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  • Is there a canonical source supporting "all-surrogates"?

    - by user61852
    Background The "all-PK-must-be-surrogates" approach is not present in Codd's Relational Model or any SQL Standard (ANSI, ISO or other). Canonical books seems to elude this restrictions too. Oracle's own data dictionary scheme uses natural keys in some tables and surrogate keys in other tables. I mention this because these people must know a thing or two about RDBMS design. PPDM (Professional Petroleum Data Management Association) recommend the same canonical books do: Use surrogate keys as primary keys when: There are no natural or business keys Natural or business keys are bad ( change often ) The value of natural or business key is not known at the time of inserting record Multicolumn natural keys ( usually several FK ) exceed three columns, which makes joins too verbose. Also I have not found canonical source that says natural keys need to be immutable. All I find is that they need to be very estable, i.e need to be changed only in very rare ocassions, if ever. I mention PPDM because these people must know a thing or two about RDBMS design too. The origins of the "all-surrogates" approach seems to come from recommendations from some ORM frameworks. It's true that the approach allows for rapid database modeling by not having to do much business analysis, but at the expense of maintainability and readability of the SQL code. Much prevision is made for something that may or may not happen in the future ( the natural PK changed so we will have to use the RDBMS cascade update funtionality ) at the expense of day-to-day task like having to join more tables in every query and having to write code for importing data between databases, an otherwise very strightfoward procedure (due to the need to avoid PK colisions and having to create stage/equivalence tables beforehand ). Other argument is that indexes based on integers are faster, but that has to be supported with benchmarks. Obviously, long, varying varchars are not good for PK. But indexes based on short, fix-length varchar are almost as fast as integers. The questions - Is there any canonical source that supports the "all-PK-must-be-surrogates" approach ? - Has Codd's relational model been superceded by a newer relational model ?

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  • relational data from xml

    - by Beta033
    Our problem is this, we have a relational database to store objects in tables. As any relational database could, several of these tables have multiple foreign keys pointing to other tables (all pretty normal stuff) We've been trying to identify a solution to allow export of this relational data, ideally, only 1 of the objects in the model, to some sort of file (xml, text, ??). So it wouldn't be simple enough to just export 1 table as data stored in other tables would contribute to the complete model of the object. Something like the following picture: Toward this, i've written a routine to export the structure by following the foreign key paths which exports something similar to the following. <Tables> <TableA PK="1", val1, val2, val3> <TableC PK="1", FK_A="1", Val1, val2, val3> <TableC PK="2", FK_A="1", val1, val2, val3> <TableB PK="1", FK_A="1", FK_C="1", val1, val2, val3> <TableB PK="2", FK_A="1", FK_C="2", val1, val2, val3> <TableD PK="1", FK_B="1", FK_C="1", val1> <TableD PK="2", FK_B="2", FK_C="1", val1> </Tables> However, given this structure, it cannot be placed into a heirarchial format (ie D2 is a child of C1 and B2; and B2 is a child of C2) Which in turn, makes my life very difficult when trying to identify a methodology to reimport (and reKey) these objects. Has anybody done anything like this? how do you do it? are there tools or documentation on how this is best accomplished? Thanks for your help.

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  • Umlaute from JSP-page are misinterpreted

    - by Karin
    I'm getting Input from a JSP page, that can contain Umlaute. (e.g. Ä,Ö,Ü,ä,ö,ü,ß). Whenever an Umlaut is entered in the Input field an incorrect value gets passed on. e.g. If an "ä" (UTF-8:U+00E4) gets entered in the input field, the String that is extracted from the argument is "ä" (UTF-8: U+00C3 and U+00A4) It seems to me as if the UTF-8 hex encoding (which is c3 a4 for an "ä") gets used for the conversion. How can I retrieved the correct value? Here are snippets from the current implementation The JSP-page passes the input value "pk" on to the processing logic: <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> ... <input type="text" name="<%=pk.toString()%>" value="<%=value%>" size="70"/> <button type="submit" title="Edit" value='Save' onclick="action.value='doSave';pk.value='<%=pk.toString()%>'"><img src="icons/run.png"/>Save</button> The value gets retrieved from args and converted to a string: UUID pk = UUID.fromString(args.get("pk")); //$NON-NLS-1$ String value = args.get(pk.toString()); Note: Umlaute that are saved in the Database get displayed correctly on the page.

