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• Entity Framework autoincrement key

  - by Tommy Ong

  I'm facing an issue of duplicated incremental field on a concurrency scenario. I'm using EF as the ORM tool, attempting to insert an entity with a field that acts as a incremental INT field. Basically this field is called "SequenceNumber", where each new record before insert, will read the database using MAX to get the last SequenceNumber, append +1 to it, and saves the changes. Between the getting of last SequenceNumber and Saving, that's where the concurrency is happening. I'm not using ID for SequenceNumber as it is not a unique constraint, and may reset on certain conditions such as monthly, yearly, etc. InvoiceNumber | SequenceNumber | DateCreated INV00001_08_14 | 1 | 25/08/2014 INV00001_08_14 | 1 | 25/08/2014 <= (concurrency is creating two SeqNo 1) INV00002_08_14 | 2 | 25/08/2014 INV00003_08_14 | 3 | 26/08/2014 INV00004_08_14 | 4 | 27/08/2014 INV00005_08_14 | 5 | 29/08/2014 INV00001_09_14 | 1 | 01/09/2014 <= (sequence number reset) Invoice number is formatted based on the SequenceNumber. After some research I've ended up with these possible solutions, but wanna know the best practice 1) Optimistic Concurrency, locking the table from any reads until the current transaction is completed (not fancy of this idea as I guess performance will be of a great impact?) 2) Create a Stored Procedure solely for this purpose, does select and insert on a single statement as such concurrency is at minimum (would prefer a EF based approach if possible)

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• NHibernate unintential lazy property loading

  - by chiccodoro

  I introduced a mapping for a business object which has (among others) a property called "Name": public class Foo : BusinessObjectBase { ... public virtual string Name { get; set; } } For some reason, when I fetch "Foo" objects, NHibernate seems to apply lazy property loading (for simple properties, not associations): The following code piece generates n+1 SQL statements, whereof the first only fetches the ids, and the remaining n fetch the Name for each record: ISession session = ...IQuery query = session.CreateQuery(queryString); ITransaction tx = session.BeginTransaction(); List<Foo> result = new List<Foo>(); foreach (Foo foo in query.Enumerable()) { result.Add(foo); } tx.Commit(); session.Close(); produces: NHibernate: select foo0_.FOO_ID as col_0_0_ from V1_FOO foo0_ NHibernate: SELECT foo0_.FOO_ID as FOO1_2_0_, foo0_.NAME as NAME2_0_ FROM V1_FOO foo0_ WHERE foo0_.FOO_ID=:p0;:p0 = 81 NHibernate: SELECT foo0_.FOO_ID as FOO1_2_0_, foo0_.NAME as NAME2_0_ FROM V1_FOO foo0_ WHERE foo0_.FOO_ID=:p0;:p0 = 36470 NHibernate: SELECT foo0_.FOO_ID as FOO1_2_0_, foo0_.NAME as NAME2_0_ FROM V1_FOO foo0_ WHERE foo0_.FOO_ID=:p0;:p0 = 36473 Similarly, the following code leads to a LazyLoadingException after session is closed: ISession session = ... ITransaction tx = session.BeginTransaction(); Foo result = session.Load<Foo>(id); tx.Commit(); session.Close(); Console.WriteLine(result.Name); Following this post, "lazy properties ... is rarely an important feature to enable ... (and) in Hibernate 3, is disabled by default." So what am I doing wrong? I managed to work around the LazyLoadingException by doing a NHibernateUtil.Initialize(foo) but the even worse part are the n+1 sql statements which bring my application to its knees. This is how the mapping looks like: <class name="Foo" table="V1_FOO"> ... <property name="Name" column="NAME"/> </class> BTW: The abstract "BusinessObjectBase" base class encapsulates the ID property which serves as the internal identifier.

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• rails 4 -- working with js format from ajax

  - by user101289

  I'm still working on learning Rails, and I have a page with team information that will get updated based on a team's icon click, which fires an ajax call to the controller to populate some tabs. I've read some good info about how to use format.js in the controller to render a partial from a js.coffee or js.erb file. The problem I'm running into is in the coffeescript I think. Right now, I'm getting some data called @schedules from the controller, and passing it to a schedule.js.coffee file that should populate a partial for each record returned and attach it to a table. // schedule.js.coffee $.each @schedules, (schedule) -> ($ '#schedule_data').append("<%= j render(partial: 'schedules/schedule', locals: { s: schedule }) %>") This throws an error `> undefined local variable or method `schedule' for #<#<Class:0x007fe535cd2900>:0x007fe535d32a30>` I tried simplifying the coffeescript to just log the output: $.each @schedules, (schedule) -> console.log(schedule) but this prints nothing. Am I missing something? I am very inexperienced with coffeescript, but it seems like I should be getting some data-- I verified that the schedule items do exist for this team item.

