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  • What's the proper way to use sqlite on the iPhone?

    - by Elliot Chen
    Hi, Experts: Can you please give some suggestions on sqlite using on the iPhone? Within my application, I use a sqlite DB to store all local data. Two methods can be used to retrieve those data during running time. 1, Load all the data into memory at initialization stage. (More memory used, less DB open/close operation needed) 2, Read corresponding records when necessary, free the occupied memory after using. (Good habit for memory using, but much DB open/close operations needs). I prefer to use method 2, but not sure whether too many DB opening/closing operations could affect app's efficiency. Or do you think I can 'upgrade' method 2 by opening DB when app launches and closing DB when app quits? Thanks for your suggestions very much!

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  • Update table without using cursor and on date

    - by Muhammad Kashif Nadeem
    Please copy and run following script DECLARE @Customers TABLE (CustomerId INT) DECLARE @Orders TABLE ( OrderId INT, CustomerId INT, OrderDate DATETIME ) DECLARE @Calls TABLE (CallId INT, CallTime DATETIME, CallToId INT, OrderId INT) ----------------------------------------------------------------- INSERT INTO @Customers SELECT 1 INSERT INTO @Customers SELECT 2 ----------------------------------------------------------------- INSERT INTO @Orders SELECT 10, 1, DATEADD(d, -20, GETDATE()) INSERT INTO @Orders SELECT 11, 1, DATEADD(d, -10, GETDATE()) ----------------------------------------------------------------- INSERT INTO @Calls SELECT 101, DATEADD(d, -19, GETDATE()), 1, NULL INSERT INTO @Calls SELECT 102, DATEADD(d, -17, GETDATE()), 1, NULL INSERT INTO @Calls SELECT 103, DATEADD(d, -9, GETDATE()), 1, NULL INSERT INTO @Calls SELECT 104, DATEADD(d, -6, GETDATE()), 1, NULL INSERT INTO @Calls SELECT 105, DATEADD(d, -5, GETDATE()), 1, NULL ----------------------------------------------------------------- I want to update @Calls table and need following results. I am using the following query UPDATE @Calls SET OrderId = ( CASE WHEN (s.CallTime > e.OrderDate) THEN e.OrderId END ) FROM @Calls s INNER JOIN @Orders e ON s.CallToId = e.CustomerId and the result of my query is not what I need. Requirement: As you can see there are two orders. One is on 2010-12-12 and one is on 2010-12-22. I want to update @Calls table with relevant OrderId with respect to CallTime. In short If subsequent Orders are added, and there are further calls then we assume that a new call is associated with the most recent Order Note: This is sample data so this is not the case that I always have two Orders. There might be 10+ Orders and 100+ calls. Note2 I could not find good title for this question. Please change it if you think of any better. Thanks.

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  • Letting users try your web app before sign-up: sessions or temp db?

    - by Mat
    I've seen a few instances now where web applications are letting try them out without you having to sign-up (though to save you need to of course). example: try at http://minutedock.com/ I'm wondering about doing this for my own web app and the fundamental question is whether to store their info into sessions or into a temp user table? The temp user table would allow logging and potentially be less of a hit on the server, correct? Is there a best practice here?

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  • how do i load an image from a DB inside a jsf using managed beans?

    - by RhigoHR
    Hi.. i have a database with some images...could anyone tell me or explain me how could i can load an image in a jsf? I alredy have a managed bean that converts an Image object into a streamcontent...and this streamcontent is called from the page in a tag , but when a i check the source code of the page, there's no src where the image could be loaded. Hope an answer, thx

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  • SQL query - choosing 'last updated' record in a group, better db design?

