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• What are the "Navigation Properties" in this data model for?

  - by d03boy

  I've been wondering how to properly set up many-to-many relationships in ASP.NET MVC 2 using Linq2Sql for quite some time now. I found this blog post that seems to have a similar model layout as mine. If you take a look at the first screenshot showing the data model you can see that each model has "Navigation Properties" at the bottom of it. What exactly is this and why don't my models have them? I have the proper foreign keys put in to place. Most specifically, I am looking at the relationship between the Article and Category models since that is the only many-to-many relationship that I see and that's what I'm trying to model. Obviously I use an intermediary joining table between these two tables but I am having trouble understanding the proper methodology for modeling that relationship and I'm not finding this information anywhere on The Google.

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• Deadlock error in INSERT statement

  - by Gnanam

  We've got a web-based application. There is a time-bound database operation (INSERTs and UPDATEs) in the application which takes more time to complete, hence this particular flow has been changed into Java Thread so it will not wait (block) for the complete database operation to be completed. My problem is, if more than 1 user come across this particular flow, I'm facing the following error thrown by PostgreSQL: org.postgresql.util.PSQLException: ERROR: deadlock detected Detail: Process 13560 waits for ShareLock on transaction 3147316424; blocked by process 13566. Process 13566 waits for ShareLock on transaction 3147316408; blocked by process 13560. Above error is consistently thrown in INSERT statements. Additional Information: 1) I have PRIMARY KEY defined in this table. 2) There are FOREIGN KEY references in this table. 3) Separate database connection is passed to each Java Thread. Technologies Web Server: Tomcat v6.0.10 Java v1.6.0 Servlet Database: PostgreSQL v8.2.3 Connection Management: pgpool II

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• Integrate forum software into existing Zend site

  - by mrbubblesort

  I've searched around and haven't really found anything on this, so maybe someone here has tried this before. My company already has a website built with Zend, and we'd like to add in a forum as well. All I really need is something that will work with postgresql and has foreign language support (particularly Japanese, but if worst comes to worst, I'll just translate it myself). phpBB fits all my needs though. Is it possible to get the two working together? Or is there another forum software that'll work with Zend? Or is it better to just build the thing from scratch? Thanks!

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• mysql medium int vs. int performance?

  - by aviv

  Hi, I have a simple users table, i guess the maximum users i am going to have is 300,000. Currently i am using: CREATE TABLE users ( id INT UNSIGEND AUTOINCEREMENT PRIMARY KEY, .... Of course i have many other tables that the users(id) is a FOREIGN KEY in them. I read that since the id is not going to use the full maximum of INT it is better to use: MEDIUMINT and it will give better performance. Is it true? (I am using mysql on Windows Server 2008) Thanks.

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• Problems with contenttypes when loading a fixture in Django

  - by gerdemb

  I am having trouble loading Django fixtures into my MySQL database because of contenttypes conflicts. First I tried dumping the data from only my app like this: ./manage.py dumpdata escola > fixture.json but I kept getting missing foreign key problems, because my app "escola" uses tables from other applications. I kept adding additional apps until I got to this: ./manage.py dumpdata contenttypes auth escola > fixture.json Now the problem is the following constraint violation when I try to load the data as a test fixture: IntegrityError: (1062, "Duplicate entry 'escola-t23aluno' for key 2") It seems the problem is that Django is trying to dynamically recreate contenttypes with different primary key values that conflict with the primary key values from the fixture. This appears to be the same as bug documented here: http://code.djangoproject.com/ticket/7052 The problem is that the recommended workaround is to dump the contenttypes app which I'm already doing!? What gives? If it makes any difference I do have some custom model permissions as documented here: http://docs.djangoproject.com/en/dev/ref/models/options/#permissions

