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Posted to users@openjpa.apache.org by is_maximum <mn...@gmail.com> on 2009/05/20 14:14:54 UTC
Can we have an entity with no @Id?
Hi
We have some tables in which id is not important and actually it is useless.
For example we have two logging tables, one is master and the other is
keeping details. The only foreign key from the master table is enough and
the second table has no relationship with other tables so if we remove its
ID we can get rid of its sequence and this will be great in terms of
performance since this table is considered to keep lots of records and its
purpose is for preserving events took place in the system
Now my question is how to remove its @Id from the entity since the OpenJPA
complains if the entity has no field marked as id
Thanks
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Re: Can we have an entity with no @Id?
Posted by Andrei Tchijov <an...@tchijov.com>.
Why do you need to use JPA at all in this scenario? If you concern about
performance, just use simple JDBC.
Keeping in mind that id is the only way to distinct one Entity from another,
I am fairly sure that it is impossible to define Entity without ID.
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Re: Can we have an entity with no @Id?
Posted by Craig L Russell <Cr...@Sun.COM>.
Hi,
Tables without primary keys is one of the features of JDO that was not
adopted by JPA.
Maybe you should look at JDO implementations.
Craig
On May 20, 2009, at 8:12 AM, is_maximum wrote:
>
> Hello
>
> To Andrei I want to say that because it is simple to create an
> object and
> send it to be persisted however this could be a good idea.
>
> And to Kevin, if in secondary table we have only a foreign key to
> distinct
> records that would be enough because the id for the secondary table
> is not
> used anywhere. All we need from these two tables is a report that
> tells us
> what kind of events (secondary table) have been occurred for a
> specific
> operation in specific time (master table) and order is not important
> since
> the time of event will order those records in right way. So what is
> this ID
> good for? In case of existence of this ID we have to either create
> an Oracle
> sequence (which is a bottleneck in database because it takes up cache
> particularly in a clustered environment) or selecting the maximum ID
> (which
> is required to scan all the records) or create a sequence table
> managed by
> ORM (That will end up with a select statement and an update
> following that)
> or create that id manually (that it is almost impossible)
>
>
> Kevin Sutter wrote:
>>
>> Hi is_maximum,
>> I'm still a little confused by your scenario. Following your
>> described
>> scenario... Your master table would have an Id field, but your
>> secondary
>> table would not have an explicit Id field. The foreign key from your
>> master
>> to secondary would just be some arbitrary column from the secondary
>> table?
>> Do I have that right? And, why would removing an Id field help with
>> performance? You mention to get rid of its sequence, but there's no
>> requirement to define an Id field with a sequence.
>>
>> Even though I'm still a little confused by your scenario, there are a
>> couple
>> of items to be aware of from an OpenJPA perspective. The JPA spec
>> requires
>> an Id field, but OpenJPA does not require one. Well, not exactly.
>> Instead
>> of declaring an explicit Id field, you could instead declare an Id
>> via the
>> @DataStoreId annotation [1]. This hides the Id field from your
>> Entity
>> definition, but under the covers we still use an implicit Id field in
>> order
>> to insert and find records.
>>
>> Another possibility is coming with the updated JPA 2 specification
>> and the
>> use of derived identities. I'm probably stretching this one a bit,
>> but
>> this
>> support would allow you to derive an identity for an Entity based
>> on the
>> identity of a "parent" Entity. This is normally used when the
>> dependent
>> Entity is the owner of a many-to-one or one-to-one relationship to
>> the
>> parent entity. Here again, OpenJPA provides a similar
>> functionality with
>> their Entities as Identity fields.
>>
>> So, bottom line is that some type of Identity is required for proper
>> Entity
>> definition and usage. But, OpenJPA (and eventually the JPA 2 spec)
>> provides
>> for some methods to get around the explicit definition of an Id
>> field.
>>
>> Hope this helps,
>> Kevin
>>
>> [1]
>> http://openjpa.apache.org/builds/latest/docs/manual/manual.html#ref_guide_pc_oid_datastore
>> [2]
>> http://openjpa.apache.org/builds/latest/docs/manual/manual.html#ref_guide_pc_oid_entitypk
>>
>> On Wed, May 20, 2009 at 7:14 AM, is_maximum <mn...@gmail.com> wrote:
>>
>>>
>>> Hi
>>> We have some tables in which id is not important and actually it is
>>> useless.
