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Posted to users@openjpa.apache.org by xavihendrix <xa...@gmail.com> on 2008/03/31 11:40:36 UTC
Custom StoreManager
Hello, I am implementing a custom StoreManager to access relational data
through a propietary product API, wich my company has bought but don't want
to use in all data accesses. The JPA has to be the uniform persistence layer
for all units, which can be configured to use a particular StoreManager
(JDBC, propietary API, etc.)
So, at the moment of executing internally the query in my StoreQuery and
construct the delegate object (of the propietary API), I walk through the
expressions provided by InMemoryExpressionFactory with an ExpressionVisitor
(I use this factory because in-memory post-processing can be required due to
limitations on the propitary API).
The problem is that all expressions have a protected visibility, so I cannot
know wich expression I am processing and cannot construct my delegate query.
Is there a way to obtain the type of expression of a
org.apache.openjpa.kernel.exps.Expression? A kind of JavaTypes for
expressions that tells you if it is and AND, OR... ?
It's a bit weird, I hope someone has been found the same problem. Thanks!
--
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Sent from the OpenJPA Users mailing list archive at Nabble.com.
Re: Custom StoreManager
Posted by xaviarias <xa...@gmail.com>.
Yes I would need to write the code to act on the tree. The initial idea was
to build a tree from an custom expression factory which can decide wether to
create a propietary API expression or an in-memory expression. But I didn't
want to code all the expressions and that's why I switched to an expression
visitor.
After an essay of coding it, I think is better to go back to first solution
and do something like:
class MyExpressionFactory extends InMemoryExpressionFactory {
...
public Expression and(Expression exp1, Expression exp2) {
if (inMemory(AND, exp1, exp2)) {
return super.and(exp1, exp2);
}
return new MyAndExpression(exp1, exp2);
}
...
}
The problem now is to decide when an expression must be evaluated by the
propietary API or in-memory. Is it the AST builded bottom-up I guess?
A good thing would be to execute a query in two phases: first, build one
partial AST query and execute against the propietary api (Val.eval(...)
methods could return API objects), and second filter the results with the
in-memory partial AST. Do you think it would be possible? There's a logical
problem here, maybe a transformation of the expression to its CNF or DNF
would be needed at AST build time?
Xavi
Patrick Linskey-2 wrote:
>
> There's definitely a convenience benefit to having an existing
> hierarchy. However, even if there were an existing AST, wouldn't you
> still need to write code to act on the tree? One of the advantages of
> the ExpressionFactory-based approach is that you can hook directly
> into the initial query parse, which I believe can be more efficient
> than parsing to an AST and then walking that AST.
>
> One thing to bear in mind when implementing an ExpressionFactory is
> that the generated object graph can be cached in the
> QueryCompilationCache (and is by default), so you should take care to
> not store EM-related (i.e., Brokers, StoreManagers, StateManagers,
> etc.) or mutable state in the instances.
>
> -Patrick
>
> On Tue, Apr 1, 2008 at 1:44 AM, xaviarias <xa...@gmail.com> wrote:
>>
>>
>> Thanks, definetely I'll implement my own ExpressionFactory based on the
>> in-memory implementation. I wanted to avoid copy-paste the existing
>> code,
>> but I guess it's too specific to be fully reused.
>>
>> It could be interesting to uniform the expression hierarchy for general
>> purposes, if it is possible. I also saw conversations about subclassing
>> JDBC
>> StoreManager for a particular rdbms, which is not the underlying idea I
>> think, but for the moment could be convenient.
>>
>>
>>
>>
>> Patrick Linskey-2 wrote:
>> >
>> > Hi,
>> >
>> > Generally, no -- those classes were created to implement the in-memory
>> > parser, not to be a general-purpose AST.
>> >
>> > That said, I think it would certainly be reasonable to extend their
>> > role to help meet yours. I think that it would take more than just
>> > making the classes public, though; there might be classes for which an
>> > instanceof check is not sufficient, and for which more methods would
>> > need to be exposed.
>> >
>> > I believe that it's possible for you to create your own AST (i.e.,
>> > your own ExpressionFactory that builds your own instances) and still
>> > take advantage of in-mem query processing when a particular query
>> > cannot be executed against the data store directly.
>> >
>> > -Patrick
>> >
>> > On Mon, Mar 31, 2008 at 2:40 AM, xavihendrix <xa...@gmail.com>
>> > wrote:
>> >>
>> >> Hello, I am implementing a custom StoreManager to access relational
>> data
>> >> through a propietary product API, wich my company has bought but
>> don't
>> >> want
>> >> to use in all data accesses. The JPA has to be the uniform
>> persistence
>> >> layer
>> >> for all units, which can be configured to use a particular
>> StoreManager
>> >> (JDBC, propietary API, etc.)
>> >>
>> >> So, at the moment of executing internally the query in my StoreQuery
>> and
>> >> construct the delegate object (of the propietary API), I walk
>> through
>> >> the
>> >> expressions provided by InMemoryExpressionFactory with an
>> >> ExpressionVisitor
>> >> (I use this factory because in-memory post-processing can be
>> required
>> >> due to
>> >> limitations on the propitary API).