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• PHP Tag Cloud System

  - by deniz

  Hi, I am implementing a tag cloud system based on this recommendation. (However, I am not using foreign keys) I am allowing up to 25 tags. My question is, how can I handle editing on the items? I have this item adding/editing page: Title: Description: Tags: (example data) computer, book, web, design If someone edits an item details, do I need to delete all the tags from Item2Tag table first, then add the new elements? For instance, someone changed the data to this: Tags: (example data) computer, book, web, newspaper Do I need to delete all the tags from Item2Tag table, and then add these elements? It seems inefficient, but I could find a more efficient way. The other problem is with this way is, if someone edits description but does not change the tags box, I still need to delete all the elements from Item2Tag table and add the same element. I am not an experienced PHP coder, so could you suggest a better way to handle this? (pure PHP/MySQL solution is preferable) Thanks in advance,

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• T-SQL query to check number of existences

  - by abatishchev

  I have next approximate tables structure: accounts: ID INT, owner_id INT, currency_id TINYINT related to clients: ID INT and currency_types: ID TINYINT, name NVARCHAR(25) I need to write a stored procedure to check existence of accounts with specific currency and all others, i.e. client can have accounts in specific currency, some other currencies and both. I have already written this query: SELECT ISNULL(( SELECT 1 WHERE EXISTS ( SELECT 1 FROM [accounts] AS A, [currency_types] AS CT WHERE A.[owner_id] = @client -- sp param AND A.[currency_id] = CT.[ID] AND CT.[name] = N'Ruble' )), 0) AS [ruble], ISNULL(( SELECT 1 WHERE EXISTS ( SELECT A.[ID] FROM [accounts] AS A, [currency_types] AS CT WHERE A.[owner_id] = @client AND A.[currency_id] = CT.[ID] AND CT.[name] != N'Ruble' )), 0) AS [foreign] Is it possible to optimize it? I'm new to (T)SQL, so thanks in advance!

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• ALTER TABLE on dependant column

  - by Sharmi

  I am trying to alter column datatype of a primary key to tinyint from int.This column is a foreign key in other tables.So,I get the following error: Msg 5074, Level 16, State 1, Line 1 The object 'PK_User_tbl' is dependent on column 'appId'. Msg 5074, Level 16, State 1, Line 1 The object 'FK_Details_tbl_User_tbl' is dependent on column 'appId'. Msg 5074, Level 16, State 1, Line 1 The object 'FK_Log_tbl_User_tbl' is dependent on column 'appId'. Msg 4922, Level 16, State 9, Line 1 ALTER TABLE ALTER COLUMN appId failed because one or more objects access this column. Howw should i rectify this?

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• SQL Average Data Based on Distance

  - by jsmith

  I'm pretty new to SQL. I have a database with records based on road/milepoints. My goal is to get an average value every 52.8 ft along the road. My related table has data every 15 ft, this table of course has a foreign key relating it to the primary table. If I wanted to pull out the average value every 52.8 ft, along a given milepost, how would I go about this? Example Data: RecID Begin_MP End_MP 100 0 0.56 RecID MP Value1 Value2 100 0 159 127.7 100 0.003 95.3 115.3 100 0.006 82.3 107 100 0.009 56.5 74.5 100 0.011 58.1 89.1 100 0.014 95.2 78.8 100 0.017 108.9 242.5 100 0.02 71.8 73.3 100 0.023 84.1 80.2 100 0.026 65.5 66.1 100 0.028 122 135.8 100 0.031 99.9 230.7 100 0.034 95.7 111.5 100 0.037 127.3 74.3 100 0.04 140.7 543.1 The first Data is an example of a Road. The second subset of data are the values I need to query out every 52.8 ft. Thank you

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• Creating a customized video using Flash and XML

  - by Aaron Ladage

  The problem: I have to create a Flash video (in CS3) that will query a MySQL database and display that data at certain points in the video. The bigger problem: I'm not a Flash/ActionScript developer, so this is all very foreign to me! I've divided this project into two parts: a.) dynamically generate an XML feed from the data using PHP (using an ID number passed in the URL's query string), and b.) be able to work with it in Flash. I've got the first part working, but am pretty lost in Flash. I can parse the XML, but I'm not sure how to set the data up as variables and attach it to a video's cue points. Can anyone point me in the direction of a good tutorial or offer some advice?

