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  • Database design and foreign keys: Where should they be added in related tables?

    - by Carvell Fenton
    I have a relatively simple subset of tables in my database for tracking something called sessions. These are academic sessions (think offerings of a particular program). The tables to represent a sessions information are: sessions session_terms session_subjects session_mark_item_info session_marks All of these tables have their own primary keys, and are like a tree, in that sessions have terms, terms have subjects, subjects have mark items, etc. So each on would have at least its "parent's" foreign key. My question is, design wise is it a good idea to include the sessions primary key in the other tables as a foreign key to easily select related session items, or is that too much redundency? If I include the session foreign key (or all parent foreign keys from tables up the heirarchy) in all the tables, I can easily select all the marks for a session. As an example, something like SELECT mark FROM session_marks WHERE sessionID=... If I don't, then I would have to combine selects with something like WHERE something IN (SELECT... Which approach is "more correct" or efficient? Thanks in advance!

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  • Public property List needs to Concat 2 types with inheritance

    - by Bernard
    I have 2 lists: one of type A and one of type Aa. type Aa is inherited from type A. So: List<A> listA = new List<A>(); List<Aa> listAa = new List<Aa>(); with class Aa : A I have: public property Lists<A> { get { List<A> newList = new List<A>(); //return concat of both lists foreach(List l in listA) { newList.Add(l); } foreach(List l in listAa) { newList.Add(l); } } Can I somehow use Concat instead of the foreach loop? i.e. get { return listA.Concat(listAa); } // this doesn't work And secondly, how do I do the set part of the property? set { //figure out the type of variable value and put into appropriate list? }

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  • Fastest way to modify a decimal-keyed table in MySQL?

    - by javanix
    I am dealing with a MySQL table here that is keyed in a somewhat unfortunate way. Instead of using an auto increment table as a key, it uses a column of decimals to preserve order (presumably so its not too difficult to insert new rows while preserving a primary key and order). Before I go through and redo this table to something more sane, I need to figure out how to rekey it without breaking everything. What I would like to do is something that takes a list of doubles (the current keys) and outputs a list of integers (which can be cast down to doubles for rekeying). For example, input {1.00, 2.00, 2.50, 2.60, 3.00} would give output {1, 2, 3, 4, 5). Since this is a database, I also need to be able to update the rows nicely: UPDATE table SET `key`='3.00' WHERE `key`='2.50'; Can anyone think of a speedy algorithm to do this? My current thought is to read all of the doubles into a vector, take the size of the vector, and output a new vector with values from 1 => doubleVector.size. This seems pretty slow, since you wouldn't want to read every value into the vector if, for instance, only the last n/100 elements needed to be modified. I think there is probably something I can do in place, since only values after the first non-integer double need to be modified, but I can't for the life of me figure anything out that would let me update in place as well. For instance, setting 2.60 to 3.00 the first time you see 2.50 in the original key list would result in an error, since the key value 3.00 is already used for the table.

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  • Fastest way to convert a list of doubles to a unique list of integers?

    - by javanix
    I am dealing with a MySQL table here that is keyed in a somewhat unfortunate way. Instead of using an auto increment table as a key, it uses a column of decimals to preserve order (presumably so its not too difficult to insert new rows while preserving a primary key and order). Before I go through and redo this table to something more sane, I need to figure out how to rekey it without breaking everything. What I would like to do is something that takes a list of doubles (the current keys) and outputs a list of integers (which can be cast down to doubles for rekeying). For example, input {1.00, 2.00, 2.50, 2.60, 3.00} would give output {1, 2, 3, 4, 5). Since this is a database, I also need to be able to update the rows nicely: UPDATE table SET `key`='3.00' WHERE `key`='2.50'; Can anyone think of a speedy algorithm to do this? My current thought is to read all of the doubles into a vector, take the size of the vector, and output a new vector with values from 1 => doubleVector.size. This seems pretty slow, since you wouldn't want to read every value into the vector if, for instance, only the last n/100 elements needed to be modified. I think there is probably something I can do in place, since only values after the first non-integer double need to be modified, but I can't for the life of me figure anything out that would let me update in place as well. For instance, setting 2.60 to 3.00 the first time you see 2.50 in the original key list would result in an error, since the key value 3.00 is already used for the table.

