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  • Setting up a "to-many" relationship value dependency for a transient Core Data attribute

    - by Greg Combs
    I've got a relatively complicated Core Data relationship structure and I'm trying to figure out how to set up value dependencies (or observations) across various to-many relationships. Let me start out with some basic info. I've got a classroom with students, assignments, and grades (students X assignments). For simplicity's sake, we don't really have to focus much on the assignments yet. StudentObj <--->> ScoreObj <<---> AssignmentObj Each ScoreObj has a to-one relation with the StudentObj and the AssignmentObj. ScoreObj has real attributes for the numerical grade, the turnInDate, and notes. AssignmentObj.scores is the set of Score objects for that assignment (N = all students). AssignmentObj has real attributes for name, dueDate, curveFunction, gradeWeight, and maxPoints. StudentObj.scores is the set of Score objects for that student (N = all assignments). StudentObj also has real attributes like name, studentID, email, etc. StudentObj has a transient (calculated, not stored) attribute called gradeTotal. This last item, gradeTotal, is the real pickle. it calculates the student's overall semester grade using the scores (ScoreObj) from all their assignments, their associated assignment gradeWeights, curves, and maxPoints, and various other things. This gradeTotal value is displayed in a table column, along with all the students and their individual assignment grades. Determining the value of gradeTotal is a relatively expensive operation, particularly with a large class, therefore I want to run it only when necessary. For simplicity's sake, I'm not storing that gradeTotal value in the core data model. I don't mind caching it somewhere, but I'm having a bitch of a time determining where and how to best update that cache. I need to run that calculation for each student whenever any value changes that affects their gradeTotal. If this were a simple to-one relationship, I know I could use something like keyPathsForValuesAffectingGradeTotal ... but it's more like a many-to-one-to-many relationship. Does anyone know of an elegant (and KVC correct) solution? I guess I could tear through all those score and assignment objects and tell them to register their students as observers. But this seems like a blunt force approach.

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  • In a star schema, are foreign key constraints between facts and dimensions neccessary?

    - by Garett
    I'm getting my first exposure to data warehousing, and I’m wondering is it necessary to have foreign key constraints between facts and dimensions. Are there any major downsides for not having them? I’m currently working with a relational star schema. In traditional applications I’m used to having them, but I started to wonder if they were needed in this case. I’m currently working in a SQL Server 2005 environment.

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  • Reading column header and column values of a data table using LAMBDA(C#3.0)

    - by Newbie
    Consider the folowing where I am reading the data table values and writing to a text file using (StreamWriter sw = new StreamWriter(@"C:\testwrite.txt",true)) { DataPreparation().AsEnumerable().ToList().ForEach(i => { string col1 = i[0].ToString(); string col2 = i[1].ToString(); string col3 = i[2].ToString(); string col4 = i[3].ToString(); sw.WriteLine( col1 + "\t" + col2 + "\t" + col3 + "\t" + col4 + Environment.NewLine ); }); } The data preparation function is as under private static DataTable DataPreparation() { DataTable dt = new DataTable(); dt.Columns.Add("Col1", typeof(string)); dt.Columns.Add("Col2", typeof(int)); dt.Columns.Add("Col3", typeof(DateTime)); dt.Columns.Add("Col4", typeof(bool)); for (int i = 0; i < 10; i++) { dt.Rows.Add("String" + i.ToString(), i, DateTime.Now.Date, (i % 2 == 0) ? true : false); } return dt; } It is working fine. Now in the above described program, it is known to me the Number of columns and the column headers. How to achieve the same in case when the column headers and number of columns are not known at compile time using the lambda expression? I have already done that which is as under public static void WriteToTxt(string directory, string FileName, DataTable outData, string delimiter) { FileStream fs = null; StreamWriter streamWriter = null; using (fs = new FileStream(directory + "\\" + FileName + ".txt", FileMode.Append, FileAccess.Write)) { try { streamWriter = new StreamWriter(fs); streamWriter.BaseStream.Seek(0, SeekOrigin.End); streamWriter.WriteLine(); DataTableReader datatableReader = outData.CreateDataReader(); for (int header = 0; header < datatableReader.FieldCount; header++) { streamWriter.Write(outData.Columns[header].ToString() + delimiter); } streamWriter.WriteLine(); int row = 0; while (datatableReader.Read()) { for (int field = 0; field < datatableReader.FieldCount; field++) { streamWriter.Write(outData.Rows[row][field].ToString() + delimiter); } streamWriter.WriteLine(); row++; } } catch (Exception ex) { throw ex; } } } I am using C#3.0 and framework 3.5 Thanks in advance

