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  • using dummy row with NOT NULL to solve DEFAULT NULL

    - by Tony38
    I know having DEFAULT NULLS is not a good practice but I have many optional lookup values which are FK in the system so to solve this issue here is what i am doing: I use NOT NULL for every FK / lookup colunms. I have the first row in every lookup table which is PK id = 1 as a dummy row with just "none" in all the columns. This way I can use NOT NULL in my schema and if needed reference to the none row values PK =1 for FKs which do not have any lookup value. Is this a good design or any other work arounds? EDIT: I have: Neighborhood table Postal table. Every neighborhood has a city, so the FK can be NOT NULL. But not every postal code belongs to a neighborhood. Some do, some don't depending on the country. So if i use NOT NULL for the FK between postal and neighborhood then I will be screwed as there has to be some value entered. So what i am doing in essence is: have a row in every table to be a dummy row just to link the FKs. This way row one in neighborhood table will be: n_id = 1 name =none etc... In postal table I can have: postal_code = 3456A3 FK (city) = Moscow FK (neighborhood_id)=1 as a NOT NULL. If I don't have a dummy row in the neighborhood lookup table then I have to declare FK (neighborhood_id) as a Default null column and store blanks in the table. This is an example but there is a huge number of values which will have blanks then in many tables.

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  • How do I delete orphan entities using hibernate and JPA on a many-to-many relationship?

    - by user368453
    I want to delete orphan entities using hibernate and JPA on a many-to-many relationship but all that I found was this atibute the attribute. org.hibernate.annotations.CascadeType.DELETE_ORPHAN ( i.e. @Cascade(value={org.hibernate.annotations.CascadeType.DELETE_ORPHAN) ), which works only for one-to-many relationships. I want to know if I can delete the orphan ones on my many-to-many relationship. I´d be happy if anyone could help me... Thanks in advance !

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  • The trust relationship between the primary domain and the trusted domain failed. ASP.NET 2.0

    - by Dasupalouie
    Anyone run into this issue? Any help would be appretiated :) Server Error in '/CTCWeb' Application. The trust relationship between the primary domain and the trusted domain failed. 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.SystemException: The trust relationship between the primary domain and the trusted domain failed. 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: [SystemException: The trust relationship between the primary domain and the trusted domain failed. ] System.Security.Principal.NTAccount.TranslateToSids(IdentityReferenceCollection sourceAccounts, Boolean& someFailed) +1185 System.Security.Principal.NTAccount.Translate(IdentityReferenceCollection sourceAccounts, Type targetType, Boolean& someFailed) +44 System.Security.Principal.NTAccount.Translate(IdentityReferenceCollection sourceAccounts, Type targetType, Boolean forceSuccess) +47 System.Security.Principal.WindowsPrincipal.IsInRole(String role) +101 System.Web.Configuration.AuthorizationRule.IsTheUserInAnyRole(StringCollection roles, IPrincipal principal) +123 System.Web.Configuration.AuthorizationRule.IsUserAllowed(IPrincipal user, String verb) +256 System.Web.Configuration.AuthorizationRuleCollection.IsUserAllowed(IPrincipal user, String verb) +199 System.Web.Security.UrlAuthorizationModule.OnEnter(Object source, EventArgs eventArgs) +8771980 System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +68 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +75 -------------------------------------------------------------------------------- Version Information: Microsoft .NET Framework Version:2.0.50727.3603; ASP.NET Version:2.0.50727.3053

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  • Core Data: Inverse relationship only mirrors when I edit the mutableset. Not sure why.

