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• Retrieve 2 last posts for each category.

  - by Savageman

  Hello, Lets say I have 2 tables: blog_posts and categories. Each blog post belongs to only ONE category, so there is basically a foreign key between the 2 tables here. I would like to retrieve the 2 lasts posts from each category, is it possible to achieve this in a single request? GROUP BY would group everything and leave me with only one row in each category. But I want 2 of them. It would be easy to perform 1 + N query (N = number of category). First retrieve the categories. And then retrieve 2 posts from each category. I believe it would also be quite easy to perform M queries (M = number of posts I want from each category). First query selects the first post for each category (with a group by). Second query retrieves the second post for each category. etc. I'm just wondering if someone has a better solution for this. I don't really mind doing 1+N queries for that, but for curiosity and general SQL knowledge, it would be appreciated! Thanks in advance to whom can help me with this.

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• Linq PredicateBuilder with conditional AND, OR and NOT filters.

  - by richeym

  We have a project using LINQ to SQL, for which I need to rewrite a couple of search pages to allow the client to select whether they wish to perform an and or an or search. I though about redoing the LINQ queries using PredicateBuilder and have got this working pretty well I think. I effectively have a class containing my predicates, e.g.: internal static Expression<Func<Job, bool>> Description(string term) { return p => p.Description.Contains(term); } To perform the search i'm doing this (some code omitted for brevity): public Expression<Func<Job, bool>> ToLinqExpression() { var predicates = new List<Expression<Func<Job, bool>>>(); // build up predicates here if (SearchType == SearchType.And) { query = PredicateBuilder.True<Job>(); } else { query = PredicateBuilder.False<Job>(); } foreach (var predicate in predicates) { if (SearchType == SearchType.And) { query = query.And(predicate); } else { query = query.Or(predicate); } } return query; } While i'm reasonably happy with this, I have two concerns: The if/else blocks that evaluate a SearchType property feel like they could be a potential code smell. The client is now insisting on being able to perform 'and not' / 'or not' searches. To address point 2, I think I could do this by simply rewriting my expressions, e.g.: internal static Expression<Func<Job, bool>> Description(string term, bool invert) { if (invert) { return p => !p.Description.Contains(term); } else { return p => p.Description.Contains(term); } } However this feels like a bit of a kludge, which usually means there's a better solution out there. Can anyone recommend how this could be improved? I'm aware of dynamic LINQ, but I don't really want to lose LINQ's strong typing.

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• Specifying ASP.NET MVC attributes for auto-generated data models

  - by Lyubomyr Shaydariv

  Hello to everyone. I'm very new to ASP.NET MVC (as well as ASP.NET in general), and going to gain some knowledge for this technology, so I'm sorry I can ask some trivial questions. I have installed ASP.NET MVC 3 RC1 and I'm trying to do the following. Let's consider that I have a model that's completely auto-generated from a table using the "LINQ to SQL Classes" template in VS2010. The template generates 3 files (two .cs files and one .layout file respectively), and the generated partial class is expected to be used as an MVC model. Let's also consider, a single DB column, that's mapped into the model, may look like this: [global::System.Data.Linq.Mapping.ColumnAttribute(Storage = "_Name", DbType = "VarChar(128)")] public string Name { get { return this._Name; } set { if ( (this._Name != value) ) { // ... generated stuff goes here } } } The ASP.NET MVC engine also provides a beautiful declarative way to specify some additional stuff, like RequiredAttribute, DisplayNameAttribute and other nice attributes. But since the mapped model is a purely auto-genereated model, I've realized that I should not change the model manually, and specify the fields like: [Required] [DisplayName("Project name")] [StringLength(128)] [global::System.Data.Linq.Mapping.ColumnAttribute(Storage = "_Name", DbType = "VarChar(128)")] public string Name { ... though this approach works perfectly... until I change the model in the DBML-designer removing the ASP.NET MVC attributes automatically. So, how do I specify ASP.NET MVC attributes for the DBML models and their fields safely? Thanks in advance, and Merry Christmas.