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  • NSSortDescriptor for NSFetchRequestController causes crash when value of sorted attribute is changed

    - by AJ
    I have an Core Data Entity with a number of attributes, which include amount(float), categoryTotal(float) and category(string) The initial ViewController uses a FethchedResultsController to retrieve the entities, and sorts them based on the category and then the categoryTotal. No problems so far. NSManagedObjectContext *moc = [self managedObjectContext]; NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Transaction" inManagedObjectContext:moc]; NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease]; [request setEntity:entityDescription]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(dateStamp >= %@) AND (dateStamp =< %@)", startDate, endDate]; [request setPredicate:predicate]; NSSortDescriptor *sortByCategory = [[NSSortDescriptor alloc] initWithKey:@"category" ascending:sortOrder]; NSSortDescriptor *sortByTotals = [[NSSortDescriptor alloc] initWithKey:@"categoryTotal" ascending:sortOrder]; NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortByTotals, sortByCategory, nil]; [request setSortDescriptors:sortDescriptors]; NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:managedObjectContext sectionNameKeyPath:@"category" cacheName:nil]; aFetchedResultsController.delegate = self; self.fetchedResultsController = aFetchedResultsController; On selecting a row (tableView:didSelectRowAtIndexPath), another view controller is loaded that allows editing of the amount field for the selected entity. Before returning to the first view, categoryTotal is updated by the new ‘amount’. The problem comes when returning to the first view controller, the app bombs with *Serious application error. Exception was caught during Core Data change processing: Invalid update: invalid number of rows in section 0. The number of rows contained in an existing section after the update (1) must be equal to the number of rows contained in that section before the update (1), plus or minus the number of rows inserted or deleted from that section (0 inserted, 1 deleted). with userInfo (null) Program received signal: “EXC_BAD_ACCESS”.* This seems to be courtesy of NSSortDescriptor *sortByTotals = [[NSSortDescriptor alloc] initWithKey:@"categoryTotal" ascending:sortOrder]; If I remove this everything works as expected, but obviously without the sorting I want. I'm guessing this is to do with the sorting order changing due to categoryTotal changing (deletion / insertion) but can't find away fix this. I've verified that values are being modified correctly in the second view, so it appears down to the fetchedResultsController being confused. If the categoryAmount is changed to one that does not change the sort order, then no error is generated I'm not physically changing (ie deleting) the number of items the fetchedResultsController is returning ... the only other issue I can find that seem to generate this error Any ideas would be most welcome Thanks, AJ

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  • How much Maximum Data we can store in a File in salesforce

    - by Ritesh Mehandiratta
    i searched a little for the size of file in salesforce . i found this link http://help.salesforce.com/HTViewHelpDoc?id=collab_files_size_limits.htm&language=en_US its showing that file size can be upto 2 GB.i have to store IDs in a text file and want to make it scalable for for nearly about 1 Million record .file size will be equal to 15 MB .can any one please provide some good tutorial how to create such kind of files and using it in apex for retrieving and updating data

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  • blank to numeric conversion derived column

    - by praveen
    Hi All, I have a source column with blank (not "NULL"), and target as numeric. while converting using the data conversion it is not converting due to balnk source value so I used derived column to replace a blank value with NULL or 0 as (source column == " ") ? "0" : source column but its not giving the value as 0 in the blank place. thanks prav

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  • Group Specific set of data by Day

    - by Jacques444
    Need to get a certian subgroup of data per day (Seperated by weekday) For example Select weekday,bla,blabla,blablabla from dbo.blabla where bla = @StartDate and bla <=@endDate I need the output to be: Monday bla blabla blablabla Tuesday bla blabla blablabla If someone could help me that would be awesome. Thanks & Regards Jacques

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  • one to many jpa relationship