    - by zorn
    My model is setup so Business has many clients, Client has one business. Inverse relationship is setup in the mom file. I have a unit test like this: - (void)testNewClientFromBusiness { PTBusiness *business = [modelController newBusiness]; STAssertTrue([[business clients] count] == 0, @"is actually %d", [[business clients] count]); PTClient *client = [business newClient]; STAssertTrue([business isEqual:[client business]], nil); STAssertTrue([[business clients] count] == 1, @"is actually %d", [[business clients] count]); } I implement -newClient inside of PTBusiness like this: - (PTClient *)newClient { PTClient *client = [NSEntityDescription insertNewObjectForEntityForName:@"Client" inManagedObjectContext:[self managedObjectContext]]; [client setBusiness:self]; [client updateLocalDefaultsBasedOnBusiness]; return client; } The test fails because [[business clients] count] is still 0 after -newClient is called. If I impliment it like this: - (PTClient *)newClient { PTClient *client = [NSEntityDescription insertNewObjectForEntityForName:@"Client" inManagedObjectContext:[self managedObjectContext]]; NSMutableSet *group = [self mutableSetValueForKey:@"clients"]; [group addObject:client]; [client updateLocalDefaultsBasedOnBusiness]; return client; } The tests passes. My question(s): So am I right in thinking the inverse relationship is only updated when I interact with the mutable set? That seems to go against some other Core Data docs I've read. Is the fact that this is running in a unit test without a run loop have anything to do with it? Any other troubleshooting recommendations? I'd really like to figure out why I can't set up the relationship at the client end.

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  • What are advantages of using a one-to-one table relationship? (MySQL)

    - by byronh
    What are advantages of using a one-to-one table relationship as opposed to simply storing all the data in one table? I understand and make use of one-to-many, many-to-one, and many-to-many all the time, but implementing a one-to-one relationship seems like a tedious and unnecessary task, especially if you use naming conventions for relating (php) objects to database tables. I couldn't find anything on the net or on this site that could supply a good real-world example of a one-to-one relationship. At first I thought it might be logical to separate 'users', for example, into two tables, one containing public information like an 'about me' for profile pages and one containing private information such as login/password, etc. But why go through all the trouble of using unnecessary JOINS when you can just choose which fields to select from that table anyway? If I'm displaying the user's profile page, obviously I would only SELECT id,username,email,aboutme etc. and not the fields containing their private info. Anyone care to enlighten me with some real-world examples of one-to-one relationships?

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  • str is not callable error in python .

    - by mekasperasky
    import sys import md5 from TOSSIM import * from RadioCountMsg import * t = Tossim([]) #The Tossim object is defined here m = t.mac()#The mac layer is defined here , in which the communication takes place r = t.radio()#The radio communication link object is defined here , as the communication needs Rf frequency to transfer t.addChannel("RadioCountToLedsC", sys.stdout)# The various channels through which communication will take place t.addChannel("LedsC", sys.stdout) #The no of nodes that would be required in the simulation has to be entered here print("enter the no of nodes you want ") n=input() for i in range(0, n): m = t.getNode(i) m.bootAtTime((31 + t.ticksPerSecond() / 10) * i + 1) #The booting time is defined so that the time at which the node would be booted is given f = open("topo.txt", "r") #The topography is defined in topo.txt so that the RF frequencies of the transmission between nodes are are set lines = f.readlines() for line in lines: s = line.split() if (len(s) > 0): if (s[0] == "gain"): r.add(int(s[1]), int(s[2]), float(s[3])) #The topogrography is added to the radio object noise = open("meyer-heavy.txt", "r") #The noise model is defined for the nodes lines = noise.readlines() for line in lines: str = line.strip() if (str != ""): val = int(str) for i in range(0, 4): t.getNode(i).addNoiseTraceReading(val) for i in range (0, n): t.getNode(i).createNoiseModel() #The noise model is created for each node for i in range(0,n): t.runNextEvent() fk=open("key.txt","w") for i in range(0,n): if i ==0 : key=raw_input() fk.write(key) ak=key key=md5.new() key.update(str(ak)) ak=key.digest() fk.write(ak) fk.close() fk=open("key.txt","w") plaint=open("pt.txt") for i in range(0,n): msg = RadioCountMsg() msg.set_counter(7) pkt = t.newPacket()#A packet is defined according to a certain format print("enter message to be transported") ms=raw_input()#The message to be transported is taken as input #The RC5 encryption has to be done here plaint.write(ms) pkt.setData(msg.data) pkt.setType(msg.get_amType()) pkt.setDestination(i+1)#The destination to which the packet will be sent is set print "Delivering " + " to" ,i+1 pkt.deliver(i+1, t.time() + 3) fk.close() print "the key to be displayed" ki=raw_input() fk=open("key.txt") for i in range(0,n): if i==ki: ms=fk.readline() for i in range(0,n): msg=RadioCountMsg() msg.set_counter(7) pkt=t.newPacket() msg.data=ms pkt.setData(msg.data) pkt.setType(msg.get_amType()) pkt.setDestination(i+1) pkt.deliver(i+1,t.time()+3) #The key has to be broadcasted here so that the decryption can take place for i in range(0, n): t.runNextEvent(); this code gives me error here key.update(str(ak)) . when i run a similar code on the python terminal there is no such error but this code pops up an error . why so?