>>> For example we have two logging tables, one is master and the
>>> other is
>>> keeping details. The only foreign key from the master table is
>>> enough and
>>> the second table has no relationship with other tables so if we
>>> remove
>>> its
>>> ID we can get rid of its sequence and this will be great in terms of
>>> performance since this table is considered to keep lots of records
>>> and
>>> its
>>> purpose is for preserving events took place in the system
>>>
>>> Now my question is how to remove its @Id from the entity since the
>>> OpenJPA
>>> complains if the entity has no field marked as id
>>>
>>> Thanks
>>> --
>>> View this message in context:
>>> http://n2.nabble.com/Can-we-have-an-entity-with-no-%40Id--tp2945752p2945752.html
>>> Sent from the OpenJPA Users mailing list archive at Nabble.com.
>>>
>>>
>>
>>
>
>
> -----
> --
> Regards
> Mohammad
> http://pixelshot.wordpress.com Pixelshot
> --
> View this message in context: http://n2.nabble.com/Can-we-have-an-entity-with-no-%40Id--tp2945752p2946693.html
> Sent from the OpenJPA Users mailing list archive at Nabble.com.
>
Craig L Russell
Architect, Sun Java Enterprise System http://db.apache.org/jdo
408 276-5638 mailto:Craig.Russell@sun.com
P.S. A good JDO? O, Gasp!
Re: Can we have an entity with no @Id?
Posted by is_maximum <mn...@gmail.com>.
Hello
To Andrei I want to say that because it is simple to create an object and
send it to be persisted however this could be a good idea.
And to Kevin, if in secondary table we have only a foreign key to distinct
records that would be enough because the id for the secondary table is not
used anywhere. All we need from these two tables is a report that tells us
what kind of events (secondary table) have been occurred for a specific
operation in specific time (master table) and order is not important since
the time of event will order those records in right way. So what is this ID
good for? In case of existence of this ID we have to either create an Oracle
sequence (which is a bottleneck in database because it takes up cache
particularly in a clustered environment) or selecting the maximum ID (which
is required to scan all the records) or create a sequence table managed by
ORM (That will end up with a select statement and an update following that)
or create that id manually (that it is almost impossible)
Kevin Sutter wrote:
>
> Hi is_maximum,
> I'm still a little confused by your scenario. Following your described
> scenario... Your master table would have an Id field, but your secondary
> table would not have an explicit Id field. The foreign key from your
> master
> to secondary would just be some arbitrary column from the secondary table?
> Do I have that right? And, why would removing an Id field help with
> performance? You mention to get rid of its sequence, but there's no
> requirement to define an Id field with a sequence.
>
> Even though I'm still a little confused by your scenario, there are a
> couple
> of items to be aware of from an OpenJPA perspective. The JPA spec
> requires
> an Id field, but OpenJPA does not require one. Well, not exactly.
> Instead
> of declaring an explicit Id field, you could instead declare an Id via the
> @DataStoreId annotation [1]. This hides the Id field from your Entity
> definition, but under the covers we still use an implicit Id field in
> order
> to insert and find records.
>
> Another possibility is coming with the updated JPA 2 specification and the
> use of derived identities. I'm probably stretching this one a bit, but
> this
> support would allow you to derive an identity for an Entity based on the
> identity of a "parent" Entity. This is normally used when the dependent
> Entity is the owner of a many-to-one or one-to-one relationship to the
> parent entity. Here again, OpenJPA provides a similar functionality with
> their Entities as Identity fields.
>
> So, bottom line is that some type of Identity is required for proper
> Entity
> definition and usage. But, OpenJPA (and eventually the JPA 2 spec)
> provides
> for some methods to get around the explicit definition of an Id field.
>
> Hope this helps,
> Kevin
>
> [1]
> http://openjpa.apache.org/builds/latest/docs/manual/manual.html#ref_guide_pc_oid_datastore
> [2]
> http://openjpa.apache.org/builds/latest/docs/manual/manual.html#ref_guide_pc_oid_entitypk
>
> On Wed, May 20, 2009 at 7:14 AM, is_maximum <mn...@gmail.com> wrote:
>
>>
>> Hi
>> We have some tables in which id is not important and actually it is
>> useless.
