[Lift] Re: Using TemplatePf for JPA powered templates
Will do, if I figure it out. But my comment wasn't complaining. I am
honestly mystified. Am I the only one using trees in Hibernate? Is there
a tree library in Scala that I'm missing? What the heck does everyone
else do? It just blows my mind.
Chas.
Viktor Klang wrote:
On Mon, Dec 1, 2008 at 5:42 AM, Charles F. Munat [EMAIL PROTECTED]
mailto:[EMAIL PROTECTED] wrote:
Doing nested sets in your Lift snippet is pretty easy with JPA. I'm
doing it on one of my Lift sites. One thing to remember, however, is to
use a transaction. You don't want to do half the update to the tree and
then have another use start an update before you've finished yours (or
have half of it fail). Once it gets messed up it's a disaster.
Nested tables are good when you have lots of lookups, particularly
pulling ancestors or descendants, but not too many updates. Inserts are
not too bad, but if you have to move whole subtrees, that's a pain.
I'm using one for, among other things, a forum, so messages once posted
never get moved. Nested sets work great for that.
But, honestly, it is astonishing to me that Java, Scala, and especially
JPA/Hibernate apparently have no built in features for creating,
manipulating, and persisting trees (and networks are even less
supported). These problems were largely solved long ago. Why aren't they
built in?
Charles, I hate to say this, but Hibernate is Open Source, so you can
add the support for it. :)
Rails has a cool set of plugins -- acts_as_list, acts_as_tree, and
acts_as_nested_set -- that make it drop-dead simple to implement trees.
I was thinking that it would be cool if Lift had something similar but
maybe as a trait? So my object extends ActsAsNestedSet?
I tried to do this in Hibernate, but it would require the object to
query for other similar objects. For example, if I had a Node object
that I was persisting, I'd like to do
class Node extends ActsAsNestedSet
And then define methods such as moveToChildOf(node), moveToFirst,
moveBack, moveForth, moveToLast, etc. But it appears that you need an
EntityManager to run a query, and there doesn't seem to be a way to go
backwards from the Node to the EntityManager (probably because, if I
understand it correctly, there will only be one copy of a given Node in
memory but there may be multiple EntityManagers?).
So I put the code in the snippet.
If you come up with any clever solutions, I'd love to hear them.
Chas.
Tim Perrett wrote:
Hey Derek,
I've been playing around with this nested set stuff today - it's
pretty
cool. I nearly have an app working that uses the db for page
content and
maps the urls out however you want, it's pretty neat.
I have a slight HQL problem with subquery's but I'll post that
2mro :-)
Thanks for all your help
Tim
Sent from my iPhone
On 30 Nov 2008, at 23:37, Derek Chen-Becker
[EMAIL PROTECTED] mailto:[EMAIL PROTECTED]
mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] wrote:
IIRC, JPA has support for batch updates, but I'm not 100%
positive on
that. I'll have more time tomorrow to look at this if you'd
still like
to discuss it.
Derek
On Sun, Nov 30, 2008 at 12:32 PM, Tim Perrett
mailto:[EMAIL PROTECTED]
mailto:[EMAIL PROTECTED][EMAIL PROTECTED]
mailto:[EMAIL PROTECTED]
mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] wrote:
Derek,
Those links are *extremely* good - thank you! I've not
really done
anything with tree structures before and they are really, really
usefull.
One thing however, it appears the optimal way of doing the
insert
queries would be with stored procedures, however that im not
down
with, and ideally, i want to keep database vendor
independent (part of
the point of using JPA) so ideally i want to suck that up
into the
application logic. For instance:
--START
SELECT @myRight := rgt FROM nested_category WHERE name =
'TELEVISIONS';
UPDATE nested_category SET rgt = rgt + 2 WHERE rgt @myRight;
UPDATE nested_category SET lft = lft + 2 WHERE lft @myRight;
INSERT INTO nested_category(name, lft, rgt) VALUES('GAME
CONSOLES',
@myRight + 1, @myRight + 2);
--END
This makes use of variables, and i could of course do this via 3
separate queries in JPA, but i wondered if there was a
neater way to
construct this type of thing with JPA?
