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  • can I put my sqlite connection and cursor in a function?

    - by steini
    I was thinking I'd try to make my sqlite db connection a function instead of copy/pasting the ~6 lines needed to connect and execute a query all over the place. I'd like to make it versatile so I can use the same function for create/select/insert/etc... Below is what I have tried. The 'INSERT' and 'CREATE TABLE' queries are working, but if I do a 'SELECT' query, how can I work with the values it fetches outside of the function? Usually I'd like to print the values it fetches and also do other things with them. When I do it like below I get an error Traceback (most recent call last): File "C:\Users\steini\Desktop\py\database\test3.py", line 15, in <module> for row in connection('testdb45.db', "select * from users"): ProgrammingError: Cannot operate on a closed database. So I guess the connection needs to be open so I can get the values from the cursor, but I need to close it so the file isn't always locked. Here's my testing code: import sqlite3 def connection (db, arg): conn = sqlite3.connect(db) conn.execute('pragma foreign_keys = on') cur = conn.cursor() cur.execute(arg) conn.commit() conn.close() return cur connection('testdb.db', "create table users ('user', 'email')") connection('testdb.db', "insert into users ('user', 'email') values ('joey', 'foo@bar')") for row in connection('testdb45.db', "select * from users"): print row How can I make this work?

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  • Check if date is allowed weekday in php?

    - by moogeek
    Hello! I'm stuck with a problem how to check if a specific date is within allowed weekdays array in php. For example, function dateIsAllowedWeekday($_date,$_allowed) { if ((isDate($_date)) && (($_allowed!="null") && ($_allowed!=null))){ $allowed_weekdays=json_decode($_allowed); $weekdays=array(); foreach($allowed_weekdays as $wd){ $weekday=date("l",date("w",strtotime($wd))); array_push($weekdays,$weekday); } if(in_array(date("l",strtotime($_date)),$weekdays)){return TRUE;} else {return FALSE;} } else {return FALSE;} } ///////////////////////////// $date="21.05.2010"; $wd="[0,1,2]"; if(dateIsAllowedWeekday($date,$wd)){echo "$date is within $wd weekday values!";} else{echo "$date isn't within $wd weekday values!"} I have input dates formatted as "d.m.Y" and an array returned from database with weekday numbers (formatted as 'Numeric representation of the day of the week') like [0,1,2] - (Sunday,Monday,Tuesday). The returned string from database can be "null", so i check it too. Them, the isDate function checks whether date is a date and it is ok. I want to check if my date, for example 21.05.2010 is an allowed weekday in this array. My function always returns TRUE and somehow weekday is always 'Thursday' and i don't know why... Is there any other ways to check this or what can be my error in the code above? thx

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  • Out of memory when creating a lot of objects C#

    - by Bas
    I'm processing 1 million records in my application, which I retrieve from a MySQL database. To do so I'm using Linq to get the records and use .Skip() and .Take() to process 250 records at a time. For each retrieved record I need to create 0 to 4 Items, which I then add to the database. So the average amount of total Items that has to be created is around 2 million. while (objects.Count != 0) { using (dataContext = new LinqToSqlContext(new DataContext())) { foreach (Object objectRecord in objects) { // Create a list of 0 - 4 Random Items and add each Item to the Object for (int i = 0; i < Random.Next(0, 4); i++) { Item item = new Item(); item.Id = Guid.NewGuid(); item.Object = objectRecord.Id; item.Created = DateTime.Now; item.Changed = DateTime.Now; dataContext.InsertOnSubmit(item); } } dataContext.SubmitChanges(); } amountToSkip += 250; objects = objectCollection.Skip(amountToSkip).Take(250).ToList(); } Now the problem arises when creating the Items. When running the application (and not even using dataContext) the memory increases consistently. It's like the items are never getting disposed. Does anyone notice what I'm doing wrong? Thanks in advance!