    - by Jimmy
    Hi, Let's say I have a MySQL database with 3 tables: table 1: Persons, with 1 column ID (int) table 2: Newsletters, with 1 column ID (int) table 3: Subscriptions, with columns Person_ID (int), Newsletter_ID (int), Subscribed (bool), Updated (Datetime) Subscriptions.Person_ID points to a Person, and Subscription.Newsletter_ID points to a Newsletter. Thus, each person may have 0 or more subscriptions to 0 or more magazines at once. The table Subscriptions will also store the entire history of each person's subscriptions to each newsletter. If a particular Person_ID-Newsletter_ID pair doesn't have a row in the Subscriptions table, then it's equivalent to that pair having a subscription status of 'false'. Here is a sample dataset Persons ID 1 2 3 Newsletters ID 4 5 6 Subscriptions Person_ID Newsletter_ID Subscribed Updated 2 4 true 2010-05-01 3 4 true 2010-05-01 3 5 true 2010-05-10 3 4 false 2010-05-15 Thus, as of 2010-05-16, Person 1 has no subscription, Person 2 has a subscription to Newsletter 4, and Person 3 has a subscription to Newsletter 5. Person 3 had a subscription to Newsletter 4 for a while, but not anymore. I'm trying to do 2 kinds of query. A query that shows everyone's active subscriptions as of query time (we can assume that updated will never be in the future -- thus, this means returning the record with the latest 'updated' value for each Person_ID-Newsletter_ID pair, as long as Subscribed is true (if the latest record for a Person_ID-Newsletter_ID pair has a Subscribed status of false, then I don't want that record returned)). A query that returns all active subscriptions for a specific newsletter - same qualification as in 1. regarding records with 'false' in the Subscribed column. I don't use SQL/databases often enough to tell if this design is good, or if the SQL queries needed would be slow on a database with, say, 1M records in the Subscriptions table. I was using the Visual query builder tool in Visual Studio 2010 but I can't even get the query to return the latest updated record for each Person_ID-Newsletter_ID pair. Is it possible to come up with SQL queries that don't involve using subqueries (presumably because they would become too slow with a larger data set)? If not, would it be a better design to have a separate Subscriptions_History table, and every time a subscription status for a Person_ID-Newsletter-ID pair is added to Subscriptions, any existing record for that pair is moved to Subscriptions_History (that way the Subscriptions table only ever contains the latest status update for any Person_ID-Newsletter_ID pair)? I'm using .net on Windows, so would it be easier (or the same, or harder) to do this kind of queries using Linq? Entity Framework? Thanks!

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  • The question about the basics of LINQ to SQL working

    - by Alex
    I just started learning LINQ to SQL, and so far I'm impressed with the easy of use and good performance. I used to think that when doing LINQ queries like from Customer in DB.Customers where Customer.Age > 30 select Customer Get all customers from the database ("SELECT * FROM Customers"), move them to the Customers array and then make a search in that Array using .NET methods. This is very inefficient, what if there are hundreds of thousands of customers in the database? Making such big SELECT queries would kill the web application. Now after experiencing how actually fast LINQ to SQL is, I start to suspect that when doing that query I just wrote, LINQ somehow converts it to a SQL Query string SELECT * FROM Customers WHERE Age > 30 And only when necessary it will run the query. So my question is: am I right? And when is the query actually run? The reason why I'm asking is not only because I want to understand how it works in order to build good optimized applications, but because I came across the following problem. I have 2 tables, one of them is Books, the other has information on how many books were sold on certain days. My goal is to select books that had at least 50 sales/day in past 10 days. It's done with this simple query: from Book in DB.Books where (from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID).Contains(Book.ID) select Book The point is, I have to use the checking part in several queries and I decided to create an array with IDs of all popular books: var popularBooksIDs = from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID; BUT when I try to do the query now: from Book in DB.Books where popularBooksIDs.Contains(Book.ID) select Book It doesn't work! That's why I think that we can't use thins kinds of shortcuts in LINQ to SQL queries, like we can't use them in real SQL. We have to create straightforward queries, am I right?