Any advice you guys have is most welcome
[Lift] Re: Using TemplatePf for JPA powered templates
Are you including a link to the parent node or are you just using the left and right values to figure out which nodes are children? I always include a foreign key to the parent so I can just select the children of that parent directly. Then to get all descendants, I use the left and right values. Similarly, to get the parent I use the foreign key, to get all ancestors, I use the left/right values. Does this help? (Sometimes I also include a calculated field called level which indicates how far away I am from the root node. It's a simple matter of counting the ancestors, but you have to remember to update it on moves. The level field is very useful if you want to go, say, two levels deep on children, or to parent and grandparent, but not great-grandparent.) Chas. Tim Perrett wrote: On Dec 1, 9:21 am, Charles F. Munat [EMAIL PROTECTED] wrote: Will do, if I figure it out. But my comment wasn't complaining. I am honestly mystified. Am I the only one using trees in Hibernate? Is there a tree library in Scala that I'm missing? What the heck does everyone else do? It just blows my mind. I found someone's contribution on Hibernate JIRA for handling sets, but it never seems to make it into core or the proper distro; it does seem odd its not in there. Anyway, the HQL problem I mentioned last night... I have the following HQL, which is just a slight mod from what was in that mysql article; effectivly I want to list all the children of a single leaf: SELECT node.name, (COUNT(parent.name) - (sub_tree.depth + 1)) AS depth FROM Content AS node, Content AS parent, Content AS sub_parent, ( SELECT node.name, (COUNT(parent.name) - 1) AS depth FROM Content AS node, Content AS parent WHERE node.lft BETWEEN parent.lft AND parent.rft AND node.name = :leaf GROUP BY node.name ORDER BY node.lft ) AS sub_tree WHERE node.lft BETWEEN parent.lft AND parent.rft AND node.lft BETWEEN sub_parent.lft AND sub_parent.rft AND sub_parent.name = sub_tree.name GROUP BY node.name HAVING depth = 1 ORDER BY node.lft However, it bombs on the sub-query in the SELECT ... FROM ... subquery statement im guessing you guys are using get all leaf nodes type queries, so what are you doing instead of this? Cheers Tim --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Lift group. To post to this group, send email to liftweb@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/liftweb?hl=en -~--~~~~--~~--~--~---
[Lift] Re: Using TemplatePf for JPA powered templates
Im not sure I follow? Can you use this diagram to try and explain?: http://dev.mysql.com/tech-resources/articles/hierarchical-data-4.png If you wanted to select the direct children of 'electronics', how would one go about doing that? Is there a simpler way than all that HQL? Cheers Tim On Dec 1, 10:28 am, Charles F. Munat [EMAIL PROTECTED] wrote: Are you including a link to the parent node or are you just using the left and right values to figure out which nodes are children? I always include a foreign key to the parent so I can just select the children of that parent directly. Then to get all descendants, I use the left and right values. Similarly, to get the parent I use the foreign key, to get all ancestors, I use the left/right values. Does this help? (Sometimes I also include a calculated field called level which indicates how far away I am from the root node. It's a simple matter of counting the ancestors, but you have to remember to update it on moves. The level field is very useful if you want to go, say, two levels deep on children, or to parent and grandparent, but not great-grandparent.) Chas. Tim Perrett wrote: On Dec 1, 9:21 am, Charles F. Munat [EMAIL PROTECTED] wrote: Will do, if I figure it out. But my comment wasn't complaining. I am honestly mystified. Am I the only one using trees in Hibernate? Is there a tree library in Scala that I'm missing? What the heck does everyone else do? It just blows my mind. I found someone's contribution on Hibernate JIRA for handling sets, but it never seems to make it into core or the proper distro; it does seem odd its not in there. Anyway, the HQL problem I mentioned last night... I have the following HQL, which is just a slight mod from what was in that mysql article; effectivly I want to list all the children of a single leaf: SELECT node.name, (COUNT(parent.name) - (sub_tree.depth + 1)) AS depth FROM Content AS node, Content AS parent, Content AS sub_parent, ( SELECT node.name, (COUNT(parent.name) - 1) AS depth FROM Content AS node, Content AS parent WHERE node.lft BETWEEN parent.lft AND parent.rft AND node.name = :leaf GROUP BY node.name ORDER BY node.lft ) AS sub_tree WHERE node.lft BETWEEN parent.lft AND parent.rft AND node.lft BETWEEN sub_parent.lft AND sub_parent.rft AND sub_parent.name = sub_tree.name GROUP BY node.name HAVING depth = 1 ORDER BY node.lft However, it bombs on the sub-query in the SELECT ... FROM ... subquery statement im guessing you guys are using get all leaf nodes type queries, so what are you doing instead of this? Cheers Tim --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Lift group. To post to this group, send email to liftweb@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/liftweb?hl=en -~--~~~~--~~--~--~---
[Lift] Re: Using TemplatePf for JPA powered templates
