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• Using LINQ to SQL and chained Replace

  - by White Dragon

  I have a need to replace multiple strings with others in a query from p in dx.Table where p.Field.Replace("A", "a").Replace("B", "b").ToLower() = SomeVar select p Which provides a nice single SQL statement with the relevant REPLACE() sql commands. All good :) I need to do this in a few queries around the application... So i'm looking for some help in this regard; that will work as above as a single SQL hit/command on the server It seems from looking around i can't use RegEx as there is no SQL eq Being a LINQ newbie is there a nice way for me to do this? eg is it possible to get it as a IQueryable "var result" say and pass that to a function to add needed .Replace()'s and pass back? Can i get a quick example of how if so? EDIT: This seems to work! does it look like it would be a problem? var data = from p in dx.Videos select p; data = AddReplacements(data, checkMediaItem); theitem = data.FirstOrDefault(); ... public IQueryable<Video> AddReplacements(IQueryable<Video> DataSet, string checkMediaItem) { return DataSet.Where(p => p.Title.Replace(" ", "-").Replace("&", "-").Replace("?", "-") == checkMediaItem); }

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• Python SQLite FTS3 alternatives?

  - by Mike Cialowicz

  Are there any good alternatives to SQLite + FTS3 for python? I'm iterating over a series of text documents, and would like to categorize them according to some text queries. For example, I might want to know if a document mentions the words "rating" or "upgraded" within three words of "buy." The FTS3 syntax for this query is the following: (rating OR upgraded) NEAR/3 buy That's all well and good, but if I use FTS3, this operation seems rather expensive. The process goes something like this: # create an SQLite3 db in memory conn = sqlite3.connect(':memory:') c = conn.cursor() c.execute('CREATE VIRTUAL TABLE fts USING FTS3(content TEXT)') conn.commit() Then, for each document, do something like this: #insert the document text into the fts table, so I can run a query c.execute('insert into fts(content) values (?)', content) conn.commit() # execute my FTS query here, look at the results, etc # remove the document text from the fts table before working on the next document c.execute('delete from fts') conn.commit() This seems rather expensive to me. The other problem I have with SQLite FTS is that it doesn't appear to work with Python 2.5.4. The 'CREATE VIRTUAL TABLE' syntax is unrecognized. This means that I'd have to upgrade to Python 2.6, which means re-testing numerous existing scripts and programs to make sure they work under 2.6. Is there a better way? Perhaps a different library? Something faster? Thank you.

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• Saving twice don't update my object in JDO

  - by Javi

  Hello I have an object persisted in the GAE datastore using JDO. The object looks like this: public class MyObject implements Serializable, StoreCallback { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String id; @Persistent private String firstId; ... } As usually when the object is stored for the first time a new id value is generated for the identifier. I need that if I don't provide a value for firstId it sets the same value as the id. I don't want to solve it with a special getter which checks for null value in firstId and then return the id value because I want to make queries relating on firstId. I can do it in this way by saving the object twice (Probably there's a better way to do this, but I'll do it in this way until I find a better one). But it is not working. when I debug it I can see that result.firstId is set with the id value and it seems to be persisted, but when I go into the datastore I see that firstId is null (as it was saved the first time). This save method is in my DAO and it is called in another save method in the service annotated with @Transactional. Does anyone have any idea why the second object in not persisted properly? @Override public MyObject save(MyObject obj) { PersistenceManager pm = JDOHelper.getPersistenceManagerFactory("transactions-optional"); MyObject result = pm.makePersistent(obj); if(result.getFirstId() == null){ result.setFirstId(result.getId()); result = pm.makePersistent(result); } return result; } Thanks.

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• When *not* to use prepared statements?

