1:25 p.m.
I have a little proposal for supporting the use of a KEY expression in
the FROM clause and I'd like to hear your opinions on that.
Unfortunately the JPA spec does not support that, but since a key of a
java.util.Map mapping may be an entity type, we need to specify how one
can "join" that key explicitly.
Right now(pre HHH-10537), when joining a java.util.Map mapping, an inner
join is generated for the map key entity type. In my fix for HHH-10537 I
changed the behavior to respect/inherit the join type of the collection
join.
The problem is, that one can't further join any attributes on that key,
because there is no syntax in the HQL or the JPA spec that allows to do
that.
We need to decide (1) whether we always want to join the entity key or
require the user to do that specifically via e.g. something like "JOIN
alias.map m JOIN KEY(m) k"
and also (2) how the syntax for joining further attributes should look
like. If we decide to not allow the "JOIN KEY(m)" syntax for (1) we have
to support something like "JOIN KEY(m).association", otherwise we can
just use the alias like for normal joins "JOIN k.association".
Either way, we have to change the grammar but I'd rather like to
support/implement the map key joining syntax like "JOIN KEY(m) k" for
(1). A further change to that would be to not generate the implicit key
table join anymore but require the user to do the join explicitly. Since
that would break backwards compatibility, I'd like to make that behavior
configurable and of course, by default it will generate the implicit key
join to maintain backwards compatibility. I also propose to switch the
default in 6.0 so that the join is not generate anymore.
The usage in the JPA Criteria API will unfortunately require a cast
since the return type of javax.persistence.metamodel.MapAttribute#key()
is javax.persistence.metamodel.Path instead of
javax.persistence.metamodel.SingularAttribute but essentially the same
functionality is available to a user out of the box.
Specifying a custom join for a key would look like this in the Criteria API
MapAttribute<Entity, MapKeyEntity, MapValueEntity> mapAttribute = ...
Join<Entity, MapKeyEntity> keyEntity =
mapAttribute.join((SingularAttribute<? super Entity, ? extends
MapKeyEntity>) mapAttribute.key(), JoinType.LEFT);
keyEntity.join(...)
So the questions again.
1. Do you all agree that this is important and should be done?
2. Agree to not generate implicit joins for keys in future versions?
3. Allow joining the key in a separate join?
4. Allow further joins on a key?
5. Happy with how it can be done in JPA Criteria?
In addition to that, it would be nice if anyone could make someone from
the JPA EG aware of this.
From a JPQL BNF point of view, I'd propose the following changes
from
join_single_valued_path_expression::=
identification_variable.{single_valued_embeddable_object_field.}*single_valued_object_field
to
join_single_valued_path_expression::=
identification_variable.{single_valued_embeddable_object_field.}*single_valued_object_field
|
map_field_identification_variable
Regards,
Christian
2:28 p.m.
Fwiw EclipseLink supports both syntaxes "JOIN KEY(m) k" and also "JOIN
KEY(m).association".
Am 27.01.2017 um 20:25 schrieb Christian Beikov:
I have a little proposal for supporting the use of a KEY expression
in
the FROM clause and I'd like to hear your opinions on that.
Unfortunately the JPA spec does not support that, but since a key of a
java.util.Map mapping may be an entity type, we need to specify how
one can "join" that key explicitly.
Right now(pre HHH-10537), when joining a java.util.Map mapping, an
inner join is generated for the map key entity type. In my fix for
HHH-10537 I changed the behavior to respect/inherit the join type of
the collection join.
The problem is, that one can't further join any attributes on that
key, because there is no syntax in the HQL or the JPA spec that allows
to do that.
We need to decide (1) whether we always want to join the entity key or
require the user to do that specifically via e.g. something like "JOIN
alias.map m JOIN KEY(m) k"
and also (2) how the syntax for joining further attributes should look
like. If we decide to not allow the "JOIN KEY(m)" syntax for (1) we
have to support something like "JOIN KEY(m).association", otherwise we
can just use the alias like for normal joins "JOIN k.association".
Either way, we have to change the grammar but I'd rather like to
support/implement the map key joining syntax like "JOIN KEY(m) k" for
(1). A further change to that would be to not generate the implicit
key table join anymore but require the user to do the join explicitly.
Since that would break backwards compatibility, I'd like to make that
behavior configurable and of course, by default it will generate the
implicit key join to maintain backwards compatibility. I also propose
to switch the default in 6.0 so that the join is not generate anymore.
The usage in the JPA Criteria API will unfortunately require a cast
since the return type of
javax.persistence.metamodel.MapAttribute#key() is
javax.persistence.metamodel.Path instead of
javax.persistence.metamodel.SingularAttribute but essentially the same
functionality is available to a user out of the box.