Tim, Please remember that Lift's Snippet processing is recursive. Thus, you don't really need to hook into the templating system in order to be able to using Lift's templates. For example, if your snippet returned: spanlift:comet type=Dog/lift:comet type=Cat//span Lift would then interpret the two comet tags and you'd wind up with two comet components on the page. However, I think it's a security risk to allow arbitrary users to be able to embed lift:xxx/ tags in their content. This would in effect allow any user access to any resource that any snippet has access to. On the caching front, I'd hand-roll my own caching mechanism. You'll probably end up caching all (or almost all) the content. Rather than doing some goofy stuff in SQL trying to do object graph traversals, just do it in objects. You can use immutability and actors to deal with most of the concurrency issues. Thanks, David On Sat, Nov 29, 2008 at 6:25 PM, Tim Perrett [EMAIL PROTECTED] wrote: I've been playing around with this and extending the template loader is actually pretty easy. Its much simpler than I thought it would be! I have a dilemma however - store the templates (and associated meta data) in the database and then have to do a fetch / read on every request, or, use the file system and hold (for instance): example.html and example.meta // java properties file format The tree structure of the file system is the path of least resistance for my particular use case i think, but i guess im after some input / advice...? I feel as either way has a couple of hang-ups! The kind of meta data is just simple key-value pair stuff, but my plan would be to extend Record so that the save() etc became transparent and was abstracted away (i.e. don't need to worry about InputStreams etc) Appreciate any input / advice people have Cheers Tim On Nov 29, 2:31 pm, Derek Chen-Becker [EMAIL PROTECTED] wrote: Looking at findVisibleTemplate in LiftSession (line 512) certainly makes it appear that the template table defined by addTemplateBefore/After is consulted before it checks the filesystem. Derek On Fri, Nov 28, 2008 at 10:26 AM, Tim Perrett [EMAIL PROTECTED] wrote: Hey guys, I want to user lifts LiftRules.addTemplateBefore/After to load templates from a database, where my persistence is JPA. With TemplatePf can I do this? Im also thinking this will be one of the nice things about having lift tags, as it will mean i shouldn't need to build a custom tagging language or anything (as we already have it!). I presume that TemplatePf just tells lift where to get the XHTML from then it continues to do the processing on it (process snippets etc)? Cheers Tim -- Lift, the simply functional web framework http://liftweb.net Collaborative Task Management http://much4.us Follow me: http://twitter.com/dpp Git some: http://github.com/dpp --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Lift group. To post to this group, send email to liftweb@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/liftweb?hl=en -~--~~~~--~~--~--~---
[Lift] Re: Using TemplatePf for JPA powered templates
Hey David, Thanks for the response - I have been reflecting on the whole L2 cache thing today and kind of came to the same conclusion. If the content has been served, it might as well be cached in its entirety as a HTML file so it can then be served by the front end web-server (nginx, apache etc) and i'll just expire the cache on a ad-hoc basis from the admin application. As for your concerns over security - I agree, it has grounding, but on the other hand, my plan was to provide a couple of snippets and document those, things like: - list all leaf nodes - list all nodes etc, etc I can also then take advantage of the lift localization mechanism - so all in all, I think the pro's out weigh the cons. Potentially in the XML page parser I could add a step which checked for the presence of un-allowed tags (like comet) via some XML DOM checking. Just a thought anyways :-) Cheers Tim On Dec 1, 5:11 pm, David Pollak [EMAIL PROTECTED] wrote: Tim, Please remember that Lift's Snippet processing is recursive. Thus, you don't really need to hook into the templating system in order to be able to using Lift's templates. For example, if your snippet returned: spanlift:comet type=Dog/lift:comet type=Cat//span Lift would then interpret the two comet tags and you'd wind up with two comet components on the page. However, I think it's a security risk to allow arbitrary users to be able to embed lift:xxx/ tags in their content. This would in effect allow any user access to any resource that any snippet has access to. On the caching front, I'd hand-roll my own caching mechanism. You'll probably end up caching all (or almost all) the content. Rather than doing some goofy stuff in SQL trying to do object graph traversals, just do it in objects. You can use immutability and actors to deal with most of the concurrency issues. Thanks, David --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Lift group. To post to this group, send email to liftweb@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/liftweb?hl=en -~--~~~~--~~--~--~---
[Lift] Re: Using TemplatePf for JPA powered templates