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  • Django unit testing: South-migrated DB works in MySQL, throws duplicate PK error in PostGreSQL. Am I

    - by unclaimedbaggage
    Hi folks, (Worth starting off with a disclaimer: I'm very new to PostGreSQL) I have a django site which involves a standard app/tests.py testing file. If I migrate the DB to MySQL (through South),, the tests all pass. However in PostGresQL, I'm getting the following error: IntegrityError: duplicate key value violates unique constraint "business_contact_pkey" Note this happens while unit testing only - the actual page runs fine in both MySQL & PostGresql. Really having a heckuva time figuring this one out. Anyone have ideas? Below are the Postgresql "\d business_contact" & offending tests.py method if they help. No changes made to either DB except the (same) South migrations Thanks first_name | character varying(200) | not null mobile_phone | character varying(100) | surname | character varying(200) | not null business_id | integer | not null created | timestamp with time zone | not null deleted | boolean | not null default false updated | timestamp with time zone | not null slug | character varying(150) | not null phone | character varying(100) | email | character varying(75) | id | integer | not null default nextval('business_contact_id_seq'::regclass) Indexes: "business_contact_pkey" PRIMARY KEY, btree (id) "business_contact_slug_key" UNIQUE, btree (slug) "business_contact_business_id" btree (business_id) Foreign-key constraints: "business_id_refs_id_772cc1b7b40f4b36" FOREIGN KEY (business_id) REFERENCES business(id) DEFERRABLE INITIALLY DEFERRED Referenced by: TABLE "business" CONSTRAINT "primary_contact_id_refs_id_dfaf59c4041c850" FOREIGN KEY (primary_contact_id) REFERENCES business_contact(id) DEFERRABLE INITIALLY DEFERRED TEST DEF: def test_add_business_contact(self): """ Add a business contact """ contact_slug = 'test-new-contact-added-new-adf' business_id = 1 business = Business.objects.get(id=business_id) postdata = { 'first_name': 'Test', 'surname': 'User', 'business': '1', 'slug': contact_slug, 'email': '[email protected]', 'phone': '12345678', 'mobile_phone': '9823452', 'business': 1, 'business_id': 1, } #Test to ensure contacts that should not exist are not returned contact_not_exists = Contact.objects.filter(slug=contact_slug) self.assertFalse(contact_not_exists) #Add the contact and ensure it is present in the DB afterwards """ contact_add_url = '%s%s/contact/add/' % (settings.BUSINESS_URL, business.slug) self.client.post(contact_add_url, postdata) added_contact = Contact.objects.filter(slug=contact_slug) print added_contact try: self.assertTrue(added_contact) except: formset = ContactForm(postdata) print formset.errors self.assertFalse(True, "Contact not found in the database - most likely, the post values in the test didn't validate against the form")

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  • Database PK-FK design for future-effective-date entries?

    - by Scott Balmos
    Ultimately I'm going to convert this into a Hibernate/JPA design. But I wanted to start out from purely a database perspective. We have various tables containing data that is future-effective-dated. Take an employee table with the following pseudo-definition: employee id INT AUTO_INCREMENT ... data fields ... effectiveFrom DATE effectiveTo DATE employee_reviews id INT AUTO_INCREMENT employee_id INT FK employee.id Very simplistic. But let's say Employee A has id = 1, effectiveFrom = 1/1/2011, effectiveTo = 1/1/2099. That employee is going to be changing jobs in the future, which would in theory create a new row, id = 2 with effectiveFrom = 7/1/2011, effectiveTo = 1/1/2099, and id = 1's effectiveTo updated to 6/30/2011. But now, my program would have to go through any table that has a FK relationship to employee every night, and update those FK to reference the newly-effective employee entry. I have seen various postings in both pure SQL and Hibernate forums that I should have a separate employee_versions table, which is where I would have all effective-dated data stored, resulting in the updated pseudo-definition below: employee id INT AUTO_INCREMENT employee_versions id INT AUTO_INCREMENT employee_id INT FK employee.id ... data fields ... effectiveFrom DATE effectiveTo DATE employee_reviews id INT AUTO_INCREMENT employee_id INT FK employee.id Then to get any actual data, one would have to actually select from employee_versions with the proper employee_id and date range. This feels rather unnatural to have this secondary "versions" table for each versioned entity. Anyone have any opinions, suggestions from your own prior work, etc? Like I said, I'm taking this purely from a general SQL design standpoint first before layering in Hibernate on top. Thanks!