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• Client-server synchronization pattern / algorithm?

  - by tm_lv

  I have a feeling that there must be client-server synchronization patterns out there. But i totally failed to google up one. Situation is quite simple - server is the central node, that multiple clients connect to and manipulate same data. Data can be split in atoms, in case of conflict, whatever is on server, has priority (to avoid getting user into conflict solving). Partial synchronization is preferred due to potentially large amounts of data. Are there any patterns / good practices for such situation, or if you don't know of any - what would be your approach? Below is how i now think to solve it: Parallel to data, a modification journal will be held, having all transactions timestamped. When client connects, it receives all changes since last check, in consolidated form (server goes through lists and removes additions that are followed by deletions, merges updates for each atom, etc.). Et voila, we are up to date. Alternative would be keeping modification date for each record, and instead of performing data deletes, just mark them as deleted. Any thoughts?

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• SQL Server getdate() to a string like "2009-12-20"

  - by Adam Kane

  In Microsoft SQL Server 2005 and .NET 2.0, I want to convert the current date to a string of this format: "YYYY-MM-DD". For example, December 12th 2009 would become "2009-12-20". How do I do this in SQL. The context of this SQL statement in the table definiton. In other words, this is the default value. So when a new record is created the default value of the current date is stored as a string in the above format. I'm trying: SELECT CONVERT(VARCHAR(10), GETDATE(), 102) AS [YYYY.MM.DD] But SQL server keeps converting that to: ('SELECT CONVERT(VARCHAR(10), GETDATE(), 102) AS [YYYY.MM.DD]') so the result is just: 'SELECT CONVERT(VARCHAR(10), GETDATE(), 102) AS [YYYY.MM.DD]' Here's a screen shot of what the Visual Studio server explorer, table, table definition, properties shows: These wrapper bits are being adding automatically and converting it all to literal string: (N' ') Here's the reason I'm trying to use something other than the basic DATETIME I was using previously: This is the error I get when hooking everything to an ASP.NET GridView and try to do an update via the grid view: Server Error in '/' Application. The version of SQL Server in use does not support datatype 'date'. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.ArgumentException: The version of SQL Server in use does not support datatype 'date'. Source Error: An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. Stack Trace: [ArgumentException: The version of SQL Server in use does not support datatype 'date'.] Note: I've added a related question to try to get around the SQL Server in use does not support datatype 'date' error so that I can use a DATETIME as recommended.

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• How to get around DnsRecordListFree error in .NET Framework 4.0?

  - by Greg Finzer

  I am doing an MxRecordLookup. I am getting an error when calling the DnsRecordListFree in the .NET Framework 4.0. I am using Windows 7. How do I get around it? Here is the error: System.MethodAccessException: Attempt by security transparent method to call native code through method. Here is my code: [DllImport("dnsapi", EntryPoint = "DnsQuery_W", CharSet = CharSet.Unicode, SetLastError = true, ExactSpelling = true)] private static extern int DnsQuery([MarshalAs(UnmanagedType.VBByRefStr)]ref string pszName, QueryTypes wType, QueryOptions options, int aipServers, ref IntPtr ppQueryResults, int pReserved); [DllImport("dnsapi", CharSet = CharSet.Auto, SetLastError = true)] private static extern void DnsRecordListFree(IntPtr pRecordList, int FreeType); public List<string> GetMXRecords(string domain) { List<string> records = new List<string>(); IntPtr ptr1 = IntPtr.Zero; IntPtr ptr2 = IntPtr.Zero; MXRecord recMx; try { int result = DnsQuery(ref domain, QueryTypes.DNS_TYPE_MX, QueryOptions.DNS_QUERY_BYPASS_CACHE, 0, ref ptr1, 0); if (result != 0) { if (result == 9003) { //No Record Exists } else { //Some other error } } for (ptr2 = ptr1; !ptr2.Equals(IntPtr.Zero); ptr2 = recMx.pNext) { recMx = (MXRecord)Marshal.PtrToStructure(ptr2, typeof(MXRecord)); if (recMx.wType == 15) { records.Add(Marshal.PtrToStringAuto(recMx.pNameExchange)); } } } finally { DnsRecordListFree(ptr1, 0); } return records; }