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• Problem with between join for sqlalchemy orm relation.

  - by Gary van der Merwe

  I'm trying to create a relation that has a between join. Here is a shortish example of what I'm trying to do: #!/usr/bin/env python import sqlalchemy as sa from sqlalchemy import orm from sqlalchemy.engine.base import Engine from sqlalchemy.ext.declarative import declarative_base metadata = sa.MetaData() Base = declarative_base(metadata=metadata) engine = sa.create_engine('sqlite:///:memory:') class Network(Base): __tablename__ = "network" id = sa.Column(sa.Integer, primary_key=True) ip_net_addr_db = sa.Column('ip_net_addr', sa.Integer, index=True) ip_broadcast_addr_db = sa.Column('ip_broadcast_addr', sa.Integer, index=True) # This can be determined from the net address and the net mask, but we store # it in the db so that we can join with the address table. ip_net_mask_len = sa.Column(sa.SmallInteger) class Address(Base): __tablename__ = "address" ip_addr_db = sa.Column('ip_addr', sa.Integer, primary_key=True, index=True, unique=True) Network.addresses = orm.relation(Address, primaryjoin=Address.ip_addr_db.between( Network.ip_net_addr_db, Network.ip_broadcast_addr_db), foreign_keys=[Address.ip_addr_db]) metadata.create_all(engine) Session = orm.sessionmaker(bind=engine) Network() I you run this, you get this error: ArgumentError: Could not determine relation direction for primaryjoin condition 'address.ip_addr BETWEEN network.ip_net_addr AND network.ip_broadcast_addr', on relation Network.addresses. Do the columns in 'foreign_keys' represent only the 'foreign' columns in this join condition ? The answer to that question is Yes, but I cant figure out how to tell it that

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• One repository per table or one per functional section?

  - by Ian Roke

  I am using ASP.NET MVC 2 and C# with Entity Framework 4.0 to code against a normalised SQL Server database. A part of my database structure contains a table of entries with foreign keys relating to sub-tables containing drivers, cars, engines, chassis etc. I am following the Nerd Dinner tutorial which sets up a repository for dinners which is fair enough. Do I do one for drivers, one for engines, one for cars and so on or do I do one big one for entries? Which is the best practise for this type of work? I am still new to this method of coding.

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• ACCESS VBA - DAO in VB - problem with creating relations

  - by Justin

  So take the following example: Sub CreateRelation() Dim db As Database Dim rel As Relation Dim fld As Field Set db = CurrentDb Set rel = db.CreateRelation("OrderID", "Orders", "Products") 'refrential integrity rel.Attributes = dbRelationUpdateCascade 'specify the key in the referenced table Set fld = rel.CreateField("OrderID") fld.ForeignName = "OrderID" rel.Fields.Append fld db.Relations.Append rel End Sub I keep getting the error, No unique index found for the referenced field of the primary table. if i include the vb before this sub to create in index on the field, it gives me the error: Index already exists. so i am trying to figure this out. if there are not any primary keys set, will that cause this not to work? i am confused by this, but i really really want to figure this out. So orderID is a FOREIGN KEY in the Products Table please help thanks justin

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• Using the ASP.NET membership provider database with your own database?

  - by Shaharyar

  Hello everybody, We are developing an ASP.NET MVC Application that currently uses it's own databse ApplicationData for the domain models and another one Membership for the user management / membership provider. We do access restrictions using data-annotations in our controllers. [Authorize(Roles = "administrators, managers")] This worked great for simple use cases. As we are scaling our application our customer wants to restrict specific users to access specific areas of our ApplicationData database. Each of our products contains a foreign key referring to the region the product was assembled in. A user story would be: Users in the role NewYorkManagers should only be able to edit / see products that are assembled in New York. We created a placeholder table UserRightsRegions that contains the UserId and the RegionId. How can I link both the ApplicationData and the Membership databases in order to work properly / having cross-database-key-references? (Is something like this even possible?) All help is more than appreciated!

