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Posted to user@cayenne.apache.org by Hugi Thordarson <hu...@karlmenn.is> on 2016/02/29 13:25:58 UTC

Counting the number of destination objects for a to-many relationship (or checking if empty)

Hi all,

Is there any simple way or me to count the number of destination objects of a to-many relationship? (without fetching) If not, is there some way to generate an expression from a relationship, so I can use that expression in my own counting functions?

Cheers,
- hugi

Re: Counting the number of destination objects for a to-many relationship (or checking if empty)

Posted by Hugi Thordarson <hu...@karlmenn.is>.
> Hmm, I'll look into the connection issue.  Perhaps I did something
> incorrectly.  I'll look at your CayenneUtils.  Always in the market for
> more ideas.  :-)

I think it was something I did while I was attempting to adapt the code for Cayenne 4.0. It was in my early Cayenne days, so I should really look into it again.

> I really should get around to finishing/updating/expanding/etc CBE ... one
> of these days.

:)

- hugi


> 
> Thanks,
> 
> mrg
> 
> 
> On Tue, Mar 1, 2016 at 5:12 AM, Hugi Thordarson <hu...@karlmenn.is> wrote:
> 
>> Hi Michael!
>> 
>> Thanks for the pointer. I did try to use your AggregateUtils with Cayenne
>> 4.0 a while back but it’s not API compatible with 4.0. I was able to get it
>> to work with some changes, but turned out I was creating a new DB
>> connection for each DB function invocation and some other things I didn’t
>> quite like. So I ended up constructing my own utility class that uses EJBQL
>> (still determining how sensible that was).
>> 
>> 
>> https://bitbucket.org/loftfar/jambalaya/src/22d799925a2c110b4823b36d335889e2ccfc3d06/src/main/java/jambalaya/CayenneUtils.java?at=master&fileviewer=file-view-default
>> 
>> But thanks for CBE! IT’s been one of the most useful resources for me
>> while learning Cayenne.
>> 
>> Cheers,
>> - hugi
>> 
>> 
>> 
>>> On 29. feb. 2016, at 18:09, Michael Gentry <mg...@masslight.net>
>> wrote:
>>> 
>>> PS. I think the code works correctly, but let me know if it doesn't.
>>> 
>>> 
>>> On Mon, Feb 29, 2016 at 1:09 PM, Michael Gentry <mg...@masslight.net>
>>> wrote:
>>> 
>>>> Hi Hugi,
>>>> 
>>>> I'm not sure if this will work for 4.0 (since earlier you said you are
>>>> using it), but this is what I'd use for 3.1:
>>>> 
>>>> 
>>>> 
>> https://github.com/mrg/cbe/blob/master/FetchingObjects/Aggregates/src/main/java/cbe/fetching/utilities/AggregateUtils.java
>>>> 
>>>> If you have A->>B, you'd construct a SelectQuery to fetch B's where toA
>> =
>>>> your A object.  Basically, invert your query and count the matches.
>>>> Something like:
>>>> 
>>>> SelectQuery selectQuery = new SelectQuery(B.class);
>>>> selectQuery.setQualifier(ExpressionFactory.matchExp("toA", a));
>>>> int countOfB = AggregateUtils.count(dataContext, selectQuery);
>>>> 
>>>> Some other example uses:
>>>> 
>>>> 
>>>> 
>> https://github.com/mrg/cbe/blob/master/FetchingObjects/Aggregates/src/main/java/cbe/fetching/Aggregates.java
>>>> 
>>>> mrg
>>>> 
>>>> 
>>>> On Mon, Feb 29, 2016 at 7:25 AM, Hugi Thordarson <hu...@karlmenn.is>
>> wrote:
>>>> 
>>>>> Hi all,
>>>>> 
>>>>> Is there any simple way or me to count the number of destination
>> objects
>>>>> of a to-many relationship? (without fetching) If not, is there some
>> way to
>>>>> generate an expression from a relationship, so I can use that
>> expression in
>>>>> my own counting functions?
>>>>> 
>>>>> Cheers,
>>>>> - hugi
>>>> 
>>>> 
>>>> 
>> 
>>

Re: Counting the number of destination objects for a to-many relationship (or checking if empty)

Posted by Michael Gentry <mg...@masslight.net>.
Hmm, I'll look into the connection issue.  Perhaps I did something
incorrectly.  I'll look at your CayenneUtils.  Always in the market for
more ideas.  :-)

I really should get around to finishing/updating/expanding/etc CBE ... one
of these days.