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• Doing without partial commits the "Mercurial way"

  - by David Moles

  Subversion shop considering switching to Mercurial, trying to figure out in advance what all the complaints from developers are going to be. There's one fairly common use case here that I can't see how to handle. I'm working on some largish feature, and I have a significant part of the code -- or possibly several significant parts of the code -- in pieces all over the garage floor, totally unsuitable for checkin, maybe not even compiling. An urgent bugfix request comes in. The fix is nice and local and doesn't touch any of the code I've been working on. I make the fix in my working copy. Now what? I've looked at "Mercurial cherry picking changes for commit" and "best practices in mercurial: branch vs. clone, and partial merges?" and all the suggestions seem to be extensions of varying complexity, from Record and Shelve to Queues. The fact that there apparently isn't any core functionality for this makes me suspect that in some sense this working style is Doing It Wrong. What would a Mercurial-like solution to this use case look like?

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• Need little assistance

  - by Umaid

  I am iterating in current days, so need little assistance for (int I=-1; I<30; I++) { for (int J=0; J=30; J++) { for (int K=1; K=30; K++) { SELECT rowid,Month, Day, Advice from MainCategory where Month= 'May ' and Day in ((cast(strftime('%d',date('now','I day')) as Integer)),(cast(strftime('%d',date('now','J day')) as Integer)),(cast(strftime('%d',date('now','K day')) as Integer))); } } } What if i want to go in reverse order also for (int I=-1; I<30; I--) { for (int J=0; J=30; J--) { for (int K=1; K=30; K--) { SELECT rowid,Month, Day, Advice from MainCategory where Month= 'May ' and Day in ((cast(strftime('%d',date('now','I day')) as Integer)),(cast(strftime('%d',date('now','J day')) as Integer)),(cast(strftime('%d',date('now','K day')) as Integer))); } } } On every previous click, i want to fetch 3 records so do i need to iterate till 3 or make it on all record 30 in a month from which i want to fetch.

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• White Screen of Death (WSOD) in Browser

  - by nickyt

  Here's the specs: ASP.NET 3.5 using ASP.NET AJAX AJAX Control Toolkit jQuery 1.3.2 web services IIS6 on Windows Server 2003 SP1 SP1 SQLServer 2005 SP3 Site is SSL Here's the problem: I'm getting the White Screen of Death (WSOD) in pretty much any browser (at least FireFox and IE 7/8). We have an application that uses one popup window for updating records. Most of the time when you click on the [Edit] button to edit a record, the popup window opens and loads the update page. However, after editing records for a while, all of a sudden the popup window will open, but it stays blank and just hangs. The URL is in the address bar. Loading up Fiddler I noticed that the request for the update page is never sent which leads me to believe it's some kind of lockup on the client-side. If I copy the same URL that's in the popup window into a new browser window, the page generally loads fine. Observations: - Since the request is never sent to the server, it's definitely something client-side - Only appears to happen when there is some semblance of traffic on the site which is weird because this appears to be contained within client-side code - There is a web service being called in the background every few seconds checking if the user is logged on, but this doesn't cause the freeze. I'm really at a loss here. I've googled WSOD but not much seems to appear related to my specific WSOD. Any ideas?

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• SQL different joins not making any difference to result

  - by Chrissi

  I'm trying to write a quick (ha!) program to organise some of my financial information. What I ideally want is a query that will return all records with financial information in them from TableA. There should be one row for each month, but in instances where there were no transactions for a month there will be no record. I get results like this: SELECT Period,Year,TotalValue FROM TableA WHERE Year='1997' Result: Period Year TotalValue 1 1997 298.16 2 1997 435.25 4 1997 338.37 8 1997 336.07 9 1997 578.97 11 1997 361.23 By joining on a table (well a View in this instance) which just contains a field Period with values from 1 to 12, I expect to get something like this: SELECT p.Period,a.Year,a.TotalValue FROM Periods AS p LEFT JOIN TableA AS a ON p.Period = a.Period WHERE Year='1997' Result: Period Year TotalValue 1 1997 298.16 2 1997 435.25 3 NULL NULL 4 1997 338.37 5 NULL NULL 6 NULL NULL 7 NULL NULL 8 1997 336.07 9 1997 578.97 10 NULL NULL 11 1997 361.23 12 NULL NULL What I'm actually getting though is the same result no matter how I join it (except CROSS JOIN which goes nuts, but it's really not what I wanted anyway, it was just to see if different joins are even doing anything). LEFT JOIN, RIGHT JOIN, INNER JOIN all fail to provide the NULL records I am expecting. Is there something obvious that I'm doing wrong in the JOIN? Does it matter that I'm joining onto a View?

