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  • ActiveRecord field normalization

    - by Bill
    I feel bad asking this question, as I thought I knew enough about Activerecord to answer this myslef. But such is the way of having SO available ... I'm trying to remove the commas from a field in a model of mine, I want the user to be able to type a number , ie 10,000 and that number be stored in the database as 10000. I was hoping that I could do some model-side normalization to remove the comma. I don't want to depend on the view or controller to properly format my data. I tried ; before_validation :normalize def normalize self['thenumber'] = self['thenumber'].to_s.gsub(',','') end no worky :(

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  • Deploying and hosting scala in the cloud?

    - by TiansHUo
    I am starting a web app considering scalability as one of the top priorities. What would be the benefits of this: cassandra scala lift vs the traditional LAMP on the cloud? Since from what I've read, please correct me, the cloud itself is scalable I have never seen anyone deploy scala on the cloud before. Is it worth the effort to learn the platform? Is it ready for production use?

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  • Model a Zero or One to Many Relationship

    - by John
    How should I model a zero or one to a many relationship in the database? For example, a user record may or may not have a parent. So should my user table have a t_user.parent_id or should I have an associative table called t_user_hierarchy with the columns t_user_hierarchy.parent_id and t_user_hierarchy.user_id?

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  • PostgreSQL: Why does this simple query not use the index?

    - by David
    I have a table t with a column c, which is an int and has a btree index on it. Why does the following query not utilize this index? explain select c from t group by c; The result I get is: HashAggregate (cost=1005817.55..1005817.71 rows=16 width=4) -> Seq Scan on t (cost=0.00..946059.84 rows=23903084 width=4) My understanding of indexes is limited, but I thought such queries were the purpose of indexes.

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

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

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  • 3d model viewer in Flash or Java

    - by Magnetic_dud
    I want to show a box in 3d on my website, and I was thinking to do it in Flash. How I can show a 3d model? I need something very simple, it's a textured cube, no interaction required, just let the user pan and zoom. There is a 3ds viewer in flash or something like that? Java is also ok (but flash is preferred)

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  • De-normalization for the sake of reports - Good or Bad?

    - by Travis
    What are the pros/cons of de-normalizing an enterprise application database because it will make writing reports easier? Pro - designing reports in SSRS will probably be "easier" since no joins will be necessary. Con - developing/maintaining the app to handle de-normalized data will become more difficult due to duplication of data and synchronization. Others?

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  • C# Importing Large Volume of Data from CSV to Database

    - by guazz
    What's the most efficient method to load large volumes of data from CSV (3 million + rows) to a database. The data needs to be formatted(e.g. name column needs to be split into first name and last name, etc.) I need to do this in a efficiently as possible i.e. time constraints I am siding with the option of reading, transforming and loading the data using a C# application row-by-row? Is this ideal, if not, what are my options? Should I use multithreading?

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  • Value Object and View Model Property

    - by William
    I am working on a solution that used DDD for architecture. I have a property in my ViewModel which points to a ValueObject, the view model also implements INotifyPropertyChanged interface. The value of the ValueObject will change as a user enters data on the front end. The problem I am running into is the value object is suppose to be immutable. How can I work around this issue? Thank you in advance.

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  • Do ORMs normally allow circular relations? If so, how would they handle it?

    - by SeanJA
    I was hacking around trying to make a basic orm that has support for the one => one and one => many relationships. I think I succeeded somewhat, but I am curious about how to handle circular relationships. Say you had something like this: user::hasOne('car'); car::hasMany('wheels'); car::property('type'); wheel::hasOne('car'); You could then do this (theoretically): $u = new user(); echo $u->car->wheels[0]->car->wheels[1]->car->wheels[2]->car->wheels[3]->type; #=> "monster truck" Now, I am not sure why you would want to do this. It seems like it wastes a whole pile of memory and time just to get to something that could have been done in a much shorter way. In my small ORM, I now have 4 copies of the wheel class, and 4 copies of the car class in memory, which causes a problem if I update one of them and save it back to the database, the rest get out of date, and could overwrite the changes that were already made. How do other ORMs handle circular references? Do they even allow it? Do they go back up the tree and create a pointer to one of the parents? DO they let the coder shoot themselves in the foot if they are silly enough to go around in circles?