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  • When should I consider representing the primary-key ...?

    - by JMSA
    When should I consider representing the primary-key as classes? Should we only represent primary keys as classes when a table uses composite-key? For example: public class PrimaryKey { ... ... ...} Then private PrimaryKey _parentID; public PrimaryKey ParentID { get { return _parentID; } set { _parentID = value; } } And public void Delete(PrimaryKey id) {...} When should I consider storing data as comma-separated values in a column in a DB table rather than storing them in different columns?

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  • Windows 7 Public Documents Folder - how to move it to drive d: [closed]

    - by Bazza Formez
    Hi, I've just bought a new pc, and it is running Windows 7. I'm wanting to set up all of the documents folders such that they point to folders on a second drive partition (ie. disk D:) so that I have a nice separation of os from docs. I have managed to do this for each user on the machine (by opening up properties for documents folder and changing location). Hwoever, this procedure doesn't seem to work for the public documents folder. I cannot change the location for that one (even though I have administrator privileges). It is greyed out and cannot be changed. Any ideas ? Thanks!!

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  • SQL Server problems reading columns with a foreign key

    - by illdev
    I have a weird situation, where simple queries seem to never finish for instance SELECT top 100 ArticleID FROM Article WHERE ProductGroupID=379114 returns immediately SELECT top 1000 ArticleID FROM Article WHERE ProductGroupID=379114 never returns SELECT ArticleID FROM Article WHERE ProductGroupID=379114 never returns SELECT top 1000 ArticleID FROM Article returns immediately By 'returning' I mean 'in query analyzer the green check mark appears and it says "Query executed successfully"'. I sometimes get the rows painted to the grid in qa, but still the query goes on waiting for my client to time out - 'sometimes': SELECT ProductGroupID AS Product23_1_, ArticleID AS ArticleID1_, ArticleID AS ArticleID18_0_, Inventory_Name AS Inventory3_18_0_, Inventory_UnitOfMeasure AS Inventory4_18_0_, BusinessKey AS Business5_18_0_, Name AS Name18_0_, ServesPeople AS ServesPe7_18_0_, InStock AS InStock18_0_, Description AS Descript9_18_0_, Description2 AS Descrip10_18_0_, TechnicalData AS Technic11_18_0_, IsDiscontinued AS IsDisco12_18_0_, Release AS Release18_0_, Classifications AS Classif14_18_0_, DistributorName AS Distrib15_18_0_, DistributorProductCode AS Distrib16_18_0_, Options AS Options18_0_, IsPromoted AS IsPromoted18_0_, IsBulkyFreight AS IsBulky19_18_0_, IsBackOrderOnly AS IsBackO20_18_0_, Price AS Price18_0_, Weight AS Weight18_0_, ProductGroupID AS Product23_18_0_, ConversationID AS Convers24_18_0_, DistributorID AS Distrib25_18_0_, type AS Type18_0_ FROM Article AS articles0_ WHERE (IsDiscontinued = '0') AND (ProductGroupID = 379121) shows this behavior. I have no idea what is going on. Probably select is broken ;) I got a foreign key on ProductGroups ALTER TABLE [dbo].[Article] WITH CHECK ADD CONSTRAINT [FK_ProductGroup_Articles] FOREIGN KEY([ProductGroupID]) REFERENCES [dbo].[ProductGroup] ([ProductGroupID]) GO ALTER TABLE [dbo].[Article] CHECK CONSTRAINT [FK_ProductGroup_Articles] there are some 6000 rows and IsDiscontinued is a bit, not null, but leaving this condition out does not change the outcome. Anyone can tell me how to handle such a situation? More info, anyone? Additional Info: this does not seem to be restricted to this Foreign Key, but all/some referencing this entity.

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  • How to configure SHIFT+LEFT, SHIFT+RIGHT, SHIFT+HOME and SHIFT+END keys in terminal on Mac?