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  • Entity diagram with tables that have foreign keys that point to a non-PK column do not show relation

    - by Jason Coyne
    I have two tables parent and child. If I make a foreign key on child that points to the primary key of parent, and then make an entity diagram, the relationship is shown correctly. If I make the foreign key point to a different column, the relationship is not shown. I have tried adding indexes to the column, but it does not have an effect. The database is sqlite, but I am not sure if that has an effect since its all hidden behind ADO.net. How do I get the relationship to work correctly?

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  • Advice Needed To Normalise Database

    - by c11ada
    hey all, im trying to create a database for a feedback application in ASP.net i have the following database design. Username (PK) QuestionNo (PK) QuestionText FeedbackNo (PK) Username UserFeedbackNo (PK) FeedbackNo (FK) QuestionNo (FK) Answer Comment a user has a unique username a user can have multiple feedbacks i was wondering if the database design i have here is normalised and suitable for the application

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  • L2E many to many query

    - by 5YrsLaterDBA
    I have four tables: Users PrivilegeGroups rdPrivileges LinkPrivilege ----------- ---------------- --------------- --------------- userId(pk) privilegeGroupId(pk) privilegeId(pk) privilegeId(pk, fk) privilegeGroupId(fk) name code privilegeGroupId(pk, fk) L2E will not create LinkPrivilege entity for me. So we only have Users, PrivilegeGroups and rdPrivileges entities. PrivilegeGroups and rdPrivileges are many to many relationship. What I need to do is retrieve all code from rdPrivileges table based on a passed in userId. How can I do it? EDIT working code: var acc = from u in db.Users from pg in db.PrivilegeGroups from p in pg.rdPrivileges where u.UserId == userId && u.PrivilegeGroups.PrivilegeGroupId == pg.PrivilegeGroupId select p.Code;

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  • Django unable to update model

    - by user292652
    i have the following function to override the default save function in a model match def save(self, *args, **kwargs): if self.Match_Status == "F": Team.objects.filter(pk=self.Team_one.id).update(Played=F('Played')+1) Team.objects.filter(pk=self.Team_two.id).update(Played=F('Played')+1) if self.Winner !="": Team.objects.filter(pk=self.Winner.id).update(Win=F('Win')+1, Points=F('Points')+3) else: return if self.Match_Status == "D": Team.objects.filter(pk=self.Team_one.id).update(Played=F('Played')+1, Draw = F('Draw')+1, Points=F('Points')+1) Team.objects.filter(pk=self.Team_two.id).update(Played=F('Played')+1, Draw = F('Draw')+1, Points=F('Points')+1) super(Match, self).save(*args, **kwargs) I am able to save the match model just fine but Team model does not seem to be updating at all and no error is being thrown. am i missing some thing here ?

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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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  • Possible to get PrimayKey IDs back after a SQL BulkCopy?

    - by chobo2
    Hi I am using C# and using SqlBulkCopy. I have a problem though. I need to do a mass insert into one table then another mass insert into another table. These 2 have a PK/FK relationship. Table A Field1 -PK auto incrementing (easy to do SqlBulkCopy as straight forward) Table B Field1 -PK/FK - This field makes the relationship and is also the PK of this table. It is not auto incrementing and needs to have the same id as to the row in Table A. So these tables have a one to one relationship but I am unsure how to get back all those PK Id that the mass insert made since I need them for Table B.