Specifying a custom join for a key would look like this in the
Criteria API
MapAttribute<Entity, MapKeyEntity, MapValueEntity> mapAttribute = ...
Join<Entity, MapKeyEntity> keyEntity =
mapAttribute.join((SingularAttribute<? super Entity, ? extends
MapKeyEntity>) mapAttribute.key(), JoinType.LEFT);
keyEntity.join(...)
So the questions again.
1. Do you all agree that this is important and should be done?
2. Agree to not generate implicit joins for keys in future versions?
3. Allow joining the key in a separate join?
4. Allow further joins on a key?
5. Happy with how it can be done in JPA Criteria?
In addition to that, it would be nice if anyone could make someone
from the JPA EG aware of this.
From a JPQL BNF point of view, I'd propose the following changes
from
join_single_valued_path_expression::=
identification_variable.{single_valued_embeddable_object_field.}*single_valued_object_field
to
join_single_valued_path_expression::=
identification_variable.{single_valued_embeddable_object_field.}*single_valued_object_field
|
map_field_identification_variable
Regards,
Christian
4:59 p.m.
FWIW = for what it is worth.
TBH, to me it is not worth much ;)
I don't do things "just because EclipseLink does it".
On Fri, Jan 27, 2017 at 2:33 PM Christian Beikov <christian.beikov(a)gmail.com>
wrote:
Fwiw EclipseLink supports both syntaxes "JOIN KEY(m) k" and
also "JOIN
KEY(m).association".
Am 27.01.2017 um 20:25 schrieb Christian Beikov:
> I have a little proposal for supporting the use of a KEY expression in
> the FROM clause and I'd like to hear your opinions on that.
> Unfortunately the JPA spec does not support that, but since a key of a
> java.util.Map mapping may be an entity type, we need to specify how
> one can "join" that key explicitly.
>
> Right now(pre HHH-10537), when joining a java.util.Map mapping, an
> inner join is generated for the map key entity type. In my fix for
> HHH-10537 I changed the behavior to respect/inherit the join type of
> the collection join.
> The problem is, that one can't further join any attributes on that
> key, because there is no syntax in the HQL or the JPA spec that allows
> to do that.
>
> We need to decide (1) whether we always want to join the entity key or
> require the user to do that specifically via e.g. something like "JOIN
> alias.map m JOIN KEY(m) k"
> and also (2) how the syntax for joining further attributes should look
> like. If we decide to not allow the "JOIN KEY(m)" syntax for (1) we
> have to support something like "JOIN KEY(m).association", otherwise we
> can just use the alias like for normal joins "JOIN k.association".
> Either way, we have to change the grammar but I'd rather like to
> support/implement the map key joining syntax like "JOIN KEY(m) k" for
> (1). A further change to that would be to not generate the implicit
> key table join anymore but require the user to do the join explicitly.
> Since that would break backwards compatibility, I'd like to make that
> behavior configurable and of course, by default it will generate the
> implicit key join to maintain backwards compatibility. I also propose
> to switch the default in 6.0 so that the join is not generate anymore.
> The usage in the JPA Criteria API will unfortunately require a cast
> since the return type of
> javax.persistence.metamodel.MapAttribute#key() is
> javax.persistence.metamodel.Path instead of
> javax.persistence.metamodel.SingularAttribute but essentially the same
> functionality is available to a user out of the box.
> Specifying a custom join for a key would look like this in the
> Criteria API
>
> MapAttribute<Entity, MapKeyEntity, MapValueEntity> mapAttribute = ...
> Join<Entity, MapKeyEntity> keyEntity =
> mapAttribute.join((SingularAttribute<? super Entity, ? extends
> MapKeyEntity>) mapAttribute.key(), JoinType.LEFT);
> keyEntity.join(...)
>
> So the questions again.
> 1. Do you all agree that this is important and should be done?
> 2. Agree to not generate implicit joins for keys in future versions?
> 3. Allow joining the key in a separate join?
> 4. Allow further joins on a key?
> 5. Happy with how it can be done in JPA Criteria?
>
> In addition to that, it would be nice if anyone could make someone
> from the JPA EG aware of this.
> From a JPQL BNF point of view, I'd propose the following changes
>
> from
>
> join_single_valued_path_expression::=
>
identification_variable.{single_valued_embeddable_object_field.}*single_valued_object_field
>
>
> to
>
> join_single_valued_path_expression::=
>
identification_variable.{single_valued_embeddable_object_field.}*single_valued_object_field
> |
> map_field_identification_variable
>
> Regards,
> Christian
_______________________________________________
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hibernate-dev(a)lists.jboss.org
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4:58 p.m.
My initial thoughts...