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  • hibernate: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException

    - by user121196
    when saving an object to database using hibernate, sometimes it fails because certain fields of the object exceed the maximum varchar length defined in the database. There force I am using the following approach: 1. attempt to save 2. if getting an DataException, then I truncate the fields in the object to the max length specified in the db definition, then try to save again. However, in the second save after truncation. I'm getting the following exception: hibernate: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails here's the relevant code, what's wrong? public static void saveLenientObject(Object obj){ try { save2(rec); } catch (org.hibernate.exception.DataException e) { // TODO Auto-generated catch block e.printStackTrace(); saveLenientObject(rec, e); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } private static void saveLenientObject(Object rec, DataException e) { Util.truncateObject(rec); System.out.println("after truncation "); save2(rec); } public static void save2(Object obj) throws Exception{ try{ beginTransaction(); getSession().save(obj); commitTransaction(); }catch(Exception e){ e.printStackTrace(); rollbackTransaction(); //closeSession(); throw e; }finally{ closeSession(); } }

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  • Does new JUnit 4.8 @Category render test suites almost obsolete?

    - by grigory
    Given question 'How to run all tests belonging to a certain Category?' and the answer would the following approach be better for test organization? define master test suite that contains all tests (e.g. using ClasspathSuite) design sufficient set of JUnit categories (sufficient means that every desirable collection of sets is identifiable using one or more categories) define targeted test suites based on master test suite and set of categories For example: identify categories for speed (slow, fast), dependencies (mock, database, integration), function (), domain ( demand that each test is properly qualified (tagged) with relevant set of categories. create master test suite using ClasspathSuite (all tests found in classpath) create targeted suites by qualifying master test suite with categories, e.g. mock test suite, fast database test suite, slow integration for domain X test suite, etc. My question is more like soliciting approval rate for such approach vs. classic test suite approach. One unbeatable benefit is that every new test is immediately contained by relevant suites with no suite maintenance. One concern is proper categorization of each test.

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  • Not getting key value from Identity column back after inserting new row with SubSonic ActiveRecord

    - by mikedevenney
    I'm sure I'm missing the obvious answer here, but could use a hand. I'm new to SubSonic and using version 3. I've got myself to the point of being able to query and insert, but I'm stuck with how I would get the value of the identity column back after my insert. I saw another post that mentioned Linq Templates. I'm not using those (at least I don't think I am...?) TIA ... UPDATE ... So I've been debugging through my code watching how the SubSonic code works and I found where the indentity column is being ignored. I use int as the datatype for my ID columns in the database and set them as identity. Since int is a non-nullable data type in c# the logical test in the Add method (public void Add(IDataProvider provider)) that checks if there is a value in the key column by doing a (key==null) could be the issue. The code that gets the new value for the identity field is in the 'true path', since an int can't be null and I use ints as my identity column data types this test will never pass. The ID field for my object has a 0 in it that I didn't put there. I assume it's set during the initialization of the object. Am I off base here? Is the answer to change my data types in the database? Another question (more a curiosity). I noticed that some of the properties in the generated classes are declared with a ? after the datatype. I'm not familiar with this declaration construct... what gives? There are some declared as an int (non key fields) and others that are declared as int? (key fields). Does this have something to do with how they're treated at initialization? Any help is appreciated! --BUMP--

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  • transaction handling in dataset based insert/update in c#

    - by user3703611
    I am trying to insert bulk records in a sql server database table using dataset. But i am unable to do transaction handling. Please help me to apply transaction handling in below code. I am using adapter.UpdateCommand.Transaction = trans; but this line give me an error of Object reference not set to an instance of an object. Code: string ConnectionString = "server=localhost\\sqlexpress;database=WindowsApp;Integrated Security=SSPI;"; SqlConnection conn = new SqlConnection(ConnectionString); conn.Open(); SqlTransaction trans = conn.BeginTransaction(IsolationLevel.Serializable); SqlDataAdapter adapter = new SqlDataAdapter("SELECT * FROM Test ORDER BY Id", conn); SqlCommandBuilder builder = new SqlCommandBuilder(adapter); adapter.UpdateCommand.Transaction = trans; // Create a dataset object DataSet ds = new DataSet("TestSet"); adapter.Fill(ds, "Test"); // Create a data table object and add a new row DataTable TestTable = ds.Tables["Test"]; for (int i=1;i<=50;i++) { DataRow row = TestTable.NewRow(); row["Id"] = i; TestTable .Rows.Add(row); } // Update data adapter adapter.Update(ds, "Test"); trans.Commit(); conn.Close();