    - by Misha Moroshko
    To configure the Home and End keys in terminal on MacBook Air (OS X 10.7.2) I defined in Terminal -> Preferences -> Keyboard: Key Action ---- ------ Home \033OH End \033OF What are the codes to configure the following combinations so that they will work like in Windows? Shift+Left (should select the character on the left) Shift+Right (should select the character on the right) Shift+Home (should select all the characters on the left) Shift+End (should select all the characters on the right)

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  • What is the corrrect way to increment a field making up part of a composit key

    - by Tr1stan
    I have a bunch of tables whose primary key is made up of the foreign keys of other tables (Composite key). Therefore for example the attributes (as a very cut down version) might look like this: A[aPK, SomeFields] 1:M B[bPK, aFK, SomeFields] 1:M C[cPK, bFK, aFK, SomeFields] as data this could look like: A[aPK, SomeFields]: 1, Foo 2, Bar B[bPK, aFK, SomeFields]: 1, 1, FooData1 2, 1, FooData2 1, 2, BarData1 2, 2, BarData2 C[cPK, bFK, aFK, SomeFields]: 1, 1, 1, FooData1More 2, 1, 1, FooData1More 1, 2, 1, FooData2More 2, 2, 1, FooData2More 1, 1, 2, BarData1More 2, 1, 2, BarData1More 1, 2, 2, BarData2More 2, 2, 2, BarData2More I've got this running in a MSSQL DBMS and I'm looking for the best way to increment the left most column, in each table when a new tuple is added to it. I can't use the Auto Increment Identity Specification option as that has no idea that it is part of a composite key. I also don't want to use any aggregate function such as: MAX(field)+1 as this will have adverse affects with multiple users inputting data, rolling back etc. There might however be a nice trigger based option here, but I'm not sure. This must be a common issue so I'm hoping that someone has a lovely solution. As a side which may or may not affect the answer, I'm using Entity Framework 1.0 as my ORM, within a c# MVC application.

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  • A GUID as the MySQL table's Primary Key or as a separate column

    - by Ben
    I have a multi-process program that performs, in a 2 hour period, 5-10 million inserts to a 34GB table within a single Master/Slave MySQL setup (plus an equal number of reads in that period). The table in question has only 5 fields and 3 (single field) indexes. The primary key is auto-incrementing. I am far from a DBA, but the database appears to be crippled during this two hour period. So, I have a couple of general questions. 1) How much bang will I get out of batching these writes into units of 10? Currently, I am writing each insert serially because, after writing, I immediately need to know, in my program, the resulting primary key of each insert. The PK is the only unique field presently and approximating the order of insertion with something like a Datetime field or a multi-column value is not acceptable. If I perform a bulk insert, I won't know these IDs, which is a problem. So, I've been thinking about turning the auto-increment primary key into a GUID and enforcing uniqueness. I've also been kicking around the idea of creating a new column just for the purposes of the GUID. I don't really see the what that achieves though, that the PK approach doesn't already offer. As far as I can tell, the big downside to making the PK a randomly generated number is that the index would take a long time to update on each insert (since insertion order would not be sequential). Is that an acceptable approach for a table that is taking this number of writes? Thanks, Ben

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  • Fetching just the Key/id from a ReferenceProperty in App Engine

    - by ozone
    Hi SO, I could use a little help in AppEngine land... Using the [Python] API I create relationships like this example from the docs: class Author(db.Model): name = db.StringProperty() class Story(db.Model): author = db.ReferenceProperty(Author) story = db.get(story_key) author_name = story.author.name As I understand it, that example will make two datastore queries. One to fetch the Story and then one to deference the Author inorder to access the name. But I want to be able to fetch the id, so do something like: story = db.get(story_key) author_id = story.author.key().id() I want to just get the id from the reference. I do not want to have to deference (therefore query the datastore) the ReferenceProperty value. From reading the documentation it says that the value of a ReferenceProperty is a Key Which leads me to think that I could just call .id() on the reference's value. But it also says: The ReferenceProperty model provides features for Key property values such as automatic dereferencing. I can't find anything that explains when this referencing takes place? Is it safe to call .id() on the ReferenceProperty's value? Can it be assumed that calling .id() will not cause a datastore lookup?