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• Locking a table for getting MAX in LINQ

  - by Hossein Margani

  Hi Every one! I have a query in LINQ, I want to get MAX of Code of my table and increase it and insert new record with new Code. just like the IDENTITY feature of SQL Server, but here my Code column is char(5) where can be alphabets and numeric. My problem is when inserting a new row, two concurrent processes get max and insert an equal Code to the record. my command is: var maxCode = db.Customers.Select(c=>c.Code).Max(); var anotherCustomer = db.Customers.Where(...).SingleOrDefault(); anotherCustomer.Code = GenerateNextCode(maxCode); db.SubmitChanges(); I ran this command cross 1000 threads and each updating 200 customers, and used a Transaction with IsolationLevel.Serializable, after two or three execution an error occured: using (var db = new DBModelDataContext()) { DbTransaction tran = null; try { db.Connection.Open(); tran = db.Connection.BeginTransaction(IsolationLevel.Serializable); db.Transaction = tran; . . . . tran.Commit(); } catch { tran.Rollback(); } finally { db.Connection.Close(); } } error: Transaction (Process ID 60) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction. other IsolationLevels generates this error: Row not found or changed. Please help me, thank you.

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• Proper DateTime Format for a Web Service

  - by user48408

  I have a webservice with a method which is called via a xmlhttprequest object in my javascript. The method accepts a datetime parameter which is subsequently converted to a string and run against the database to perform a calculation. I get the value from m_txtDateAdd and send off the xmlHttprequest <asp:textbox id=m_txtDateAdd tabIndex=4 runat="server" Width="96px" Text="<%# Today %>"> </asp:textbox> which has a validator attacted to it <asp:CustomValidator id="m_DateAddValidator" runat="server" ErrorMessage="Please Enter a Valid Date" ControlToValidate="m_txtDateAdd">&#x25CF;</asp:CustomValidator> My webmethod looks something like this [WebMethod] public decimal GetTotalCost(DateTime transactionDate) { String sqlDateString = transactionDate.Year+"/"+transactionDate.Month+"/"+transactionDate.Day; I use sqlDateString as part of the commandtext i send off to the database. Its a legacy application and its inline sql so I don't have the freedom to set up a stored procedure and create and assign parameters in my code behind. This works 90% of the time. The webservice is called on the onchange event of m_txtDateAdd. Every now and again the response i get from the server is System.ArgumentException: Cannot convert 25/06/2009 to System.DateTime. System.ArgumentException: Cannot convert 25/06/2009 to System.DateTime. Parameter name: type --- System.FormatException: String was not recognized as a valid DateTime. at System.DateTimeParse.Parse(String s, DateTimeFormatInfo dtfi, DateTimeStyles styles) at System.DateTime.Parse(String s, IFormatProvider provider) at System.Convert.ToDateTime(String value, IFormatProvider provider) at System.String.System.IConvertible.ToDateTime(IFormatProvider provider) at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider) at System.Web.Services.Protocols.ScalarFormatter.FromString(String value, Type type) --- End of inner exception stack trace --- at System.Web.Services.Protocols.ScalarFormatter.FromString(String value, Type type) at System.Web.Services.Protocols.ValueCollectionParameterReader.Read(NameValueCollection collection) at System.Web.Services.Protocols.HtmlFormParameterReader.Read(HttpRequest request) at System.Web.Services.Protocols.HttpServerProtocol.ReadParameters() at System.Web.Services.Protocols.WebServiceHandler.CoreProcessRequest()

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• Difficulty setting ArrayList to java.sql.Blob to save in DB using hibernate

  - by me_here

  I'm trying to save a java ArrayList in a database (H2) by setting it as a blob, for retrieval later. If this is a bad approach, please say - I haven't been able to find much information on this area. I have a column of type Blob in the database, and Hibernate maps to this with java.sql.Blob. The code I'm struggling with is: Drawings drawing = new Drawings(); try { ByteArrayOutputStream bos = new ByteArrayOutputStream(); ObjectOutputStream oos = null; oos = new ObjectOutputStream(bos); oos.writeObject(plan.drawingPane21.pointList); byte[] buff = bos.toByteArray(); Blob drawingBlob = null; drawingBlob.setBytes(0, buff); drawing.setDrawingObject(drawingBlob); } catch (Exception e){ System.err.println(e); } The object I'm trying to save into a blob (plan.drawingPane21.pointList) is of type ArrayList<DrawingDot>, DrawingDot being a custom class implementing Serializable. My code is failing on the line drawingBlob.setBytes(0, buff); with a NullPointerException. Help appreciated.