Thanks,

mrg


On Tue, Mar 1, 2016 at 5:12 AM, Hugi Thordarson <hu...@karlmenn.is> wrote:

> Hi Michael!
>
> Thanks for the pointer. I did try to use your AggregateUtils with Cayenne
> 4.0 a while back but it’s not API compatible with 4.0. I was able to get it
> to work with some changes, but turned out I was creating a new DB
> connection for each DB function invocation and some other things I didn’t
> quite like. So I ended up constructing my own utility class that uses EJBQL
> (still determining how sensible that was).
>
>
> https://bitbucket.org/loftfar/jambalaya/src/22d799925a2c110b4823b36d335889e2ccfc3d06/src/main/java/jambalaya/CayenneUtils.java?at=master&fileviewer=file-view-default
>
> But thanks for CBE! IT’s been one of the most useful resources for me
> while learning Cayenne.
>
> Cheers,
> - hugi
>
>
>
> > On 29. feb. 2016, at 18:09, Michael Gentry <mg...@masslight.net>
> wrote:
> >
> > PS. I think the code works correctly, but let me know if it doesn't.
> >
> >
> > On Mon, Feb 29, 2016 at 1:09 PM, Michael Gentry <mg...@masslight.net>
> > wrote:
> >
> >> Hi Hugi,
> >>
> >> I'm not sure if this will work for 4.0 (since earlier you said you are
> >> using it), but this is what I'd use for 3.1:
> >>
> >>
> >>
> https://github.com/mrg/cbe/blob/master/FetchingObjects/Aggregates/src/main/java/cbe/fetching/utilities/AggregateUtils.java
> >>
> >> If you have A->>B, you'd construct a SelectQuery to fetch B's where toA
> =
> >> your A object.  Basically, invert your query and count the matches.
> >> Something like:
> >>
> >> SelectQuery selectQuery = new SelectQuery(B.class);
> >> selectQuery.setQualifier(ExpressionFactory.matchExp("toA", a));
> >> int countOfB = AggregateUtils.count(dataContext, selectQuery);
> >>
> >> Some other example uses:
> >>
> >>
> >>
> https://github.com/mrg/cbe/blob/master/FetchingObjects/Aggregates/src/main/java/cbe/fetching/Aggregates.java
> >>
> >> mrg
> >>
> >>
> >> On Mon, Feb 29, 2016 at 7:25 AM, Hugi Thordarson <hu...@karlmenn.is>
> wrote:
> >>
> >>> Hi all,
> >>>
> >>> Is there any simple way or me to count the number of destination
> objects
> >>> of a to-many relationship? (without fetching) If not, is there some
> way to
> >>> generate an expression from a relationship, so I can use that
> expression in
> >>> my own counting functions?
> >>>
> >>> Cheers,
> >>> - hugi
> >>
> >>
> >>
>
>

Re: Counting the number of destination objects for a to-many relationship (or checking if empty)

Posted by Hugi Thordarson <hu...@karlmenn.is>.
Hi Michael!

Thanks for the pointer. I did try to use your AggregateUtils with Cayenne 4.0 a while back but it’s not API compatible with 4.0. I was able to get it to work with some changes, but turned out I was creating a new DB connection for each DB function invocation and some other things I didn’t quite like. So I ended up constructing my own utility class that uses EJBQL (still determining how sensible that was).

https://bitbucket.org/loftfar/jambalaya/src/22d799925a2c110b4823b36d335889e2ccfc3d06/src/main/java/jambalaya/CayenneUtils.java?at=master&fileviewer=file-view-default

But thanks for CBE! IT’s been one of the most useful resources for me while learning Cayenne.