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  • Mapping composite foreign keys in a many-many relationship, with overlapping components.

    - by Kirk Broadhurst
    I have a Page table and a View table. There is a many-many relationship between these two via a PageView table. Unfortunately all of these tables need to have composite keys (for business reasons). Page has a primary key of (PageCode, Version), View has a primary key of (ViewCode, Version). PageView obviously enough has PageCode, ViewCode, and Version. The FK to Page is (PageCode, Version) and the FK to View is (ViewCode, Version) Makes sense and works, but when I try to map this in Entity framework I get Error 3021: Problem in mapping fragments...: Each of the following columns in table PageView is mapped to multiple conceptual side properties: PageView.Version is mapped to (PageView_Association.View.Version, PageView_Association.Page.Version) So clearly enough, EF is having a complain about the Version column being a common component of the two foreign keys. Obviously I could create a PageVersion and ViewVersion column in the join table, but that kind of defeats the point of the constraint, i.e. the Page and View must have the same Version value. Has anyone encountered this, and is there anything I can do get around it? Thanks!

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  • What relationship do software Scrum or Lean have to industrial engineering concepts like theory of constraints?

    - by DeveloperDon
    In Scrum, work is delivered to customers through a series of sprints in which project work is time boxed to a fixed number of days or weeks, usually 30 days. In lean software development, the goal is to deliver as soon as possible, permitting early feedback for the next iteration. Both techniques stress the importance of workflow in which software work product does not accumulate in development awaiting release at some future date. Both permit new or refined requirements and feedback from QA and customers to be acted on with as little delay as possible based on priority. A few years ago I heard a lecture where the speaker talked briefly about a family of concepts from industrial engineering called theory of constraints. In the factory, they use an operations model based on three components: drum, buffer, and rope. The drum synchronizes work product as it flows through the system. Buffers that protect the system by holding output from one stage as it waits to be consumed by the next. The rope pulls product from one work station to the next. Historically, are these ideas part of the heritage of Scrum and Lean, or are they on a separate track? It we wanted to think about Scrum and Lean in terms of drum-buffer-rope, what are the parts? Drum = {daily scrum meeting, monthly release)? Buffer = {burn down list, source control system)? Rope = { daily meeting, constant integration server, monthly releases}? Industrial engineers define work flow in terms of different kinds of factories. I-Factories: straight pipeline. One input, one output. A-Factories: many inputs and one output. V-Factories: one input, many output products. T-Plants: many inputs, many outputs. If it applies, what kind of factory is most like Scrum or Lean and why?

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  • Using Recursive SQL and XML trick to PIVOT(OK, concat) a "Document Folder Structure Relationship" table, works like MySQL GROUP_CONCAT