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• Practical size limitations for RDBMS

  - by grenade

  I am working on a project that must store very large datasets and associated reference data. I have never come across a project that required tables quite this large. I have proved that at least one development environment cannot cope at the database tier with the processing required by the complex queries against views that the application layer generates (views with multiple inner and outer joins, grouping, summing and averaging against tables with 90 million rows). The RDBMS that I have tested against is DB2 on AIX. The dev environment that failed was loaded with 1/20th of the volume that will be processed in production. I am assured that the production hardware is superior to the dev and staging hardware but I just don't believe that it will cope with the sheer volume of data and complexity of queries. Before the dev environment failed, it was taking in excess of 5 minutes to return a small dataset (several hundred rows) that was produced by a complex query (many joins, lots of grouping, summing and averaging) against the large tables. My gut feeling is that the db architecture must change so that the aggregations currently provided by the views are performed as part of an off-peak batch process. Now for my question. I am assured by people who claim to have experience of this sort of thing (which I do not) that my fears are unfounded. Are they? Can a modern RDBMS (SQL Server 2008, Oracle, DB2) cope with the volume and complexity I have described (given an appropriate amount of hardware) or are we in the realm of technologies like Google's BigTable? I'm hoping for answers from folks who have actually had to work with this sort of volume at a non-theoretical level.

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• Passing a LINQ DataRow Reference in a GridView's ItemTemplate

  - by Bob Kaufman

  Given the following GridView: <asp:GridView runat="server" ID="GridView1" AutoGenerateColumns="false" DataKeyNames="UniqueID" OnSelectedIndexChanging="GridView1_SelectedIndexChanging" > <Columns> <asp:BoundField HeaderText="Remarks" DataField="Remarks" /> <asp:TemplateField HeaderText="Listing"> <ItemTemplate> <%# ShowListingTitle( ( ( System.Data.DataRowView ) ( Container.DataItem ) ).Row ) %> </ItemTemplate> </asp:TemplateField> <asp:BoundField HeaderText="Amount" DataField="Amount" DataFormatString="{0:C}" /> </Columns> </asp:GridView> which refers to the following code-behind method: protected String ShowListingTitle( DataRow row ) { Listing listing = ( Listing ) row; return NicelyFormattedString( listing.field1, listing.field2, ... ); } The cast from DataRow to Listing is failing (cannot convert from DataRow to Listing) I'm certain the problem lies in what I'm passing from within the ItemTemplate, which is simply not the right reference to the current record from the LINQ to SQL data set that I've created, which looks like this: private void PopulateGrid() { using ( MyDataContext context = new MyDataContext() ) { IQueryable < Listing > listings = from l in context.Listings where l.AccountID == myAccountID select l; GridView1.DataSource = listings; GridView1.DataBind(); } }

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• LINQ Normalizing data

  - by Brennan Mann

  I am using an OMS that stores up to three line items per record in the database. Below is an example of an order containing five line items. Order Header Order Detail Prod 1 Prod 2 Prod 3 Order Detail Prod 4 Prod 5 One order header record and two detail records. My goal is have a one to one relation for details records(i.e., one detail record per line item). In the past, I used an UNION ALL SQL statement to extract the data. Is there a better approcach to this problem using LINQ? Below is my first attempt at using LINQ. Any feedback, suggestions or recommendations would greatly be appreciated. For what I have read, an UNION statement can tax the process? var orderdetail = (from o in context.ORDERSUBHEADs select new { edpNo = o.EDPNOS_001, price = o.EXTPRICES_001, qty = o.ITEMQTYS_001 } ).Union(from o in context.ORDERSUBHEADs select new { edpNo = o.EDPNOS_002, price = o.EXTPRICES_002, qty = o.ITEMQTYS_002 } ).Union(from o in context.ORDERSUBHEADs select new { edpNo = o.EDPNOS_003, price = o.EXTPRICES_003, qty = o.ITEMQTYS_003 });

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• PHP/SQL/Wordpress: Group a user list by alphabet

