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• Blocking on DBCP connection pool (open and close connnection). Is database connection pooling in OpenEJB pluggable?

  - by topchef

  We use OpenEJB on Tomcat (used to run on JBoss, Weblogic, etc.). While running load tests we experience significant performance problems with handling JMS messages (queues). Problem was localized to blocking on database connection pool getting or releasing connection to the pool. Blocking prevented concurrent MDB instances (threads) from running hence performance suffered 10-fold and worse. The same code used to run on application servers (with their respective connection pool implementations) with no blocking at all. Example of thread blocked: Name: JMS Resource Adapter-worker-23 State: BLOCKED on org.apache.commons.pool.impl.GenericObjectPool@1ea6b4a owned by: JMS Resource Adapter-worker-19 Total blocked: 18,426 Total waited: 0 Stack trace: org.apache.commons.pool.impl.GenericObjectPool.returnObject(GenericObjectPool.java:916) org.apache.commons.dbcp.PoolableConnection.close(PoolableConnection.java:91) - locked org.apache.commons.dbcp.PoolableConnection@1bcba8 org.apache.commons.dbcp.managed.ManagedConnection.close(ManagedConnection.java:147) com.xxxxx.persistence.DbHelper.closeConnection(DbHelper.java:290) .... Couple of questions. I am almost certain that some transactional attributes and properties contribute to this blocking, but MDBs are defined as non-transactional (we use both annotations and ejb-jar.xml). Some EJBs do use container-managed transactions though (and we can observe blocking there as well). Are there any DBCP configurations that may fix blocking? Is DBCP connection pool implementation replaceable in OpenEJB? How easy (difficult) to replace it with another library? Just in case this is how we define data source in OpenEJB (openejb.xml): <Resource id="MyDataSource" type="DataSource"> JdbcDriver oracle.jdbc.driver.OracleDriver JdbcUrl ${oracle.jdbc} UserName ${oracle.user} Password ${oracle.password} JtaManaged true InitialSize 5 MaxActive 30 ValidationQuery SELECT 1 FROM DUAL TestOnBorrow true </Resource>

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• PostgreSQL insert on primary key failing with contention, even at serializable level

  - by Steven Schlansker

  I'm trying to insert or update data in a PostgreSQL db. The simplest case is a key-value pairing (the actual data is more complicated, but this is the smallest clear example) When you set a value, I'd like it to insert if the key is not there, otherwise update. Sadly Postgres does not have an insert or update statement, so I have to emulate it myself. I've been working with the idea of basically SELECTing whether the key exists, and then running the appropriate INSERT or UPDATE. Now clearly this needs to be be in a transaction or all manner of bad things could happen. However, this is not working exactly how I'd like it to - I understand that there are limitations to serializable transactions, but I'm not sure how to work around this one. Here's the situation - ab: => set transaction isolation level serializable; a: => select count(1) from table where id=1; --> 0 b: => select count(1) from table where id=1; --> 0 a: => insert into table values(1); --> 1 b: => insert into table values(1); --> ERROR: duplicate key value violates unique constraint "serial_test_pkey" Now I would expect it to throw the usual "couldn't commit due to concurrent update" but I'm guessing since the inserts are different "rows" this does not happen. Is there an easy way to work around this?

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• Spring - Transaction Readonly

  - by AAK

  Hello Gurus! Just wanted your expert opinions on declarative transaction management for Spring. Here is my setup - A. DAO Layer is Plain old JDBC using jdbcTemplete (No hibernate etc) B. Service Layer is POJO with declarative trasnactions as follows - save*, readonly=false, rollback for Throwable Things work fine with above setup. However when I say get*, readonly=true I see errors in my log file saying - Database connection cannot be marked as readonly. This happens for all get* methods in Service Layer. Now my questions - A. Do I have to say get* as readonly? All my get* methods are pure read DB operations. I do not wish to run them in any transaction context. How serious is the above error? B. When I remove the get* confiiguration, I do not see the errors, morever all my simple get* operations are performed without transactions. Is this the way to go? C. Why would anyone want to have transactional methods where readonly = true? Is there any practical significance of this configuration? Thank you! As always your resposes are much appreciated!