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  • Cannot add an entity that already exists. (LINQ to SQL)

    - by Vicheanak
    Hello guys, in my database there are 3 tables CustomerType CusID EventType EventTypeID CustomerEventType CusID EventTypeID Dim db = new CustomerEventDataContext Dim newEvent = new EventType newEvent.EventTypeID = txtEventID.text db.EventType.InsertOnSubmit(newEvent) db.SubmitChanges() 'To select the last ID of event' Dim lastEventID = (from e in db.EventType Select e.EventTypeID Order By EventTypeID Descending).first() Dim chkbx As CheckBoxList = CType(form1.FindControl("CheckBoxList1"), CheckBoxList) Dim newCustomerEventType = New CustomerEventType Dim i As Integer For i = 0 To chkbx.Items.Count - 1 Step i + 1 If (chkbx.Items(i).Selected) Then newCustomerEventType.INTEVENTTYPEID = lastEventID newCustomerEventType.INTSTUDENTTYPEID = chkbxStudentType.Items(i).Value db.CustomerEventType.InsertOnSubmit(newCustomerEventType) db.SubmitChanges() End If Next It works fine when I checked only 1 Single ID of CustomerEventType from CheckBoxList1. It inserts data into EventType with ID 1 and CustomerEventType ID 1. However, when I checked both of them, the error message said Cannot add an entity that already exists. Any suggestions please? Thx in advance.

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  • How can i insert large files in mysql db using php?

    - by anjan
    Hi! I want to upload a large file of size 10M max to my mysql database. Using .htaccess i changed the PHP's own file upload limit to "10485760" = 10M, i am able to upload files upto 10M size without any problem. But i can not insert the file in database if it is more that 1M in size. i am using file_get_contents to read all file data and pass it to the insert query as a string to be inserted into a LONGBLOB field. But files with more than 1M size is not being added to database, though i can use print_r($_FILES) to examine that the file uploaded correctly. Any help will be appreciated and i will need it within next 6 hours. So, please help! best regards, Anjan

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  • Is it ok to perform DB operation on UI thread?

    - by user648462
    I am using a database to persist the state of a search form. I am using the onPause method to persist the data and the onResume method to restore it. My opinion is that restoring and persisting state should be a blocking operation so I plan to perform the database operations on the UI thread. I know this is generally discouraged but the operations should be quick and I think if they were done asynchronously they could lead to inconsistent UI behaviour. Any advice

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  • What's the proper way to use sqlite at xCode?

    - by Elliot Chen
    Hi, Experts: Can you please give some suggestions on sqlite using at xcode? Within my application, I use a sqlite DB to store all local data. Two methods can be used to retrieve those data during running time. 1, Load all the data into memory at initialization stage. (More memory used, less DB open/close operation needed) 2, Read corresponding records when necessary, free the occupied memory after using. (Good habit for memory using, but much DB open/close operations needs). I prefer to use method 2, but not sure whether too many DB opening/closing operations could affect app's efficiency. Or do you think I can 'upgrade' method 2 by opening DB when app launches and closing DB when app quits? Thanks for your suggestions very much!

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  • SQL: How to Return One DB Row from Two That Have The Same Values In Opposite Columns Using the MAX F

    - by OneSource
    Hi, This is what I'm trying to do. I have three columns in a table - ID, Column1, Column2 - with this example data: ID Column1 Column2 1     1            2 2     2            1 3     4            3 4     3            4 Since, in the first two rows, Column1 and Column2 have the same values (but in different columns), I want my MAX query to return an ID of 2. Same thing with rows 3 and 4 .... since Columns 1 and 2 have the same values (but in different columns), I want MAX(ID) to return 4. Of course, with MAX, you use Group By, but that will not work in my case. In effect, I need a Group By to work across two columns. Is this possible? If not, what's the best way to accomplish getting the IDs of 2 and 4 given the matching values that are in different columns? Thanks!

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  • Threaded Django task doesn't automatically handle transactions or db connections?