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• How to prevent a dll from being loaded in other apps

  - by dhh

  Hello, currently I develop a C#.Net application in which I'm using a custom control I developed some time ago. I need the dll to be shipped within the new application - but understandably I do not want the dll file to be used for foreign apps. That's why I need the custom dll to be somehow compiled within the new application. Currently the dll is copied into the application directory. Any ideas? Should be trivial imho. Thanks & regards, Daniel

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• After extending the User model in django, how do you create a ModelForm?

  - by mlissner

  I extended the User model in django to include several other variables, such as location, and employer. Now I'm trying to create a form that has the following fields: First name (from User) Last name (from User) Location (from UserProfile, which extends User via a foreign key) Employer (also from UserProfile) I have created a modelform: from django.forms import ModelForm from django.contrib import auth from alert.userHandling.models import UserProfile class ProfileForm(ModelForm): class Meta: # model = auth.models.User # this gives me the User fields model = UserProfile # this gives me the UserProfile fields So, my question is, how can I create a ModelForm that has access to all of the fields, whether they are from the User model or the UserProfile model? Hope this makes sense. I'll be happy to clarify if there are any questions.

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• Global find object references in NHibernate

  - by Miral

  Is it possible to perform a global reversed-find on NHibernate-managed objects? Specifically, I have a persistent class called "Io". There are a huge number of fields across multiple tables which can potentially contain an object of that type. Is there a way (given a specific instance of an Io object), to retrieve a list of objects (of any type) that actually do reference that specific object? (Bonus points if it can identify which specific fields actually contain the reference, but that's not critical.) Since the NHibernate mappings define all the links (and the underlying database has corresponding foreign key links), there ought to be some way to do it.

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• Separating arguments to a function, in locales with comma as decimal marker

  - by Chris Pousset

  In locales, e.g. French, with comma as decimal indicator (where "5,2" means five and two-tenths), how do users separate function arguments from each other? For example, in many programming/scripting languages, I could specify MAX(1.5, X) in a EN-US locale. How do you avoid the ambiguity between the comma as decimal indicator, and as argument separator? In particular, I'm interested in how software that's perceived as user-friendly in the foreign locale does it. Obviously, it's a no-brainer to say, "thou shalt use decimal POINTs", but that's not particularly "friendly".

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• Multiple Tables or Multiple Schema

  - by Yan Cheng CHEOK

  http://stackoverflow.com/questions/1152405/postgresql-is-better-using-multiple-databases-with-1-schema-each-or-1-database I am new in schema concept for PostgreSQL. For the above mentioned scenario, I was wondering Why don't we use a single database (with default schema named public) Why don't we have a single table, to store multiple users row? Other tables which hold users related information, with foreign key point to the user table. Can anyone provide me a real case scenario, which single database, multiple schema will be extremely useful, and can't solve by conventional single database, single schema.

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• What is the proper way to create a recursive entity in the Entity Framework?

  - by Orion Adrian

  I'm currently using VS 2010 RC, and I'm trying to create a model that contains a recursive self-referencing entity. Currently when I import the entity from the model I get an error indicating that the parent property cannot be part of the association because it's set to 'Computed' or 'Identity', though I'm not sure why it does it that way. I've been hand-editing the file to get around that error, but then the model simply doesn't work. What is the proper way to get recursive entities to work in the Entity Framework. CREATE TABLE [dbo].[Appointments]( [AppointmentId] [int] IDENTITY(1,1) NOT NULL, [Description] [nvarchar](1024) NULL, [Start] [datetime] NOT NULL, [End] [datetime] NOT NULL, [Username] [varchar](50) NOT NULL, [RecurrenceRule] [nvarchar](1024) NULL, [RecurrenceState] [varchar](20) NULL, [RecurrenceParentId] [int] NULL, [Annotations] [nvarchar](50) NULL, [Application] [nvarchar](100) NOT NULL, CONSTRAINT [PK_Appointments] PRIMARY KEY CLUSTERED ( [AppointmentId] ASC ) ) GO ALTER TABLE [dbo].[Appointments] WITH CHECK ADD CONSTRAINT [FK_Appointments_ParentAppointments] FOREIGN KEY([RecurrenceParentId]) REFERENCES [dbo].[Appointments] ([AppointmentId]) GO ALTER TABLE [dbo].[Appointments] CHECK CONSTRAINT [FK_Appointments_ParentAppointments] GO