  - by Ben Blank

  I'm re-engineering a PHP-driven web site which uses a minimal database. The original version used "pseudo-prepared-statements" (PHP functions which did quoting and parameter replacement) to prevent injection attacks and to separate database logic from page logic. It seemed natural to replace these ad-hoc functions with an object which uses PDO and real prepared statements, but after doing my reading on them, I'm not so sure. PDO still seems like a great idea, but one of the primary selling points of prepared statements is being able to reuse them… which I never will. Here's my setup: The statements are all trivially simple. Most are in the form SELECT foo,bar FROM baz WHERE quux = ? ORDER BY bar LIMIT 1. The most complex statement in the lot is simply three such selects joined together with UNION ALLs. Each page hit executes at most one statement and executes it only once. I'm in a hosted environment and therefore leery of slamming their servers by doing any "stress tests" personally. Given that using prepared statements will, at minimum, double the number of database round-trips I'm making, am I better off avoiding them? Can I use PDO::MYSQL_ATTR_DIRECT_QUERY to avoid the overhead of multiple database trips while retaining the benefit of parametrization and injection defense? Or do the binary calls used by the prepared statement API perform well enough compared to executing non-prepared queries that I shouldn't worry about it? EDIT: Thanks for all the good advice, folks. This is one where I wish I could mark more than one answer as "accepted" — lots of different perspectives. Ultimately, though, I have to give rick his due… without his answer I would have blissfully gone off and done the completely Wrong Thing even after following everyone's advice. :-) Emulated prepared statements it is!

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• How to profile Doctrine in Zend Framework

  - by David Zapata

  Good day. I'm using Doctrine as ORM for my Zend Framework project. This is the first time I use it. I've followed the ZendCasts Doctrine chapters, and everything works for me, but I needed to perform some profiling; There is a Doctrine_Connection_Profiler class that should be used to profile the Doctrine Model internal queries, but I've tried to use it without success. I always get a "PDOException: You cannot serialize or unserialize PDOStatement instances" exception when I perform my Unit Tests. Here is a example: $conn = Doctrine_Manager::connection($doctrineConfig['dsn'], $dbconfname); ... if( APPLICATION_ENV != 'production'){ $obj_doctrine_profiler = new Doctrine_Connection_Profiler(); $conn->setListener($obj_doctrine_profiler); } All of my Unit Tests works if I comment/delete the $conn->setListener($obj_doctrine_profiler); line. This code block is located in my Bootstrap.php class; the weird thing is, the web application works just fine even with the mentioned code line. Thank you so much for your help. please excuse me if my english is not the best.

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• Got a table of people, who I want to link to each other, many-to-many, with the links being bidirect

  - by dflock

  Imagine you live in very simplified example land - and imagine that you've got a table of people in your MySQL database: create table person ( person_id int, name text ) select * from person; +-------------------------------+ | person_id | name | +-------------------------------+ | 1 | Alice | | 2 | Bob | | 3 | Carol | +-------------------------------+ and these people need to collaborate/work together, so you've got a link table which links one person record to another: create table person__person ( person__person_id int, person_id int, other_person_id int ) This setup means that links between people are uni-directional - i.e. Alice can link to Bob, without Bob linking to Alice and, even worse, Alice can link to Bob and Bob can link to Alice at the same time, in two separate link records. As these links represent working relationships, in the real world they're all two-way mutual relationships. The following are all possible in this setup: select * from person__person; +---------------------+-----------+--------------------+ | person__person_id | person_id | other_person_id | +---------------------+-----------+--------------------+ | 1 | 1 | 2 | | 2 | 2 | 1 | | 3 | 2 | 2 | | 4 | 3 | 1 | +---------------------+-----------+--------------------+ For example, with person__person_id = 4 above, when you view Carol's (person_id = 3) profile, you should see a relationship with Alice (person_id = 1) and when you view Alice's profile, you should see a relationship with Carol, even though the link goes the other way. I realize that I can do union and distinct queries and whatnot to present the relationships as mutual in the UI, but is there a better way? I've got a feeling that there is a better way, one where this issue would neatly melt away by setting up the database properly, but I can't see it. Anyone got a better idea?

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• ASP.NET MVC intermittent slow response

  - by arehman

  Problem In our production environment, system occasionally delays the page response of an ASP.NET MVC application up to 30 seconds or so, even though same page renders in 2-3 seconds most of the times. This happens randomly with any arbitrary page, and GET or POST type requests. For example, log files indicates, system took 15 seconds to complete a request for jquery script file or for other small css file it took 10 secs. Similar Problems: Random Slow Downs Production Environment: Windows Server 2008 - Standard (32-bit) - App Pool running in integrated mode. ASP.NET MVC 1.0 We have tried followings/observations: Moved the application to a stand alone web server, but, it didn't help. We didn't ever notice same issue on the server for any 'ASP.NET' application. App Pool settings are fine. No abrupt recycles/shutdowns. No cpu spikes or memory problems. No delays due to SQL queries or so. It seems as something causing delay along HTTP Pipeline or worker processor seeing the request late. Looking for other suggestions. -- Thanks