>> >>
>> >> The problem is that all expressions have a protected visibility, so
>> I
>> >> cannot
>> >> know wich expression I am processing and cannot construct my
>> delegate
>> >> query.
>> >> Is there a way to obtain the type of expression of a
>> >> org.apache.openjpa.kernel.exps.Expression? A kind of JavaTypes for
>> >> expressions that tells you if it is and AND, OR... ?
>> >>
>> >> It's a bit weird, I hope someone has been found the same problem.
>> >> Thanks!
>> >>
>> >> --
>> >> View this message in context:
>> >> http://www.nabble.com/Custom-StoreManager-tp16394955p16394955.html
>> >> Sent from the OpenJPA Users mailing list archive at Nabble.com.
>> >>
>> >>
>> >
>> >
>> >
>> > --
>> > Patrick Linskey
>> > 202 669 5907
>> >
>> >
>>
>> --
>> View this message in context:
>> http://www.nabble.com/Custom-StoreManager-tp16394955p16416900.html
>>
>>
>> Sent from the OpenJPA Users mailing list archive at Nabble.com.
>>
>>
>
>
>
> --
> Patrick Linskey
> 202 669 5907
>
>
--
View this message in context: http://www.nabble.com/Custom-StoreManager-tp16394955p16446344.html
Sent from the OpenJPA Users mailing list archive at Nabble.com.
Re: Custom StoreManager
Posted by Patrick Linskey <pl...@gmail.com>.
There's definitely a convenience benefit to having an existing
hierarchy. However, even if there were an existing AST, wouldn't you
still need to write code to act on the tree? One of the advantages of
the ExpressionFactory-based approach is that you can hook directly
into the initial query parse, which I believe can be more efficient
than parsing to an AST and then walking that AST.
One thing to bear in mind when implementing an ExpressionFactory is
that the generated object graph can be cached in the
QueryCompilationCache (and is by default), so you should take care to
not store EM-related (i.e., Brokers, StoreManagers, StateManagers,
etc.) or mutable state in the instances.
-Patrick
On Tue, Apr 1, 2008 at 1:44 AM, xaviarias <xa...@gmail.com> wrote:
>
>
> Thanks, definetely I'll implement my own ExpressionFactory based on the
> in-memory implementation. I wanted to avoid copy-paste the existing code,
> but I guess it's too specific to be fully reused.
>
> It could be interesting to uniform the expression hierarchy for general
> purposes, if it is possible. I also saw conversations about subclassing JDBC
> StoreManager for a particular rdbms, which is not the underlying idea I
> think, but for the moment could be convenient.
>
>
>
>
> Patrick Linskey-2 wrote:
> >
> > Hi,
> >
> > Generally, no -- those classes were created to implement the in-memory
> > parser, not to be a general-purpose AST.
> >
> > That said, I think it would certainly be reasonable to extend their
> > role to help meet yours. I think that it would take more than just
> > making the classes public, though; there might be classes for which an
> > instanceof check is not sufficient, and for which more methods would
> > need to be exposed.
> >
> > I believe that it's possible for you to create your own AST (i.e.,
> > your own ExpressionFactory that builds your own instances) and still
> > take advantage of in-mem query processing when a particular query
> > cannot be executed against the data store directly.
> >
> > -Patrick
> >
> > On Mon, Mar 31, 2008 at 2:40 AM, xavihendrix <xa...@gmail.com>
> > wrote:
> >>
> >> Hello, I am implementing a custom StoreManager to access relational data
> >> through a propietary product API, wich my company has bought but don't
> >> want
> >> to use in all data accesses. The JPA has to be the uniform persistence
> >> layer
> >> for all units, which can be configured to use a particular StoreManager
> >> (JDBC, propietary API, etc.)
> >>
> >> So, at the moment of executing internally the query in my StoreQuery and
> >> construct the delegate object (of the propietary API), I walk through
> >> the
> >> expressions provided by InMemoryExpressionFactory with an
> >> ExpressionVisitor
> >> (I use this factory because in-memory post-processing can be required
> >> due to
> >> limitations on the propitary API).
> >>
> >> The problem is that all expressions have a protected visibility, so I
> >> cannot
> >> know wich expression I am processing and cannot construct my delegate
> >> query.
> >> Is there a way to obtain the type of expression of a
> >> org.apache.openjpa.kernel.exps.Expression? A kind of JavaTypes for
> >> expressions that tells you if it is and AND, OR... ?
> >>
> >> It's a bit weird, I hope someone has been found the same problem.
> >> Thanks!
> >>
> >> --
> >> View this message in context:
> >> http://www.nabble.com/Custom-StoreManager-tp16394955p16394955.html
> >> Sent from the OpenJPA Users mailing list archive at Nabble.com.