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• With NHibernate and Transaction do I rollback on commit failure or does it auto rollback on single c

  - by mattcodes

  I've built the following Dispose method for my Unit Of Work which essentially wraps the active NH session & transaction (transaction set as variable after opening session as to not be replaced if NH session gets new transaction after error) public void Dispose() { Func<ITransaction,bool> transactionStateOkayFunc = trans => trans != null && trans.IsActive && !trans.WasRolledBack; try { if(transactionStateOkayFunc(this.transaction)) { if (HasErrored) { transaction.Rollback(); } else { try { transaction.Commit(); } catch (Exception) { if(transactionStateOkayFunc(transaction)) transaction.Rollback(); throw; } } } } finally { if(transaction != null) transaction.Dispose(); if(session.IsOpen) session.Close(); } I can't help feeling that code is a little bloated, will a transaction automatically rollback is a discrete Commit fails in the case of non-nested transactions? Will Commit or Rollback automatically Dipose the transaction? If not will Session.Close() automatically dispose the associated transaction?

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• wrapping user controls in a transaction

  - by Hans Gruber

  I'm working on heavily dynamic and configurable CMS system. Therefore, many pages are composed of a dynamically loaded set of user controls. To enable loose coupling between containers (pages) and children (user controls), all user controls are responsible for their own persistence. Each User Control is wired up to its data/service layer dependencies via IoC. They also implement an IPersistable interface, which allows the container .aspx page to issue a Save command to its children without knowledge of the number or exact nature of these user controls. Note: what follows is only pseudo-code: public class MyUserControl : IPersistable, IValidatable { public void Save() { throw new NotImplementedException(); } public bool IsValid() { throw new NotImplementedException(); } } public partial class MyPage { public void btnSave_Click(object sender, EventArgs e) { foreach (IValidatable control in Controls) { if (!control.IsValid) { throw new Exception("error"); } } foreach (IPersistable control in Controls) { if (!control.Save) { throw new Exception("error"); } } } } I'm thinking of using declarative transactions from the System.EnterpriseService namespace to wrap the btnSave_Click in a transaction in case of an exception, but I'm not sure how this might be achieved or any pitfalls to such an approach.

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• wrapping aspx user controls commands in a transaction

  - by Hans Gruber

  I'm working on heavily dynamic and configurable CMS system. Therefore, many pages are composed of a dynamically loaded set of user controls. To enable loose coupling between containers (pages) and children (user controls), all user controls are responsible for their own persistence. Each User Control is wired up to its data/service layer dependencies via IoC. They also implement an IPersistable interface, which allows the container .aspx page to issue a Save command to its children without knowledge of the number or exact nature of these user controls. Note: what follows is only pseudo-code: public class MyUserControl : IPersistable, IValidatable { public void Save() { throw new NotImplementedException(); } public bool IsValid() { throw new NotImplementedException(); } } public partial class MyPage { public void btnSave_Click(object sender, EventArgs e) { foreach (IValidatable control in Controls) { if (!control.IsValid) { throw new Exception("error"); } } foreach (IPersistable control in Controls) { if (!control.Save) { throw new Exception("error"); } } } } I'm thinking of using declarative transactions from the System.EnterpriseService namespace to wrap the btnSave_Click in a transaction in case of an exception, but I'm not sure how this might be achieved or any pitfalls to such an approach.

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• Message driven bean not responding until client method is complete

  - by poijoi

  Hi, I have a MDB deployed on Jboss 4.2.2 and a client on the same server that produces messages and expects a reply from the MDB via a temporary queue created before the message is sent. When I run the client, I see that it creates the message, puts it in the queue and waits for the reply (no problem so far) ... but when I check in the logs I see that the timeout is reached and no response is received. When the timeout occurs and the client's method is complete the MDB starts processing the message that should have been processed the moment the client put it in the queue. As a consequence of this timing issue, when the MDB tries to reply to the temp queue, it fails since the client is already gone. If I run the same client from a remote server, I have no problem... The MDB picks up the message from the queue right away and the client receives its response right after the processing is complete. I'm using container managed transactions. I suspect it has something to do with that... I think the client's "send message/receive reply" might be all be considered a transaction before it commits to put the message in the queue... but I'm not sure if this is correct. If this is the case, why did I not see the same behavior from the remote client? is client managed transaction the default setting and that's what my remote server was using? Any idea how to fix this? Thanks in advance! PJ

