fromString() method even for queries entered by a user in a web page.  Map the text
fields to hash map entries and fire it off.  Cayenne figures out what parameters are missing
in the map and will omit them from the final SQL.  This means the more text fields the user
enters, the more specific the query.  The less entered, the more general the query.

>From my example yesterday, if you only have:

expression = Expression.fromString("firstName = $firstName and lastName = $lastName");
parameters.put("lastName", "Gentry");

Then Cayenne will automatically reduce the query string to "lastName = $lastName" when you
call expWithParameters().  (There is a flag to make all fields required, though.)  So you
can write your query to be detailed and have sections drop out if they aren't needed without
changing your query -- just leave them out of the map.  Of course, you can glue it together
yourself, too.  :-)

/dev/mrg


-----Original Message-----
From: Eric Lazarus [mailto:ericllazarus@yahoo.com] 
Sent: Wednesday, May 24, 2006 5:14 PM
To: cayenne-user@incubator.apache.org
Subject: RE: Query Examples Needed � Expression.fromString() syntax?


Oh, I'm not being clear... what I mean is, we will end
up with a composite data structure. I assume that
Cayenne does the right thing unpacking the composite
and turning it into one flat "where" clause in the
eventual sql, right? That's what I meant: am I doing
the right thing in terms of generating good SQL?

It does seem clear to me that for our case where we
don't know how many causes there will be until we see
which things the user has filled in, it does seem that
the 

e = e.and(... 

style will make for pretty simple code. 

--- "Gentry, Michael (Contractor)"
<michael_gentry@fanniemae.com> wrote:

> I don't know which is more efficient as I've never
> timed them.  I'd be willing to wager that your
> database latency will be significantly higher than
> having to choose between Expression and
> ExpressionFactory, though.  Perhaps a case of trying
> to optimize too early?
> 
> I just prefer the way fromString() works so that is
> what I use.  It fits my brain better.  I believe
> fromString() appeared in Cayenne 1.1, so before that
> you had to do it the other way (unless I'm just
> totally off here).
> 
> Use whichever one feels better to you.  :-)
> 
> /dev/mrg
> 
> 
> -----Original Message-----
> From: Eric Lazarus [mailto:ericllazarus@yahoo.com] 
> Sent: Wednesday, May 24, 2006 3:45 PM
> To: cayenne-user@incubator.apache.org
> Subject: Re: Query Examples Needed �
> Expression.fromString() syntax?
> 
> 
> Thank you, Michael and Joshua! 
> 
> What about efficiency? If I want to "and" in a bunch
> of things, like as many as 10 things if the user
> fills
> in all the fields of the web query form, then it
> would
> look like this? :
> 
> Expression e =
> ExpressionFactory.greaterExp("estimatedPrice", new
> BigDecimal(100000.0));
> 
> e = e.and(
> ExpressionFactory.lessExp("estimatedPrice",
> new
> BigDecimal(5000.0)) );
> 
> e = e.and( ExpressionFactory.lessExp("productSize",
> BigDecimal(100.0) );
> 
> e = e.and(
> ExpressionFactory.lessExp("productWeight",
> new
> BigDecimal(200.0)) );
> 
> I can just keep appending conditions on like this?
> Will this turn into efficient SQL code if done this
> way? If not, what is the best way?
> 
> Thanks,
> 
> Eric
> 
> --- Joshua Pyle <joshua.t.pyle@gmail.com> wrote:
> 
> > I never use fromString any more.
> > 
> > But using the expressionFactory to and and or
> > expressions is very simple...
> > 
> > Expression e =
> > ExpressionFactory.greaterExp("estimatedPrice", new
> > BigDecimal(100000.0));
> > 
> > e = e.and(
> > ExpressionFactory.lessExp("estimatedPrice", new
> > BigDecimal(5000.0)) );
> > 
> > -- 
> > Joshua T. Pyle
> > Go has always existed.
> > 
> > On 5/24/06, Eric Lazarus <ericllazarus@yahoo.com>
> > wrote:
> > > Would anyone reply with some nice examples of
> > > SelectQuery beside the simple one here:
> > >
> > >
> >
>
http://www.objectstyle.org/cayenne/userguide/dataobjects/dataobjects-example.html
> > >
> > > Expression e =
> > >   ExpressionFactory.greaterExp("estimatedPrice",
> > >                         new
> BigDecimal(100000.0))
> > >
> > > I need to do things with ANDS and ORs and I'm
> not
> > sure
> > > how to use expression factory (or should I use
> > > Expression.fromString() ?) to do it.
> > >
> > > Right now my immediate need is to be able to
> > construct
> > > a query with an arbitary number of possible
> "and"
> > > clauses depending on what the user types.
> > >
> > > Seems like fromString() is going to be easy and
> > > powerful but I can't find an example of the
> syntax
> > > using google.
> > >
> > > Even just a few nice examples would be helpful.
> > >
> > > Can I look at the attributes of sub objects
> using
> > this
> > > syntax? How?
> > >
> > > Thanks!
> > >
> > > Eric
> > >
> > >
> > >
> __________________________________________________
> > > Do You Yahoo!?
> > > Tired of spam?  Yahoo! Mail has the best spam
> > protection around
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> > >
> > 
> > 
> > -- 
> > Joshua T. Pyle
> > Go has always existed.
> > 
> 
> 
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> 


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