    - by Kevin Shyr
    I'm in the process of building out a Data Warehouse and encountered this issue along the way.In the environment, there is a table that stores all the folders with the individual level.  For example, if a document is created here:{App Path}\Level 1\Level 2\Level 3\{document}, then the DocumentFolder table would look like this:IDID_ParentFolderName1NULLLevel 121Level 232Level 3To my understanding, the table was built so that:Each proposal can have multiple documents stored at various locationsDifferent users working on the proposal will have different access level to the folder; if one user is assigned access to a folder level, she/he can see all the sub folders and their content.Now we understand from an application point of view why this table was built this way.  But you can quickly see the pain this causes the report writer to show a document link on the report.  I wasn't surprised to find the report query had 5 self outer joins, which is at the mercy of nobody creating a document that is buried 6 levels deep, and not to mention the degradation in performance.With the help of 2 posts (at the end of this post), I was able to come up with this solution:Use recursive SQL to build out the folder pathUse SQL XML trick to concat the strings.Code (a reminder, I built this code in a stored procedure.  If you copy the syntax into a simple query window and execute, you'll get an incorrect syntax error) Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} -- Get all folders and group them by the original DocumentFolderID in PTSDocument table;WITH DocFoldersByDocFolderID(PTSDocumentFolderID_Original, PTSDocumentFolderID_Parent, sDocumentFolder, nLevel)AS (-- first member      SELECT 'PTSDocumentFolderID_Original' = d1.PTSDocumentFolderID            , PTSDocumentFolderID_Parent            , 'sDocumentFolder' = sName            , 'nLevel' = CONVERT(INT, 1000000)      FROM (SELECT DISTINCT PTSDocumentFolderID                  FROM dbo.PTSDocument_DY WITH(READPAST)            ) AS d1            INNER JOIN dbo.PTSDocumentFolder_DY AS df1 WITH(READPAST)                  ON d1.PTSDocumentFolderID = df1.PTSDocumentFolderID      UNION ALL      -- recursive      SELECT ddf1.PTSDocumentFolderID_Original            , df1.PTSDocumentFolderID_Parent            , 'sDocumentFolder' = df1.sName            , 'nLevel' = ddf1.nLevel - 1      FROM dbo.PTSDocumentFolder_DY AS df1 WITH(READPAST)            INNER JOIN DocFoldersByDocFolderID AS ddf1                  ON df1.PTSDocumentFolderID = ddf1.PTSDocumentFolderID_Parent)-- Flatten out folder path, DocFolderSingleByDocFolderID(PTSDocumentFolderID_Original, sDocumentFolder)AS (SELECT dfbdf.PTSDocumentFolderID_Original            , 'sDocumentFolder' = STUFF((SELECT '\' + sDocumentFolder                                         FROM DocFoldersByDocFolderID                                         WHERE (PTSDocumentFolderID_Original = dfbdf.PTSDocumentFolderID_Original)                                         ORDER BY PTSDocumentFolderID_Original, nLevel                                         FOR XML PATH ('')),1,1,'')      FROM DocFoldersByDocFolderID AS dfbdf      GROUP BY dfbdf.PTSDocumentFolderID_Original) And voila, I use the second CTE to join back to my original query (which is now a CTE for Source as we can now use MERGE to do INSERT and UPDATE at the same time).Each part of this solution would not solve the problem by itself because:If I don't use recursion, I cannot build out the path properly.  If I use the XML trick only, then I don't have the originating folder ID info that I need to link to the document.If I don't use the XML trick, then I don't have one row per document to show in the report.I could conceivably do this in the report function, but I'd rather not deal with the beginning or ending backslash and how to attach the document name.PIVOT doesn't do strings and UNPIVOT runs into the same problem as the above.I'm excited that each version of SQL server provides us new tools to solve old problems and/or enables us to solve problems in a more elegant wayThe 2 posts that helped me along:Recursive Queries Using Common Table ExpressionHow to use GROUP BY to concatenate strings in SQL server?

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  • What is a useful pattern to maintaining an object state in a one to many relationship?