> >>
> >>
> >
> >
> >
> > --
> > Patrick Linskey
> > 202 669 5907
> >
> >
>
> --
> View this message in context: http://www.nabble.com/Custom-StoreManager-tp16394955p16416900.html
>
>
> Sent from the OpenJPA Users mailing list archive at Nabble.com.
>
>
--
Patrick Linskey
202 669 5907
Re: Custom StoreManager
Posted by xaviarias <xa...@gmail.com>.
Thanks, definetely I'll implement my own ExpressionFactory based on the
in-memory implementation. I wanted to avoid copy-paste the existing code,
but I guess it's too specific to be fully reused.
It could be interesting to uniform the expression hierarchy for general
purposes, if it is possible. I also saw conversations about subclassing JDBC
StoreManager for a particular rdbms, which is not the underlying idea I
think, but for the moment could be convenient.
Patrick Linskey-2 wrote:
>
> Hi,
>
> Generally, no -- those classes were created to implement the in-memory
> parser, not to be a general-purpose AST.
>
> That said, I think it would certainly be reasonable to extend their
> role to help meet yours. I think that it would take more than just
> making the classes public, though; there might be classes for which an
> instanceof check is not sufficient, and for which more methods would
> need to be exposed.
>
> I believe that it's possible for you to create your own AST (i.e.,
> your own ExpressionFactory that builds your own instances) and still
> take advantage of in-mem query processing when a particular query
> cannot be executed against the data store directly.
>
> -Patrick
>
> On Mon, Mar 31, 2008 at 2:40 AM, xavihendrix <xa...@gmail.com>
> wrote:
>>
>> Hello, I am implementing a custom StoreManager to access relational data
>> through a propietary product API, wich my company has bought but don't
>> want
>> to use in all data accesses. The JPA has to be the uniform persistence
>> layer
>> for all units, which can be configured to use a particular StoreManager
>> (JDBC, propietary API, etc.)
>>
>> So, at the moment of executing internally the query in my StoreQuery and
>> construct the delegate object (of the propietary API), I walk through
>> the
>> expressions provided by InMemoryExpressionFactory with an
>> ExpressionVisitor
>> (I use this factory because in-memory post-processing can be required
>> due to
>> limitations on the propitary API).
>>
>> The problem is that all expressions have a protected visibility, so I
>> cannot
>> know wich expression I am processing and cannot construct my delegate
>> query.
>> Is there a way to obtain the type of expression of a
>> org.apache.openjpa.kernel.exps.Expression? A kind of JavaTypes for
>> expressions that tells you if it is and AND, OR... ?
>>
>> It's a bit weird, I hope someone has been found the same problem.
>> Thanks!
>>
>> --
>> View this message in context:
>> http://www.nabble.com/Custom-StoreManager-tp16394955p16394955.html
>> Sent from the OpenJPA Users mailing list archive at Nabble.com.
>>
>>
>
>
>
> --
> Patrick Linskey
> 202 669 5907
>
>
--
View this message in context: http://www.nabble.com/Custom-StoreManager-tp16394955p16416900.html
Sent from the OpenJPA Users mailing list archive at Nabble.com.
Re: Custom StoreManager
Posted by Patrick Linskey <pl...@gmail.com>.
Hi,
Generally, no -- those classes were created to implement the in-memory
parser, not to be a general-purpose AST.
That said, I think it would certainly be reasonable to extend their
role to help meet yours. I think that it would take more than just
making the classes public, though; there might be classes for which an
instanceof check is not sufficient, and for which more methods would
need to be exposed.
I believe that it's possible for you to create your own AST (i.e.,
your own ExpressionFactory that builds your own instances) and still
take advantage of in-mem query processing when a particular query
cannot be executed against the data store directly.
-Patrick
On Mon, Mar 31, 2008 at 2:40 AM, xavihendrix <xa...@gmail.com> wrote:
>
> Hello, I am implementing a custom StoreManager to access relational data
> through a propietary product API, wich my company has bought but don't want
> to use in all data accesses. The JPA has to be the uniform persistence layer
> for all units, which can be configured to use a particular StoreManager
> (JDBC, propietary API, etc.)
>
> So, at the moment of executing internally the query in my StoreQuery and
> construct the delegate object (of the propietary API), I walk through the
> expressions provided by InMemoryExpressionFactory with an ExpressionVisitor
> (I use this factory because in-memory post-processing can be required due to
> limitations on the propitary API).
>
> The problem is that all expressions have a protected visibility, so I cannot
> know wich expression I am processing and cannot construct my delegate query.
> Is there a way to obtain the type of expression of a
> org.apache.openjpa.kernel.exps.Expression? A kind of JavaTypes for
> expressions that tells you if it is and AND, OR... ?
>
> It's a bit weird, I hope someone has been found the same problem. Thanks!
>
> --
> View this message in context: http://www.nabble.com/Custom-StoreManager-tp16394955p16394955.html
> Sent from the OpenJPA Users mailing list archive at Nabble.com.
>
>
--
Patrick Linskey
202 669 5907