>> For example we have two logging tables, one is master and the other is
>> keeping details. The only foreign key from the master table is enough and
>> the second table has no relationship with other tables so if we remove
>> its
>> ID we can get rid of its sequence and this will be great in terms of
>> performance since this table is considered to keep lots of records and
>> its
>> purpose is for preserving events took place in the system
>>
>> Now my question is how to remove its @Id from the entity since the
>> OpenJPA
>> complains if the entity has no field marked as id
>>
>> Thanks
>> --
>> View this message in context:
>> http://n2.nabble.com/Can-we-have-an-entity-with-no-%40Id--tp2945752p2945752.html
>> Sent from the OpenJPA Users mailing list archive at Nabble.com.
>>
>>
>
>
-----
--
Regards
Mohammad
http://pixelshot.wordpress.com Pixelshot
--
View this message in context: http://n2.nabble.com/Can-we-have-an-entity-with-no-%40Id--tp2945752p2946693.html
Sent from the OpenJPA Users mailing list archive at Nabble.com.
Re: Can we have an entity with no @Id?
Posted by Kevin Sutter <kw...@gmail.com>.
Hi is_maximum,
I'm still a little confused by your scenario. Following your described
scenario... Your master table would have an Id field, but your secondary
table would not have an explicit Id field. The foreign key from your master
to secondary would just be some arbitrary column from the secondary table?
Do I have that right? And, why would removing an Id field help with
performance? You mention to get rid of its sequence, but there's no
requirement to define an Id field with a sequence.
Even though I'm still a little confused by your scenario, there are a couple
of items to be aware of from an OpenJPA perspective. The JPA spec requires
an Id field, but OpenJPA does not require one. Well, not exactly. Instead
of declaring an explicit Id field, you could instead declare an Id via the
@DataStoreId annotation [1]. This hides the Id field from your Entity
definition, but under the covers we still use an implicit Id field in order
to insert and find records.
Another possibility is coming with the updated JPA 2 specification and the
use of derived identities. I'm probably stretching this one a bit, but this
support would allow you to derive an identity for an Entity based on the
identity of a "parent" Entity. This is normally used when the dependent
Entity is the owner of a many-to-one or one-to-one relationship to the
parent entity. Here again, OpenJPA provides a similar functionality with
their Entities as Identity fields.
So, bottom line is that some type of Identity is required for proper Entity
definition and usage. But, OpenJPA (and eventually the JPA 2 spec) provides
for some methods to get around the explicit definition of an Id field.
Hope this helps,
Kevin
[1]
http://openjpa.apache.org/builds/latest/docs/manual/manual.html#ref_guide_pc_oid_datastore
[2]
http://openjpa.apache.org/builds/latest/docs/manual/manual.html#ref_guide_pc_oid_entitypk
On Wed, May 20, 2009 at 7:14 AM, is_maximum <mn...@gmail.com> wrote:
>
> Hi
> We have some tables in which id is not important and actually it is
> useless.
> For example we have two logging tables, one is master and the other is
> keeping details. The only foreign key from the master table is enough and
> the second table has no relationship with other tables so if we remove its
> ID we can get rid of its sequence and this will be great in terms of
> performance since this table is considered to keep lots of records and its
> purpose is for preserving events took place in the system
>
> Now my question is how to remove its @Id from the entity since the OpenJPA
> complains if the entity has no field marked as id
>
> Thanks
> --
> View this message in context:
> http://n2.nabble.com/Can-we-have-an-entity-with-no-%40Id--tp2945752p2945752.html
> Sent from the OpenJPA Users mailing list archive at Nabble.com.
>
>
Re: Can we have an entity with no @Id?
Posted by Andrei Tchijov <an...@tchijov.com>.
Why do you need to use JPA at all in this scenario? If you concern about
performance, just use simple JDBC.
Keeping in mind that id is the only way to distinct one Entity from another,
I am fairly sure that it is impossible to define Entity without ID.
--
View this message in context: http://n2.nabble.com/Can-we-have-an-entity-with-no-%40Id--tp2945752p2946110.html
Sent from the OpenJPA Users mailing list archive at Nabble.com.