    - by ahenderson
    I am looking for a design for my application, here are the players(classes) involved. struct Transform { // Uses a matrix to transform the position. // Also acts acts as the state of a Dialog. Position transform(Position p); //other methods. }; struct Dialog { // There are multiple dialog for the user to transform the output. Transform& t; void ChangeTranformation(){t.rotate(360);} } struct Algorithm { //gives us a position based on an implementation. For example this can return points on a circle or line. Transform& t; Position m_p; Dialog& d; Position GetCurrentPosition(){ return t.transform(m_p);} //other methods. } Properties I need: Each algorithms has one dialog and each dialog can have many algorithms associated with it. When the user selects an algorithm a dialog associated with that algorithm is displayed. If the user selects a different algorithm then re-selects back the state is restored in the dialog. Basically I want a good design pattern to maintain the state of the dialog given that many algorithms use it and they can be switched back and forth. Does anyone have any suggestions? Here is a use case: Dialog1 has a single edit box to control the radius. Algorithm1 generates points on a unit circle. Algorithm2 is the same as Algorithm1. The user has selected Algorithm1 and entered 2 into the edit box. This will generate points on a circle of radius 2. The user then selects Algorithm2 and enters 10 into the edit box of Dialog1. This will generate points on a circle of radius 10. Finally Algorithm1 is selected again. The edit box of Dialog1 should show 2 and points on a circle of radius 2 should be generated.

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  • What is the relationship between the command line, the OS and the microprocessor? [closed]

    - by ssbrewster
    I'm not totally clear on how using the command line differs from working through the OS' interface using an editor for example. Obviously the UI is different but I want to understand how the command line interacts with the kernel and microprocessor, and how this compares to how kernel interfaces with the OS' GUI. I know I'm missing several layers of abstraction but would be grateful for someone to explain this.

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  • What is the relationship between OpenGL, GLX, DRI, and Mesa3D?

    - by user65308
    I am starting out doing some low-level 3D programming in Linux. I have a lot of experience using the higher level graphics API OpenInventor. I know it is not strictly necessary to be aware of how all these things fit together but I'm just curious. I know OpenGL is just a standard for graphics applications. Mesa3D seems to be an open source implementation of this standard. So where do GLX and DRI fit? Digging around on Wikipedia and all these websites, I've yet to find an explanation of exactly how it all goes together. Where does hardware acceleration happen? What do proprietary drivers have to do with this? Thanks!

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  • Entity Framework 4 relationship management in POCO Templates - More lazy than FixupCollection?

    - by Joe Wood
    I've been taking a look at EF4 POCO templates in beta 2. The FixupCollection looks fine for maintaining the model correctness after updating the relationship collection property (i.e. product.Orders it would set the order.Product reference ). But what about support for handling the scenario when some of those Order objects are removed from the context? The use-case of maintaining cascading deletes in the in-memory model. The old Typed DataSet model used to do this by performing the query through the container to derive the relationship results. Like the DataSet, this would require a reference to the ObjectContext inside the entity class so that it could query the top-level Order collection. Better support for Separation of Concerns in the ObjectContext would be required. It looks like EF is not suited to this use-case that DataSets did out of the box.... am I right?

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  • How do I migrate a ManyToOne to a ManyToMany relationship in Hibernate?

    - by spderosso
    I have a instance field of a class X that is mapped using Hibernate as a Many to One relationship. E.g: public class X{ ... @ManyToOne(optional=false) private Y iField; ... } That is correctly working with a particular schema. I know want to change this instance field iField to a List and a Many to Many relationship. public class X{ ... @ManyToMany(optional=false) private List<Y> iField; ... } What steps should I follow? Do I have to change the schema? in which way? In case you need more info let me know. Thanks!

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  • What can I do about a SQL Server ghost FK constraint?

    - by rcook8601
    I'm having some trouble with a SQL Server 2005 database that seems like it's keeping a ghost constraint around. I've got a script that drops the constraint in question, does some work, and then re-adds the same constraint. Normally, it works fine. Now, however, it can't re-add the constraint because the database says that it already exists, even though the drop worked fine! Here are the queries I'm working with: alter table individual drop constraint INDIVIDUAL_EMP_FK ALTER TABLE INDIVIDUAL ADD CONSTRAINT INDIVIDUAL_EMP_FK FOREIGN KEY (EMPLOYEE_ID) REFERENCES EMPLOYEE After the constraint is dropped, I've made sure that the object really is gone by using the following queries: select object_id('INDIVIDUAL_EMP_FK') select * from sys.foreign_keys where name like 'individual%' Both return no results (or null), but when I try to add the query again, I get: The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "INDIVIDUAL_EMP_FK". Trying to drop it gets me a message that it doesn't exist. Any ideas?