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• Ruby on Rails ActiveRecord/Include/Associations can't get my query to work

  - by Cypher

  I just started learning Rails and I'm just trying to set up query via associations. All the queries I try to write seem to be doing bizzare things and end up trying to query two tables parsed together with an '_' as one table. I have no clue why this would ever happen My tables are as follows: schools: id name variables: id name type var_entries: id variable_id entry school_entries: id school_id var_entry_id my rails association tables are $local = { :adapter => "mysql", :host => "localhost", :port => "3306".to_i, :database => "spy_2", :username =>"root", :password => "vertrigo" } class School < ActiveRecord::Base establish_connection $local has_many :school_entries has_many :var_entries, :through => school_entries end class Variable < ActiveRecord::Base establish_connection $local has_many :var_entries has_many :school_entries, :through => :var_entries end class VarEntry < ActiveRecord::Base establish_connection $local has_many_and_belongs_to :school_entries belongs_to :variables end class SchoolEntry < ActiveRecord::Base establish_connection $local belongs_to :school has_many :var_entries end I want to do this sql query: SELECT school_id, variable_id,rank FROM school_entries, variables, var_entries, schools WHERE var_entries.variable_id = variables.id AND school_entries.var_entry_id = var_entries.id AND schools.id = school_entries.school_id AND variables.type = 'number'; and put it into Rails notation: here is one of my many failed attempts schools = VarEntry.all(:include => [:school_entries, :variables], :conditions => "variables.type = 'number'") the error: 'const_missing': uninitialized constant VarEntry::Variables (NameError) if i remove variables schools = VarEntry.all(:include => [:school_entries, :variables], :conditions => "type = 'number'") the error is: Mysql::Error: Unkown column 'type' in 'where clause': SELECT * FROM 'var_entries' WHERE (type=number) (ActiveRecord::StatementInvalid) Can anyone tell me where I'm going horribly wrong?

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• Graph-structured databases and Php

  - by stagas

  I want to use a graph database using php. Can you point out some resources on where to get started? Is there any example code / tutorial out there? Or are there any other methods of storing data that relate to each other in totally random/abstract situations? - Very abstract example of the relations needed: John relates to Mary, both relate to School, John is Tall, Mary is Short, John has Blue Eyes, Mary has Green Eyes, query I want is which people are related to 'Short people that have Green Eyes and go to School' - answer John - Another example: TrackA -> ArtistA -> ArtistB -> AlbumA -----> [ label ] -> AlbumB -----> [ A ] -> TrackA:Remix -> Genre:House -> [ Album ] -----> [ label ] TrackB -> [ C ] [ B ] Example queries: Which Genre is TrackB closer to? answer: House - because it's related to Album C, which is related to TrackA and is related to Genre:House Get all Genre:House related albums of Label A : result: AlbumA, AlbumB - because they both have TrackA which is related to Genre:House - It is possible in MySQL but it would require a fixed set of attributes/columns for each item and a complex non-flexible query, instead I need every attribute to be an item by itself and instead of 'belonging' to something, to be 'related' to something.

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• What's the fastest way to bulk insert a lot of data in SQL Server (C# client)

  - by Andrew

  I am hitting some performance bottlenecks with my C# client inserting bulk data into a SQL Server 2005 database and I'm looking for ways in which to speed up the process. I am already using the SqlClient.SqlBulkCopy (which is based on TDS) to speed up the data transfer across the wire which helped a lot, but I'm still looking for more. I have a simple table that looks like this: CREATE TABLE [BulkData]( [ContainerId] [int] NOT NULL, [BinId] [smallint] NOT NULL, [Sequence] [smallint] NOT NULL, [ItemId] [int] NOT NULL, [Left] [smallint] NOT NULL, [Top] [smallint] NOT NULL, [Right] [smallint] NOT NULL, [Bottom] [smallint] NOT NULL, CONSTRAINT [PKBulkData] PRIMARY KEY CLUSTERED ( [ContainerIdId] ASC, [BinId] ASC, [Sequence] ASC )) I'm inserting data in chunks that average about 300 rows where ContainerId and BinId are constant in each chunk and the Sequence value is 0-n and the values are pre-sorted based on the primary key. The %Disk time performance counter spends a lot of time at 100% so it is clear that disk IO is the main issue but the speeds I'm getting are several orders of magnitude below a raw file copy. Does it help any if I: Drop the Primary key while I am doing the inserting and recreate it later Do inserts into a temporary table with the same schema and periodically transfer them into the main table to keep the size of the table where insertions are happening small Anything else? -- Based on the responses I have gotten, let me clarify a little bit: Portman: I'm using a clustered index because when the data is all imported I will need to access data sequentially in that order. I don't particularly need the index to be there while importing the data. Is there any advantage to having a nonclustered PK index while doing the inserts as opposed to dropping the constraint entirely for import? Chopeen: The data is being generated remotely on many other machines (my SQL server can only handle about 10 currently, but I would love to be able to add more). It's not practical to run the entire process on the local machine because it would then have to process 50 times as much input data to generate the output. Jason: I am not doing any concurrent queries against the table during the import process, I will try dropping the primary key and see if that helps. ~ Andrew