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• Jquery Find an XML element based on the value of one of it's children

  - by NateD

  I'm working on a simple XML phonebook app to learn JQuery, and I can't figure out how to do something like this: When the user enters the first name of a contact in a textbox I want to find the entire record of that person. The XML looks like this: <phonebook> <person> <number> 555-5555</number> <first_name>Evelyn</first_name> <last_name>Remington</last_name> <address>Edge of the Abyss</address> <image>path/to/image</image> </person> <person> <number>+34 1 6444 333 2223230</number> <first_name>Max</first_name> <last_name>Muscle</last_name> <address>Mining Belt</address> <image>path/to/image</image> </person> </phonebook> and the best I've been able to do with the jQuery is something like this: var myXML; function searchXML(){ $.ajax({ type:"GET", url: "phonebook.xml", dataType: "xml", success: function(xml){myXML = $("xml").find("#firstNameBox").val())} }); } What I want it to do is return the entire <person> element so I can iterate through and display all that person's information. Any help would be appreciated.

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• PHP/Javascript limiting amount of checkboxes

  - by Carl294

  Hi everyone Im trying to limit the amount of checkboxes that can be checked, in this case only 3 can be checked. When using plain HTML this works fine. The code can be seen below. HTML example <td ><input type=checkbox name=ckb value=2 onclick='chkcontrol()';></td><td>Perl</td> Javascript Function <script type="text/javascript"> function chkcontrol(j) { var total=0; for(var i=0; i < document.form1.ckb.length; i++){ if(document.form1.ckb[i].checked){ total =total +1;} if(total > 3){ alert("Please Select only three") document.form1.ckb[j].checked = false; return false; } } } </script> The problem appears when replacing the fixed HTML values with values from a MYSQL database. All the information appears correctly, and can be posted to another page via a submit button. However, it seems like the 'value' assigned to each record from the database is not making its way too the javascript function. <td><input name="checkbox[]" type="checkbox" value="<?php echo $rows['TCA_QID'];?>" onclick="chkcontrol();"></td> I have tried changed the name in the javascript function to match the 'checkbox' name.Any advice would be greatly appreciated Thanks

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• SQL trigger to delete rows from database

  - by wpearse

  I have an industrial system that logs alarms to a remotely hosted MySQL database. The industrial system inserts a new row whenever a property of the alarm changes (such as the time the alarm was activated, acknowledged or switched off) into a table named 'alarms'. I don't want multiple records for each alarm, so I have set up two database triggers. The first trigger mirrors each new record to a second table, creating/updating rows as required: CREATE TRIGGER `mirror_alarms` BEFORE INSERT ON `alarms` FOR EACH ROW INSERT INTO `alarm_display` (Tag,...,OffTime) VALUES (new.Tag,...,new.OffTime) ON DUPLICATE KEY UPDATE OnDate=new.OnDate,...,OffTime=new.OffTime The second trigger should execute after the first and (ideally) delete all rows from the alarms table. (I used the Tag property of the alarm because the Tag property never changes, although I suspect I could just use a 'DELETE FROM alarms WHERE 1' statement to the same effect). CREATE TRIGGER `remove_alarms` AFTER INSERT ON `alarms` FOR EACH ROW DELETE FROM alarms WHERE Tag=new.Tag My problem is that the second trigger doesn't appear to run, or if it does, the second trigger doesn't delete any rows from the database. So here's the question: why does my second trigger not do what I expect it to do?

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• Best way to use PL/SQL Pacakge Cursors from Pro*C

  - by Greg Reynolds

  I have a cursor defined in PL/SQL, and I am wondering what the best way to use it from Pro*C is. Normally for a cursor defined in Pro*C you would do: EXEC SQL DECLARE curs CURSOR FOR SELECT 1 FROM DUAL; EXEC SQL OPEN curs; EXEC SQL FETCH curs INTO :foo; EXEC SQL CLOSE cusr; I was hoping that the same (or similar) syntax would work for a packaged cursor. For example, I have a package MyPack, with a declaration type MyType is record (X integer); cursor MyCurs(x in integer) return MyType; Now I have in my Pro*C code a rather unsatisfying piece of embedded PL/SQL that opens the cursor, does the fetching etc., as I couldn't get the first style of syntax to work. Using the example EXEC SQL EXECUTE DECLARE XTable is table of MyPack.MyType; BEGIN OPEN MyPack.MyCurs(:param); FETCH MyPack.MyCurs INTO XTable; CLOSE MyPack.MyCurs; END; END-EXEC; Does anyone know if there is a more "Pure" Pro*C approach?