When I use a nested set, I make it like a combination of nested set and a simple tree. So in my database, I have: idparent_idlftrgtname -- 1 NULL 1 20Electronics 21 2 9Televisions 32 3 4Tube 42 5 6LCD 52 7 8Plasma 61 10 19Portable Electronics 76 11 14MP3 Players 87 12 13Flash 96 15 16CD Players 106 17 182-way Radios Then I get things the following way: For MP3 Players (#7): -- Ancestors select * from mytable where lft 11 and rgt 14; -- Ancestors and self select * from mytable where lft = 11 and rgt = 14; -- Parent select * from mytable where id = 6; -- Siblings and self select * from mytable where parent_id = 6; -- Siblings select * from mytable where parent_id = 6 and id 7; -- Siblings on the left select * from mytable where parent_id = 6 and rgt 11; -- Siblings on the right select * from mytable where parent_id = 6 and lft 14; -- Immediate children select * from mytable where parent_id = 7; -- Descendants and self select * from mytable where lft = 11 and rgt = 14; -- Descendants select * from mytable where lft 11 and rgt 14; In JPA/Hibernate, you'd have to modify this slightly. Each node in the tree would have a parent: Node attribute and a children: java.util.Set[Node] attribute. So then for example to get immediate children you would do: from Node n where n.parent.id = :id (But you could just access them through node.children as well.) Is this helping at all? Chas. Tim Perrett wrote: Im not sure I follow? Can you use this diagram to try and explain?: http://dev.mysql.com/tech-resources/articles/hierarchical-data-4.png If you wanted to select the direct children of 'electronics', how would one go about doing that? Is there a simpler way than all that HQL? Cheers Tim On Dec 1, 10:28 am, Charles F. Munat [EMAIL PROTECTED] wrote: Are you including a link to the parent node or are you just using the left and right values to figure out which nodes are children? I always include a foreign key to the parent so I can just select the children of that parent directly. Then to get all descendants, I use the left and right values. Similarly, to get the parent I use the foreign key, to get all ancestors, I use the left/right values. Does this help? (Sometimes I also include a calculated field called level which indicates how far away I am from the root node. It's a simple matter of counting the ancestors, but you have to remember to update it on moves. The level field is very useful if you want to go, say, two levels deep on children, or to parent and grandparent, but not great-grandparent.) Chas. Tim Perrett wrote: On Dec 1, 9:21 am, Charles F. Munat [EMAIL PROTECTED] wrote: Will do, if I figure it out. But my comment wasn't complaining. I am honestly mystified. Am I the only one using trees in Hibernate? Is there a tree library in Scala that I'm missing? What the heck does everyone else do? It just blows my mind. I found someone's contribution on Hibernate JIRA for handling sets, but it never seems to make it into core or the proper distro; it does seem odd its not in there. Anyway, the HQL problem I mentioned last night... I have the following HQL, which is just a slight mod from what was in that mysql article; effectivly I want to list all the children of a single leaf: SELECT node.name, (COUNT(parent.name) - (sub_tree.depth + 1)) AS depth FROM Content AS node, Content AS parent, Content AS sub_parent, ( SELECT node.name, (COUNT(parent.name) - 1) AS depth FROM Content AS node, Content AS parent WHERE node.lft BETWEEN parent.lft AND parent.rft AND node.name = :leaf GROUP BY node.name ORDER BY node.lft ) AS sub_tree WHERE node.lft BETWEEN parent.lft AND parent.rft AND node.lft BETWEEN sub_parent.lft AND sub_parent.rft AND sub_parent.name = sub_tree.name GROUP BY node.name HAVING depth = 1 ORDER BY node.lft However, it bombs on the sub-query in the SELECT ... FROM ... subquery statement im guessing you guys are using get all leaf nodes type queries, so what are you doing instead of this? Cheers Tim --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Lift group. To post to this group, send email to liftweb@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/liftweb?hl=en -~--~~~~--~~--~--~---
[Lift] Re: Using TemplatePf for JPA powered templates
On Sun, Nov 30, 2008 at 6:27 AM, Derek Chen-Becker [EMAIL PROTECTED] wrote: If you're heavily skewed towards reads and not writes (as it seems in the case of a CMS), you might want to look at Celko nested sets: http://www.intelligententerprise.com/001020/celko.jhtml http://dev.mysql.com/tech-resources/articles/hierarchical-data.html If you're going down this path, you should also read some of Vadim Tropashko's work on hierarchical SQL approaches. This blog post of his offers a good comparison of adjacency relations, nested sets, materialized paths, and nested intervals via matrix encoding: http://vadimtropashko.wordpress.com/2008/08/09/one-more-nested-intervals-vs-adjacency-list-comparison Trees in SQL http://www.dbazine.com/oracle/or-articles/tropashko4 http://www.dbazine.com/oracle/or-articles/tropashko5 Nested Intervals Tree Encoding with Continued Fractions http://arxiv.org/pdf/cs.DB/0402051 And here's an example circa 2004 Postgres There are some other options to consider, though. 1. You might be using a database that implements Recursive SQL 2. You might consider something like JCR instead here's an example of scaffolding for nodes with scalascii art: http://dev.day.com/microsling/content/blogs/main/scalajcr2.html 3. Why doesn't a template/metadata name without hierarchy work in your example? Shawn --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Lift group. To post to this group, send email to liftweb@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/liftweb?hl=en -~--~~~~--~~--~--~---
[Lift] Re: Using TemplatePf for JPA powered templates
Hey Viktor, If you use Hibernate you could simply configure the L2-cache and have Hibernate manage it for you. (EHCache or whatever cache-provider you like) This means you won't have to manually use the filesystem and can let the cache-provider do what it's good at :) I tried to implement L2 cache before with lift and didnt get very far - perhaps i'll give it another go. My other concern is performance - given a table like: create table tree_items ( id int(11) unsigned not null auto_increment, parent_id int(11) unsigned, name varchar(20), other_content varchar(255), primary key (id) ); where parent_id defines the tree structure, im a little worried that the queries would be come fairly bloated? I also did some looking around to see if there were any examples online of tree structures in JPA but alas could not find anything usefull - it appears its quite problematic...? Cheers Tim --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Lift group. To post to this group, send email to liftweb@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/liftweb?hl=en -~--~~~~--~~--~--~---