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• MySQL ORDER BY DESC is fast but ASC is very slow

  - by Pepper

  Hello, I'm completely stumped on this one. For some reason when I sort this query by DESC it's super fast, but if sorted by ASC it's extremely slow. This takes about 150 milliseconds: SELECT posts.id FROM posts USE INDEX (published) WHERE posts.feed_id IN ( 4953,622,1,1852,4952,76,623,624,10 ) ORDER BY posts.published DESC LIMIT 0, 50; This takes about 32 seconds: SELECT posts.id FROM posts USE INDEX (published) WHERE posts.feed_id IN ( 4953,622,1,1852,4952,76,623,624,10 ) ORDER BY posts.published ASC LIMIT 0, 50; The EXPLAIN is the same for both queries. id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE posts index NULL published 5 NULL 50 Using where I've tracked it down to "USE INDEX (published)". If I take that out it's the same performance both ways. But the EXPLAIN shows the query is less efficient overall. id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE posts range feed_id feed_id 4 \N 759 Using where; Using filesort And here's the table. CREATE TABLE `posts` ( `id` int(20) NOT NULL AUTO_INCREMENT, `feed_id` int(11) NOT NULL, `post_url` varchar(255) NOT NULL, `title` varchar(255) NOT NULL, `content` blob, `author` varchar(255) DEFAULT NULL, `published` int(12) DEFAULT NULL, `updated` datetime NOT NULL, `created` datetime NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `post_url` (`post_url`,`feed_id`), KEY `feed_id` (`feed_id`), KEY `published` (`published`) ) ENGINE=InnoDB AUTO_INCREMENT=196530 DEFAULT CHARSET=latin1; Is there a fix for this? Thanks!

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• SQL GUID Vs Integer

  - by Dal

  Hi I have recently started a new job and noticed that all the SQL tables use the GUID data type for the primary key. In my previous job we used integers (Auto-Increment) for the primary key and it was a lot more easier to work with in my opinion. For example, say you had two related tables; Product and ProductType - I could easily cross check the 'ProductTypeID' column of both tables for a particular row to quickly map the data in my head because its easy to store the number (2,4,45 etc) as opposed to (E75B92A3-3299-4407-A913-C5CA196B3CAB). The extra frustration comes from me wanting to understand how the tables are related, sadly there is no Database diagram :( A lot of people say that GUID's are better because you can define the unique identifer in your C# code for example using NewID() without requiring SQL SERVER to do it - this also allows you to know provisionally what the ID will be.... but I've seen that it is possible to still retrieve the 'next auto-incremented integer' too. A DBA contractor reported that our queries could be up to 30% faster if we used the Integer type instead of GUIDS... Why does the GUID data type exist, what advantages does it really provide?... Even if its a choice by some professional there must be some good reasons as to why its implemented?

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• AJAX CascadingDropDown ViewState Problem