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  • Unserializing an API return object (PHP/Ebay API)

    - by DavidYell
    I have been working with the Ebay api for a project and have found it great. I have however found a problem now, more PHP related. When I read my items from Ebay, I store a bunch of details in the database. Currently, just for the sake of it really, I serialize the whole return object and store it in the database in a related table. The idea being, that when I display my information, I have all the details to hand should I need them. The problem arises in that the pricing information is always in a sub object. [ConvertedAdjustmentAmount] => __PHP_Incomplete_Class Object ( [__PHP_Incomplete_Class_Name] => eBayAmountType [_] => 0 [currencyID] => USD ) As you can see when I unserialize my object, my cunning plan falls foul of the Incomplete class problem. I have checked the following question, without success. http://stackoverflow.com/questions/965611/forcing-access-to-php-incomplete-class-object-properties The main issue lies, as far as I can see, in that the price class is stored in the Ebay api, so how do I recreate it? I have been reading this page, http://uk3.php.net/manual/en/function.unserialize.php and trying to figure out, unserialize_callback_func which I can't figure out either, so any help would be appreciated!

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  • Excel - Best Way to Connect With Access Data

    - by gamerzfuse
    Hello there, Here is the situation we have: a) I have an Access database / application that records a significant amount of data. Significant fields would be hours, # of sales, # of unreturned calls, etc b) I have an Excel document that connects to the Access database and pulls data in to visualize it As it stands now, the Excel file has a Refresh button that loads new data. The data is loaded into a large PivotTable. The main 'visual form' then uses VLOOKUP to get the results from the form, based on the related hours. This operation is slow (~10 seconds) and seems to be redundant and inefficient. Is there a better way to do this? I am willing to go just about any route - just need directions. Thanks in advance! Update: I have confirmed (due to helpful comments/responses) that the problem is with the data loading itself. removing all the VLOOKUPs only took a second or two out of the load time. So, the questions stands as how I can rapidly and reliably get the data without so much time involvement (it loads around 3000 records into the PivotTables).

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  • PHP Check slave status without mysql_connect timeout issues

    - by Jonathon
    I have a web-app that has a master mysql db and four slave dbs. I want to handle all (or almost all) read-only (SELECT) queries from the slaves. Our load-balancer sends the user to one of the slave machines automatically, since they are also running Apache/PHP and serving webpages. I am using an include file to setup the connection to the databases, such as: //for master server (i.e. - UPDATE/INSERT/DELETE statements) $Host = "10.0.0.x"; $User = "xx"; $Password = "xx"; $Link = mysql_connect( $Host, $User, $Password ); if( !$Link ) ) { die( "Master database is currently unavailable. Please try again later." ); } //this connection can be used for READ-ONLY (i.e. - SELECT statements) on the localhost $Host_Local = "localhost"; $User_Local = "xx"; $Password_Local = "xx"; $Link_Local = mysql_connect( $Host_Local, $User_Local, $Password_Local ); //fail back to master if slave db is down if( !$Link_Local ) ) { $Link_Local = mysql_connect( $Host, $User, $Password ); } I then use $Link for all update queries and $Link_Local as the connection for SELECT statements. Everything works fine until the slave server database goes down. If the local db is down, the $Link_Local = mysql_connect() call takes at least 30 seconds before it gives up on trying to connect to the localhost and returns back to the script. This causes a huge backlog of page serves and basically shuts down the system (due to the extremely slow response time). Does anyone know of a better way to handle connections to slave servers via PHP? Or, is there some kind of timeout function that could be used to stop the mysql_connect call after 2-3 seconds? Thanks for the help. I searched the other mysql_connect threads, but didn't see any that addressed this issue.