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  • Core Data: Fetch all entities in a to-many-relationship of a particular object?

    - by Björn Marschollek
    Hi there, in my iPhone application I am using simple Core Data Model with two entities (Item and Property): Item name properties Property name value item Item has one attribute (name) and one one-to-many-relationship (properties). Its inverse relationship is item. Property has two attributes the according inverse relationship. Now I want to show my data in table views on two levels. The first one lists all items; when one row is selected, a new UITableViewController is pushed onto my UINavigationController's stack. The new UITableView is supposed to show all properties (i.e. their names) of the selected item. To achieve this, I use a NSFetchedResultsController stored in an instance variable. On the first level, everything works fine when setting up the NSFetchedResultsController like this: -(NSFetchedResultsController *) fetchedResultsController { if (fetchedResultsController) return fetchedResultsController; // goal: tell the FRC to fetch all item objects. NSFetchRequest *fetch = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Item" inManagedObjectContext:self.moContext]; [fetch setEntity:entity]; NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES]; [fetch setSortDescriptors:[NSArray arrayWithObject:sort]]; [fetch setFetchBatchSize:10]; NSFetchedResultsController *frController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetch managedObjectContext:self.moContext sectionNameKeyPath:nil cacheName:@"cache"]; self.fetchedResultsController = frController; fetchedResultsController.delegate = self; [sort release]; [frController release]; [fetch release]; return fetchedResultsController; } However, on the second-level UITableView, I seem to do something wrong. I implemented the fetchedresultsController in a similar way: -(NSFetchedResultsController *) fetchedResultsController { if (fetchedResultsController) return fetchedResultsController; // goal: tell the FRC to fetch all property objects that belong to the previously selected item NSFetchRequest *fetch = [[NSFetchRequest alloc] init]; // fetch all Property entities. NSEntityDescription *entity = [NSEntityDescription entityForName:@"Property" inManagedObjectContext:self.moContext]; [fetch setEntity:entity]; // limit to those entities that belong to the particular item NSPredicate *predicate = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"item.name like '%@'",self.item.name]]; [fetch setPredicate:predicate]; // sort it. Boring. NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES]; [fetch setSortDescriptors:[NSArray arrayWithObject:sort]]; NSError *error = nil; NSLog(@"%d entities found.",[self.moContext countForFetchRequest:fetch error:&error]); // logs "3 entities found."; I added those properties before. See below for my saving "problem". if (error) NSLog("%@",error); // no error, thus nothing logged. [fetch setFetchBatchSize:20]; NSFetchedResultsController *frController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetch managedObjectContext:self.moContext sectionNameKeyPath:nil cacheName:@"cache"]; self.fetchedResultsController = frController; fetchedResultsController.delegate = self; [sort release]; [frController release]; [fetch release]; return fetchedResultsController; } Now it's getting weird. The above NSLog statement returns me the correct number of properties for the selected item. However, the UITableViewDelegate method tells me that there are no properties: -(NSInteger) tableView:(UITableView *)table numberOfRowsInSection:(NSInteger)section { id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section]; NSLog(@"Found %d properties for item \"%@\". Should have found %d.",[sectionInfo numberOfObjects], self.item.name, [self.item.properties count]); // logs "Found 0 properties for item "item". Should have found 3." return [sectionInfo numberOfObjects]; } The same implementation works fine on the first level. It's getting even weirder. I implemented some kind of UI to add properties. I create a new Property instance via Property *p = [NSEntityDescription insertNewObjectForEntityForName:@"Property" inManagedObjectContext:self.moContext];, set up the relationships and call [self.moContext save:&error]. This seems to work, as error is still nil and the object gets saved (I can see the number of properties when logging the Item instance, see above). However, the delegate methods are not fired. This seems to me due to the possibly messed up fetchRequest(Controller). Any ideas? Did I mess up the second fetch request? Is this the right way to fetch all entities in a to-many-relationship for a particular instance at all?