  - by Steven

  Question: How do I maintain both the contents (from queries) and selected value of both dropdowns after postback? Source Code: Download my source code from this link (link now works). Just add a reference to your AjaxControlToolkit User Action: Select a value from each dropdown. Click Submit. After Postback: StatesDrop: (Selected value), CitiesDrop "Select a City" Before and after: I believe that when the first dropdown gets its selected value, the second dropdown refreshes and therefore loses its selected value. C# answers also welcome. Default.aspx Active States<br /><asp:DropDownList ID="StatesDrop" runat="server" /><br /> Active Cities<br /><asp:DropDownList ID="CitiesDrop" runat="server" /><br /> <ajax:CascadingDropDown ID="StatesCasc" TargetControlID="StatesDrop" ServicePath="WebService1.asmx" ServiceMethod="GetActiveStates" Category="States" runat="server" PromptText="Select a State" PromptValue="?" /> <ajax:CascadingDropDown ID="CitiesCasc" TargetControlID="CitiesDrop" ServicePath="WebService1.asmx" ServiceMethod="GetActiveCities" Category="Cities" runat="server" ParentControlID="StatesDrop" PromptText="Select a City" PromptValue="?" /> WebService1.asmx.vb Imports System.Web.Services Imports System.Web.Services.Protocols Imports System.ComponentModel Imports System.Web.Script.Services Imports AjaxControlToolkit <System.Web.Script.Services.ScriptService()> _ <System.Web.Services.WebService(Namespace:="http://tempuri.org/")> _ <System.Web.Services.WebServiceBinding _ (ConformsTo:=WsiProfiles.BasicProfile1_1)> _ <ToolboxItem(False)> _ Public Class WebService1: Inherits System.Web.Services.WebService <WebMethod()> _ Public Function GetActiveStates (ByVal knownCategoryValues As String, _ ByVal category As String) As CascadingDropDownNameValue() Dim values As New List(Of CascadingDropDownNameValue)() 'Fill values array' Return values.ToArray() End Function <WebMethod()> _ Public Function GetActiveCities (ByVal knownCategoryValues As String, _ ByVal category As String) As CascadingDropDownNameValue() Dim values As New List(Of CascadingDropDownNameValue)() Dim kv As StringDictionary = _ CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues) Dim SelState As String = "" If kv.ContainsKey("State") Then SelState = kv("State") 'Fill values array' Return values.ToArray() End Function End Class Default.aspx.vb Imports System.Web.Services Imports System.Web.Script.Services Imports AjaxControlToolkit Partial Public Class _Default Inherits System.Web.UI.Page Protected Sub Submit_Click(ByVal sender As Object, _ ByVal e As EventArgs) Handles SubmitBtn.Click ResultsGrid.DataBind() End Sub End Class

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• Help! The log file for database 'tempdb' is full. Back up the transaction log for the database to fr

  - by michael.lukatchik

  We're running SQL Server 2000. In our database, we have an "Orders" table with approximately 750,000 rows. We can perform simple SELECT statements on this table. However, when we want to run a query like SELECT TOP 100 * FROM Orders ORDER BY Date_Ordered DESC, we receive the following message: Error: 9002, Severity: 17, State: 6 The log file for database 'tempdb' is full. Back up the transaction log for the database to free up some log space. We have other tables in our database which are similar in size of the amount of records that are in the tables (i.e. 700,000 records). On these tables, we can run any queries we'd like and we never receive a message about 'tempdb being full'. To resolve this, we've backed up our database, shrunk the actual database and also shrunk the database and files in the tempdb system database, but this hasn't resolved the issue. The size of our log file is set to autogrow. We're not sure where to go next. Are there any ideas why we still might be receiving this message? Error: 9002, Severity: 17, State: 6 The log file for database 'tempdb' is full. Back up the transaction log for the database to free up some log space.

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• LINQ to SQL and DataPager

  - by Jonathan S.

  I'm using LINQ to SQL to search a fairly large database and am unsure of the best approach to perform paging with a DataPager. I am aware of the Skip() and Take() methods and have those working properly. However, I'm unable to use the count of the results for the datapager, as they will always be the page size as determined in the Take() method. For example: var result = (from c in db.Customers where c.FirstName == "JimBob" select c).Skip(0).Take(10); This query will always return 10 or fewer results, even if there are 1000 JimBobs. As a result, the DataPager will always think there's a single page, and users aren't able to navigate across the entire result set. I've seen one online article where the author just wrote another query to get the total count and called that. Something like: int resultCount = (from c in db.Customers where c.FirstName == "JimBob" select c).Count(); and used that value for the DataPager. But I'd really rather not have to copy and paste every query into a separate call where I want to page the results for obvious reasons. Is there an easier way to do this that can be reused across multiple queries? Thanks.