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  • Preventing ActiveRecord save() on an instance

    - by Craig Walker
    I have an ActiveRecord model object Foo; it represents a standard database row. I want to be able to display modified versions of instances of this object. I'd like to reuse the class itself, as it already has all the hooks & aspects I'll need. (For example: I already have a view that displays the appropriate attributes). Basically I want to clone the model instance, modify some of its properties, and feed it back to the caller (view, test, etc). I do not want these attribute modifications getting back into the database. However, I do want to include the id attribute in the cloned version, as it makes dealing with the route-helpers much easier. Thus, I plan on calling ActiveRecord::Base.clone(), manually setting the ID of the cloned instance, and then making the appropriate attribute changes to the new instance. This has me worried though; one save() on the modified instance and my original data will get clobbered. So, I'm looking to lock down the new instance so that it won't hurt anything else. I'm already planning on calling freeze() (on the understanding that this prevents further modification to the object, though the documentation isn't terribly clear). However, I don't see any obvious way to prevent a save(). What would be the best approach to achieving this?

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  • why is Active Record firing extra query when I use Includes method to fetch data

    - by riddhi_agrawal
    I have the following model structure: class Group < ActiveRecord::Base has_many :group_products, :dependent => :destroy has_many :products, :through => :group_products end class Product < ActiveRecord::Base has_many :group_products, :dependent => :destroy has_many :groups, :through => :group_products end class GroupProduct < ActiveRecord::Base belongs_to :group belongs_to :product end I wanted to minimize my database queries so I decided to use includes.In the console I tried something like, groups = Group.includes(:products) my development logs show the following calls, Group Load (403.0ms) SELECT `groups`.* FROM `groups` GroupProduct Load (60.0ms) SELECT `group_products`.* FROM `group_products` WHERE (`group_products`.group_id IN (1,3,14,15,16,18,19,20,21,22,23,24,25,26,27,28,29,30,33,42,49,51)) Product Load (22.0ms) SELECT `products`.* FROM `products` WHERE (`products`.`id` IN (382,304,353,12,63,103,104,105,262,377,263,264,265,283,284,285,286,287,302,306,307,308,328,335,336,337,340,355,59,60,61,247,309,311,66,30,274,294,324,350,140,176,177,178,64,240,327,332,338,380,383,252,254,255,256,257,325,326)) Product Load (10.0ms) SELECT `products`.* FROM `products` WHERE (`products`.`id` = 377) LIMIT 1 I could analyze the initial three calls were necessary but don't get the reason why the last database call is made, Product Load (10.0ms) SELECT `products`.* FROM `products` WHERE (`products`.`id` = 377) LIMIT 1 Any idea why this is happening? Thanks in advance. :)

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  • Is something along the lines of nested memoization needed here?

    - by Daniel
    System.Transactions notoriously escalates transactions involving multiple connections to the same database to the DTC. The module and helper class, ConnectionContext, below are meant to prevent this by ensuring multiple connection requests for the same database return the same connection object. This is, in some sense, memoization, although there are multiple things being memoized and the second is dependent on the first. Is there some way to hide the synchronization and/or mutable state (perhaps using memoization) in this module, or perhaps rewrite it in a more functional style? (It may be worth nothing that there's no locking when getting the connection by connection string because Transaction.Current is ThreadStatic.) type ConnectionContext(connection:IDbConnection, ownsConnection) = member x.Connection = connection member x.OwnsConnection = ownsConnection interface IDisposable with member x.Dispose() = if ownsConnection then connection.Dispose() module ConnectionManager = let private _connections = new Dictionary<string, Dictionary<string, IDbConnection>>() let private getTid (t:Transaction) = t.TransactionInformation.LocalIdentifier let private removeConnection tid = let cl = _connections.[tid] for (KeyValue(_, con)) in cl do con.Close() lock _connections (fun () -> _connections.Remove(tid) |> ignore) let getConnection connectionString (openConnection:(unit -> IDbConnection)) = match Transaction.Current with | null -> new ConnectionContext(openConnection(), true) | current -> let tid = getTid current // get connections for the current transaction let connections = match _connections.TryGetValue(tid) with | true, cl -> cl | false, _ -> let cl = Dictionary<_,_>() lock _connections (fun () -> _connections.Add(tid, cl)) cl // find connection for this connection string let connection = match connections.TryGetValue(connectionString) with | true, con -> con | false, _ -> let initial = (connections.Count = 0) let con = openConnection() connections.Add(connectionString, con) // if this is the first connection for this transaction, register connections for cleanup if initial then current.TransactionCompleted.Add (fun args -> let id = getTid args.Transaction removeConnection id) con new ConnectionContext(connection, false)

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  • Can a T-SQL variable represent an entire row?