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  • Still Confused About Identifying vs. Non-Identifying Relationships

    - by Jason
    So, I've been reading up on identifying vs. non-identifying relationships in my database design, and a number of the answers on SO seem contradicting to me. Here are the two questions I am looking at: What's the Difference Between Identifying and Non-Identifying Relationships Trouble Deciding on Identifying or Non-Identifying Relationship Looking at the top answers from each question, I appear to get two different ideas of what an identifying relationship is. The first question's response says that an identifying relationship "describes a situation in which the existence of a row in the child table depends on a row in the parent table." An example of this that is given is, "An author can write many books (1-to-n relationship), but a book cannot exist without an author." That makes sense to me. However, when I read the response to question two, I get confused as it says, "if a child identifies its parent, it is an identifying relationship." The answer then goes on to give examples such as SSN (is identifying of a Person), but an address is not (because many people can live at an address). To me, this sounds more like a case of the decision between primary key and non-primary key. My own gut feeling (and additional research on other sites) points to the first question and its response being correct. However, I wanted to verify before I continued forward as I don't want to learn something wrong as I am working to understand database design. Thanks in advance.

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  • Mysql random rows

    - by n00b
    please read the whole question... 90% of you dont seem to do that and some of you only read the title obviously... and if you dont know the solution, dont answer - i wont have to downvote you -.-'' im entertaining the idea of getting random rows directly from mysql. what i found was SELECT * FROM tablename WHERE somefield='something' ORDER BY RAND() LIMIT 5 but even i see how slow that would be.. is the only way to do this doing something like SELECT * FROM tablename WHERE somefield='something' LIMIT RAND(aincrementvalue-5), 1 5 times? or is there a way that i with my little knowlege of databases cant come up with ? (no i dont want random indexes. i hate the idea of them...) @commenters - please first look, then think, then look again, think again and then post. i wont point fingers but i dislike stupid comments and why i think random indexes are a nasty hack ? it doesnt give you random results. it gives you x results from a random index in a predefined order its like a gapless id only in the wrong order if you fetch by 1 row and get true randomness you fall back to my method but with an additional junk field finally the reason the field exists is only to serve as a helper to something that can be done without it with almost same performance (but the quality (randomness) is better), so it is a nasty hack ;) i solved it, look @ my answer... if you think its incorrect please tell me :)

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  • Help needed with Linq To Sql Query

    - by fearofawhackplanet
    I have the concept of valid/ordered transitions. So for example, it's not possible to move to status In progress from status Complete. Current and Next in table StatusTransition are FK (StatusType.Id). The Linq generator has created the following relations: Child Property Name: StatusTransitions1 Parent Property Name: StatusType1 Participating Properties: StatusType.Id -> StatusTransition.Next Child Property Name: StatusTransitions Parent Property Name: StatusType Participating Properties: StatusType.Id -> StatusTransition.Current I'm normally ok with Linq but I'm having difficulty getting the list of valid Next StatusTypes from the Current status. public List<StatusType> GetValidStatusTransitions(int statusId) { // trying to write something like the following // (obviously not correct) return _statusRepository .Where(s => s.Id == statusId) .Next.StatusTypes; }

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  • Entity Framework 4 missing features?

    - by Roger Alsing
    I'm well aware that similair topics have been brought up before e.g. http://stackoverflow.com/questions/1639043/entity-framework-4-vs-nhibernate But instead of arguments like: NHibernate have been around longer and is more mature EF4 is drag n drop and not enterprisy EF4 and LinqToSql are ... I would like to see a more detailed list of features that you consider missing from EF4. Personally, I think the lack of enum support is the biggest drawback of EF4.