[Lift] Re: Using TemplatePf for JPA powered templates
If you're heavily skewed towards reads and not writes (as it seems in the case of a CMS), you might want to look at Celko nested sets: http://www.intelligententerprise.com/001020/celko.jhtml http://dev.mysql.com/tech-resources/articles/hierarchical-data.html A little more work on updates than an adjacency model, but a lot more efficient. Derek On Sun, Nov 30, 2008 at 6:29 AM, Viktor Klang [EMAIL PROTECTED]wrote: Hi Tim! I'm not sure I follow. What do you need the tree-structure for? /Vik On Sun, Nov 30, 2008 at 1:11 PM, Tim Perrett [EMAIL PROTECTED] wrote: Hey Viktor, If you use Hibernate you could simply configure the L2-cache and have Hibernate manage it for you. (EHCache or whatever cache-provider you like) This means you won't have to manually use the filesystem and can let the cache-provider do what it's good at :) I tried to implement L2 cache before with lift and didnt get very far - perhaps i'll give it another go. My other concern is performance - given a table like: create table tree_items ( id int(11) unsigned not null auto_increment, parent_id int(11) unsigned, name varchar(20), other_content varchar(255), primary key (id) ); where parent_id defines the tree structure, im a little worried that the queries would be come fairly bloated? I also did some looking around to see if there were any examples online of tree structures in JPA but alas could not find anything usefull - it appears its quite problematic...? Cheers Tim -- Viktor Klang Senior Systems Analyst --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Lift group. To post to this group, send email to liftweb@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/liftweb?hl=en -~--~~~~--~~--~--~---
[Lift] Re: Using TemplatePf for JPA powered templates
Hey viktor, I need the tree structure because it's for this publishing engine I'm writing. The idea is that you could create a page, and that page can have x number of children, and there children cab have children etc etc Does that make sense? Perhaps there is a more intuitive way to do this? Cheers Tim Sent from my iPhone On 30 Nov 2008, at 13:29, Viktor Klang [EMAIL PROTECTED] wrote: Hi Tim! I'm not sure I follow. What do you need the tree-structure for? /Vik On Sun, Nov 30, 2008 at 1:11 PM, Tim Perrett [EMAIL PROTECTED] wrote: Hey Viktor, If you use Hibernate you could simply configure the L2-cache and have Hibernate manage it for you. (EHCache or whatever cache-provider you like) This means you won't have to manually use the filesystem and can let the cache-provider do what it's good at :) I tried to implement L2 cache before with lift and didnt get very far - perhaps i'll give it another go. My other concern is performance - given a table like: create table tree_items ( id int(11) unsigned not null auto_increment, parent_id int(11) unsigned, name varchar(20), other_content varchar(255), primary key (id) ); where parent_id defines the tree structure, im a little worried that the queries would be come fairly bloated? I also did some looking around to see if there were any examples online of tree structures in JPA but alas could not find anything usefull - it appears its quite problematic...? Cheers Tim -- Viktor Klang Senior Systems Analyst --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Lift group. To post to this group, send email to liftweb@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/liftweb?hl=en -~--~~~~--~~--~--~---
[Lift] Re: Using TemplatePf for JPA powered templates
IIRC, JPA has support for batch updates, but I'm not 100% positive on that.
I'll have more time tomorrow to look at this if you'd still like to discuss
it.
Derek
On Sun, Nov 30, 2008 at 12:32 PM, Tim Perrett [EMAIL PROTECTED] wrote:
Derek,
Those links are *extremely* good - thank you! I've not really done
anything with tree structures before and they are really, really
usefull.
One thing however, it appears the optimal way of doing the insert
queries would be with stored procedures, however that im not down
with, and ideally, i want to keep database vendor independent (part of
the point of using JPA) so ideally i want to suck that up into the
application logic. For instance:
--START
SELECT @myRight := rgt FROM nested_category WHERE name =
'TELEVISIONS';
UPDATE nested_category SET rgt = rgt + 2 WHERE rgt @myRight;
UPDATE nested_category SET lft = lft + 2 WHERE lft @myRight;
INSERT INTO nested_category(name, lft, rgt) VALUES('GAME CONSOLES',
@myRight + 1, @myRight + 2);
--END
This makes use of variables, and i could of course do this via 3
separate queries in JPA, but i wondered if there was a neater way to
construct this type of thing with JPA?
Any advice you guys have is most welcome
Cheers
Tim
On Nov 30, 2:27 pm, Derek Chen-Becker [EMAIL PROTECTED] wrote:
If you're heavily skewed towards reads and not writes (as it seems in the
case of a CMS), you might want to look at Celko nested sets:
http://www.intelligententerprise.com/001020/celko.jhtml
http://dev.mysql.com/tech-resources/articles/hierarchical-data.html
A little more work on updates than an adjacency model, but a lot more
efficient.
Derek
--~--~-~--~~~---~--~~
You received this message because you are subscribed to the Google Groups
Lift group.