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• Access DB Transaction Insert limit

  - by user986363

  Is there a limit to the amount of inserts you can do within an Access transaction before you need to commit or before Access/Jet throws an error? I'm currently running the following code in hopes to determine what this maximum is. OleDbConnection cn = new OleDbConnection( @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\temp\myAccessFile.accdb;Persist Security Info=False;"); try { cn.Open(); oleCommand = new OleDbCommand("BEGIN TRANSACTION", cn); oleCommand.ExecuteNonQuery(); oleCommand.CommandText = "insert into [table1] (name) values ('1000000000001000000000000010000000000000')"; for (i = 0; i < 25000000; i++) { oleCommand.ExecuteNonQuery(); } oleCommand.CommandText = "COMMIT"; oleCommand.ExecuteNonQuery(); } catch (Exception ex) { } finally { try { oleCommand.CommandText = "COMMIT"; oleCommand.ExecuteNonQuery(); } catch{} if (cn.State != ConnectionState.Closed) { cn.Close(); } } The error I received on a production application when I reached 2,333,920 inserts in a single uncommited transaction was: "File sharing lock count exceeded. Increase MaxLocksPerFile registry entry". Disabling transactions fixed this problem.

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• Difference between SET autocommit=1 and START TRANSACTION in mysql (Have I missed something?)

  - by tkolar

  Hey there, I am reading up on transactions in mysql and am not sure whether I have grasped something specific correctly, and I want to be sure I understood that correctly, so here goes. I know what a transaction is supposed to do, I'm just not sure whether I understood the statement semantics or not. So, my question is, is anything wrong, (and, if that is the case, what is wrong) with the following: By default, autocommit mode is enabled in mysql. Now, SET autocommit=0; will begin a transaction, SET autocommit=1; will implicitly commit. It is possible to COMMIT; as well as ROLLBACK;, in both of which cases autocommit is still set to 0 afterwards (and a new transaction is implicitly started). START TRANSACTION; will basically SET autocommit=0; until a COMMIT; or ROLLBACK; takes place. In other words, START TRANSACTION; and SET autocommit=0; are equivalent, except for the fact that START TRANSACTION; does the equivalent of implicitly adding a SET autocommit=0; after COMMIT; or ROLLBACK; If that is the case, I don't understand http://dev.mysql.com/doc/refman/5.5/en/set-transaction.html#isolevel_serializable - seeing as having an isolation level implies that there is a transaction, meaning that autocommit should be off anyway? And if there is another difference (other than the one described above) between beginning a transaction and setting autocommit, what is it? Thanks a lot in advance for your help!

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• Datapager in silverlight 4 -Nested datagrid visibility issue

  - by Archie

  I have a datagrid in silverlight with child datagrid nested in it. Also I have a DataPager on the outer datagrid. The code looks like this: <data:DataGrid x:Name="dgData" Width="600" ItemsSource="{Binding}" AutoGenerateColumns="False" IsReadOnly="True" HorizontalScrollBarVisibility="Hidden" CanUserSortColumns="False" RowDetailsVisibilityChanged="dgData_RowDetailsVisibilityChanged" Margin="20,0" Grid.RowSpan="2"> <data:DataGrid.Columns> <data:DataGridTextColumn Header="Item" Width="*" Binding="{Binding ItemName,Mode=TwoWay}"/> <data:DataGridTextColumn Header="Company" Width="*" Binding="{Binding Company,Mode=TwoWay}"/> </data:DataGrid.Columns> <data:DataGrid.RowDetailsTemplate> <DataTemplate> <data:DataGrid x:Name="dgRowDetail" Width="400" HorizontalScrollBarVisibility="Hidden" AutoGenerateColumns="False" Visibility="Collapsed"> <data:DataGrid.Columns> <data:DataGridTextColumn Header="Date" Width="*" Binding="{Binding Date,Mode=TwoWay}"/> <data:DataGridTextColumn Header="Price" Width="*" Binding="{Binding Price,Mode=TwoWay}"/> </data:DataGrid.Columns> </data:DataGrid> </DataTemplate> </data:DataGrid.RowDetailsTemplate> </data:DataGrid> <data:DataPager x:Name="dpData" HorizontalAlignment="Center" DisplayMode="FirstLastPreviousNextNumeric" Source="{Binding}"/> I have one PagedCollectionView pgv which is bound to outer datagrid as: DataContext = pgv; When the row is clicked I set the child datagrid's ItemsSource property to another PagedCollectionView. My problem is it works fine except for the first row for the first time. When I click on it, it doesn't fire the dgData_RowDetailsVisibilityChanged event. Also, when I click on second row, firstly first row fires the event and then the second row fires it and shows the nested grid. Please help.