  - by rayne

  I want to create a (fairly big) Wordpress user index with the users categorized alphabetically, like this: A Amy Adam B Bernard Bianca and so on. I've created a custom Wordpress query which works fine for this, except for one problem: It also displays "empty" letters, letters where there aren't any users whose name begins with that letter. I'd be glad if you could help me fix this code so that it only displays the letter if there's actually a user with a name of that letter :) I've tried my luck by checking how many results there are for that letter, but somehow that's not working. (FYI, I use the user photo plugin and only want to show users in the list who have an approved picture, hence the stuff in the SQL query). <?php $alphabet = range('A', 'Z'); foreach ($alphabet as $letter) { $user_count = $wpdb->get_results("SELECT COUNT(*) FROM wp_users WHERE display_name LIKE '".$letter."%' ORDER BY display_name ASC"); if ($user_count > 0) { $user_row = $wpdb->get_results("SELECT wp_users.user_login, wp_users.display_name FROM wp_users, wp_usermeta WHERE wp_users.display_name LIKE '".$letter."%' AND wp_usermeta.meta_key = 'userphoto_approvalstatus' AND wp_usermeta.meta_value = '2' AND wp_usermeta.user_id = wp_users.ID ORDER BY wp_users.display_name ASC"); echo '<li class="letter">'.$letter.''; echo '<ul>'; foreach ($user_row as $user) { echo '<li><a href="/author/'.$user->user_login.'">'.$user->display_name.'</a></li>'; } echo '</ul></li>'; } } ?> Thanks in advance!

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• SQL (mySQL) update some value in all records processed by a select

  - by jdmuys

  I am using mySQL from their C API, but that shouldn't be relevant. My code must process records from a table that match some criteria, and then update the said records to flag them as processed. The lines in the table are modified/inserted/deleted by another process I don't control. I am afraid in the following, the UPDATE might flag some records erroneously since the set of records matching might have changed between step 1 and step 3. SELECT * FROM myTable WHERE <CONDITION>; # step 1 <iterate over the selected set of lines. This may take some time.> # step 2 UPDATE myTable SET processed=1 WHERE <CONDITION> # step 3 What's the smart way to ensure that the UPDATE updates all the lines processed, and only them? A transaction doesn't seem to fit the bill as it doesn't provide isolation of that sort: a recently modified record not in the originally selected set might still be targeted by the UPDATE statement. For the same reason, SELECT ... FOR UPDATE doesn't seem to help, though it sounds promising :-) The only way I can see is to use a temporary table to memorize the set of rows to be processed, doing something like: CREATE TEMPORARY TABLE workOrder (jobId INT(11)); INSERT INTO workOrder SELECT myID as jobId FROM myTable WHERE <CONDITION>; SELECT * FROM myTable WHERE myID IN (SELECT * FROM workOrder); <iterate over the selected set of lines. This may take some time.> UPDATE myTable SET processed=1 WHERE myID IN (SELECT * FROM workOrder); DROP TABLE workOrder; But this seems wasteful and not very efficient. Is there anything smarter? Many thanks from a SQL newbie.

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• LinqToSQL Double Insert issue

  - by Vaccano

  I have a WCF service with an object structure similar to this: public class MyClass { public List<MySubItem> SubItems { get; set; } } public class MySubItem { public List<MySubSubItem> SubSubItems { get; set; } } public class MySubSubItem { public string DataValue { get; set; } } public class MyClassDAL { public void InsertMyClass(MyClass myClass) { ctx.MyClasses.InsertOnSubmit(myClass); ctx.SubmitChanges(); } } Sometimes my client will call in with a MyClass that submits only half of the values that it has in the list SubSubItems. Later it calls the insert with the rest of the list. The problem is that when it does this I get a Primary Key violation. The reason is that it is trying to insert the MySubItem again (because there are more items in the SubSubItems owned by the same MySubItem object). How do I deal with this? Do I just call an Update? Do I have to try to separate them out (updates from inserts)? SQL Server 2008 has a really cool Merge functionally. Is there some way to access that from LinqToSQL?

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• Calling SubmitChanges on DataContext does not update database.

  - by drasto

  In C# ASP.NET MVC application I use Link to SQL to provide data for my application. I have got simple database schema like this: In my controller class I reference this data context called Model (as you can see on the right side of picture in properties) like this: private Model model = new Model(); I've got a table (List) of Series rendered on my page. It renders properly and I was able to add delete functionality to delete Series like this: public ActionResult Delete(int id) { model.Series.DeleteOnSubmit(model.Series.SingleOrDefault(s => s.ID == id)); model.SubmitChanges(); return RedirectToAction("Index"); } Where appropriate action link looks like this: <%: Html.ActionLink("Delete", "Delete", new { id=item.ID })%> Also create (implemented in similar way) works fine. However edit does not work. My edit looks like this: public ActionResult Edit(int id) { return View(model.Series.SingleOrDefault(s => s.ID == id)); } [HttpPost] public ActionResult Edit(Series series) { if (ModelState.IsValid) { UpdateModel(series); series.Title = series.Title + " some string to ensure title has changed"; model.SubmitChanges(); return RedirectToAction("Index"); } I have controlled that my database has a primary key set up correctly. I debugged my application and found out that everything works as expected until the line with model.SubmitChanges();. This command does not apply the changes of Title property(or any other) against the database. Please help.