Cheers,
- hugi



> On 29. feb. 2016, at 18:09, Michael Gentry <mg...@masslight.net> wrote:
> 
> PS. I think the code works correctly, but let me know if it doesn't.
> 
> 
> On Mon, Feb 29, 2016 at 1:09 PM, Michael Gentry <mg...@masslight.net>
> wrote:
> 
>> Hi Hugi,
>> 
>> I'm not sure if this will work for 4.0 (since earlier you said you are
>> using it), but this is what I'd use for 3.1:
>> 
>> 
>> https://github.com/mrg/cbe/blob/master/FetchingObjects/Aggregates/src/main/java/cbe/fetching/utilities/AggregateUtils.java
>> 
>> If you have A->>B, you'd construct a SelectQuery to fetch B's where toA =
>> your A object.  Basically, invert your query and count the matches.
>> Something like:
>> 
>> SelectQuery selectQuery = new SelectQuery(B.class);
>> selectQuery.setQualifier(ExpressionFactory.matchExp("toA", a));
>> int countOfB = AggregateUtils.count(dataContext, selectQuery);
>> 
>> Some other example uses:
>> 
>> 
>> https://github.com/mrg/cbe/blob/master/FetchingObjects/Aggregates/src/main/java/cbe/fetching/Aggregates.java
>> 
>> mrg
>> 
>> 
>> On Mon, Feb 29, 2016 at 7:25 AM, Hugi Thordarson <hu...@karlmenn.is> wrote:
>> 
>>> Hi all,
>>> 
>>> Is there any simple way or me to count the number of destination objects
>>> of a to-many relationship? (without fetching) If not, is there some way to
>>> generate an expression from a relationship, so I can use that expression in
>>> my own counting functions?
>>> 
>>> Cheers,
>>> - hugi
>> 
>> 
>>

Re: Counting the number of destination objects for a to-many relationship (or checking if empty)

Posted by Michael Gentry <mg...@masslight.net>.
PS. I think the code works correctly, but let me know if it doesn't.


On Mon, Feb 29, 2016 at 1:09 PM, Michael Gentry <mg...@masslight.net>
wrote:

> Hi Hugi,
>
> I'm not sure if this will work for 4.0 (since earlier you said you are
> using it), but this is what I'd use for 3.1:
>
>
> https://github.com/mrg/cbe/blob/master/FetchingObjects/Aggregates/src/main/java/cbe/fetching/utilities/AggregateUtils.java
>
> If you have A->>B, you'd construct a SelectQuery to fetch B's where toA =
> your A object.  Basically, invert your query and count the matches.
> Something like:
>
> SelectQuery selectQuery = new SelectQuery(B.class);
> selectQuery.setQualifier(ExpressionFactory.matchExp("toA", a));
> int countOfB = AggregateUtils.count(dataContext, selectQuery);
>
> Some other example uses:
>
>
> https://github.com/mrg/cbe/blob/master/FetchingObjects/Aggregates/src/main/java/cbe/fetching/Aggregates.java
>
> mrg
>
>
> On Mon, Feb 29, 2016 at 7:25 AM, Hugi Thordarson <hu...@karlmenn.is> wrote:
>
>> Hi all,
>>
>> Is there any simple way or me to count the number of destination objects
>> of a to-many relationship? (without fetching) If not, is there some way to
>> generate an expression from a relationship, so I can use that expression in
>> my own counting functions?
>>
>> Cheers,
>> - hugi
>
>
>

Re: Counting the number of destination objects for a to-many relationship (or checking if empty)

Posted by Michael Gentry <mg...@masslight.net>.
Hi Hugi,

I'm not sure if this will work for 4.0 (since earlier you said you are
using it), but this is what I'd use for 3.1:

https://github.com/mrg/cbe/blob/master/FetchingObjects/Aggregates/src/main/java/cbe/fetching/utilities/AggregateUtils.java

If you have A->>B, you'd construct a SelectQuery to fetch B's where toA =
your A object.  Basically, invert your query and count the matches.
Something like:

SelectQuery selectQuery = new SelectQuery(B.class);
selectQuery.setQualifier(ExpressionFactory.matchExp("toA", a));
int countOfB = AggregateUtils.count(dataContext, selectQuery);

Some other example uses:

https://github.com/mrg/cbe/blob/master/FetchingObjects/Aggregates/src/main/java/cbe/fetching/Aggregates.java

mrg


On Mon, Feb 29, 2016 at 7:25 AM, Hugi Thordarson <hu...@karlmenn.is> wrote:

> Hi all,
>
> Is there any simple way or me to count the number of destination objects
> of a to-many relationship? (without fetching) If not, is there some way to
> generate an expression from a relationship, so I can use that expression in
> my own counting functions?
>
> Cheers,
> - hugi