To post to this group, send email to liftweb@googlegroups.com
To unsubscribe from this group, send email to [EMAIL PROTECTED]
For more options, visit this group at
http://groups.google.com/group/liftweb?hl=en
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[Lift] Re: Using TemplatePf for JPA powered templates
Hey Derek,
I've been playing around with this nested set stuff today - it's
pretty cool. I nearly have an app working that uses the db for page
content and maps the urls out however you want, it's pretty neat.
I have a slight HQL problem with subquery's but I'll post that 2mro :-)
Thanks for all your help
Tim
Sent from my iPhone
On 30 Nov 2008, at 23:37, Derek Chen-Becker [EMAIL PROTECTED]
wrote:
IIRC, JPA has support for batch updates, but I'm not 100% positive
on that. I'll have more time tomorrow to look at this if you'd still
like to discuss it.
Derek
On Sun, Nov 30, 2008 at 12:32 PM, Tim Perrett [EMAIL PROTECTED]
wrote:
Derek,
Those links are *extremely* good - thank you! I've not really done
anything with tree structures before and they are really, really
usefull.
One thing however, it appears the optimal way of doing the insert
queries would be with stored procedures, however that im not down
with, and ideally, i want to keep database vendor independent (part of
the point of using JPA) so ideally i want to suck that up into the
application logic. For instance:
--START
SELECT @myRight := rgt FROM nested_category WHERE name =
'TELEVISIONS';
UPDATE nested_category SET rgt = rgt + 2 WHERE rgt @myRight;
UPDATE nested_category SET lft = lft + 2 WHERE lft @myRight;
INSERT INTO nested_category(name, lft, rgt) VALUES('GAME CONSOLES',
@myRight + 1, @myRight + 2);
--END
This makes use of variables, and i could of course do this via 3
separate queries in JPA, but i wondered if there was a neater way to
construct this type of thing with JPA?
Any advice you guys have is most welcome
Cheers
Tim
On Nov 30, 2:27 pm, Derek Chen-Becker [EMAIL PROTECTED] wrote:
If you're heavily skewed towards reads and not writes (as it seems
in the
case of a CMS), you might want to look at Celko nested sets:
http://www.intelligententerprise.com/001020/celko.jhtml
http://dev.mysql.com/tech-resources/articles/hierarchical-data.html
A little more work on updates than an adjacency model, but a lot
more
efficient.
Derek
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[Lift] Re: Using TemplatePf for JPA powered templates
Doing nested sets in your Lift snippet is pretty easy with JPA. I'm
doing it on one of my Lift sites. One thing to remember, however, is to
use a transaction. You don't want to do half the update to the tree and
then have another use start an update before you've finished yours (or
have half of it fail). Once it gets messed up it's a disaster.
Nested tables are good when you have lots of lookups, particularly
pulling ancestors or descendants, but not too many updates. Inserts are
not too bad, but if you have to move whole subtrees, that's a pain.
I'm using one for, among other things, a forum, so messages once posted
never get moved. Nested sets work great for that.
But, honestly, it is astonishing to me that Java, Scala, and especially
JPA/Hibernate apparently have no built in features for creating,
manipulating, and persisting trees (and networks are even less
supported). These problems were largely solved long ago. Why aren't they
built in?
Rails has a cool set of plugins -- acts_as_list, acts_as_tree, and
acts_as_nested_set -- that make it drop-dead simple to implement trees.
I was thinking that it would be cool if Lift had something similar but
maybe as a trait? So my object extends ActsAsNestedSet?
I tried to do this in Hibernate, but it would require the object to
query for other similar objects. For example, if I had a Node object
that I was persisting, I'd like to do
class Node extends ActsAsNestedSet
And then define methods such as moveToChildOf(node), moveToFirst,
moveBack, moveForth, moveToLast, etc. But it appears that you need an
EntityManager to run a query, and there doesn't seem to be a way to go
backwards from the Node to the EntityManager (probably because, if I
understand it correctly, there will only be one copy of a given Node in
memory but there may be multiple EntityManagers?).
So I put the code in the snippet.
If you come up with any clever solutions, I'd love to hear them.
Chas.
Tim Perrett wrote:
Hey Derek,
I've been playing around with this nested set stuff today - it's pretty
cool. I nearly have an app working that uses the db for page content and
maps the urls out however you want, it's pretty neat.
I have a slight HQL problem with subquery's but I'll post that 2mro :-)
Thanks for all your help
Tim
Sent from my iPhone
On 30 Nov 2008, at 23:37, Derek Chen-Becker [EMAIL PROTECTED]
mailto:[EMAIL PROTECTED] wrote:
IIRC, JPA has support for batch updates, but I'm not 100% positive on
that. I'll have more time tomorrow to look at this if you'd still like
to discuss it.
Derek
On Sun, Nov 30, 2008 at 12:32 PM, Tim Perrett
mailto:[EMAIL PROTECTED][EMAIL PROTECTED]
mailto:[EMAIL PROTECTED] wrote:
Derek,
Those links are *extremely* good - thank you! I've not really done
anything with tree structures before and they are really, really
usefull.