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• Refactoring ADO.NET - SqlTransaction vs. TransactionScope

  - by marc_s

  I have "inherited" a little C# method that creates an ADO.NET SqlCommand object and loops over a list of items to be saved to the database (SQL Server 2005). Right now, the traditional SqlConnection/SqlCommand approach is used, and to make sure everything works, the two steps (delete old entries, then insert new ones) are wrapped into an ADO.NET SqlTransaction. using (SqlConnection _con = new SqlConnection(_connectionString)) { using (SqlTransaction _tran = _con.BeginTransaction()) { try { SqlCommand _deleteOld = new SqlCommand(......., _con); _deleteOld.Transaction = _tran; _deleteOld.Parameters.AddWithValue("@ID", 5); _con.Open(); _deleteOld.ExecuteNonQuery(); SqlCommand _insertCmd = new SqlCommand(......, _con); _insertCmd.Transaction = _tran; // add parameters to _insertCmd foreach (Item item in listOfItem) { _insertCmd.ExecuteNonQuery(); } _tran.Commit(); _con.Close(); } catch (Exception ex) { // log exception _tran.Rollback(); throw; } } } Now, I've been reading a lot about the .NET TransactionScope class lately, and I was wondering, what's the preferred approach here? Would I gain anything (readibility, speed, reliability) by switching to using using (TransactionScope _scope = new TransactionScope()) { using (SqlConnection _con = new SqlConnection(_connectionString)) { .... } _scope.Complete(); } What you would prefer, and why? Marc

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• Fuzzy Search on Material Descriptions including numerical sizes & general descriptions of material t

  - by Kyle

  We're looking to provide a fuzzy search on an electrical materials database (i.e. conduit, cable, etc.). The problem is that, because of a lack of consistency across all material types, we could not split sizes into separate fields from the text description because some materials are rated by things other than size. I've attempted a combination of a full text search & a SQL CLR implementation of the Levenshtein search algorithm (for assistance in ranking), but my results are a little funky (i.e. they are not sorting correctly due to improper ranking). For example, if the search term is "3/4" ABCD Conduit", I'll might get back several irrelevant results in the following order: 1/2" Conduit 1/4" X 3/4" Cable 1/4" Cable Ties 3/4" DFC Conduit Tees 3/4" ABCD Conduit 3/4" Conduit I believe I've nailed the problem down to the fact that these two search algorithms do not factor in the relevance of punctuation & numeric. That is, in such a search, I'd expect the size to take precedence over any fuzzy match on the rest of the description, but my results don't reflect that. My question is: Can anyone recommend better search algorithms or different approaches that may be better suited for searching a combination of alphanumerics & punctuation characters?

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• LINQ Datacontext Disposal Issues