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• How to improve performance of non-scalar aggregations on denormalized tables

  - by The Lazy DBA

  Suppose we have a denormalized table with about 80 columns, and grows at the rate of ~10 million rows (about 5GB) per month. We currently have 3 1/2 years of data (~400M rows, ~200GB). We create a clustered index to best suit retrieving data from the table on the following columns that serve as our primary key... [FileDate] ASC, [Region] ASC, [KeyValue1] ASC, [KeyValue2] ASC ... because when we query the table, we always have the entire primary key. So these queries always result in clustered index seeks and are therefore very fast, and fragmentation is kept to a minimum. However, we do have a situation where we want to get the most recent FileDate for every Region, typically for reports, i.e. SELECT [Region] , MAX([FileDate]) AS [FileDate] FROM HugeTable GROUP BY [Region] The "best" solution I can come up to this is to create a non-clustered index on Region. Although it means an additional insert on the table during loads, the hit isn't minimal (we load 4 times per day, so fewer than 100,000 additional index inserts per load). Since the table is also partitioned by FileDate, results to our query come back quickly enough (200ms or so), and that result set is cached until the next load. However I'm guessing that someone with more data warehousing experience might have a solution that's more optimal, as this, for some reason, doesn't "feel right".

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• Design pattern to keep track UITableView rows correspondance to underlying data in constant time.

  - by DenNukem

  When my model changes I want to animate changes in UITableView by inserting/deleting rows. For that I need to know the ordinal of the given row (so I can construct NSIndexPath), which I find hard to do in better-than-linear time. For example, consider that I have a list of addressbook entries which are manualy sorted by the user, i.e. there is no ordering "key" that represents the sort order. There is also a corresponding UITableView that shows one row per addressbook entry. When UITableView queries the datasource I query the NSMUtableArray populated with my entries and return required data in constant time for each row. However, if there is a change in underlying model I am getting a notification "Joe Smith, id#123 has been removed". Now I have a dilemma. A naive approach would be to scan the array, determine the index at which Joe Smith is and then ask UITableView to remove that precise row from the view, also removing it form the array. However, the scan will take linear time to finish. Now I could have an NSDictionary which allows me to find Joe Smith in constant time, but that doesn't do me a lot of good because I still need to find his ordinal index within the array in order to instruct UITableView to remove that row, which is again a linear search. I could further decide to store each object's ordinal inside the object itself to make it constant, but it will become outdated after first such update as all subsequent index values will have changed due to removal of an object. So what is the correct design pattern to accurately reflect model changes in the UITableView in costant (or at least logarithmic) time?

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• getting proxies of the correct type in nhibernate

  - by Nir

  I have a problem with uninitialized proxies in nhibernate The Domain Model Let's say I have two parallel class hierarchies: Animal, Dog, Cat and AnimalOwner, DogOwner, CatOwner where Dog and Cat both inherit from Animal and DogOwner and CatOwner both inherit from AnimalOwner. AnimalOwner has a reference of type Animal called OwnedAnimal. Here are the classes in the example: public abstract class Animal { // some properties } public class Dog : Animal { // some more properties } public class Cat : Animal { // some more properties } public class AnimalOwner { public virtual Animal OwnedAnimal {get;set;} // more properties... } public class DogOwner : AnimalOwner { // even more properties } public class CatOwner : AnimalOwner { // even more properties } The classes have proper nhibernate mapping, all properties are persistent and everything that can be lazy loaded is lazy loaded. The application business logic only let you to set a Dog in a DogOwner and a Cat in a CatOwner. The Problem I have code like this: public void ProcessDogOwner(DogOwner owner) { Dog dog = (Dog)owner.OwnedAnimal; .... } This method can be called by many diffrent methods, in most cases the dog is already in memory and everything is ok, but rarely the dog isn't already in memory - in this case I get an nhibernate "uninitialized proxy" but the cast throws an exception because nhibernate genrates a proxy for Animal and not for Dog. I understand that this is how nhibernate works, but I need to know the type without loading the object - or, more correctly I need the uninitialized proxy to be a proxy of Cat or Dog and not a proxy of Animal. Constraints I can't change the domain model, the model is handed to me by another department, I tried to get them to change the model and failed. The actual model is much more complicated then the example and the classes have many references between them, using eager loading or adding joins to the queries is out of the question for performance reasons. I have full control of the source code, the hbm mapping and the database schema and I can change them any way I want (as long as I don't change the relationships between the model classes). I have many methods like the one in the example and I don't want to modify all of them. Thanks, Nir

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• How to prevent Hibernate from nullifying relationship column during entity removal