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  • Change master table PK and update related table FK (changing PK from Autoincrement to UUID on Mysql)

    - by eleonzx
    I have two related tables: Groups and Clients. Clients belongs to Groups so I have a foreign key "group_id" that references the group a client belongs to. I'm changing the Group id from an autoincrement to a UUID. So what I need is to generate a UUID for each Group and update the Clients table at once to reflect the changes and keep the records related. Is there a way to do this with multiple-table update on MySQL? Adding tables definitions for clarification. CREATE TABLE `groups` ( `id` char(36) NOT NULL, `name` varchar(255) DEFAULT NULL, `created` datetime DEFAULT NULL, `modified` datetime DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8$$ CREATE TABLE `clients` ( `id` char(36) NOT NULL, `name` varchar(255) NOT NULL, `group_id` char(36) DEFAULT NULL, `active` tinyint(1) DEFAULT '1' PRIMARY KEY (`id`), KEY `fkgp` (`group_id`), CONSTRAINT `fkgp` FOREIGN KEY (`group_id`) REFERENCES `groups` (`id`) ON DELETE NO ACTION ON UPDATE CASCADE ) ENGINE=InnoDB DEFAULT CHARSET=utf8$$

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  • Database model for keeping track of likes/shares/comments on blog posts over time

    - by gage
    My goal is to keep track of the popular posts on different blog sites based on social network activity at any given time. The goal is not to simply get the most popular now, but instead find posts that are popular compared to other posts on the same blog. For example, I follow a tech blog, a sports blog, and a gossip blog. The tech blog gets waaay more readership than the other two blogs, so in raw numbers every post on the tech blog will always out number views on the other two. So lets say the average tech blog post gets 500 facebook likes and the other two get an average of 50 likes per post. Then when there is a sports blog post that has 200 fb likes and a gossip blog post with 300 while the tech blog posts today have 500 likes I want to highlight the sports and gossip blog posts (more likes than average vs tech blog with more # of likes but just average for the blog) The approach I am thinking of taking is to make an entry in a database for each blog post. Every x minutes (say every 15 minutes) I will check how many likes/shares/comments an entry has received on all the social networks (facebook, twitter, google+, linkeIn). So over time there will be a history of likes for each blog post, i.e post 1234 after 15 min: 10 fb likes, 4 tweets, 6 g+ after 30 min: 15 fb likes, 15 tweets, 10 g+ ... ... after 48 hours: 200 fb likes, 25 tweets, 15 g+ By keeping a history like this for each blog post I can know the average number of likes/shares/tweets at any give time interval. So for example the average number of fb likes for all blog posts 48hrs after posting is 50, and a particular post has 200 I can mark that as a popular post and feature/highlight it. A consideration in the design is to be able to easily query the values (likes/shares) for a specific time-frame, i.e. fb likes after 30min or tweets after 24 hrs in-order to compute averages with which to compare against (or should averages be stored in it's own table?) If this approach is flawed or could use improvement please let me know, but it is not my main question. My main question is what should a database scheme for storing this info look like? Assuming that the above approach is taken I am trying to figure out what a database schema for storing the likes over time would look like. I am brand new to databases, in doing some basic reading I see that it is advisable to make a 3NF database. I have come up with the following possible schema. Schema 1 DB Popular Posts Table: Post post_id ( primary key(pk) ) url title Table: Social Activity activity_id (pk) url (fk) type (i.e. facebook,twitter,g+) value timestamp This was my initial instinct (base on my very limited db knowledge). As far as I under stand this schema would be 3NF? I searched for designs of similar database model, and found this question on stackoverflow, http://stackoverflow.com/questions/11216080/data-structure-for-storing-height-and-weight-etc-over-time-for-multiple-users . The scenario in that question is similar (recording weight/height of users overtime). Taking the accepted answer for that question and applying it to my model results in something like: Schema 2 (same as above, but break down the social activity into 2 tables) DB Popular Posts Table: Post post_id (pk) url title Table: Social Measurement measurement_id (pk) post_id (fk) timestamp Table: Social stat stat_id (pk) measurement_id (fk) type (i.e. facebook,twitter,g+) value The advantage I see in schema 2 is that I will likely want to access all the values for a given time, i.e. when making a measurement at 30min after a post is published I will simultaneous check number of fb likes, fb shares, fb comments, tweets, g+, linkedIn. So with this schema it may be easier get get all stats for a measurement_id corresponding to a certain time, i.e. all social stats for post 1234 at time x. Another thought I had is since it doesn't make sense to compare number of fb likes with number of tweets or g+ shares, maybe it makes sense to separate each social measurement into it's own table? Schema 3 DB Popular Posts Table: Post post_id (pk) url title Table: fb_likes fb_like_id (pk) post_id (fk) timestamp value Table: fb_shares fb_shares_id (pk) post_id (fk) timestamp value Table: tweets tweets__id (pk) post_id (fk) timestamp value Table: google_plus google_plus_id (pk) post_id (fk) timestamp value As you can see I am generally lost/unsure of what approach to take. I'm sure this typical type of database problem (storing measurements overtime, i.e temperature statistic) that must have a common solution. Is there a design pattern/model for this, does it have a name? I tried searching for "database periodic data collection" or "database measurements over time" but didn't find anything specific. What would be an appropriate model to solve the needs of this problem?