    - by user309944
    Hai I have created two table first table as student package com.crimson.rship; import javax.persistence.Basic; import javax.persistence.Entity; import javax.persistence.FetchType; import javax.persistence.Id; import javax.persistence.OneToMany; @Entity(name="student") public class student { @Id private String stumailid; @Basic private String fathername; @Basic private String mothername; @Basic private String doa; @Basic private String dob; public student(String stumailid,String fathername,String mothername,String doa,String dob) { // TODO Auto-generated constructor stub this.stumailid=stumailid; this.fathername=fathername; this.mothername=mothername; this.doa=doa; this.dob=dob; } public void setStumailid(String stumailid) { this.stumailid = stumailid; } public String getStumailid() { return stumailid; } public void setFathername(String fathername) { this.fathername = fathername; } public String getFathername() { return fathername; } public void setMothername(String mothername) { this.mothername = mothername; } public String getMothername() { return mothername; } public void setDoa(String doa) { this.doa = doa; } public String getDoa() { return doa; } public void setDob(String dob) { this.dob = dob; } public String getDob() { return dob; } } Second table as mark package com.crimson.rship; import java.util.Collection; import javax.persistence.Basic; import javax.persistence.Entity; import javax.persistence.FetchType; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.JoinTable; import javax.persistence.OneToMany; @Entity(name="mark") public class mark { @Id private String stumailid; @Basic private String fathername; @Basic private String mothername; @OneToMany(mappedBy="mark",targetEntity=student.class,fetch=FetchType.EAGER) private Collection orders; public mark(String stumailid,String fathername,String mothername) { // TODO Auto-generated constructor stub this.stumailid=stumailid; this.fathername=fathername; this.mothername=mothername; } public void setStumailid(String stumailid) { this.stumailid = stumailid; } public String getStumailid() { return stumailid; } public void setFathername(String fathername) { this.fathername = fathername; } public String getFathername() { return fathername; } public void setMothername(String mothername) { this.mothername = mothername; } public String getMothername() { return mothername; } public void setOrders(Collection orders) { this.orders = orders; } public Collection getOrders() { return orders; } } But this above coding working is not working correctly.can any one help me Thanks in advance

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  • How to pick a chunksize for python multiprocessing with large datasets

    - by Sandro
    I am attempting to to use python to gain some performance on a task that can be highly parallelized using http://docs.python.org/library/multiprocessing. When looking at their library they say to use chunk size for very long iterables. Now, my iterable is not long, one of the dicts that it contains is huge: ~100000 entries, with tuples as keys and numpy arrays for values. How would I set the chunksize to handle this and how can I transfer this data quickly? Thank you.

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  • Show all data in column

    - by user342391
    I am trying to show all of the data in the 'status' column of my table but am having troubles. What am I doing wrong: <?php $query1 = "SELECT id, status FROM alerts WHERE customerid='".$_SESSION['customerid']."' ORDER BY id LIMIT $start, $limit "; $result = mysql_query($query1); while ($row = mysql_fetch_array($result)) { echo $row['status'] ; } ?>

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  • Best way to gather, then import data into drupal?

    - by Frank
    I am building my first database driven website with Drupal and I have a few questions. I am currently populating a google docs excel spreadsheet with all of the data I want to eventually be able to query from the website (after it's imported). Is this the best way to start? If this is not the best way to start what would you recommend? My plan is to populate the spreadsheet then import it as a csv into the mysql db via the CCK Node. I've seen two ways to do this. http://drupal.org/node/133705 (importing data into CCK nodes) http://drupal.org/node/237574 (Inserting data using spreadsheet/csv instead of SQL insert statements) Basically my question(s) is what is the best way to gather, then import data into drupal? Thanks in advance for any help, suggestions.

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  • PHP Show all data in column

    - by user342391
    I am trying to show all of the data in the 'status' column of my table but am having troubles. What am I doing wrong: <?php $query1 = "SELECT id, status FROM alerts WHERE customerid='".$_SESSION['customerid']."' ORDER BY id LIMIT $start, $limit "; $result = mysql_query($query1); while ($row = mysql_fetch_array($result)) { echo $row['status'] ; } ?>

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  • Removing a file from TortoiseHG data source

    - by Hossein Margani
    Hi! I am using TortoiseHG for source code control in Windows, I forgot to edit the ".hgignor" file, and now I have a huge folder ".hg" which I know it's because of DLL and EXE and PDB files which I do not need them. Now changing the ignor file does not remove those files. What should I do for deleting these files completely from my TortoiseHg data source? Thank you.

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