  - by Refracted Paladin

  I am getting a Cannot access object: DataContext after it's been disposed in the below DAL method. I thought that I would be okay calling dispose there. result is an IEnumurable and I thought it was IQueryable that caused these kinds of problems. What am I doing wrong? How SHOULD I be disposing of my DataContext. Is there something better to be returning then a DataTable? This is a Desktop app that points at SQL 2005. Example method that causes this error -- public static DataTable GetEnrolledMembers(Guid workerID) { var DB = CmoDataContext.Create(); var AllEnrollees = from enrollment in DB.tblCMOEnrollments where enrollment.CMOSocialWorkerID == workerID || enrollment.CMONurseID == workerID join supportWorker in DB.tblSupportWorkers on enrollment.EconomicSupportWorkerID equals supportWorker.SupportWorkerID into workerGroup from worker in workerGroup.DefaultIfEmpty() select new { enrollment.ClientID, enrollment.CMONurseID, enrollment.CMOSocialWorkerID, enrollment.EnrollmentDate, enrollment.DisenrollmentDate, ESFirstName = worker.FirstName, ESLastName = worker.LastName, ESPhone = worker.Phone }; var result = from enrollee in AllEnrollees.AsEnumerable() where (enrollee.DisenrollmentDate == null || enrollee.DisenrollmentDate > DateTime.Now) //let memberName = BLLConnect.MemberName(enrollee.ClientID) let lastName = BLLConnect.MemberLastName(enrollee.ClientID) let firstName = BLLConnect.MemberFirstName(enrollee.ClientID) orderby enrollee.DisenrollmentDate ascending, lastName ascending select new { enrollee.ClientID, //MemberName = memberName, LastName = lastName, FirstName = firstName, NurseName = BLLAspnetdb.NurseName(enrollee.CMONurseID), SocialWorkerName = BLLAspnetdb.SocialWorkerName(enrollee.CMOSocialWorkerID), enrollee.EnrollmentDate, enrollee.DisenrollmentDate, ESWorkerName = enrollee.ESFirstName + " " + enrollee.ESLastName, enrollee.ESPhone }; DB.Dispose(); return result.CopyLinqToDataTable(); } partial class where I create the DataContext -- partial class CmoDataContext { public static bool IsDisconnectedUser { get { return Settings.Default.IsDisconnectedUser; } } public static CmoDataContext Create() { var cs = IsDisconnectedUser ? Settings.Default.CMOConnectionString : Settings.Default.Central_CMOConnectionString; return new CmoDataContext(cs); }

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• Table Design For SystemSettings, Best Model

  - by Chris L

  Someone suggested moving a table full of settings, where each column is a setting name(or type) and the rows are the customers & their respective settings for each setting. ID | IsAdmin | ImagePath ------------------------------ 12 | 1          | \path\to\images 34 | 0          | \path\to\images The downside to this is every time we want a new setting name(or type) we alter the table(via sql) and add the new (column)setting name/type. Then update the rows(so that each customer now has a value for that setting). The new table design proposal. The proposal is to have a column for setting name and another column for setting. ID | SettingName | SettingValue ---------------------------- 12 | IsAdmin        | 1 12 | ImagePath   | \path\to\images 34 | IsAdmin        | 0 34 | ImagePath   | \path\to\images The point they made was that adding a new setting was as easy as a simple insert statement to the row, no added column. But something doesn't feel right about the second design, it looks bad, but I can't come up with any arguments against it. Am I wrong?

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• New Perl user: using a hash of arrays

  - by Zach H

  I'm doing a little datamining project where a perl script grabs info from a SQL database and parses it. The data consists of several timestamps. I want to find how many of a particular type of timestamp exist on any particular day. Unfortunately, this is my first perl script, and the nature of perl when it comes to hashes and arrays is confusing me quite a bit. Code segment: my %values=();#A hash of the total values of each type of data of each day. #The key is the day, and each key stores an array of each of the values I need. my @proposal; #[drafted timestamp(0), submitted timestamp(1), attny approved timestamp(2),Organiziation approved timestamp(3), Other approval timestamp(4), Approved Timestamp(5)] while(@proposal=$sqlresults->fetchrow_array()){ #TODO: check to make sure proposal is valid #Increment the number of timestamps of each type on each particular date my $i; for($i=0;$i<=5;$i++) $values{$proposal[$i]}[$i]++; #Update rolling average of daily #TODO: To check total load, increment total load on all dates between attourney approve date and accepted date for($i=$proposal[1];$i<=$proposal[2];$i++) $values{$i}[6]++; } I keep getting syntax errors inside the for loops incrementing values. Also, considering that I'm using strict and warnings, will Perl auto-create arrays of the right values when I'm accessing them inside the hash, or will I get out-of bounds errors everywhere? Thanks for any help, Zach

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• CLR Stored Procedures

  - by Paul Hatcherian

  In an ASP.NET application, I have a small number of fairly complex, frequently used operations to execute against a database. In these operations, one or more of several tables needs updates or inserts based a logical evaluation of both input parameters and values of certain tables. I've maintained a separation of logic and data access, so the operation currently looks like this: Request received from client Business layer invokes data layer to retrieve data from database Business layer processes result and determines which operation to execute Business layer invokes appropriate data operation Response sent to client As you can see, the client is kept waiting while two separate requests are made to the database. In searching for a solution to this, I've found CLR Stored Procedures, but I'm not sure if I have the right idea about what they are useful for. I have written a replacement for the code above which especially places steps 2-4 in a CLR SP. My understanding is that the SP will be executed locally by SQL Server and result in only one call being made to the server. My initial benchmark tests show this is actually orders of magnitude slower than my original code, but I attribute that recompilation of the code I have not worked out yet and/or some flaw in my environment. My question is basically, is this the intended use of CLR SPs or am I missing something? I realize this is a bit of a compromise structurally, so if there's a better way to do it I'd love to hear it.