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• Chinese records of sqlite databse are in not accessable in iphone app

  - by Mas

  Hi! I'm creating an iphone app. In which I'm reading data from the sqlite db and presenting it in the tableview control. Problem is that the data is in chinese language. Due to unknown reason, when I read/fetch record from the sqlite table, some records are presented and other are missed by objc. Even objc reads some columns of the missing values, But returns the nil results of the some columns. In reality these columns are not empty. I tried many solutions but didn't find any suitable. Same database is working perfectly in the android version of the app. Any one can help here is the code of reading the chinese records from table Quote *q = [[Quote alloc] init]; q.catId = sqlite3_column_int(statement, 0); q.subCatId = sqlite3_column_int(statement, 1); q.quote = [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement, 2)]; and here is the some records which iphone misses ??????·??? ??????,????????! ??????,??????? Thanks

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• MongoDB complex MapReduce of video logs

  - by Justin Hourigan

  I have a dataset from video streaming logs. Each video is identified by a FileGUID. The log entries record the FileGUID, the fragment of the video watched and the bandwidth it was watched at. I would like to create a mapreduce outputting, for each video, a count for fragments both total and for each bandwidth. Ideally it would look like; {"FileGUID":"50acb3a5796634df0e073285", { "1":{"total":76, "0832":34, "1028":42}, "2":{"total":42, "0832":28, "1028":14}, ... } } Is this possible with one mapreduce or is it a multi-step process, or should I use a different method? Here is a sample of the data. { "_id": ObjectId("50acb3a5796634df0e073285"), "IP": "46.7.1.88", "DateTime": ISODate("2012-10-24T22:59:57.0Z"), "FileGUID": "8cdde821fb934a6da7c125a012a26612", "Bandwidth": NumberInt(1028), "Segment": NumberInt(1), "Fragment": NumberInt(237), "Status": NumberInt(200), "Size": NumberInt(576790), "UserAgent": "Mozilla\/5.0 (Windows NT 6.1; WOW64; rv:16.0) Gecko\/20100101 Firefox\/16.0" } { "_id": ObjectId("50acb3a5796634df0e073284"), "IP": "46.7.1.88", "DateTime": ISODate("2012-10-24T22:59:52.0Z"), "FileGUID": "8cdde821fb934a6da7c125a012a26612", "Bandwidth": NumberInt(1028), "Segment": NumberInt(1), "Fragment": NumberInt(236), "Status": NumberInt(200), "Size": NumberInt(577100), "UserAgent": "Mozilla\/5.0 (Windows NT 6.1; WOW64; rv:16.0) Gecko\/20100101 Firefox\/16.0" } { "_id": ObjectId("50acb3a5796634df0e073283"), "IP": "46.7.1.88", "DateTime": ISODate("2012-10-24T22:59:47.0Z"), "FileGUID": "8cdde821fb934a6da7c125a012a26612", "Bandwidth": NumberInt(0832), "Segment": NumberInt(1), "Fragment": NumberInt(234), "Status": NumberInt(200), "Size": NumberInt(576664), "UserAgent": "Mozilla\/5.0 (Windows NT 6.1; WOW64; rv:16.0) Gecko\/20100101 Firefox\/16.0" } { "_id": ObjectId("50acb3a5796634df0e073282"), "IP": "46.7.1.88", "DateTime": ISODate("2012-10-24T22:59:42.0Z"), "FileGUID": "8cdde821fb934a6da7c125a012a26612", "Bandwidth": NumberInt(0832), "Segment": NumberInt(1), "Fragment": NumberInt(233), "Status": NumberInt(200), "Size": NumberInt(575692), "UserAgent": "Mozilla\/5.0 (Windows NT 6.1; WOW64; rv:16.0) Gecko\/20100101 Firefox\/16.0" }

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• Getting the first of a GROUP BY clause in SQL