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  • Document key usage in Dictionary

    - by phq
    How can I document the key usage in a Dictionary so that it shows in Visual studio when coding using that object? I'm looking for something like: /// <param name="SpecialName">That Special Name</param> public Dictionary<string,string> bar; So far the best attempt has been to write my own class: public class SpecialNameDictionary : IDictionary<string, string> { private Dictionary<string, string> data = new Dictionary<string, string>(); /// <param name="specialName">That Special Name</param> public string this[string specialName] { get { return data[specialName]; } } } But It adds a lot of code that doesn't do anything. Additionally I must retype every Dictionary method to make it compile. Is there a better way to achive the above?

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  • PHP Array To Class Static Public Values.

    - by what
    I want to make a class that has all the values of an array as a static object in that class. For example: $vars=array(... );//some array with actual values $Class_code='class MyClass{'; for($i=0; $i<count($vars); $i++){ $Class_code.='static public $'.strval($vars[i]).';'; } eval($Class_code.'}'); /* When I echo the line above it says that the vars for MyClass (MyClass::vars) are missing even with strval(). */ So, how can I get $vars[i] to be a string if strval didn't work?

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  • Tilde not recognised in XML public identifier

    - by phantom-99w
    Hi everyone I found an interesting bug and wanted to know you think. Brief background: I've written a custom DTD and an example XML file (both UTF-8). I have now implemented a SAX parser in Java which I want to test. I got a SAXException complaining "An invalid XML character (Unicode: 0x7e) was found in the public identifier". Now, the URL of my DTD does contain a tilde character (unicode 0x7e). If I move the DTD file to another URL which does not contain a tilde, then my example XML file parses without causing a SAXException. So I have a work-around for this problem, but I am interested to know: why does this happen? Is this a bug? If so, is it with UTF-8, Java (1.6.0_18 x86), Windows (Server 2008 R2 x86_64) or what? Or is this one of those little obscure nuances of the XML 1.0 specification?

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  • Dictionaries with more than one key per value in Python

    - by nickname
    I am attempting to create a nice interface to access a data set where each value has several possible keys. For example, suppose that I have both a number and a name for each value in the data set. I want to be able to access each value using either the number OR the name. I have considered several possible implementations: Using two separate dictionaries, one for the data values organized by number, and one for the data values organized by name. Simply assigning two keys to the same value in a dictionary. Creating dictionaries mapping each name to the corresponding number, and vice versa Attempting to create a hash function that maps each name to a number, etc. (related to the above) Creating an object to encapsulate all three pieces of data, then using one key to map dictionary keys to the objects and simply searching the dictionary to map the other key to the object. None of these seem ideal. The first seems ugly and unmaintainable. The second also seems fragile. The third/fourth seem plausible, but seem to require either much manual specification or an overly complex implementation. Finally, the fifth loses constant-time performance for one of the lookups. In C/C++, I believe that I would use pointers to reference the same piece of data from different keys. I know that the problem is rather similar to a database lookup problem by a non-key column, however, I would like (if possible), to maintain the approximate O(1) performance of Python dictionaries. What is the most Pythonic way to achieve this data structure?

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  • exporting non_public type through public API

    - by user329820
    Hi I have written this code in Netbeans but it will show this warning for the name of this method ,would you please help me for what it shows this warning? thanks public Node returnNode(int index) throws IndexOutOfBoundsException { if (index < 0 || index > size) { throw new IndexOutOfBoundsException(); } else { for (int i = 0; i < index; i++) { pointer = pointer.getNext(); } } return pointer; }

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  • Generate a commutative hash based on three sets of numbers?

    - by DarkAmgine
    I need to generate a commutative hash based on three sets of "score" structs. Each score has a "start", an "end" and a "number". Both start and end are usually huge numbers (8-9 digits) but number is just from 1 to 4. I need them to be commutative so the order does not matter. I'm using XOR at the moment but it seems to be giving bad results. Since I'm working with large large datasets, I'd prefer a performance-friendly solution. Any suggestions? Thanks =] public static int getCustomHash(cnvRegion c1, cnvRegion c2, cnvRegion c3) { int part1 = (c1.startLocation * c2.startLocation * c3.startLocation); int part2 = (c1.endLocation * c2.endLocation * c3.endLocation); int part3 = (c1.copyNumber + c2.copyNumber + c3.copyNumber)*23735160; return part1 ^ part2 ^ part3; }