    - by Gabriel Hurley
    I've got Django set up to run some recurring tasks in their own threads, and I noticed that they were always leaving behind unfinished database connection processes (pgsql "Idle In Transaction"). I looked through the Postgres logs and found that the transactions weren't being completed (no ROLLBACK). I tried using the various transaction decorators on my functions, no luck. I switched to manual transaction management and did the rollback manually, that worked, but still left the processes as "Idle". So then I called connection.close(), and all is well. But I'm left wondering, why doesn't Django's typical transaction and connection management work for these threaded tasks that are being spawned from the main Django thread?

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  • DB Interface Design Optimization: Is it better to optimise for Fewer requests of smaller data size?

    - by Overflow
    The prevailing wisdom in webservices/web requests in general is to design your api such that you use as few requests as possible, and that each request returns therefore as much data as is needed In database design, the accepted wisdom is to design your queries to minimise size over the network, as opposed to minimizing the number of queries. They are both remote calls, so what gives?

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  • How do I Order on common attribute of two models in the DB?

    - by Will
    If i have two tables Books, CDs with corresponding models. I want to display to the user a list of books and CDs. I also want to be able to sort this list on common attributes (release date, genre, price, etc.). I also have basic filtering on the common attributes. The list will be large so I will be using pagination in manage the load. items = [] items << CD.all(:limit => 20, :page => params[:page], :order => "genre ASC") items << Book.all(:limit => 20, :page => params[:page], :order => "genre ASC") re_sort(items,"genre ASC") Right now I am doing two queries concatenating them and then sorting them. This is very inefficient. Also this breaks down when I use paging and filtering. If I am on page 2 of how do I know what page of each table individual table I am really on? There is no way to determine this information without getting all items from each table. I have though that if I create a new Class called items that has a one to one relationship with either a Book or CD and do something like Item.all(:limit => 20, :page => params[:page], :include => [:books, :cds], :order => "genre ASC") However this gives back an ambiguous error. So can only be refined as Item.all(:limit => 20, :page => params[:page], :include => [:books, :cds], :order => "books.genre ASC") And does not interleave the books and CDs in a way that I want. Any suggestions.

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  • please check my MYSQL query & give me advice?

    - by Suba
    select s.s_nric as NRIC,s.s_name as NAME,s.s_psle_eng as PSLE_ENG,s.s_psle_math as PSLE_MATHS,s.s_psle_aggr as PSLE_AGGR, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEEN%' AND re.re_year='2008' AND re.re_semester='2' AND re.re_nric=s.s_nric ) as English_2008, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEMA%' AND re.re_year='2008' AND re.re_semester='2' AND re.re_nric=s.s_nric ) Maths_2008, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEEN%' AND re.re_year='2009' AND re.re_semester='2' AND re.re_nric=s.s_nric ) as English_2009, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEMA%' AND re.re_year='2009' AND re.re_semester='2' AND re.re_nric=s.s_nric ) Maths_2009 ,isc.isc_g_gpa as ISC_GPA from si_student_data as s LEFT JOIN si_isc_gpa as isc ON isc.isc_g_nric=s.s_nric where 1=1 AND s.s_admission_year='2008' GROUP BY s.s_nric ORDER BY s.s_gender,s.s_name asc This is my query. please check my sub query this is my sub query (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEEN%' AND re.re_year='2008' AND re.re_semester='2' AND re.re_nric=s.s_nric ) as English_2008, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEMA%' AND re.re_year='2008' AND re.re_semester='2' AND re.re_nric=s.s_nric ) Maths_2008, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEEN%' AND re.re_year='2009' AND re.re_semester='2' AND re.re_nric=s.s_nric ) as English_2009, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEMA%' AND re.re_year='2009' AND re.re_semester='2' AND re.re_nric=s.s_nric ) Maths_2009 When I execute my query, server take long time to execute. So how to make simple? please advice me. Thanks.

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  • DB Architecture : Linking to intersection or to main tables?