On Fri, Jan 27, 2017 at 1:29 PM Christian Beikov <christian.beikov(a)gmail.com wrote:
I am missing how 1, 2 and 3 are any different. Anyway...
I think it is useful. I think we should plan to do it... for 6.0
> 4. Allow further joins on a key?
And this is a natural consequence of 1, 2 and 3 ;)
> 5. Happy with how it can be done in JPA Criteria?
Meh. JPA is a spec. We can make proposals, but we are not the only ones
on the EG. What is more important to me is that we make it possible from
*our* implementation of the spec.
Especially moving forward considering we dropped the legacy criteria API
and plan to develop criteria extensions on top of the JPA criteria API. It
is overall better designed - we just need to add in our extras that JPA
does not support. What that looks like exactly (to get around JPA not
defining it) is not very as relevant to me. We'll make the proposal which
is the most we can do.
> In addition to that, it would be nice if anyone could make someone from
> the JPA EG aware of this.
From a JPQL BNF point of view, I'd propose the following
changes
> from
> join_single_valued_path_expression::=
>
identification_variable.{single_valued_embeddable_object_field.}*single_valued_object_field
> to
> join_single_valued_path_expression::=
>
identification_variable.{single_valued_embeddable_object_field.}*single_valued_object_field
> |
> map_field_identification_variable
Well considering myself, Scott and
Emmanuel are all part of the JPA EG...
done ;)
That said, in my experience, the JPA EG (or certain members of it) tend to
be extremely resistent to changes. I'm not certain this is something they
would go for, specificaly because of the Criteria implication you mention.
While I'm not sure it says this specifically, the assumption is that the
BNF applies to both JPQL and Criteria. We can certainly bring it up for
discussion if/when we have serious discussions about the "next steps" for
the spec.
I have a little proposal for supporting the use of a KEY expression
in
the FROM clause and I'd like to hear your opinions on that.
Unfortunately the JPA spec does not support that, but since a key of a
java.util.Map mapping may be an entity type, we need to specify how one
can "join" that key explicitly.
Right now(pre HHH-10537), when joining a java.util.Map mapping, an
inner
join is generated for the map key entity type. In my fix for HHH-10537 I
changed the behavior to respect/inherit the join type of the collection
join.
The problem is, that one can't further join any attributes on that key,
because there is no syntax in the HQL or the JPA spec that allows to do
that.
We need to decide (1) whether we always want to join the entity key or
require the user to do that specifically via e.g. something like "JOIN
alias.map m JOIN KEY(m) k"
and also (2) how the syntax for joining further attributes should look
like. If we decide to not allow the "JOIN KEY(m)" syntax for (1) we have
to support something like "JOIN KEY(m).association", otherwise we can
just use the alias like for normal joins "JOIN k.association".
I definitely like the syntax to join the key if it happens to be an entity
(or an embedded!). That makes the syntax for further referencing or
joining it's attributes very natural.
Either way, we have to change the grammar but I'd rather like to
support/implement the map key joining syntax like "JOIN KEY(m)
k" for
(1).
By "change the grammar" I assume you mean the JPA query BNF? Because the
SQM grammar already supports this. Or perhaps you mean the pre-6.0
Hibernate grammar? If so, see below.
A further change to that would be to not generate the implicit key
table join anymore but require the user to do the join explicitly.
Since
that would break backwards compatibility, I'd like to make that behavior
configurable and of course, by default it will generate the implicit key
join to maintain backwards compatibility. I also propose to switch the
default in 6.0 so that the join is not generate anymore.
I personally would vote to *not* make this change in 5.x even in terms of
making it configurable. The grammar there is fugly enough already and this
is the kind of thing (especially making branches of it configurable) that
takes that fugliness to a new level.
But I think it is a useful change and would certainly consider it for 6.0
The usage in the JPA Criteria API will unfortunately require a cast
since the return type of javax.persistence.metamodel.MapAttribute#key()
is javax.persistence.metamodel.Path instead of
javax.persistence.metamodel.SingularAttribute but essentially the same
functionality is available to a user out of the box.
Right. In terms of SQM and 6.0 this perfectly illustrates the importance
of the Navigable/NavigableSource contracts and defining references and
joins based on them as opposed to strictly attribute-based.
I *hate* the idea of making the map key "pose" as a SingularAttribute just
for the sake of doing things we should be able to do with it. We have to
cast anyway, so I'd much prefer to cast to Hibernate-specific (this is
Hibernate specific anyway) contracts that expose this more properly
probably based on Navigable/NavigableSource above.
In those terms, a map key is always a Navigable. If the key happens to be
an entity (or an embedded!) then the key is also a NavigableSource and can
therefore be further dereferenced. I'd rather base such an extension on
this concept rather than making map key be something it is not just to make
it work. We can make it work and model it correctly!