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  • c# winforms events restore textbox contents on escape

    - by aj3jr
    Using c# in 2008 Express. I have a textbox containing a path. I append a "\" at the end on Leave Event. If the user presses 'Escape' key I want the old contents to be restored. When I type over all the text and press 'Escape' I hear a thump and the old text isn't restored. Here what I have so far ... public string _path; public string _oldPath; this.txtPath.KeyPress += new System.Windows.Forms.KeyPressEventHandler(txtPath_CheckKeys); this.txtPath.Enter +=new EventHandler(txtPath_Enter); this.txtPath.LostFocus += new EventHandler(txtPath_LostFocus); public void txtPath_CheckKeys(object sender, KeyPressEventArgs kpe) { if (kpe.KeyChar == (char)27) { _path = _oldPath; } } public void txtPath_Enter(object sender, EventArgs e) { //AppendSlash(sender, e); _oldPath = _path; } void txtPath_LostFocus(object sender, EventArgs e) { //throw new NotImplementedException(); AppendSlash(sender, e); } public void AppendSlash(object sender, EventArgs e) { //add a slash to the end of the txtPath string on ANY change except a restore this.txtPath.Text += @"\"; } Thanks in advance,

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  • INSERT..ON DUPLICATE KEY UPDATE - but NOT using the duplicate key to compare.

    - by calumbrodie
    I am trying to solve a problem I have inherited with poor treatment of different data sources. I have a user table that contains BOTH good and evil users. create table `users`( `user_id` int(13) NOT NULL AUTO_INCREMENT , `email` varchar(255) , `name` varchar(255) , PRIMARY KEY (`user_id`) ); In this table the primary key is currently set to be user_id. I have another table ('users_evil') which contains ONLY the evil users (all the users from this table are included in the first table) - the user_id's on this table do NOT correspond to those in the first table. I want to have all my users in one table, and simply flag which are good and which are evil. What I want to do is alter the user table and add a column ('evil') which defaults to 0. I then want to dump the data from my 'users_evil') table and then run an INSERT..ON DUPLICATE KEY UPDATE with this data into the first table (setting 'evil'=1 where the emails match) The problem is that the 'PK' is set to the user_id and not the 'email'. Any suggestions, or even another strategy to successfully achive this. Can I run this statement but treat another column as PK only for the duration of the statement.

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  • assign characters to key combinations in XP or Visual Studio .Net

    - by cpj
    I'm running Mac OSX on a MacBookPro (UK keyboard). I run windows XP under parallels in a VM. I run Visual Studio .Net 2003 and 2008 in XP in the VM when i need to. I have English United Kingdom and English United states keyboards setup in XP. (they switch sometimes for no apparent reason) There is no hash "#" key on my mac's keyboard. However, in OSX I can get a hash with an alt+3 key combination. But In Windows XP... I can not make a "#" character. I can go to the character map in windows and copy a hash.. switch into OSX and copy a hash.. search in code and copy a hash.. but I can not make a hash in XP using my keyboard without typing U+0023: ... which you can imagine is annoying. coding anything with hash symbols is becoming a choir. Anyone got any advice or key mapping tricks I can use to get hash characters working in XP using my mac UK keyboard?

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  • Handling primary key duplicates in a data warehouse load

    - by Meff
    I'm currently building an ETL system to load a data warehouse from a transactional system. The grain of my fact table is the transaction level. In order to ensure I don't load duplicate rows I've put a primary key on the fact table, which is the transaction ID. I've encountered a problem with transactions being reversed - In the transactional database this is done via a status, which I pick up and I can work out if the transaction is being done, or rolled back so I can load a reversal row in the warehouse. However, the reversal row will have the same transaction ID and so I get a primary key violation. I've solved this for now by negating the primary key, so transaction ID 1 would be a payment, and transaction ID -1 (In the warehouse only) would be the reversal. I have considered an alternative of generating a BIT column, where 0 is normal and 1 is reversal, then making the PK the transaction ID and the BIT column. My question is, is this a good practice, and has anyone else encountered anything like this? For reference, this is a payment processing system, so values will not be modified, so there will only ever be transactions and reversals.