    - by elbillaf
    I'm coding for MS SQL Server 10. I have two databases that contain dozens of tables. Each table in one database contains a table with the same name in the other database. Tables with the same name have identical format (fields and data types). The contents of the two tables are similar but not identical. I need to update one based on changes made to the other, but only under certain circumstances. I think I want to use a cursor for this, but I can't find a good example to go by. So far, the MSDN examples are reading one field at a time into a variable. I do need to be able to read /modify two fields which are identical in each table, but I gotta believe there's something less tedious than declaring variables for every field of every table. I would like to be able to FETCH an entire row, check a couple of fields and then make a decision of whether I want to write the entire row to the other table after changing two fields - but do I have to declare variables for EVERY field I want to fetch / write? There's no way to just FETCH an entire row and write an entire row?

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  • ASP.MVC 2 Model Data Persistance

    - by toccig
    I'm and MVC1 programmer, new to the MVC2. The data will not persist to the database in an edit scenario. Create works fine. Controller: // // POST: /Attendee/Edit/5 [Authorize(Roles = "Admin")] [AcceptVerbs(HttpVerbs.Post)] public ActionResult Edit(Attendee attendee) { if (ModelState.IsValid) { UpdateModel(attendee, "Attendee"); repository.Save(); return RedirectToAction("Details", attendee); } else { return View(attendee); } } Model: [MetadataType(typeof(Attendee_Validation))] public partial class Attendee { } public class Attendee_Validation { [HiddenInput(DisplayValue = false)] public int attendee_id { get; set; } [HiddenInput(DisplayValue = false)] public int attendee_pin { get; set; } [Required(ErrorMessage = "* required")] [StringLength(50, ErrorMessage = "* Must be under 50 characters")] public string attendee_fname { get; set; } [StringLength(50, ErrorMessage = "* Must be under 50 characters")] public string attendee_mname { get; set; } } I tried to add [Bind(Exclude="attendee_id")] above the Class declaration, but then the value of the attendee_id attribute is set to '0'. View (Strongly-Typed): <% using (Html.BeginForm()) {%> ... <%=Html.Hidden("attendee_id", Model.attendee_id) %> ... <%=Html.SubmitButton("btnSubmit", "Save") %> <% } %> Basically, the repository.Save(); function seems to do nothing. I imagine it has something to do with a primary key constraint violation. But I'm not getting any errors from SQL Server. The application appears to runs fine, but the data is never persisted to the Database.

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  • how to handle empty selection in a jface bound combobox?

    - by guido
    I am developing a search dialog in my eclipse-rcp application. In the search dialog I have a combobox as follows: comboImp = new CCombo(grpColSpet, SWT.BORDER | SWT.READ_ONLY); comboImp.setBounds(556, 46, 184, 27); comboImpViewer = new ComboViewer(comboImp); comboImpViewer.setContentProvider(new ArrayContentProvider()); comboImpViewer.setInput(ImpContentProvider.getInstance().getImps()); comboImpViewer.setLabelProvider(new LabelProvider() { @Override public String getText(Object element) { return ((Imp)element).getImpName(); } }); Imp is a database entity, ManyToOne to the main entity which is searched, and ImpContentProvider is the model class which speaks to embedded sqlite database via jpa/hibernate. This combobox is supposed to contain all instances of Imp, but to also let empty selection; it's value is bound to a service bean as follows: IObservableValue comboImpSelectionObserveWidget = ViewersObservables.observeSingleSelection(comboImpViewer); IObservableValue filterByImpObserveValue = BeansObservables.observeValue(searchPrep, "imp"); bindingContext.bindValue(comboImpSelectionObserveWidget, filterByImpObserveValue , null, null); As soon as the user clicks on the combo, a selection (first element) is made: I can see the call to a selectionlistener i added on the viewer. My question is: after a selection has been made, how do I let the user change his mind and have an empty selection in the combobox? should I add a "fake" empty instance of Imp to the List returned by the ImpContentProvider? or should I implement an alternative to ArrayContentProvider? and one additional related question is: why calling deselectAll() and clearSelection() on the combo does NOT set a null value to the bound bean?