  - by Michael Bleigh

  I'm trying to implement single-column regionalization for a Rails application and I'm running into some major headaches with a complex SQL need. For this system, a region can be represented by a country code (e.g. us) a continent code that is uppercase (e.g. NA) or it can be NULL indicating the "default" information. I need to group these items by some relevant information such as a foreign key (we'll call it external_id). Given a country and its continent, I need to be able to select only the most specific region available. So if records exist with the country code, I select them. If, not I want a records with the continent code. If not that, I want records with a NULL code so I can receive the default values. So far I've figured that I may be able to use a generated CASE statement to get an arbitrary sort order. Something like this: SELECT *, CASE region WHEN 'us' THEN 1 WHEN 'NA' THEN 2 ELSE 3 END AS region_sort FROM my_table WHERE region IN ('us','NA') OR region IS NULL GROUP BY external_id ORDER BY region_sort The problem is that without an aggregate function the actual data returned by the GROUP BY for a given row seems to be untameable. How can I massage this query to make it return only the first record of the region_sort ordered groups?

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• Improve Efficiency in Array comparison in Ruby

  - by user2985025

  Hi I am working on Ruby /cucumber and have an requirement to develop a comparison module/program to compare two files. Below are the requirements The project is a migration project . Data from one application is moved to another Need to compare the data from the existing application against the new ones. Solution : I have developed a comparison engine in Ruby for the above requirement. a) Get the data, de duplicated and sorted from both the DB's b) Put the data in a text file with "||" as delimiter c) Use the key columns (number) that provides a unique record in the db to compare the two files For ex File1 has 1,2,3,4,5,6 and file2 has 1,2,3,4,5,7 and the columns 1,2,3,4,5 are key columns. I use these key columns and compare 6 and 7 which results in a fail. Issue : The major issue we are facing here is if the mismatches are more than 70% for 100,000 records or more the comparison time is large. If the mismatches are less than 40% then comparison time is ok. Diff and Diff -LCS will not work in this case because we need key columns to arrive at accurate data comparison between two applications. Is there any other method to efficiently reduce the time if the mismatches are more thatn 70% for 100,000 records or more. Thanks

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• Rails database relationships

  - by Danny McClelland

  Hi Everyone, I have three models that I want to interact with each other. Kase, Person and and Company. I have (I think) setup the relationships correctly: class Kase < ActiveRecord::Base #HAS ONE COMPANY has_one :company #HAS MANY PERSONS has_many :persons class Person < ActiveRecord::Base belongs_to :company class Company < ActiveRecord::Base has_many :persons def to_s; companyname; end I have put the select field on the create new Kase view, and the create new Person view as follows: <li>Company<span><%= f.select :company_id, Company.all %> </span></li> All of the above successfully shows a drop down menu dynamically populated with the company names within Companies. What I am trying to do is display the contact of the Company record within the kase and person show.html.erb. For example, If I have a company called "Acme, Inc." and create a new Kase called "Random Case" and choose within the create new case page "Acme, Inc." from the companies drop down menu. I would then want to display "Acme, Inc" along with "Acme, Inc. Mobile" etc. on the "Random Case" show.html.erb. I hope this makes sense to somebody! Thanks, Danny

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• How do I serialise a graph in Java without getting StackOverflowException?

  - by Tim Cooper

  I have a graph structure in java, ("graph" as in "edges and nodes") and I'm attempting to serialise it. However, I get "StackOverflowException", despite significantly increasing the JVM stack size. I did some googling, and apparently this is a well known limitation of java serialisation: that it doesn't work for deeply nested object graphs such as long linked lists - it uses a stack record for each link in the chain, and it doesn't do anything clever such as a breadth-first traversal, and therefore you very quickly get a stack overflow. The recommended solution is to customise the serialisation code by overriding readObject() and writeObject(), however this seems a little complex to me. (It may or may not be relevant, but I'm storing a bunch of fields on each edge in the graph so I have a class JuNode which contains a member ArrayList<JuEdge> links;, i.e. there are 2 classes involved, rather than plain object references from one node to another. It shouldn't matter for the purposes of the question). My question is threefold: (a) why don't the implementors of Java rectify this limitation or are they already working on it? (I can't believe I'm the first person to ever want to serialise a graph in java) (b) is there a better way? Is there some drop-in alternative to the default serialisation classes that does it in a cleverer way? (c) if my best option is to get my hands dirty with low-level code, does someone have an example of graph serialisation java source-code that can use to learn how to do it?