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  • Entity Data Model Wizzard not creating tables in EDMX file

    - by Shawn
    I'm trying the database first approach by creating an ADO.NET Entity Data Model using the Wizard with the Adventureworks2012 DB. Testing DB connection works, and the connection string is added to the App.Config. I'm selecting all the tables except the ones marked as (dbo) AWBuildVersion, DatabaseLog, and ErrorLog. When the Wizard finishes the .edmx file is blank, and if I view the file in XML view the EntityContainer is empty. I'm using VS 2010 & .NET Framework 4.0

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  • In partial view: "The model item passed into the dictionary is of type"

    - by Dave
    I lack understanding of some basic MVC concepts, despite all my searching. I created an MVC project in Visual Studio, which contains the partial view _LogOnPartial.shtml. I just want to access information within the view pertaining to the user, to put in a user dropdown menu. When I try to put this at the top of the partial view cshtml page I get the above error: @model MyProject_MVC.Models.UserRepository When I try this I also get an error: @Html.Partial("_LogOnPartial", MyProject_MVC.Models.UserRepository) 'MyProject_MVC.Models.UserRepository' is a 'type', which is not valid in the given context

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  • Java JPA @OneToMany neededs to reciprocate @ManyToOne?

    - by bguiz
    Create Table A ( ID varchar(8), Primary Key(ID) ); Create Table B ( ID varchar(8), A_ID varchar(8), Primary Key(ID), Foreign Key(A_ID) References A(ID) ); Given that I have created two tables using the SQL statements above, and I want to create Entity classes for them, for the class B, I have these member attributes: @Id @Column(name = "ID", nullable = false, length = 8) private String id; @JoinColumn(name = "A_ID", referencedColumnName = "ID", nullable = false) @ManyToOne(optional = false) private A AId; In class A, do I need to reciprocate the many-to-one relationship? @Id @Column(name = "ID", nullable = false, length = 8) private String id; @OneToMany(cascade = CascadeType.ALL, mappedBy = "AId") private List<B> BList; //<-- Is this attribute necessary? Is it a necessary or a good idea to have a reciprocal @OneToMany for the @ManyToOne? If I make the design decision to leave out the @OneToMany annotated attribute now, will come back to bite me further down.

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  • populate CoreData data model from JSON files prior to app start

    - by johannes_d
    I am creating an iPad App that displays data I got from an API in JSON format. My Core Data model has several entities(Countries, Events, Talks, ...). For each entity I have one .json file that contains all instances of the entity and its attributes as well as its relationships. I would like to populate my Core Data data model with these entities before the start of the App (otherwise it takes about 15 minutes for the iPad to create all the instances of the entities from the several JSON files using factory methods). I am currently importing the data into CoreData like this: -(void)fetchDataIntoDocument:(UIManagedDocument *)document { dispatch_queue_t dataQ = dispatch_queue_create("Data import", NULL); dispatch_async(dataQ, ^{ //Fetching data from application bundle NSURL *tedxgroupsurl = [[NSBundle mainBundle] URLForResource:@"contries" withExtension:@"json"]; NSURL *tedxeventsurl = [[NSBundle mainBundle] URLForResource:@"events" withExtension:@"json"]; //converting the JSON files to NSDictionaries NSError *error = nil; NSDictionary *countries = [NSJSONSerialization JSONObjectWithData:[NSData dataWithContentsOfURL:countriesurl] options:kNilOptions error:&error]; countries = [countries objectForKey:@"countries"]; NSDictionary *events = [NSJSONSerialization JSONObjectWithData:[NSData dataWithContentsOfURL:eventsurl] options:kNilOptions error:&error]; events = [events objectForKey:@"events"]; //creating entities using factory methods in NSManagedObject Subclasses (Country / Event) [document.managedObjectContext performBlock:^{ NSLog(@"creating countries"); for (NSDictionary *country in countries) { [Country countryWithCountryInfo:country inManagedObjectContext:document.managedObjectContext]; //creating Country entities } NSLog(@"creating events"); for (NSDictionary *event in events) { [Event eventWithEventInfo:event inManagedObjectContext:document.managedObjectContext]; // creating Event entities } NSLog(@"done creating, saving document"); [document saveToURL:document.fileURL forSaveOperation:UIDocumentSaveForOverwriting completionHandler:NULL]; }]; }); dispatch_release(dataQ); } This combines the different JSON files into one UIManagedDocument which i can then perform fetchRequests on to populate tableViews, mapView, etc. I'm looking for a way to create this document outside my application & add it to the mainBundle. Then I could copy it once to the apps DocumentsDirectory and be able I use it (instead of creating the Document within the app from the original JSON files). Any help is appreciated!