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  • SQL: without a cursor, how to select records making a unique integer id (identity like) for dups?

    - by Dr. Zim
    If you have the select statement below where the PK is the primary key: select distinct dbo.DateAsInt( dateEntered) * 100 as PK, recordDescription as Data from MyTable and the output is something like this (the first numbers are spaced for clarity): PK Data 2010 01 01 00 New Years Day 2010 01 01 00 Make Resolutions 2010 01 01 00 Return Gifts 2010 02 14 00 Valentines day 2010 02 14 00 Buy flowers and you want to output something like this: PK Data 2010 01 01 01 New Years Day 2010 01 01 02 Make Resolutions 2010 01 01 03 Return Gifts 2010 02 14 01 Valentines day 2010 02 14 02 Buy flowers Is it possible to make the "00" in the PK have an "identity" number effect within a single select? Otherwise, how could you increment the number by 1 for each found activity for that date? I am already thinking as I type to try something like Sum(case when ?? then 1 end) with a group by.

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  • How to recalculate primary index?

    - by JohnM2
    I have table in mysql database with autoincrement PRIMARY KEY. On regular basis rows in this table are being deleted an added. So the result is that value of PK of the latest row is growing very fast, but there is not so much rows in this table. What I want to do is to "recalculate" PK in this way, that the first row has PK = 1, second PK = 2 and so on. There are no external dependencies on PK of this table so it would be "safe". Is there anyway it can be done using only mysql queries/tools? Or I have to do it from my code?

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  • Parent key of type encoded string?

    - by user246114
    Hi, How do we create a parent key which is an encoded string? Example: class Parent { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String mEncKey; } class Child { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String mEncKey; // In the doc examples, they have Key as the type here. @Persistent @Extension(vendorName="datanucleus", key="gae.parent-pk", value="true") private String mParentEncKey; } yeah I'm not sure how to make mParentEncKey an encoded string type, because the 'key' label is already being used? I would need something like?: key="gae.parent-pk.encoded-pk" not sure - is that possible? Thanks

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  • Django's post_save signal behaves weirdly with models using multi-table inheritance

    - by hekevintran
    Django's post_save signal behaves weirdly with models using multi-table inheritance I am noticing an odd behavior in the way Django's post_save signal works when using a model that has multi-table inheritance. I have these two models: class Animal(models.Model): category = models.CharField(max_length=20) class Dog(Animal): color = models.CharField(max_length=10) I have a post save callback called echo_category: def echo_category(sender, **kwargs): print "category: '%s'" % kwargs['instance'].category post_save.connect(echo_category, sender=Dog) I have this fixture: [ { "pk": 1, "model": "animal.animal", "fields": { "category": "omnivore" } }, { "pk": 1, "model": "animal.dog", "fields": { "color": "brown" } } ] In every part of the program except for in the post_save callback the following is true: from animal.models import Dog Dog.objects.get(pk=1).category == u'omnivore' # True When I run syncdb and the fixture is installed, the echo_category function is run. The output from syncdb is: $ python manage.py syncdb --noinput Installing json fixture 'initial_data' from '~/my_proj/animal/fixtures'. category: '' Installed 2 object(s) from 1 fixture(s) The weird thing here is that the dog object's category attribute is an empty string. Why is it not 'omnivore' like it is everywhere else? As a temporary (hopefully) workaround I reload the object from the database in the post_save callback: def echo_category(sender, **kwargs): instance = kwargs['instance'] instance = sender.objects.get(pk=instance.pk) print "category: '%s'" % instance.category post_save.connect(echo_category, sender=Dog) This works but it is not something I like because I must remember to do it when the model inherits from another model and it must hit the database again. The other weird thing is that I must do instance.pk to get the primary key. The normal 'id' attribute does not work (I cannot use instance.id). I do not know why this is. Maybe this is related to the reason why the category attribute is not doing the right thing?