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• C# using namespace directive in nested namespaces

  - by MoSlo

  Right, I've usually used 'using' directives as follows using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace AwesomeLib { //awesome award winning class declarations making use of Linq } i've recently seen examples of such as using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace AwesomeLib { //awesome award winning class declarations making use of Linq namespace DataLibrary { using System.Data; //Data access layers and whatnot } } Granted, i understand that i can put USING inside of my namespace declaration. Such a thing makes sense to me if your namespaces are in the same root (they organized). System; namespace 1 {} namespace 2 { System.data; } But what of nested namespaces? Personally, I would leave all USING declarations at the top where you can find them easily. Instead, it looks like they're being spread all over the source file. Is there benefit to the USING directives being used this way in nested namespaces? Such as memory management or the JIT compiler?

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• Nested Linear layout only shows first view after being set from gone to visible in Android

  - by Adam

  Hi guys, I am developing an Android app but I'm still pretty new. I want to have a button, and when you push that button, a few TextViews and Buttons will appear. So I have a main linear layout, and then another linear layout nested inside containing the things I want hidden. I have the nested linear layout set to android:visibility="gone". The problem I am having is that it only shows the first item inside the hidden linear layout instead of all of them. The way I try to make it appear is vgAddView = (ViewGroup)findViewById(R.id.add_details); btnAche.setOnClickListener(new OnClickListener(){ public void onClick(View v){ vgAddView.setVisibility(0); } }); My XML file is this <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <Button android:text="@string/but_stomach_ache" android:id="@+id/but_stomach_ache" android:layout_width="fill_parent" android:layout_height="wrap_content"> </Button> <Button android:text="@string/but_food" android:id="@+id/but_food" android:layout_width="fill_parent" android:layout_height="wrap_content"> </Button> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@+id/add_details" android:visibility="gone"> <TextView android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" android:text="@string/when_happen"> </TextView> <Button android:text="@string/happen_now" android:id="@+id/happen_now" android:layout_width="fill_parent" android:layout_height="wrap_content"> </Button> </LinearLayout> </LinearLayout>

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• For "draggable" div tags that are NOT nested: JQuery/JavaScript div tag “containment” approach/algor

  - by Pete Alvin

  Background: I've created an online circuit design application where .draggable() div tags are containers that contain smaller div containers and so forth. Question: For any particular div tag I need to quickly identify if it contains other div tags (that may in turn contain other div tags). -- Since the div tags are draggable, in the DOM they are NOT nested inside each other but I think are absolutely positioned. So I think that a "hit testing" approach is the only way to determine containment, unless there is some "secret" routine built-in somewhere that could help with this. I've searched JQuery and I don't see any built-in routine for this. Does anyone know of an algorithm that's quicker than O(n^2)? Seems like I have to walk the list of div tags in an outer loop (n) and have an inner loop (another n) to compare against all other div tags and do a "containment test" (position, width, height), building a list of contained div tags. That's n-squared. Then I have to build a list of all nested div tags by concatenating contained lists. So the total would be O(n^2)+n. There must be a better way?

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• Nested URLs and Rewrite rules in Apache2

  - by Radha Krishna. S.