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  • Activity tracking usecase for login tracking.

    - by Mdillion
    Creating an activity tracking system for a social site. All user activiti from pooint of login til logoff are to be tracked. This means the first use case is the user's login. Every activity will have the same format so once I figure out how to track one activity then I can create chema for all activities. Currently for login I have steps like: Two solutions I have: Activity 1: User attempts to login Activity 2 A: User has successfully logged in Activity 2 B: User failed to login. Activity 2 B A: User failed to login due to invalid password Activity 2 B B: User failed to login due to locked account. OR Activty 1: User login - with result = Pass or Fail and if Fail reason = flag_id of reason. Accordingly I have to create the schema. For now I have it like this: activity_id object_id (fk) session_id (fk) user_id (fk) flag_id (fk) created_dt friend_id (fk) result (pass/fail) But ofcourse this a work in progress.

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  • Are these tables respect the 3NF Database Normalization?

    - by penas
    AUTHOR table Author_ID, PK First_Name Last_Name TITLES table TITLE_ID, PK NAME Author_ID, FK DOMAIN table DOMAIN_ID, PK NAME TITLE_ID, FK READERS table READER_ID, PK First_Name Last_Name ADDRESS CITY_ID, FK PHONE CITY table CITY_ID, PK NAME BORROWING table BORROWING_ID,pk READER_ID, fk TITLE_ID, fk DATE HISTORY table READER_ID TITLE_ID DATE_OF_BORROWING DATE_OF_RETURNING Are these tables respect the 3NF Database Normalization? What if 2 authors work together for the same title? The column Addresss should have it's own table? When a reader borrows a book, I make an entry in BORROWING table. After he returns the book, I delete that entry and I make another one entry in HISTORY table. Is this a good idea? Do I brake any rule? Should I have instead one single BORROWING table with a DATE_OF_RETURNING column?

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  • Data Modeling Help - Do I add another table, change existing table's usage, or something else?

    - by StackOverflowNewbie
    Assume I have the following tables and relationships: Person - Id (PK) - Name A Person can have 0 or more pets: Pet - Id (PK) - PersonId (FK) - Name A person can have 0 or more attributes (e.g. age, height, weight): PersonAttribute _ Id (PK) - PersonId (FK) - Name - Value PROBLEM: I need to represent pet attributes, too. As it turns out, these pet attributes are, in most cases, identical to the attributes of a person (e.g. a pet can have an age, height, and weight too). How do I represent pet attributes? Do I create a PetAttribute table? PetAttribute Id (PK) PetId (FK) Name Value Do I change PersonAttribute to GenericAttribute and have 2 foreign keys in it - one connecting to Person, the other connecting to Pet? GenericAttribute Id (PK) PersonId (FK) PetId (FK) Name Value NOTE: if PersonId is set, then PetId is not set. If PetId is set, PersonId is not set. Do something else?

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