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• Transaction Isolation Level of Serializable not working for me

  - by Shahriar

  I have a website which is used by all branches of a store and what it does is that it records customer purchases into a table called myTransactions.myTransactions table has a column named SerialNumber.For each purchase i create a record in the transactions table and assign a serial to it.The stored procedure that does this calls a UDF function to get a new serialNumber before inserting the record.Like below : Create Procedure mytransaction_Insert as begin insert into myTransactions(column1,column2,column3,...SerialNumber) values( Value1 ,Value2,Value3,...., getTransactionNSerialNumber()) end Create function getTransactionNSerialNumber as begin RETURN isnull(SELECT TOP (1) SerialNumber FROM myTransactions READUNCOMMITTED ORDER BY SerialNumber DESC),0) + 1 end The website is being used by so many users in different stores at the same time and it is creating many duplicate serialNumbers(same SerialNumbers).So i added a Sql transaction with ReadCommitted level to the transaction and i still got duplicate transaction numbers.I changed it to SERIALIZABLE in order to lock the resources and i not only got duplicate transaction numbers(!!HOW!!) but i also got sporadic deadlocks between the same stored procedure calls.This is what i tried : (With ommissions of try catch blocks and rollbacks) Create Procedure mytransaction_Insert as begin SET TRANSACTION ISOLATION LEVEL SERIALIZABLE BEGIN TRASNACTION ins insert into myTransactions(column1,column2,column3,...SerialNumber) values( Value1 ,Value2 , Value3, ...., getTransactionNSerialNumber()) COMMIT TRANSACTION ins SET TRANSACTION ISOLATION READCOMMITTED end I even copied the function that gets the serial number directly into the stored procedure instead of the UDF function call and still got duplicate serialNumbers.So,How can a stored procedure line create something Like the c# lock() {} block. By the way,i have to implement the transaction serial number using the same pattern and i can't change the serialNumber to any other identity field or whatever.And for some reasons i need to generate the serialNumber inside the databse and i can't move SerialNumber generation to application level. Thank you.

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• Is it possible to convert a 40-character SHA1 hash to a 20-character SHA1 hash?

  - by ewitch

  My problem is a bit hairy, and I may be asking the wrong questions, so please bear with me... I have a legacy MySQL database which stores the user passwords & salts for a membership system. Both of these values have been hashed using the Ruby framework - roughly like this: hashedsalt = Digest::SHA1.hexdigest("--#{Time.now.to_s}--#{login}--") hashedpassword = Digest::SHA1.hexdigest("#{hashedsalt}:#{password}") So both values are stored as 40-character strings (varchar(40)) in MySQL. Now I need to import all of these users into the ASP.NET membership framework for a new web site, which uses a SQL Server database. It is my understanding that the the way I have ASP.NET membership configured, the user passwords and salts are also stored in the membership database (in table aspnet_Membership) as SHA1 hashes, which are then Base64 encoded (see here for details) and stored as nvarchar(128) data. But from the length of the Base64 encoded strings that are stored (28 characters) it seems that the SHA1 hashes that ASP.NET membership generates are only 20 characters long, rather than 40. From some other reading I have been doing I am thinking this has to do with the number of bits per character/character set/encoding or something related. So is there some way to convert the 40-character SHA1 hashes to 20-character hashes which I can then transfer to the new ASP.NET membership data table? I'm pretty familiar with ASP.NET membership by now but I feel like I'm just missing this one piece. However, it may also be known that SHA1 in Ruby and SHA1 in .NET are incompatible, so I'm fighting a losing battle... Thanks in advance for any insight.

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• Replicating SQL's 'Join' in Python

  - by Daniel Mathews

  I'm in the process of trying to switch from R to Python (mainly issues around general flexibility). With Numpy, matplotlib and ipython, I've am able to cover all my use cases save for merging 'datasets'. I would like to simulate SQL's join by clause (inner, outer, full) purely in python. R handles this with the 'merge' function. I've tried the numpy.lib.recfunctions join_by, but it critical issues with duplicates along the 'key': join_by(key, r1, r2, jointype='inner', r1postfix='1', r2postfix='2', defaults=None, usemask=True, asrecarray=False) Join arrays r1 and r2 on key key. The key should be either a string or a sequence of string corresponding to the fields used to join the array. An exception is raised if the key field cannot be found in the two input arrays. Neither r1 nor r2 should have any duplicates along key: the presence of duplicates will make the output quite unreliable. Note that duplicates are not looked for by the algorithm. source: http://presbrey.mit.edu:1234/numpy.lib.recfunctions.html Any pointers or help will be most appreciated!