    - by Jean-Nicolas
    Hi, I'm creating fantasy football system on my website but i'm very confuse about how I should link some of my table. Tables The main table is Pool which have all the info about the ruling of the fantasy draft. A standard table User, which contains the usual stuff. Intersection table called pools_users which contains id,pool_id,user_id because a user could be in more than one pool, and a pool contains more than 1 user. The problem Table Selections = that's the table that is causing problem. That's the selection that the user choose for his pool. This is related to the Player table but thats not relevant for this problem. Should I link this table to the table Pools_users or should I link it with both main table Pool and User. This table contains id,pool_id,user_id,player_id,... What is the best way link my tables? When I want to retrieve my data, I normally want the information to be divided BY users. "This user have those selections, this one those selections, etc).

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  • Need a cleaner way, which avoids too many 'if statements', to write this method for inputing data in

    - by indiehacker
    What is the best way to reference datastore model attributes without using the four 'if statements' I have in the below sample code, which seem messy and inefficient. For real-world code I may have a situation of 100 attributes such as self.var1, self.var2, ... self.varN that I want to some how reference with just an integer (or strings) as an argument to some method. class PixelObject(db.Model): zoom0 = db.ListProperty(int) zoom1 = db.ListProperty(int) zoom2 = db.ListProperty(int) zoom3 = db.ListProperty(int) zoom4 = db.ListProperty(int) def inputZoomData(self, zoomInteger, input_data): """input_data goes to specified attribute based on if 0,1,2,3,or 4 is argument""" if zoomInteger == 0: self.zoom0 = input_data if zoomInteger == 1: self.zoom1 = input_data if zoomInteger == 2: self.zoom2 = input_data if zoomInteger == 3: self.zoom3 = input_data if zoomInteger == 4: self.zoom4 = input_data

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  • jQuery Ajax loads URL multiple times, how do I unbind/rebind properly?

    - by gmoz22
    I load a SELECT element via Ajax (list of brands), get its selected value (brand id) and load another SELECT via another Ajax URL (list of templates for currently selected brand). Here's my code: $(document).ready( function() { // DO NOT cache Ajax calls $.ajaxSetup ({ cache: false }); // loader var ajax_load = "Loading..."; // Brands List URL var loadBrandUrl = "getBrandsList.php"; // Templates List URL var loadTemplateUrl = "getTemplatesList.php"; $("#brandslistSelect").html(ajax_load).load(loadBrandUrl) .ajaxComplete(function(){ // Brands select loaded /* Load Templates SELECT the first time since no .change() has happened */ var selectedBrand = $("#brandslistSelect option:selected").attr("value"); // get the value console.log(selectedBrand); // Log selected brand to console // get Templates select, commented for now since it does an infinite loop // $("#templateslistSelect").html(ajax_load).load(loadTemplateUrl, { BrandId: selectedBrand } ); /* End initial load template */ /* On interaction with the Brands SELECT */ $("#brandslistSelect").change(function () { // on interaction with select selectedBrand = $("#brandslistSelect option:selected").attr("value"); // get the value // get Templates SELECT $("#templateslistSelect").html(ajax_load).load(loadTemplateUrl, { BrandId: selectedBrand } ) }); /* End interaction with the Brands SELECT */ }); }); It returns selectedBrand in the console 3 times : selectedBrand = undefined selectedBrand = undefined selectedBrand = 101 Now, if I uncomment the following line, same output as above but it also loads the templates URL indefinitely : // $("#templateslistSelect").html(ajax_load).load(loadTemplateUrl, { BrandId: selectedBrand } ); Any idea how I could modify this code to make it work as intended? Thanks for your help stackOverflow community!

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  • In Entity framework, we can use Model first, DB first, Code first but how can we create table programmatically

    - by AukI
    In entity framework we can use 3 approaches model first , code first , database first but each one of them needs manual hand touch(means creating database or create model or write the POCO class codes or entity class codes) before proceeding to the next step ( using EF in context ). What if I want to create database and tables and table relationships programatically and still want to have to features of EntityFramework 4.3. To be more specific , from this example http://support.microsoft.com/kb/307283 we can create database , tables and everything using SQL command but we can't have the advantages of entity framework. So if we want to have that what should we do?

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