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• Implementing a bitfield using java enums

  - by soappatrol

  Hello, I maintain a large document archive and I often use bit fields to record the status of my documents during processing or when validating them. My legacy code simply uses static int constants such as: static int DOCUMENT_STATUS_NO_STATE = 0 static int DOCUMENT_STATUS_OK = 1 static int DOCUMENT_STATUS_NO_TIF_FILE = 2 static int DOCUMENT_STATUS_NO_PDF_FILE = 4 This makes it pretty easy to indicate the state a document is in, by setting the appropriate flags. For example: status = DOCUMENT_STATUS_NO_TIF_FILE | DOCUMENT_STATUS_NO_PDF_FILE; Since the approach of using static constants is bad practice and because I would like to improve the code, I was looking to use Enums to achieve the same. There are a few requirements, one of them being the need to save the status into a database as a numeric type. So there is a need to transform the enumeration constants to a numeric value. Below is my first approach and I wonder if this is the correct way to go about this? class DocumentStatus{ public enum StatusFlag { DOCUMENT_STATUS_NOT_DEFINED(1<<0), DOCUMENT_STATUS_OK(1<<1), DOCUMENT_STATUS_MISSING_TID_DIR(1<<2), DOCUMENT_STATUS_MISSING_TIF_FILE(1<<3), DOCUMENT_STATUS_MISSING_PDF_FILE(1<<4), DOCUMENT_STATUS_MISSING_OCR_FILE(1<<5), DOCUMENT_STATUS_PAGE_COUNT_TIF(1<<6), DOCUMENT_STATUS_PAGE_COUNT_PDF(1<<7), DOCUMENT_STATUS_UNAVAILABLE(1<<8), private final long statusFlagValue; StatusFlag(long statusFlagValue) { this.statusFlagValue = statusFlagValue } public long getStatusFlagValue(){ return statusFlagValue } } /** * Translates a numeric status code into a Set of StatusFlag enums * @param numeric statusValue * @return EnumSet representing a documents status */ public EnumSet<StatusFlag> getStatusFlags(long statusValue) { EnumSet statusFlags = EnumSet.noneOf(StatusFlag.class) StatusFlag.each { statusFlag -> long flagValue = statusFlag.statusFlagValue if ( (flagValue&statusValue ) == flagValue ) { statusFlags.add(statusFlag) } } return statusFlags } /** * Translates a set of StatusFlag enums into a numeric status code * @param Set if statusFlags * @return numeric representation of the document status */ public long getStatusValue(Set<StatusFlag> flags) { long value=0 flags.each { statusFlag -> value|=statusFlag.getStatusFlagValue() } return value } public static void main(String[] args) { DocumentStatus ds = new DocumentStatus(); Set statusFlags = EnumSet.of( StatusFlag.DOCUMENT_STATUS_OK, StatusFlag.DOCUMENT_STATUS_UNAVAILABLE) assert ds.getStatusValue( statusFlags )==258 // 0000.0001|0000.0010 long numericStatusCode = 56 statusFlags = ds.getStatusFlags(numericStatusCode) assert !statusFlags.contains(StatusFlag.DOCUMENT_STATUS_OK) assert statusFlags.contains(StatusFlag.DOCUMENT_STATUS_MISSING_TIF_FILE) assert statusFlags.contains(StatusFlag.DOCUMENT_STATUS_MISSING_PDF_FILE) assert statusFlags.contains(StatusFlag.DOCUMENT_STATUS_MISSING_OCR_FILE) } }

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• Auto increment with a Unit Of Work

  - by Derick

  Context I'm building a persistence layer to abstract different types of databases that I'll be needing. On the relational part I have mySQL, Oracle and PostgreSQL. Let's take the following simplified MySQL tables: CREATE TABLE Contact ( ID varchar(15), NAME varchar(30) ); CREATE TABLE Address ( ID varchar(15), CONTACT_ID varchar(15), NAME varchar(50) ); I use code to generate system specific alpha numeric unique ID's fitting 15 chars in this case. Thus, if I insert a Contact record with it's Addresses I have my generated Contact.ID and Address.CONTACT_IDs before committing. I've created a Unit of Work (amongst others) as per Martin Fowler's patterns to add transaction support. I'm using a key based Identity Map in the UoW to track the changed records in memory. It works like a charm for the scenario above, all pretty standard stuff so far. The question scenario comes in when I have a database that is not under my control and the ID fields are auto-increment (or in Oracle sequences). In this case I do not have the db generated Contact.ID beforehand, so when I create my Address I do not have a value for Address.CONTACT_ID. The transaction has not been started on the DB session since all is kept in the Identity Map in memory. Question: What is a good approach to address this? (Avoiding unnecessary db round trips) Some ideas: Retrieve the last ID: I can do a call to the database to retrieve the last Id like: SELECT Auto_increment FROM information_schema.tables WHERE table_name='Contact'; But this is MySQL specific and probably something similar can be done for the other databases. If do this then would need to do the 1st insert, get the ID and then update the children (Address.CONTACT_IDs) – all in the current transaction context.