  Hi, I need some help with rewrite rules and nested URLs. I am using TikiWiki for my website and am in the process of setting up SE friendly URLs for my projects. Specifically, I have the following rewrite rule for www.example.com/projects to point to a page that lists out all the projects hosted in example. RewriteRule ^Projects$ articles?type=Project [L] This works fine. Now, I would like to point www.example.com/projects/project1 to point to a specific project. I have this rewrite rule RewriteRule ^(Projects/Project1)$ tiki-read_article.php?articleId=6 This works, but partially. The content is all rendered as text but the theme - images/ css etc all go for a toss - the page is completely in text. I understand that this happens 'cause the relative paths in the theme/ css/ images all refer to Projects as the base folder instead of the root of the website. I don't want to touch the CMS portion - change the theme/ css/ image paths in the files, more for reasons of upgradability. Can someone help me understand and write a rule so that the above nested URL works? Regards, Radha

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• Subsonic 3 ActiveRecord nested select for NotIn bug?

  - by Junto

  I have the following Subsonic 3.0 query, which contains a nested NotIn query: public List<Order> GetRandomOrdersForNoReason(int shopId, int typeId) { // build query var q = new SubSonic.Query.Select().Top("1") .From("Order") .Where("ShopId") .IsEqualTo(shopId) .And(OrderTable.CustomerId).NotIn( new Subsonic.Query.Select("CustomerId") .From("Customer") .Where("TypeId") .IsNotEqualTo(typeId)) .OrderDesc("NewId()"); // Output query Debug.WriteLine(q.ToString()); // returned typed list return q.ExecuteTypedList<Order>(); } The internal query appears to be incorrect: SELECT TOP 1 * FROM [Order] WHERE ShopId = @0 AND CustomerId NOT IN (SELECT CustomerId FROM [Customer] WHERE TypeId = @0) ORDER BY NewId() ASC You'll notice that both parameters are @0. I'm assuming that the parameters are enumerated (starting at zero), for each "new" Select query. However, in this case where the two Select queries are nested, I would have expected the output to have two parameters named @0 and @1. My query is based on one that Rob Conery gave on his blog as a preview of the "Pakala" query tool that became Subsonic 3. His example was: int records = new Select(Northwind.Product.Schema) .Where("productid") .In( new Select("productid").From(Northwind.Product.Schema) .Where("categoryid").IsEqualTo(5) ) .GetRecordCount(); Has anyone else seen this behavior? Is it a bug, or is this an error or my part? Since I'm new to Subsonic I'm guessing that this probably programmer error on my part but I'd like confirmation if possible.

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• JQuery - nested ul/li list, keep expanded after reload of page

  - by H4mm3rHead

  Hi, I have a nested ul/li list <ul> <li>first</li> <li>second <ul> <li>Third</li> </ul> </li> ... and so on I found this JQuery on the interweb to use as inspiration, but how to keep the one item i expanded open after the page has reloaded? <script type="text/javascript"> $(document).ready(function() { $('div#sideNav li li > ul').hide(); //hide all nested ul's $('div#sideNav li > ul li a[class=current]').parents('ul').show().prev('a').addClass('accordionExpanded'); //show the ul if it has a current link in it (current page/section should be shown expanded) $('div#sideNav li:has(ul)').addClass('accordion'); //so we can style plus/minus icons $('div#sideNav li:has(ul) > a').click(function() { $(this).toggleClass('accordionExpanded'); //for CSS bgimage, but only on first a (sub li>a's don't need the class) $(this).next('ul').slideToggle('fast'); $(this).parent().siblings('li').children('ul:visible').slideUp('fast') .parent('li').find('a').removeClass('accordionExpanded'); return true; }); }); </script>

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• How can I cleanly turn a nested Perl hash into a non-nested one?