  - by Grzegorz

  I have two entities, A and B. I need to easily retrieve entities A, joined with entities B on the condition of equal values of some column (some column from A equal to some column in B). Those columns are not primary or foreign keys, they contain same business data. I just need to have access from each instance of A to the collection of B's with the same value of this column. So I model it like this: class A { @OneToMany @JoinColumn(name="column_in_B", referencedColumnName="column_in_A") Collection<B> bs; This way, I can run queries like "select A join fetch a.bs b where b...." (Actually, the real relationship here is many-to-many. But when I use @ManyToMany, Hibernate forces me to use join table, which doesnt exist here. So I have to use @OneToMany as workaround). So far so good. The main problem is: whenever I delete an instance of A, hibernate calls "Update B set column_in_B = null", becuase it thinks the column_in_B is foreign key pointing at primary key in A (and because row in A is deleted, it tries to clean the foreign key in B). BUT the column_in_B IS NOT a foreign key, and can't be modified, because it causes data lost (and this column is NOT NULL anyway in my case, causing data integerity exception to be thrown). Plese help me with this. How to model such relationships with Hibernate? (I would call it "virtual relationships", or "secondary relationships" or so: as they are not based on foreign keys, they are just some shortcuts which allows for retrieving related objects and quering for them with HQL)

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• MySql Query lag time / deadlock?

  - by Click Upvote

  When there are multiple PHP scripts running in parallel, each making an UPDATE query to the same record in the same table repeatedly, is it possible for there to be a 'lag time' before the table is updated with each query? I have basically 5-6 instances of a PHP script running in parallel, having been launched via cron. Each script gets all the records in the items table, and then loops through them and processes them. However, to avoid processing the same item more than once, I store the id of the last item being processed in a seperate table. So this is how my code works: function getCurrentItem() { $sql = "SELECT currentItemId from settings"; $result = $this->db->query($sql); return $result->get('currentItemId'); } function setCurrentItem($id) { $sql = "UPDATE settings SET currentItemId='$id'"; $this->db->query($sql); } $currentItem = $this->getCurrentItem(); $sql = "SELECT * FROM items WHERE status='pending' AND id > $currentItem'"; $result = $this->db->query($sql); $items = $result->getAll(); foreach ($items as $i) { //Check if $i has been processed by a different instance of the script, and if so, //leave it untouched. if ($this->getCurrentItem() > $i->id) continue; $this->setCurrentItem($i->id); // Process the item here } But despite of all the precautions, most items are being processed more than once. Which makes me think that there is some lag time between the update queries being run by the PHP script, and when the database actually updates the record. Is it true? And if so, what other mechanism should I use to ensure that the PHP scripts always get only the latest currentItemId even when there are multiple scripts running in parrallel? Would using a text file instead of the db help?

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• java class creation dynamically and make it accessible across the network different jvms i.e. serial

  - by inj.rav

  Hi. I have a requirement of creating java classes dynamically and make it accessible different jvms across the network. I tried to use reflection and javassist tool,but nothing worked. Let me explain the scenario we are using Coherence distributed cache. It has a power of doing aggregation/filtering in parallel across the cluster. For example if a class has [dynamic class] has amount variable and getAmount/setAmount methods. Then if we execute COHERENCE queries, it will start process in parallel across the cluster. I tried to create classes at run time by using javassist and reflection. I am able to access it from single JVM, but when I tried to access the same class from other jvm [through coherence cluster]. I am getting exception of class not found [as remote jvm is not having idea of this class].I can over come this by creating same class dynamically on remote jvm also and access the methods. But coherence in built methods/functions are not able to find the class. could some one help me on this matter

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• csc.exe not found error

  - by pokrate

  I have installed a fresh copy of windows xp 2002 with SP2, and then VS.net 2008 enterprise edition. I am trying to build a simplest possible web application, and its not compiling giving error csc.exe not found. I googled a lot, and spot the problem in the following section in web.config : <system.codedom> <compilers> <compiler language="c#;cs;csharp" extension=".cs" warningLevel="4" type="Microsoft.CSharp.CSharpCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <providerOption name="CompilerVersion" value="v3.5"/> <providerOption name="WarnAsError" value="false"/> </compiler> <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" warningLevel="4" type="Microsoft.VisualBasic.VBCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <providerOption name="CompilerVersion" value="v3.5"/> <providerOption name="OptionInfer" value="true"/> <providerOption name="WarnAsError" value="false"/> </compiler> </compilers> </system.codedom> But if i remove the csharp compiler section , and then compile, it compiles fine with vb compiler section. And if I change the value from v3.5 to v2.0 in the of csharp section, then also it compiles fine. But then all my Linq Queries are not recognized by the compiler. But System.Linq and all classes present in it are accessible in the code. Please help in this weird behavior.