One thing however, it appears the optimal way of doing the insert
queries would be with stored procedures, however that im not down
with, and ideally, i want to keep database vendor independent (part of
the point of using JPA) so ideally i want to suck that up into the
application logic. For instance:
--START
SELECT @myRight := rgt FROM nested_category WHERE name =
'TELEVISIONS';
UPDATE nested_category SET rgt = rgt + 2 WHERE rgt @myRight;
UPDATE nested_category SET lft = lft + 2 WHERE lft @myRight;
INSERT INTO nested_category(name, lft, rgt) VALUES('GAME CONSOLES',
@myRight + 1, @myRight + 2);
--END
This makes use of variables, and i could of course do this via 3
separate queries in JPA, but i wondered if there was a neater way to
construct this type of thing with JPA?
Any advice you guys have is most welcome
Cheers
Tim
On Nov 30, 2:27 pm, Derek Chen-Becker [EMAIL PROTECTED]
mailto:[EMAIL PROTECTED] wrote:
If you're heavily skewed towards reads and not writes (as it
seems in the
case of a CMS), you might want to look at Celko nested sets:
http://www.intelligententerprise.com/001020/celko.jhtmlhttp://www.intelligententerprise.com/001020/celko.jhtml
http://dev.mysql.com/tech-resources/articles/hierarchical-data.htmlhttp://dev.mysql.com/tech-resources/articles/hierarchical-data.html
A little more work on updates than an adjacency model, but a lot
more
efficient.
Derek
--~--~-~--~~~---~--~~
You received this message because you are subscribed to the Google Groups
Lift group.
To post to this group, send email to liftweb@googlegroups.com
To unsubscribe from this group, send email to [EMAIL PROTECTED]
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-~--~~~~--~~--~--~---
[Lift] Re: Using TemplatePf for JPA powered templates
On Mon, Dec 1, 2008 at 5:42 AM, Charles F. Munat [EMAIL PROTECTED] wrote:
Doing nested sets in your Lift snippet is pretty easy with JPA. I'm
doing it on one of my Lift sites. One thing to remember, however, is to
use a transaction. You don't want to do half the update to the tree and
then have another use start an update before you've finished yours (or
have half of it fail). Once it gets messed up it's a disaster.
Nested tables are good when you have lots of lookups, particularly
pulling ancestors or descendants, but not too many updates. Inserts are
not too bad, but if you have to move whole subtrees, that's a pain.
I'm using one for, among other things, a forum, so messages once posted
never get moved. Nested sets work great for that.
But, honestly, it is astonishing to me that Java, Scala, and especially
JPA/Hibernate apparently have no built in features for creating,
manipulating, and persisting trees (and networks are even less
supported). These problems were largely solved long ago. Why aren't they
built in?
Charles, I hate to say this, but Hibernate is Open Source, so you can add
the support for it. :)
Rails has a cool set of plugins -- acts_as_list, acts_as_tree, and
acts_as_nested_set -- that make it drop-dead simple to implement trees.
I was thinking that it would be cool if Lift had something similar but
maybe as a trait? So my object extends ActsAsNestedSet?
I tried to do this in Hibernate, but it would require the object to
query for other similar objects. For example, if I had a Node object
that I was persisting, I'd like to do
class Node extends ActsAsNestedSet
And then define methods such as moveToChildOf(node), moveToFirst,
moveBack, moveForth, moveToLast, etc. But it appears that you need an
EntityManager to run a query, and there doesn't seem to be a way to go
backwards from the Node to the EntityManager (probably because, if I
understand it correctly, there will only be one copy of a given Node in
memory but there may be multiple EntityManagers?).
So I put the code in the snippet.
If you come up with any clever solutions, I'd love to hear them.
Chas.
Tim Perrett wrote:
Hey Derek,
I've been playing around with this nested set stuff today - it's pretty
cool. I nearly have an app working that uses the db for page content and
maps the urls out however you want, it's pretty neat.
I have a slight HQL problem with subquery's but I'll post that 2mro :-)
Thanks for all your help
Tim
Sent from my iPhone
On 30 Nov 2008, at 23:37, Derek Chen-Becker [EMAIL PROTECTED]
mailto:[EMAIL PROTECTED] wrote:
IIRC, JPA has support for batch updates, but I'm not 100% positive on
that. I'll have more time tomorrow to look at this if you'd still like
to discuss it.
Derek
On Sun, Nov 30, 2008 at 12:32 PM, Tim Perrett
mailto:[EMAIL PROTECTED][EMAIL PROTECTED]
mailto:[EMAIL PROTECTED] wrote:
Derek,
Those links are *extremely* good - thank you! I've not really done
anything with tree structures before and they are really, really
usefull.