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  • Random problem connecting to MySQL

    - by CharlesLeaf
    Environment: RHEL 5 servers, MySQL 5.1.43, PHP 5.1.6 (using MySQLi). Currently only available within our internal VPN network. Servers ServerA: Webserver ServerB/C/D: Database server (1 master 2 slaves) The error (on ServerA) [Tue May 25 11:12:17 2010] [error] [client CLIENTIP] PHP Warning: mysqli::real_connect() [function.mysqli-real-connect]: (HY000/2003): Can't connect to MySQL server on 'ServerB' (4) in /home/**/Database.php on line 67, referer: [website] Problem description It appears that at completely random times, our website is unable to connect to one of the MySQL servers - usually the Master. Except for the forementioned error message, there is nothing to be found in any of the logs as far as I can see, and most of the times the connection is succesful and everything works as it should. It's just at completely random times, this error pops up. There's no firewall blocking any internal traffic, timeout value is 3 but it doesn't take 3 seconds before it fails to connect. With the default mysql client I can connect from ServerA to ServerB,C and D and haven't encountered a problem yet. Does anyone have a clue what I might be overlooking / could be the problem? Because I've run out of ideas myself.

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  • GridView ObjectDataSource LINQ Paging and Sorting using multiple table query.

    - by user367426
    I am trying to create a pageing and sorting object data source that before execution returns all results, then sorts on these results before filtering and then using the take and skip methods with the aim of retrieving just a subset of results from the database (saving on database traffic). this is based on the following article: http://www.singingeels.com/Blogs/Nullable/2008/03/26/Dynamic_LINQ_OrderBy_using_String_Names.aspx Now I have managed to get this working even creating lambda expressions to reflect the sort expression returned from the grid even finding out the data type to sort for DateTime and Decimal. public static string GetReturnType<TInput>(string value) { var param = Expression.Parameter(typeof(TInput), "o"); Expression a = Expression.Property(param, "DisplayPriceType"); Expression b = Expression.Property(a, "Name"); Expression converted = Expression.Convert(Expression.Property(param, value), typeof(object)); Expression<Func<TInput, object>> mySortExpression = Expression.Lambda<Func<TInput, object>>(converted, param); UnaryExpression member = (UnaryExpression)mySortExpression.Body; return member.Operand.Type.FullName; } Now the problem I have is that many of the Queries return joined tables and I would like to sort on fields from the other tables. So when executing a query you can create a function that will assign the properties from other tables to properties created in the partial class. public static Account InitAccount(Account account) { account.CurrencyName = account.Currency.Name; account.PriceTypeName = account.DisplayPriceType.Name; return account; } So my question is, is there a way to assign the value from the joined table to the property of the current table partial class? i have tried using. from a in dc.Accounts where a.CompanyID == companyID && a.Archived == null select new { PriceTypeName = a.DisplayPriceType.Name}) but this seems to mess up my SortExpression. Any help on this would be much appreciated, I do understand that this is complex stuff.

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  • codeigniter mulitple LIKE db query using associative array- but all from the same column name...?

    - by Inigo
    Hi, I'm trying to query my database using codeigniter's active record class. I have a number of blog posts stored in a table. The query is for a search function, which will pull out all the posts that have certain categories assigned to them. So the 'category' column of the table will have a list of all the categories for that post in no particular order, separated by commas, like so: Politics,History,Sociology.. etc. If a user selects, say, Politics and History, The titles of all the posts that have BOTH these categories should be returned. Right? So, the list of categories queried will be the array $cats. I thought this would work- foreach ($cats as $cat){ $this->db->like('categories',$cat); } By Producing this- $this-db-like('categories','Politics'); $this-db-like('categories','History'); (Which would produce- 'WHERE categories LIKE '%Politics%' AND categories LIKE '%History%') But it doesn't work, it seems to only produce the first statement. The problem I guess is that the column name is the same for each of the chained queries. There doesn't seem to be anything in the CI user guide about this (http://codeigniter.com/user_guide/database/active_record.html) as they seem to assume that each chained statement is going to be for a different column name. Does anyone know how I could do this? Thanks! edit- Of course it is not possible to use an associative array in one statement as it would have to contain duplicate keys- in this case every key would have to be 'categories'...