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  • Is it approproate it use django signals withing the same app

    - by Alex Lebedev
    Trying to add email notification to my app in the cleanest way possible. When certain fields of a model change, app should send a notification to a user. Here's my old solution: from django.contrib.auth import User class MyModel(models.Model): user = models.ForeignKey(User) field_a = models.CharField() field_b = models.CharField() def save(self, *args, **kwargs): old = self.__class__.objects.get(pk=self.pk) if self.pk else None super(MyModel, self).save(*args, **kwargs) if old and old.field_b != self.field_b: self.notify("b-changed") # Sevelar more events here # ... def notify(self, event) subj, text = self._prepare_notification(event) send_mail(subj, body, settings.DEFAULT_FROM_EMAIL, [self.user.email], fail_silently=True) This worked fine while I had one or two notification types, but after that just felt wrong to have so much code in my save() method. So, I changed code to signal-based: from django.db.models import signals def remember_old(sender, instance, **kwargs): """pre_save hanlder to save clean copy of original record into `old` attribute """ instance.old = None if instance.pk: try: instance.old = sender.objects.get(pk=instance.pk) except ObjectDoesNotExist: pass def on_mymodel_save(sender, instance, created, **kwargs): old = instance.old if old and old.field_b != instance.field_b: self.notify("b-changed") # Sevelar more events here # ... signals.pre_save.connect(remember_old, sender=MyModel, dispatch_uid="mymodel-remember-old") signals.post_save.connect(on_mymodel_save, sender=MyModel, dispatch_uid="mymodel-on-save") The benefit is that I can separate event handlers into different module, reducing size of models.py and I can enable/disable them individually. The downside is that this solution is more code and signal handlers are separated from model itself and unknowing reader can miss them altogether. So, colleagues, do you think it's worth it?

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  • LINQ - Querying a list filtered via a Many-to-Many reltionship

    - by user118190
    Please excuse the context of my question for I did not know how to exactly word it. To not complicate things further, here's my business requirement: "bring me back all the Employees where they belong in Department "X". So when I view this, it will display all of the Employees that belong to this Department. Here's my environment: Silverlight 3 with Entity Framework 1.0 and WCF Data Services 1.0. I am able to load and bind all kinds of lists (simple), no problem. I don't feel that my environment matters and that's why I feel it is a LINQ question more than the technologies. My question is for scenarios where I have 3 tables linked, i.e. entities (collections). For example, I have this in my EDM: Employee--EmployeeProject--Project. Here's the table design from the Database: Employee (table1) ------------- EmployeeID (PK) FirstName other Attributes ... EmployeeProject (table2) ------------- EmployeeProjectID (PK) EmployeeID (FK) ProjectID (FK) AssignedDate other Attributes ... Project (table3) ------------- ProjectID (PK) Name other Attributes ... Here's the EDM design from Entity Framework: ------------------------ Employee (entity1) ------------------------ (Scalar Properties) ------------------- EmployeeID (PK) FirstName other Attributes ... ------------------- (Navigation Properties) ------------------- EmployeeProjects ------------------------ EmployeeProject (entity2) ------------------------ (Scalar Properties) ------------------- EmployeeProjectID (PK) AssignedDate other Attributes ... ------------------- (Navigation Properties) ------------------- Employee Project ------------------------ Project (entity3) ------------------------ (Scalar Properties) ------------------- ProjectID (PK) Name other Attributes ... ------------------- (Navigation Properties) ------------------- EmployeeProjects So far, I have only been able to do: var filteredList = Context.Employees .Where(e => e.EmployeeProjects.Where(ep => ep.Project.Name == "ProjectX")) NOTE: I have updated the syntax of the query after John's post. As you can see, I can only query, the related entity (EmployeeProjects). All I want is being able to filter to Project from the Employee entity. Thanks for any advice.