  - by knorv

  Assume a nested hash structure %old_hash .. my %old_hash; $old_hash{"foo"}{"bar"}{"zonk"} = "hello"; .. which we want to "flatten" (sorry if that's the wrong terminology!) to a non-nested hash using the sub &flatten(...) so that .. my %h = &flatten(\%old_hash); die unless($h{"zonk"} eq "hello"); The following definition of &flatten(...) does the trick: sub flatten { my $hashref = shift; my %hash; my %i = %{$hashref}; foreach my $ii (keys(%i)) { my %j = %{$i{$ii}}; foreach my $jj (keys(%j)) { my %k = %{$j{$jj}}; foreach my $kk (keys(%k)) { my $value = $k{$kk}; $hash{$kk} = $value; } } } return %hash; } While the code given works it is not very readable or clean. My question is two-fold: In what ways does the given code not correspond to modern Perl best practices? Be harsh! :-) How would you clean it up?

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• Turning a nested hash structure into a non-nested hash structure - is this the cleanest way to do it

  - by knorv

  Assume a nested hash structure %old_hash .. my %old_hash; $old_hash{"foo"}{"bar"}{"zonk"} = "hello"; .. which we want to "flatten" (sorry if that's the wrong terminology!) to a non-nested hash using the sub &flatten(...) so that .. my %h = &flatten(\%old_hash); die unless($h{"zonk"} eq "hello"); The following definition of &flatten(...) does the trick: sub flatten { my $hashref = shift; my %hash; my %i = %{$hashref}; foreach my $ii (keys(%i)) { my %j = %{$i{$ii}}; foreach my $jj (keys(%j)) { my %k = %{$j{$jj}}; foreach my $kk (keys(%k)) { my $value = $k{$kk}; $hash{$kk} = $value; } } } return %hash; } While the code given works it is not very readable or clean. My question is two-fold: In what ways does the given code not correspond to modern Perl best practices? Be harsh! :-) How would you clean it up?

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• Same route nested in multiple resources ember.js

  - by Daniel Upton

  I'm building an ember.js app which has a model called "Programme". A user can drill down to a programme by going: Genre > Subgenre > Programme or Folder > List > Programme Here's my router: this.resource('mylists', { path: '/' }, function() { this.resource('folder', { path: '/folder/:folder_id' }, function() { this.resource('list', { path: '/list/:list_id' }, function() { this.resource('programme', { path: '/programme/:programme_id' }); }); }); }); this.resource('catalogue', function() { this.resource('genre', { path: '/genre/:genre_id' }, function() { this.resource('subgenre', { path: '/subgenre/:subgenre_id' }, function() { this.resource('programme', { path: '/programme/:programme_id' }); }); }); }); The UI needs to be deeply nested (the genre view renders in the outlet of the catalogue template, the subgenre in the outlet of the genre template... and so forth). The problem I have is as both generated routes are called ProgrammeRoute when I linkTo the programme route inside the list template, it actually goes to the programme route nested in the subgenre route. What should I be doing here? To work around it I've named one route ListProgrammeRoute and SubgenreProgrammeRoute but that leads to some duplication.

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• binding nested json object value to a form field

  - by Jack

  I am building a dynamic form to edit data in a json object. First, if something like this exists let me know. I would rather not build it but I have searched many times for a tool and have found only tree like structures that require entering quotes. I would be happy to treat all values as strings. This edit functionality is for end users so it needs to be easy an not intimidating. So far I have code that generates nested tables to represent a json object. For each value I display a form field. I would like to bind the form field to the associated nested json value. If I could store a reference to the json value I would build an array of references to each value in a json object tree. I have not found a way to do that with javascript. My last resort approach will be to traverse the table after edits are made. I would rather have dynamic updates but a single submit would be better than nothing. Any ideas? // the json in files nests only a few levels. Here is the format of a simple case, { "researcherid_id":{ "id_key":"researcherid_id", "description":"Use to retrieve bibliometric data", "url_template" :[ { "name": "Author Detail", "url": "http://www.researcherid.com/rid/${key}" } ] } } $.get('file.json',make_json_form); function make_json_form(response) { dataset = $.secureEvalJSON(response); // iterate through the object and generate form field for string values. } // Then after the form is edited I want to display the raw updated json (then I want to save it but that is for another thread) // now I iterate through the form and construct the json object // I would rather have the dataset object var updated on focus out after each edit. function show_json(form_id){ var r = {}; var el = document.getElementById(form_id); table_to_json(r,el,null); $('body').html(formattedJSON(r)); }