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  • Scalability 101: How can I design a scalable web application using PHP?

    - by Legend
    I am building a web-application and have a couple of quick questions. From what I learnt, one should not worry about scalability when initially building the app and should only start worrying when the traffic increases. However, this being my first web-application, I am not quite sure if I should take an approach where I design things in an ad-hoc manner and later "fix" them. I have been reading stories about how people start off with an app that gets millions of users in a week or two. Not that I will face the same situation but I can't help but wonder, how do these people do it? Currently, I bought a shared hosting account on Lunarpages and that got me started in building and testing the application. However, I am interested in learning how to build the same application in a scalable-manner using the cloud, for instance, Amazon's EC2. From my understanding, I can see a couple of components: There is a load balancer that first receives requests and then decides where to route each request This request is then handled by a server replica that then processes the request and updates (if required) the database and sends back the response to the client If a similar request comes in, then a caching mechanism like memcached kicks into picture and returns objects from the cache A blackbox that handles database replication Specifically, I am trying to do the following: Setting up a load balancer (my homework revealed that HAProxy is one such load balancer) Setting up replication so that databases can be synchronized Using memcached Configuring Apache to work with multiple web servers Partitioning application to use Amazon EC2 and Amazon S3 (my application is something that will need great deal of storage) Finally, how can I avoid burning myself when using Amazon services? Because this is just a learning phase, I can probably do with 2-3 servers with a simple load balancer and replication but until I want to avoid paying loads of money accidentally. I am able to find resources on individual topics but am unable to find something that starts off from the big picture. Can someone please help me get started?

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  • Use a foreign key mapping to get data from the other table using Python and SQLAlchemy.

    - by Az
    Hmm, the title was harder to formulate than I thought. Basically, I've got these simple classes mapped to tables, using SQLAlchemy. I know they're missing a few items but those aren't essential for highlighting the problem. class Customer(object): def __init__(self, uid, name, email): self.uid = uid self.name = name self.email = email def __repr__(self): return str(self) def __str__(self): return "Cust: %s, Name: %s (Email: %s)" %(self.uid, self.name, self.email) The above is basically a simple customer with an id, name and an email address. class Order(object): def __init__(self, item_id, item_name, customer): self.item_id = item_id self.item_name = item_name self.customer = None def __repr__(self): return str(self) def __str__(self): return "Item ID %s: %s, has been ordered by customer no. %s" %(self.item_id, self.item_name, self.customer) This is the Orders class that just holds the order information: an id, a name and a reference to a customer. It's initialised to None to indicate that this item doesn't have a customer yet. The code's job will assign the item a customer. The following code maps these classes to respective database tables. # SQLAlchemy database transmutation engine = create_engine('sqlite:///:memory:', echo=False) metadata = MetaData() customers_table = Table('customers', metadata, Column('uid', Integer, primary_key=True), Column('name', String), Column('email', String) ) orders_table = Table('orders', metadata, Column('item_id', Integer, primary_key=True), Column('item_name', String), Column('customer', Integer, ForeignKey('customers.uid')) ) metadata.create_all(engine) mapper(Customer, customers_table) mapper(Orders, orders_table) Now if I do something like: for order in session.query(Order): print order I can get a list of orders in this form: Item ID 1001: MX4000 Laser Mouse, has been ordered by customer no. 12 What I want to do is find out customer 12's name and email address (which is why I used the ForeignKey into the Customer table). How would I go about it?

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  • Any suggestions to improve my PDO connection class?