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  • JPA - Real primary key generated ID for references

    - by Val
    I have ~10 classes, each of them, have composite key, consist of 2-4 values. 1 of the classes is a main one (let's call it "Center") and related to other as one-to-one or one-to-many. Thinking about correct way of describing this in JPA I think I need to describe all the primary keys using @Embedded / @PrimaryKey annotations. Question #1: My concern is - does it mean that on the database level I will have # of additional columns in each table referring to the "Center" equal to number of column in "Center" PK? If yes, is it possible to avoid it by using some artificial unique key for references? Could you please give an idea how real PK and the artificial one needs to be described in this case? Note: The reason why I would like to keep the real PK and not just use the unique id as PK is - my application have some data loading functionality from external data sources and sometimes they may return records which I already have in local database. If unique ID will be used as PK - for new records I won't be able to do data update, since the unique ID will not be available for just downloaded ones. At the same time it is normal case scenario for application and it just need to update of insert new records depends on if the real composite primary key matches. Question #2: All of the 10 classes have common field "date" which I described in an abstract class which each of them extends. The "date" itself is never a key, but it always a part of composite key for each class. Composite key is different for each class. To be able to use this field as a part of PK should I describe it in each class or is there any way to use it as is? I experimented with @Embedded and @PrimaryKey annotations and always got an error that eclipselink can't find field described in an abstract class. Thank you in advance! PS. I'm using latest version of eclipselink & H2 database.

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  • apt-get install kernel source error

    - by MA1
    apt-get source linux-image-$(uname -r) gives me the below error Reading package lists... Done Building dependency tree Reading state information... Done Picking 'linux' as source package instead of 'linux-image-3.0.0-12-generic' NOTICE: 'linux' packaging is maintained in the 'Git' version control system at: http://kernel.ubuntu.com/git-repos/ubuntu/ubuntu-oneiric.git Skipping already downloaded file 'linux_3.0.0-17.30.dsc' Need to get 99.9 MB of source archives. Err http://pk.archive.ubuntu.com/ubuntu/ oneiric-updates/main linux 3.0.0-17.30 (tar) 500 ( The request was rejected by the HTTP filter. Contact your ISA Server administrator. ) Err http://pk.archive.ubuntu.com/ubuntu/ oneiric-updates/main linux 3.0.0-17.30 (diff) 500 ( The request was rejected by the HTTP filter. Contact your ISA Server administrator. ) Failed to fetch http://pk.archive.ubuntu.com/ubuntu/pool/main/l/linux/linux_3.0.0.orig.tar.gz 500 ( The request was rejected by the HTTP filter. Contact your ISA Server administratorThe request was rejected by the HTTP filter. Contact your ISA Server administrator. ) Failed to fetch http://pk.archive.ubuntu.com/ubuntu/pool/main/l/linux/linux_3.0.0-17.30.diff.gz 500 ( The request was rejected by the HTTP filter. Contact your ISA Server administrator. ) E: Failed to fetch some archives. Can someone suggest a solution?

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  • What is your strategy for converting RC builds into retail?

    - by Matthew PK
    We're trying to implement a strategy for how we transition our builds from RC to released retail code. When we label a build as a release candidate, we send it to QA for regression. If they approve it, that RC then becomes our released retail code. I liked the idea of "obvious" labeling of versions so that a user knows whether they have a beta or an RC or retail code... where you would have some obvious watermark in non-retail code (think Windows 7 where the RC or non-genuine builds watermark in the bottom right). ... but it seemed strange to us to manipulate the project (to remove the watermark) once it passed regression. If QA certified version a.b.c.d then our retail code should be that same version, not a.b.c.d+1 what strategies have you employed to clearly label non-release software versions without incrementing your build to disable the watermarks in your retail code? One idea I've considered is writing your build to look for a signed file in the installer archive... non-release code wouldn't include this file and so the app would know to display a watermark. But even this seems like QA is then working with non-release code. Ideas?

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  • Is the "One Description Table to rule them all" approch good?

    - by DavRob60
    Long ago, I worked (as a client) with a software which use a centralized table for it's codified element. Here, as far as I remember, how the table look like : Table_Name (PK) Field_Name (PK) Code (PK) Sort_Order Description So, instead of creating a table every time they need a codified field, they where just adding row in this table with the new Table_Name and Field_Name. I'm sometime tempted to use this pattern in some database I design, but I have resisted to this as from now, I think there's something wrong with this, but I cannot put the finger on it. It is just because you land with some of the structure logic within the Data or something else?