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• Hierarchical/Nested Database Structure for Comments

  - by Stephen Melrose

  Hi, I'm trying to figure out the best approach for a database schema for comments. The problem I'm having is that the comments system will need to allow nested/hierarchical comments, and I'm not sure how to design this out properly. My requirements are, Comments can be made on comments, so I need to store the tree hierarchy I need to be able to query the comments in the tree hierarchy order, but efficiently, preferably in a fast single query, but I don't know if this is possible I'd need to make some wierd queries, e.g. pull out the latest 5 root comments, and a maximum of 3 children for each one of those I read an article on the MySQL website on this very subject, http://dev.mysql.com/tech-resources/articles/hierarchical-data.html The "Nested Set Model" in theory sounds like it will do what I need, except I'm worried about querying the thing, and also inserting. If this is the right approach, How would I do my 3rd requirement above? If I have 2000 comments, and I add a new sub-comment on the first comment, that will be a LOT of updating to do. This doesn't seem right to me? Or is there a better approach for the type of data I'm wanting to store and query? Thank you

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• Nested parsers in happy / infinite loop?

  - by McManiaC

  I'm trying to write a parser for a simple markup language with happy. Currently, I'm having some issues with infinit loops and nested elements. My markup language basicly consists of two elements, one for "normal" text and one for bold/emphasized text. data Markup = MarkupText String | MarkupEmph [Markup] For example, a text like Foo *bar* should get parsed as [MarkupText "Foo ", MarkupEmph [MarkupText "bar"]]. Lexing of that example works fine, but the parsing it results in an infinite loop - and I can't see why. This is my current approach: -- The main parser: Parsing a list of "Markup" Markups :: { [Markup] } : Markups Markup { $1 ++ [$2] } | Markup { [$1] } -- One single markup element Markup :: { Markup } : '*' Markups1 '*' { MarkupEmph $2 } | Markup1 { $1 } -- The nested list inside *..* Markups1 :: { [Markup] } : Markups1 Markup1 { $1 ++ [$2] } | Markup1 { [$1] } -- Markup which is always available: Markup1 :: { Markup } : String { MarkupText $1 } What's wrong with that approach? How could the be resolved? Update: Sorry. Lexing wasn't working as expected. The infinit loop was inside the lexer. Sorry. :) Update 2: On request, I'm using this as lexer: lexer :: String -> [Token] lexer [] = [] lexer str@(c:cs) | c == '*' = TokenSymbol "*" : lexer cs -- ...more rules... | otherwise = TokenString val : lexer rest where (val, rest) = span isValidChar str isValidChar = (/= '*') The infinit recursion occured because I had lexer str instead of lexer cs in that first rule for '*'. Didn't see it because my actual code was a bit more complex. :)

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• CarrierWave and nested forms saving empty image object if photo :title is included in form

  - by Wasabi Developer

  I'm after some advice in regards to handling nested form data and I would be ever so grateful for any insights. The trouble is I'm not 100% sure why I require the following code in my model accepts_nested_attributes_for :holiday_image, allow_destroy: true, :reject_if => lambda { |a| a[:title].blank? } If I don't understand why I require to tact on on my accepts_nested_attributes_for association: :reject_if => lambda { |a| a[:title].blank? } If I remove this :reject_if lambda, it will save a blank holiday photo object in the database. I presume because it takes the :title field from the form as an empty string? I guess my question is, am I doing this right or is there a better way of this this within nested forms if I want to extend my HolidayImage model to include more strings like description, notes? Sorry If I can't be more succinct. My simple holiday app. # holiday.rb class Holiday < ActiveRecord::Base has_many :holiday_image accepts_nested_attributes_for :holiday_image, allow_destroy: true, :reject_if => lambda { |a| a[:title].blank? } attr_accessible :name, :content, :holiday_image_attributes end I'm using CarrierWave for image uploads. # holiday_image.rb class HolidayImage < ActiveRecord::Base belongs_to :holiday attr_accessible :holiday_id, :image, :title mount_uploader :image, ImageUploader end Inside my _form partial there is a field_for block <h3>Photo gallery</h3> <%= f.fields_for :holiday_image do |holiday_image| %> <% if holiday_image.object.new_record? %> <%= holiday_image.label :title, "Image Title" %> <%= holiday_image.text_field :title %> <%= holiday_image.file_field :image %> <% else %> Title: <%= holiday_image.object.title %> <%= image_tag(holiday_image.object.image.url(:thumb)) %> Tick to delete: <%= holiday_image.check_box :_destroy %> <% end %> Thanks again for your patience.