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  • Updating a composite primary key

    - by VBCSharp
    I am struggling with the philosophical discussions about whether or not to use composite primary keys on my SQL Server database. I have always used the surrogate keys in the past and I am challenging myself by leaving my comfort zone to try something different. I have read many discussion but can't come to any kind of solution yet. The struggle I am having is when I have to update a record with the composite PK. For example, the record in questions is like this: ContactID, RoleID, EffectiveDate, TerminationDT. The PK in this case is the ContactID, RoleID, and EffectiveDate. TerminationDT can be null. If in my UI, the user changes the RoleID and then I need to update the record. Using the surrogate key I can do an Update Table Set RoleID = 1 WHERE surrogateID = Z. However, using the Composite Key way, once one of the fields in the composite key changes I have no way to reference the old record to update it without now maintaining somewhere in the UI a reference to the old values. I do not bind datasources in my UI. I open a connection, get the data and store it in a bucket, then close the connection. What are everyone's opinions? Thanks.

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  • Why is my Type.GetFields(BindingFlags.Instance|BindingFlags.Public) not working?

    - by granadaCoder
    My code can see the non-public members, but not the public ones. Why? FieldInfo[] publicFieldInfos = t.GetFields(BindingFlags.Instance | BindingFlags.Public); is returning nothing. Note: I'm trying to get at the properties on the abstract class as well as the concrete class. (And read the attributes as well). The MSDN example works with the 2 flags (BindingFlags.Instance | BindingFlags.Public) but my mini inheritance example below does not. private void RunTest1() { try { textBox1.Text = string.Empty; Type t = typeof(MyInheritedClass); //Look at the BindingFlags *** NonPublic *** int fieldCount = 0; while (null != t) { fieldCount += t.GetFields(BindingFlags.Instance | BindingFlags.NonPublic).Length; FieldInfo[] nonPublicFieldInfos = t.GetFields(BindingFlags.Instance | BindingFlags.NonPublic); foreach (FieldInfo field in nonPublicFieldInfos) { if (null != field) { Console.WriteLine(field.Name); } } t = t.BaseType; } Console.WriteLine("\n\r------------------\n\r"); //Look at the BindingFlags *** Public *** t = typeof(MyInheritedClass); FieldInfo[] publicFieldInfos = t.GetFields(BindingFlags.Instance | BindingFlags.Public); foreach (FieldInfo field in publicFieldInfos) { if (null != field) { Console.WriteLine(field.Name); object[] attributes = field.GetCustomAttributes(t, true); if (attributes != null && attributes.Length > 0) { foreach (Attribute att in attributes) { Console.WriteLine(att.GetType().Name); } } } } } catch (Exception ex) { ReportException(ex); } } private void ReportException(Exception ex) { Exception innerException = ex; while (innerException != null) { Console.WriteLine(innerException.Message + System.Environment.NewLine + innerException.StackTrace + System.Environment.NewLine + System.Environment.NewLine); innerException = innerException.InnerException; } } public abstract class MySuperType { public MySuperType(string st) { this.STString = st; } public string STString { get; set; } public abstract string MyAbstractString { get; set; } } public class MyInheritedClass : MySuperType { public MyInheritedClass(string ic) : base(ic) { this.ICString = ic; } [Description("This is an important property"), Category("HowImportant")] public string ICString { get; set; } private string _oldSchoolPropertyString = string.Empty; public string OldSchoolPropertyString { get { return _oldSchoolPropertyString; } set { _oldSchoolPropertyString = value; } } [Description("This is a not so importarnt property"), Category("HowImportant")] public override string MyAbstractString { get; set; } }

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  • Forking Public GitHub Code that is also Sold as a Complied App

    - by Ryan Castillo
    I found a public repo on GitHub that I would like to play around with. I can see myself potentially spending a lot of time writing tests for it and expanding its functionality. The code is also being sold as an app. I have no problem with this because I admire the owner's practice of sharing his source and also providing the convenience of paying for the app for users who don't want to mess with compiling it. If I was to spend time with this code as a separate fork what would prevent the owner from merging it with his master branch? Is it ethical for him to still profit off of my added functionality? Should a line be drawn somewhere?

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