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  • Setting up your project

    - by ssoolsma
    Before any coding we first make sure that the project is setup correctly. (Please note, that this blog is all about how I do it, and incase i forget, i can return here and read how i used to do it. Maybe you come up with some idea’s for yourself too.) In these series we will create a minigolf scoring cart. Please note that we eventually create a fully functional application which you cannot use unless you pay me alot of money! (And i mean alot!)   1. Download and install the appropriate tools. Download the following: - TestDriven.Net (free version on the bottom of the download page) - nUnit TestDriven is a visual studio plugin for many unittest frameworks, which allows you to run  / test code very easily with a right click –> run test. nUnit is the test framework of choice, it works seamless with TestDriven.   2. Create your project Fire up visual studio and create your DataAccess project:  MidgetWidget.DataAccess is it’s name. (I choose MidgetWidget as name for the solution). Also, make sure that the MidgetWidget.DataAccess project is a c# ClassLibary Hit OK to create the solution. (in the above example the checkbox Create directory for solution is checked, because i’m pointing the location to the root of c:\development where i want MidgetWidget to be created.   3. Setup the database. You should have thought about a database when you reach this point. Let’s assume that you’ve created a database as followed: Table name: LoginKey Fields: Id (PK), KeyName (uniqueidentifier), StartDate (datetime), EndDate (datetime) Table name:  Party Fields: Id (PK), Key (uniqueidentifier, Created (datetime) Table name:  Person Fields: Id(PK),  PartyId (int), Name (varchar) Tablename: Score Fields: Id (PK), Trackid (int), PersonId (int), Strokes (int) Tablename: Track Fields: Id (PK), Name (varchar) A few things to take note about the database setup. I’ve singularized all tablenames (not “Persons“ but “Person”. This is because in a few minutes, when this is in our code, we refer to the database objects as single rows. We retrieve a single Person not a single “Persons” from the database.   4. Create the entity framework In your solution tree create a new folder and call it “DataModel”. Inside this folder: Add new item –> and choose ADO.NET Entity Data Model. Name it “Entities.edmx” and hit  “Add”. Once the edmx is added, open it (double click) and right click the white area and choose “Update model from database…". Now, point it to your database (i include sensitive data in the connectionstring) and select all the tables. After that hit “Finish” and let the entity framework do it’s code generation. Et Voila, after a few seconds you have set up your entity model. Next post we will start building the data-access! I’m off to the beach.

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  • Using NHibernate with an EAV data model

    - by devonlazarus
    I'm trying to leverage NH to map to a data model that is a loose interpretation of the EAV/CR data model. I have most of it working but am struggling with mapping the Entity.Attributes collection. Here are the tables in question: -------------------- | Entities | -------------------- | EntityId PK |-| | EntityType | | -------------------- | ------------- | V -------------------- | EntityAttributes | ------------------ --------------------------- -------------------- | Attributes | | StringAttributes | | EntityId PK,FK | ------------------ --------------------------- | AttributeId FK | -> | AttributeId PK | -> | StringAttributeId PK,FK | | AttributeValue | | AttributeType | | AttributeName | -------------------- ------------------ --------------------------- The AttributeValue column is implemented as an sql_variant column and I've implemented an NHibernate.UserTypes.IUserType for it. I can create an EntityAttribute entity and persist it directly so that part of the hierarchy is working. I'm just not sure how to map the EntityAttributes collection to the Entity entity. Note the EntityAttributes table could (and does) contain multiple rows for a given EntityId/AttributeId combination: EntityId AttributeId AttributeValue -------- ----------- -------------- 1 1 Blue 1 1 Green StringAttributes row looks like this for this example: StringAttributeId AttributeName ----------------- -------------- 1 FavoriteColor How can I effectively map this data model to my Entity domain such that Entity.Attributes("FavoriteColors") returns a collection of favorite colors? Typed as System.String?

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