One thing however, it appears the optimal way of doing the insert
queries would be with stored procedures, however that im not down
with, and ideally, i want to keep database vendor independent (part
of
the point of using JPA) so ideally i want to suck that up into the
application logic. For instance:
--START
SELECT @myRight := rgt FROM nested_category WHERE name =
'TELEVISIONS';
UPDATE nested_category SET rgt = rgt + 2 WHERE rgt @myRight;
UPDATE nested_category SET lft = lft + 2 WHERE lft @myRight;
INSERT INTO nested_category(name, lft, rgt) VALUES('GAME CONSOLES',
@myRight + 1, @myRight + 2);
--END
This makes use of variables, and i could of course do this via 3
separate queries in JPA, but i wondered if there was a neater way to
construct this type of thing with JPA?
Any advice you guys have is most welcome
Cheers
Tim
On Nov 30, 2:27 pm, Derek Chen-Becker [EMAIL PROTECTED]
mailto:[EMAIL PROTECTED] wrote:
If you're heavily skewed towards reads and not writes (as it
seems in the
case of a CMS), you might want to look at Celko nested sets:
http://www.intelligententerprise.com/001020/celko.jhtml
http://www.intelligententerprise.com/001020/celko.jhtml
http://dev.mysql.com/tech-resources/articles/hierarchical-data.html
http://dev.mysql.com/tech-resources/articles/hierarchical-data.html
A little more work on updates than an adjacency model, but a lot
more
efficient.
Derek
--
Viktor Klang
Senior Systems Analyst
--~--~-~--~~~---~--~~
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Lift group.
To post to this group, send email to
[Lift] Re: Using TemplatePf for JPA powered templates
I've been playing around with this and extending the template loader is actually pretty easy. Its much simpler than I thought it would be! I have a dilemma however - store the templates (and associated meta data) in the database and then have to do a fetch / read on every request, or, use the file system and hold (for instance): example.html and example.meta // java properties file format The tree structure of the file system is the path of least resistance for my particular use case i think, but i guess im after some input / advice...? I feel as either way has a couple of hang-ups! The kind of meta data is just simple key-value pair stuff, but my plan would be to extend Record so that the save() etc became transparent and was abstracted away (i.e. don't need to worry about InputStreams etc) Appreciate any input / advice people have Cheers Tim On Nov 29, 2:31 pm, Derek Chen-Becker [EMAIL PROTECTED] wrote: Looking at findVisibleTemplate in LiftSession (line 512) certainly makes it appear that the template table defined by addTemplateBefore/After is consulted before it checks the filesystem. Derek On Fri, Nov 28, 2008 at 10:26 AM, Tim Perrett [EMAIL PROTECTED] wrote: Hey guys, I want to user lifts LiftRules.addTemplateBefore/After to load templates from a database, where my persistence is JPA. With TemplatePf can I do this? Im also thinking this will be one of the nice things about having lift tags, as it will mean i shouldn't need to build a custom tagging language or anything (as we already have it!). I presume that TemplatePf just tells lift where to get the XHTML from then it continues to do the processing on it (process snippets etc)? Cheers Tim --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Lift group. To post to this group, send email to liftweb@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/liftweb?hl=en -~--~~~~--~~--~--~---
[Lift] Re: Using TemplatePf for JPA powered templates
If you use Hibernate you could simply configure the L2-cache and have Hibernate manage it for you. (EHCache or whatever cache-provider you like) This means you won't have to manually use the filesystem and can let the cache-provider do what it's good at :) Cheers, Viktor On Sun, Nov 30, 2008 at 3:25 AM, Tim Perrett [EMAIL PROTECTED] wrote: I've been playing around with this and extending the template loader is actually pretty easy. Its much simpler than I thought it would be! I have a dilemma however - store the templates (and associated meta data) in the database and then have to do a fetch / read on every request, or, use the file system and hold (for instance): example.html and example.meta // java properties file format The tree structure of the file system is the path of least resistance for my particular use case i think, but i guess im after some input / advice...? I feel as either way has a couple of hang-ups! The kind of meta data is just simple key-value pair stuff, but my plan would be to extend Record so that the save() etc became transparent and was abstracted away (i.e. don't need to worry about InputStreams etc) Appreciate any input / advice people have Cheers Tim On Nov 29, 2:31 pm, Derek Chen-Becker [EMAIL PROTECTED] wrote: Looking at findVisibleTemplate in LiftSession (line 512) certainly makes it appear that the template table defined by addTemplateBefore/After is consulted before it checks the filesystem. Derek On Fri, Nov 28, 2008 at 10:26 AM, Tim Perrett [EMAIL PROTECTED] wrote: Hey guys, I want to user lifts LiftRules.addTemplateBefore/After to load templates from a database, where my persistence is JPA. With TemplatePf can I do this? Im also thinking this will be one of the nice things about having lift tags, as it will mean i shouldn't need to build a custom tagging language or anything (as we already have it!). I presume that TemplatePf just tells lift where to get the XHTML from then it continues to do the processing on it (process snippets etc)? Cheers Tim -- Viktor Klang Senior Systems Analyst --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Lift group. To post to this group, send email to liftweb@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/liftweb?hl=en -~--~~~~--~~--~--~---