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• (nested) user controls within a mvp pattern causing sporadic problems

  - by LLEA

  hi everyone, I have a serious problem with nested user controls (UCs) in WinForms while trying to implement the mvp pattern (passive view). The project consists of one model (designed as a singleton) and a set of different presenters with corresponding view interfaces. To avoid one huge view interface and therefore an overloaded main UI, I decided to make use of a set of different UCs. Each UC has one view interface and one presenter that can access the model. But there are nested UCs: meaning that one specialised UC implements sort of a basic UC. The main UI just represents a container for all those UCs. So far, so good (if not, please ask)?! There are two problems that I am facing now (but I guess both are of the same origin): From time to time it is not possible anymore to load the UCs and test them within the Visual Studio 2008 User Control Test Container. The error message just says that a project with an output type of class library cannot be started directly etc. I can "handle" that by unloading all UC projects and reloading them afterwards. (I guess the references to all mvp components and other UCs are then updated). Assuming that the implementation of my mvp pattern is okay and all those UCs are testable within the VS Test Container at a certain time - there is the biggest problem still left: I am not able to add any UC (even the basic and unnested ones) to a simple Form (UI). The error message: error message.jpg Could it be that my basic UC causes all these Problems?! It consists of two simple ComboBoxes and implements a basic presenter and basic view interface. Whenever I add this UC to a different UC the VS designer adds two references to the public getter methods of the UC as resources. I then manually remove those resources from the resx-file and commend the corresponding lines in the designer file. thx in advance

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• Python - Checking for membership inside nested dict

  - by victorhooi

  heya, This is a followup questions to this one: http://stackoverflow.com/questions/2901422/python-dictreader-skipping-rows-with-missing-columns Turns out I was being silly, and using the wrong ID field. I'm using Python 3.x here. I have a dict of employees, indexed by a string, "directory_id". Each value is a nested dict with employee attributes (phone number, surname etc.). One of these values is a secondary ID, say "internal_id", and another is their manager, call it "manager_internal_id". The "internal_id" field is non-mandatory, and not every employee has one. (I've simplified the fields a little, both to make it easier to read, and also for privacy/compliance reasons). The issue here is that we index (key) each employee by their directory_id, but when we lookup their manager, we need to find managers by their "internal_id". Before, when employee.keys() was a list of internal_ids, I was using a membership check on this. Now, the last part of my if statement won't work, since the internal_ids is part of the dict values, instead of the key itself. def lookup_supervisor(manager_internal_id, employees): if manager_internal_idis not None and manager_internal_id!= "" and manager_internal_id in employees.keys(): return (employees[manager_internal_id]['mail'], employees[manager_internal_id]['givenName'], employees[manager_internal_id]['sn']) else: return ('Supervisor Not Found', 'Supervisor Not Found', 'Supervisor Not Found') So the first question is, how do I check whether the manager_internal_id is present in the dict's values. I've tried substituting employee.keys() with employee.values(), that didn't work. Also, I'm hoping for something a little more efficient, not sure if there's a way to get a subset of the values, specifically, all the entries for employees[directory_id]['internal_id']. Hopefully there's some Pythonic way of doing this, without using a massive heap of nested for/if loops. My second question is, how do I then cleanly return the required employee attributes (mail, givenname, surname etc.). My for loop is iterating over each employee, and calling lookup_supervisor. I'm feeling a bit stupid/stumped here. def tidy_data(employees): for directory_id, data in employees.items(): # We really shouldnt' be passing employees back and forth like this - hmm, classes? data['SupervisorEmail'], data['SupervisorFirstName'], data['SupervisorSurname'] = lookup_supervisor(data['manager_internal_id'], employees) Thanks in advance =), Victor

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