Specifying a custom join for a key would look like this in the Criteria API
MapAttribute<Entity, MapKeyEntity, MapValueEntity> mapAttribute = ...
Join<Entity, MapKeyEntity> keyEntity =
mapAttribute.join((SingularAttribute<? super Entity, ? extends
MapKeyEntity>) mapAttribute.key(), JoinType.LEFT);
keyEntity.join(...)
So the questions again.
1. Do you all agree that this is important and should be done?
2. Agree to not generate implicit joins for keys in future versions?
3. Allow joining the key in a separate join?
5 a.m.
I created an issue for this feature:
https://hibernate.atlassian.net/browse/HHH-11433
If we agree to render "domain joins" that involve multiple tables with
the ANSI SQL parenthesis join syntax, we can actually even "ignore" the
join types for key and value tables. That would make things like
referring to subtype properties in an ON clause also a lot easier.
Here a quick example:
@Entity class Entity{ Map<X, A> map; }
@Entity @Inheritance(JOINED) class A{ ... }
@Entity class B extends A { String propertyB; }
@Entity class C extends A { String propertyC; }
@Entity @Inheritance(JOINED) class X { String propertyX; }
@Entity class Y { String propertyY; }
@Entity class Z { String propertyZ; }
SELECT e.id, KEY(m), VALUE(m)
FROM Entity e
LEFT JOIN e.map m
ON KEY(m).propertyX > 0 AND TREAT(KEY(m) AS Y).propertyY = TREAT(m
AS B).propertyB
OR KEY(m).propertyX <= 0 AND TREAT(KEY(m) AS Z).propertyZ = TREAT(m
AS C).propertyC
That would render roughly like
SELECT ...
FROM table_entity e
LEFT JOIN (
table_map m
JOIN (
table_x x
LEFT JOIN table_y y ON x.id = y.id
LEFT JOIN table_z z ON x.id = z.id
) ON m.key = x.id
JOIN (
table_a a
LEFT JOIN table_b b ON a.id = b.id
LEFT JOIN table_c c ON a.id = c.id
) ON m.value = a.id
) m ON m.e_id = e.id AND (
x.property_x > 0 AND y.property_y = b.property_b
OR x.property_x <= 0 AND z.property_z = c.property_c
)
I guess the concept of the parenthesis join fits the table group idea?
Am 27.01.2017 um 23:58 schrieb Steve Ebersole
A further change to that would be to not generate the implicit key
table join anymore but require the user to do the join explicitly.
Since
that would break backwards compatibility, I'd like to make that
behavior
configurable and of course, by default it will generate the
implicit key
join to maintain backwards compatibility. I also propose to switch the
default in 6.0 so that the join is not generate anymore.
I personally would vote to *not* make this change in 5.x even in terms
of making it configurable. The grammar there is fugly enough already
and this is the kind of thing (especially making branches of it
configurable) that takes that fugliness to a new level.
I gave that another thought and don't think that requiring the user to
do a separate join is a good idea anymore. We can actually infer if a
join is required and when using the ANSI parenthesis join syntax the
join type does not really matter. If we stick to the join rendering
style we have, we should just use the collection tables join type.
Do you think it makes sense to implement support for "JOIN
KEY(m).association" in 5.2 or just leave it as it is? I would implement
that if you give your ok.
What do you think about all that so far?
2:55 p.m.
My thoughts....
On 01/28/2017 06:00 AM, Christian Beikov wrote:
I created an issue for this feature:
https://hibernate.atlassian.net/browse/HHH-11433
Am 27.01.2017 um 23:58 schrieb Steve Ebersole
> I personally would vote to *not* make this change in 5.x even in terms
> of making it configurable. The grammar there is fugly enough already
> and this is the kind of thing (especially making branches of it
> configurable) that takes that fugliness to a new level.
I gave that another thought and don't think that requiring the user to
do a separate join is a good idea anymore. We can actually infer if a
join is required and when using the ANSI parenthesis join syntax the
join type does not really matter. If we stick to the join rendering
style we have, we should just use the collection tables join type.
Do you think it makes sense to implement support for "JOIN
KEY(m).association" in 5.2 or just leave it as it is? I would implement
that if you give your ok.
What do you think about all that so far?
I'd say we likely shouldn't be putting significant effort into adding
**new features*** *into 5.2. I'd recommend adding it into the 6.0
branch and if/when we decide to consider a 5.3 branch release as a
further stepping stone to 6.0, perhaps we back-port this feature to that
branch if the team feels its relevant to do so.
But that's just my perspective :).
Chris
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Steve Ebersole