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• Dynamic Linq Property Converting to Sql

  - by Matthew Hood

  I am trying to understand dynamic linq and expression trees. Very basically trying to do an equals supplying the column and value as strings. Here is what I have so far private IQueryable<tblTest> filterTest(string column, string value) { TestDataContext db = new TestDataContext(); // The IQueryable data to query. IQueryable<tblTest> queryableData = db.tblTests.AsQueryable(); // Compose the expression tree that represents the parameter to the predicate. ParameterExpression pe = Expression.Parameter(typeof(tblTest), "item"); Expression left = Expression.Property(pe, column); Expression right = Expression.Constant(value); Expression e1 = Expression.Equal(left, right); MethodCallExpression whereCallExpression = Expression.Call( typeof(Queryable), "Where", new Type[] { queryableData.ElementType }, queryableData.Expression, Expression.Lambda<Func<tblTest, bool>>(e1, new ParameterExpression[] { pe })); // Create an executable query from the expression tree. IQueryable<tblTest> results = queryableData.Provider.CreateQuery<tblTest>(whereCallExpression); return results; } That works fine for columns in the DB. But fails for properties in my code eg public partial class tblTest { public string name_test { get { return name; } } } Giving an error cannot be that it cannot be converted into SQL. I have tried rewriting the property as a Expression<Func but with no luck, how can I convert simple properties so they can be used with linq in this dynamic way? Many Thanks

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• postgresql table for storing automation test results

  - by Martin

  I am building an automation test suite which is running on multiple machines, all reporting their status to a postgresql database. We will run a number of automated tests for which we will store the following information: test ID (a GUID) test name test description status (running, done, waiting to be run) progress (%) start time of test end time of test test result latest screenshot of the running test (updated every 30 seconds) The number of tests isn't huge (say a few thousands) and each machine (say, 50 of them) have a service which checks the database and figures out if it's time to start a new automated test on that machine. How should I organize my SQL table to store all the information? Is a single table with a column per attribute the way to go? If in the future I need to add attributes but want to keep compatibility with old database format (ie I may not want to delete and create a new table with more columns), how should I proceed? Should the new attributes just be in a different table? I'm also thinking of replicating the database. In case of failure, I don't mind if the latest screenshots aren't backed up on the slave database. Should I just store the screenshots in its own table to simplify the replication? Thanks!

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• How do I break down MySQL query results into categories, each with a specific number of rows?

  - by Mel

  Hello, Problem: I want to list n number of games from each genre (order not important) The following MySQL query resides inside a ColdFusion function. It is meant to list all games under a platform (for example, list all PS3 games; list all Xbox 360 games; etc...). The variable for PlatformID is passed through the URL. I have 9 genres, and I would like to list 10 games from each genre. SELECT games.GameID AS GameID, games.GameReleaseDate AS rDate, titles.TitleName AS tName, titles.TitleShortDescription AS sDesc, genres.GenreName AS gName, platforms.PlatformID, platforms.PlatformName AS pName, platforms.PlatformAbbreviation AS pAbbr FROM (((games join titles on((games.TitleID = titles.TitleID))) join genres on((genres.GenreID = games.GenreID))) join platforms on((platforms.PlatformID = games.PlatformID))) WHERE (games.PlatformID = '#ARGUMENTS.PlatformID#') ORDER BY GenreName ASC, GameReleaseDate DESC Once the query results come back I group them in ColdFusion as follows: <cfoutput query="ListGames" group="gName"> (first loop which lists genres) #ListGames.gName# <cfoutput> (nested loop which lists games) #ListGames.tName# </cfoutput> </cfoutput> The problem is that I only want 10 games from each genre to be listed. If I place a "limit" of 50 in the SQL, I will get ~ 50 games of the same genre (depending on how much games of that genre there are). The second issue is I don't want the overload of querying the database for all games when each person will only look at a few. What is the correct way to do this? Many thanks!

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