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• Serializing C# objects to DB

  - by Robert Koritnik

  I'm using a DB table with various different entities. This means that I can't have an arbitrary number of fields in it to save all kinds of different entities. I want instead save just the most important fields (dates, reference IDs - kind of foreign key to various other tables, most important text fields etc.) and an additional text field where I'd like to store more complete object data. the most obvious solution would be to use XML strings and store those. The second most obvious choice would be JSON, that usually shorter and probably also faster to serialize/deserialize... And is probably also faster. But is it really? My objects also wouldn't need to be strictly serializable, because JsonSerializer is usually able to serialize anything. Even anonymous objects, that may as well be used here. What would be the most optimal solution to solve this problem?

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• Use of Java constructors in persistent entities

  - by Mr Morgan

  Hello I'm new to JPA and using persistence in Java anyway and I have two questions I can't quite work out: I have generated tags as: @JoinColumn(name = "UserName", referencedColumnName = "UserName") @ManyToOne(optional = false) private User userName; @JoinColumn(name = "DatasetNo", referencedColumnName = "DatasetNo") @ManyToOne(optional = false) private Dataset datasetNo; But in one of the constructors for the class, no reference is made to columns UserName or DatasetNo whereas all other columns in the class are referenced in the constructor. Can anyone tell me why this is? Both columns UserName and DatasetNo are 'foreign keys' on the entity Visualisation which corresponds to a database table of the same name. I can't quite work out the ORM. And when using entity classes, or POJO, is it better to have class variables like: private User userName; Where an instance of a class is specified or simply the key of that class instance like: private String userName; Thanks Mr Morgan.

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• SQL: select random row from table where the ID of the row isn't in another table?

  - by johnrl

  I've been looking at fast ways to select a random row from a table and have found the following site: http://74.125.77.132/search?q=cache:http://jan.kneschke.de/projects/mysql/order-by-rand/&hl=en&strip=1 What I want to do is to select a random url from my table 'urls' that I DON'T have in my other table 'urlinfo'.The query I am using now selects a random url from 'urls' but I need it modified to only return a random url that is NOT in the 'urlinfo' table. Heres the query: SELECT url FROM urls JOIN (SELECT CEIL(RAND() * (SELECT MAX(urlid) FROM urls ) ) AS urlid ) AS r2 USING(urlid); And the two tables: CREATE TABLE urls ( urlid INT NOT NULL AUTO_INCREMENT PRIMARY KEY, url VARCHAR(255) NOT NULL, ) ENGINE=INNODB; CREATE TABLE urlinfo ( urlid INT NOT NULL PRIMARY KEY, urlinfo VARCHAR(10000), FOREIGN KEY (urlid) REFERENCES urls (urlid) ) ENGINE=INNODB;

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• When is referential integrity not appropriate?

  - by Curtis Inderwiesche

  I understand the need to have referential integrity for limiting specific values on entry or possibly preventing them from removal upon a request of deletion. However, I am unclear as to a valid use case which would exclude this mechanism from always being used. I guess this would fall into several sub-questions: When is referential integrity not appropriate? Is it appropriate to have fields containing multiple and/or possibly incomplete subsets of a foreign key's list? Typically, should this be a schema structure design decision or an interface design decision? (Or possibly neither or both) Thoughts?

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• What resources will help me understand the fundamentals of Relational Database Systems.

  - by Rachel

  This are few of the fundamental database questions which has always given me trouble. I have tried using google and wiki but I somehow I miss out on understanding the functionality rather than terminology. If possible would really appreciate if someone can share more insights on this questions using some visual representative examples. What is a key? A candidate key? A primary key? An alternate key? A foreign key? What is an index and how does it help your database? What are the data types available and when to use which ones?

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