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• Simplest way to handle and display errors in a Python Pylons controller without a helper class

  - by ensnare

  I have a class User() that throw exceptions when attributes are incorrectly set. I am currently passing the exceptions from the models through the controller to the templates by essentially catching exceptions two times for each variable. Is this a correct way of doing it? Is there a better (but still simple) way? I prefer not to use any third party error or form handlers due to the extensive database queries we already have in place in our classes. Furthermore, how can I "stop" the chain of processing in the class if one of the values is invalid? Is there like a "break" syntax or something? Thanks. >>> u = User() >>> u.name = 'Jason Mendez' >>> u.password = '1234' Traceback (most recent call last): File "<stdin>", line 1, in <module> File "topic/model/user.py", line 79, in password return self._password ValueError: Your password must be greater than 6 characters In my controller "register," I have: class RegisterController(BaseController): def index(self): if request.POST: c.errors = {} u = User() try: u.name = c.name = request.POST['name'] except ValueError, error: c.errors['name'] = error try: u.email = c.email = request.POST['email'] except ValueError, error: c.errors['email'] = error try: u.password = c.password = request.POST['password'] except ValueError, error: c.errors['password'] = error try: u.commit() except ValueError, error: pass return render('/register.mako')

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• How can I factor out repeated expressions in an SQL Query? Column aliases don't seem to be the ticke

  - by Weston C

  So, I've got a query that looks something like this: SELECT id, DATE_FORMAT(CONVERT_TZ(callTime,'+0:00','-7:00'),'%b %d %Y') as callDate, DATE_FORMAT(CONVERT_TZ(callTime,'+0:00','-7:00'),'%H:%i') as callTimeOfDay, SEC_TO_TIME(callLength) as callLength FROM cs_calldata WHERE customerCode='999999-abc-blahblahblah' AND CONVERT_TZ(callTime,'+0:00','-7:00') >= '2010-04-25' AND CONVERT_TZ(callTime,'+0:00','-7:00') <= '2010-05-25' If you're like me, you probably start thinking that maybe it would improve readability and possibly the performance of this query if I wasn't asking it to compute CONVERT_TZ(callTime,'+0:00','-7:00') four separate times. So I try to create a column alias for that expression and replace further occurances with that alias: SELECT id, CONVERT_TZ(callTime,'+0:00','-7:00') as callTimeZoned, DATE_FORMAT(callTimeZoned,'%b %d %Y') as callDate, DATE_FORMAT(callTimeZoned,'%H:%i') as callTimeOfDay, SEC_TO_TIME(callLength) as callLength FROM cs_calldata WHERE customerCode='5999999-abc-blahblahblah' AND callTimeZoned >= '2010-04-25' AND callTimeZoned <= '2010-05-25' This is when I learned, to quote the MySQL manual: Standard SQL disallows references to column aliases in a WHERE clause. This restriction is imposed because when the WHERE clause is evaluated, the column value may not yet have been determined. So, that approach would seem to be dead in the water. How is someone writing queries with recurring expressions like this supposed to deal with it?

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• Using WCF to expose underlying process

  - by Steven

  I think I must be a little dull because I'm having so much difficulty with this. I use WCF for pretty much everything in-house, it's the most appropriate technology. I have a new Silverlight 3 app that is connecting to the WCF service and that's working fine. Where the problem begins is: Because of the expense in creating the objects within this service and the high correlation of individual objects being shared between clients I want to have a console application that basically gathers/calculates/caches all the data for the service 24/7 and the service basically connects to the console app (or whatever it is) and gets the pre-processed data. eg, think of it in terms of a stock reporting app (which it is). Person A has a portfolio of x, y z Person B has a portfolio of x, q, z, r The service needs to provide updated metrics on how their portfolio is performing. So instead of every 1 second processing person A, then person B, the app independently gathers the stock price and persons position information into memory and the service just queries the in memory result. Thanks for your help, I really am feeling dumb right now.

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