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  • Parent-Child relation while using object data source

    - by Saba
    Hello guys I am experiencing with a class generator I've written, which generates a class for each table in database with each table field as a property and such. Before that, I used to add a typed dataset to the project and add some tables to it. It automatically detected the relationship between tables and when I added a parent table as data source of a datagrid, I could add another datagrid and use the foreing key data member of it's bindingsource to fill it, and when someone moved the focus on parent datagrid, the data in child datagrid would change accordingly. Now that I have my classes, I add an object as data source for my 2 datagrids, but obviously it doesn't detect a parent child relation. But It'd really help if I could have that foreign key relation in my object datasources. Is there any way to have that relation in object datasource?

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  • Hibernate - EhCache - Which region to Cache associations/sets/collections ??

    - by lifeisnotfair
    Hi all, I am a newcomer to hibernate. It would be great if someone could comment over the following query that i have: Say i have a parent class and each parent has multiple children. So the mapping file of parent class would be something like: parent.hbm.xml <hibernate-mapping > <class name="org.demo.parent" table="parent" lazy="true"> <cache usage="read-write" region="org.demo.parent"/> <id name="id" column="id" type="integer" length="10"> <generator class="native"> </generator> </id> <property name="name" column="name" type="string" length="50"/> <set name="children" lazy="true"> <cache usage="read-write" region="org.demo.parent.children" /> <key column="parent_id"/> <one-to-many class="org.demo.children"/> </set> </class> </hibernate-mapping> children.hbm.xml <hibernate-mapping > <class name="org.demo.children" table="children" lazy="true"> <cache usage="read-write" region="org.demo.children"/> <id name="id" column="id" type="integer" length="10"> <generator class="native"> </generator> </id> <property name="name" column="name" type="string" length="50"/> <many-to-one name="parent_id" column="parent_id" type="integer" length="10" not-null="true"/> </class> </hibernate-mapping> So for the set children, should we specify the region org.demo.parent.children where it should cache the association or should we use the cache region of org.demo.children where the children would be getting cached. I am using EHCache as the 2nd level cache provider. I tried to search for the answer to this question but couldnt find any answer in this direction. It makes more sense to use org.demo.children but I dont know in which scenarios one should use a separate cache region for associations/sets/collections as in the above case. Kindly provide your inputs also let me know if I am not clear in my question. Thanks all.

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  • Error(2,7): PLS-00428: an INTO clause is expected in this SELECT statement

    - by omgzor
    I'm trying to create this trigger and getting the following compiler errors: create or replace TRIGGER RESTAR_PLAZAS AFTER INSERT ON PLAN_VUELO BEGIN SELECT F.NRO_VUELO, M.CAPACIDAD, M.CAPACIDAD - COALESCE(( SELECT count(*) FROM PLAN_VUELO P WHERE P.NRO_VUELO = F.NRO_VUELO ), 0) as PLAZAS_DISPONIBLES FROM VUELO F INNER JOIN MODELO M ON M.ID = F.CODIGO_AVION; END RESTAR_PLAZAS; Error(2,7): PL/SQL: SQL Statement ignored Error(8,5): PL/SQL: ORA-00933: SQL command not properly ended Error(8,27): PLS-00103: Encountered the symbol "end-of-file" when expecting one of the following: begin case declare end exception exit for goto if loop mod null pragma raise return select update while with <an identifier> <a double-quoted delimited-identifier> <a bind variable> << close current delete fetch lock insert open rollback savepoint set sql execute commit forall merge pipe Error(2,1): PLS-00428: an INTO clause is expected in this SELECT statement What's wrong with this trigger?

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