    - by Scarface
    Hey guys I am pretty new to pdo so I basically just put together a simple connection class using information out of the introductory book I was reading but is this connection efficient? If anyone has any informative suggestions, I would really appreciate it. class PDOConnectionFactory{ public $con = null; // swich database? public $dbType = "mysql"; // connection parameters public $host = "localhost"; public $user = "user"; public $senha = "password"; public $db = "database"; public $persistent = false; // new PDOConnectionFactory( true ) <--- persistent connection // new PDOConnectionFactory() <--- no persistent connection public function PDOConnectionFactory( $persistent=false ){ // it verifies the persistence of the connection if( $persistent != false){ $this->persistent = true; } } public function getConnection(){ try{ $this->con = new PDO($this->dbType.":host=".$this->host.";dbname=".$this->db, $this->user, $this->senha, array( PDO::ATTR_PERSISTENT => $this->persistent ) ); // carried through successfully, it returns connected return $this->con; // in case that an error occurs, it returns the error; }catch ( PDOException $ex ){ echo "We are currently experiencing technical difficulties. We have a bunch of monkies working really hard to fix the problem. Check back soon: ".$ex->getMessage(); } } // close connection public function Close(){ if( $this->con != null ) $this->con = null; } }

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  • How to Store and Retrieve Images Using SQL Server (Server Management Studio)

    - by Joe Majewski
    I am having difficulties when trying to insert files into a SQL Server database. I'll try to break this down as best as I can: What data type should I be using to store image files (jpeg/png/gif/etc)? Right now my table is using the image data type, but I am curious if varbinary would be a better option. How would I go about inserting the image into the database? Does Microsoft SQL Server Management Studio have any built in functions that allow insertions of files into tables? If so, how is that done? Also, how could this be done through the use of an HTML form with PHP handling the input data and placing it into the table? How would I fetch the image from the table and display it on the page? I understand how to SELECT the cell's contents, but how would I go about translating that into a picture. Would I have to have a header(Content type: image/jpeg)? I have no problem doing any of these things with MySQL, but the SQL Server environment is still new to me, and I am working on a project for my job that requires the use of stored procedures to grab various data. Any and all help is appreciated.

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  • NHibernate / multiple sessions and nested objects

    - by bernhardrusch
    We are using NHibernate in a rich client application. It is a pretty open application (the user searches for a dataset or creates a new one, changes the data and saves the data set. We leave the session open, because sometimes we have to lazy load some properties of the object (nested object structure). This means one big problem if we leave the session open, the db (MySQL) closes the connection and we are not able to find this out and it throws an exception (socket communication error) when accessing the database (we are thinking about testing the db connection before accessing the object - but this is not really optimal neither, the other option would be to set back the timeout of the db connection , but this just doesn't seem to well). So - is it possible to reconnect the session to a new database connection ? Another problem is it possible to get an object from one session and then re-attach it to another session ? (I often hear that session.lock should work for this - but this doesn't work so well in our application - so I ended up getting a "fresh" object from the session and copy the data over manually - which is a little bit cumbersome) Any ideas for this ?

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  • Function returning a class containing a function returning a class

    - by Scott
    I'm working on an object-oriented Excel add-in to retrieve information from our ERP system's database. Here is an example of a function call: itemDescription = Macola.Item("12345").Description Macola is an instance of a class which takes care of database access. Item() is a function of the Macola class which returns an instance of an ItemMaster class. Description() is a function of the ItemMaster class. This is all working correctly. Items can be be stored in more than one location, so my next step is to do this: quantityOnHand = Macola.Item("12345").Location("A1").QuantityOnHand Location() is a function of the ItemMaster class which returns an instance of the ItemLocation class (well, in theory anyway). QuantityOnHand() is a function of the ItemLocation class. But for some reason, the ItemLocation class is not even being intialized. Public Function Location(inventoryLocation As String) As ItemLocation Set Location = New ItemLocation Location.Item = item_no Location.Code = inventoryLocation End Function In the above sample, the variable item_no is a member variable of the ItemMaster class. Oddly enough, I can successfully instantiate the ItemLocation class outside of the ItemMaster class in a non-class module. Dim test As New ItemLocation test.Item = "12345" test.Code = "A1" quantityOnHand = test.QuantityOnHand Is there some way to make this work the way I want? I'm trying to keep the API as simple as possible. So that it only takes one line of code to retrieve a value.

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