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• Deal with undefined values in code or in the template?

  - by David

  I'm writing a web application (in Python, not that it matters). One of the features is that people can leave comments on things. I have a class for comments, basically like so: class Comment: user = ... # other stuff where user is an instance of another class, class User: name = ... # other stuff And of course in my template, I have <div>${comment.user.name}</div> Problem: Let's say I allow people to post comments anonymously. In that case comment.user is None (undefined), and of course accessing comment.user.name is going to raise an error. What's the best way to deal with that? I see three possibilities: Use a conditional in the template to test for that case and display something different. This is the most versatile solution, since I can change the way anonymous comments are displayed to, say, "Posted anonymously" (instead of "Posted by ..."), but I've often been told that templates should be mindless display machines and not include logic like that. Also, other people might wind up writing alternate templates for the same application, and I feel like I should be making things as easy as possible for the template writer. Implement an accessor method for the user property of a Comment that returns a dummy user object when the real user is undefined. This dummy object would have user.name = 'Anonymous' or something like that and so the template could access it and print its name with no error. Put an actual record in my database corresponding to a user with user.name = Anonymous (or something like that), and just assign that user to any comment posted when nobody's logged in. I know I've seen some real-world systems that operate this way. (phpBB?) Is there a prevailing wisdom among people who write these sorts of systems about which of these (or some other solution) is the best? Any pitfalls I should watch out for if I go one way vs. another? Whoever gives the best explanation gets the checkmark.

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• ASP.NET MVC Unit Testing Controllers - Repositories

  - by Brian McCord

  This is more of an opinion seeking question, so there may not be a "right" answer, but I would welcome arguments as to why your answer is the "right" one. Given an MVC application that is using Entity Framework for the persistence engine, a repository layer, a service layer that basically defers to the repository, and a delete method on a controller that looks like this: public ActionResult Delete(State model) { try { if( model == null ) { return View( model ); } _stateService.Delete( model ); return RedirectToAction("Index"); } catch { return View( model ); } } I am looking for the proper way to Unit Test this. Currently, I have a fake repository that gets used in the service, and my unit test looks like this: [TestMethod] public void Delete_Post_Passes_With_State_4() { //Arrange var stateService = GetService(); var stateController = new StateController( stateService ); ViewResult result = stateController.Delete( 4 ) as ViewResult; var model = (State)result.ViewData.Model; //Act RedirectToRouteResult redirectResult = stateController.Delete( model ) as RedirectToRouteResult; stateController = new StateController( stateService ); var newresult = stateController.Delete( 4 ) as ViewResult; var newmodel = (State)newresult.ViewData.Model; //Assert Assert.AreEqual( redirectResult.RouteValues["action"], "Index" ); Assert.IsNull( newmodel ); } Is this overkill? Do I need to check to see if the record actually got deleted (as I already have Service and Repository tests that verify this)? Should I even use a fake repository here or would it make more sense just to mock the whole thing? The examples I'm looking at used this model of doing things, and I just copied it, but I'm really open to doing things in a "best practices" way. Thanks.

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• How do I send floats in window messages.

  - by yngvedh

  Hi, What is the best way to send a float in a windows message using c++ casting operators? The reason I ask is that the approach which first occurred to me did not work. For the record I'm using the standard win32 function to send messages: PostWindowMessage(UINT nMsg, WPARAM wParam, LPARAM lParam) What does not work: Using static_cast<WPARAM>() does not work since WPARAM is typedef'ed to UINT_PTR and will do a numeric conversion from float to int, effectively truncating the value of the float. Using reinterpret_cast<WPARAM>() does not work since it is meant for use with pointers and fails with a compilation error. I can think of two workarounds at the moment: Using reinterpret_cast in conjunction with the address of operator: float f = 42.0f; ::PostWindowMessage(WM_SOME_MESSAGE, *reinterpret_cast<WPARAM*>(&f), 0); Using an union: union { WPARAM wParam, float f }; f = 42.0f; ::PostWindowMessage(WM_SOME_MESSAGE, wParam, 0); Which of these are preffered? Are there any other more elegant way of accomplishing this?

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