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  • Is inheritance bad nowadays?

    - by mafutrct
    Personally, I think inheritance is a great tool, that, when applied reasonably, can greatly simplify code. However, I seems to me that many modern tools dislike inheritance. Let's take a simple example: Serialize a class to XML. As soon as inheritance is involved, this can easily turn into a mess. Especially if you're trying to serialize a derived class using the base class serializer. Sure, we can work around that. Something like a KnownType attribute and stuff. Besides being an itch in your code that you have to remember to update every time you add a derived class, that fails, too, if you receive a class from outside your scope that was not known at compile time. (Okay, in some cases you can still work around that, for instance using the NetDataContract serializer in .NET. Surely a certain advancement.) In any case, the basic principle still exists: Serialization and inheritance don't mix well. Considering the huge list of programming strategies that became possible and even common in the past decade, I feel tempted to say that inheritance should be avoided in areas that relate to serialization (in particular remoting and databases). Does that make sense? Or am messing things up? How do you handle inheritance and serialization?

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  • Beginner having difficulty with SQL query

    - by Vulcanizer
    Hi, I've been studying SQL for 2 weeks now and I'm preparing for an SQL test. Anyway I'm trying to do this question: For the table: 1 create table data { 2 id int, 3 n1 int not null, 4 n2 int not null, 5 n3 int not null, 6 n4 int not null, 7 primary key (id) 8 } I need to return the relation with tuples (n1, n2, n3) where all the corresponding values for n4 are 0. The problem asks me to solve it WITHOUT using subqueries(nested selects/views) It also gives me an example table and the expected output from my query: 01 insert into data (id, n1, n2, n3, n4) 02 values (1, 2,4,7,0), 03 (2, 2,4,7,0), 04 (3, 3,6,9,8), 05 (4, 1,1,2,1), 06 (5, 1,1,2,0), 07 (6, 1,1,2,0), 08 (7, 5,3,8,0), 09 (8, 5,3,8,0), 10 (9, 5,3,8,0); expects (2,4,7) (5,3,8) and not (1,1,2) since that has a 1 in n4 in one of the cases. The best I could come up with was: 1 SELECT DISTINCT n1, n2, n3 2 FROM data a, data b 3 WHERE a.ID <> b.ID 4 AND a.n1 = b.n1 5 AND a.n2 = b.n2 6 AND a.n3 = b.n3 7 AND a.n4 = b.n4 8 AND a.n4 = 0 but I found out that also prints (1,1,2) since in the example (1,1,2,0) happens twice from IDs 5 and 6. Any suggestions would be really appreciated.

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  • How to properly design a simple favorites and blocked table?

    - by Nils Riedemann
    Hey, i am currently writing a webapp in rails where users can mark items as favorites and also block them. I came up two ways and wondered which one is more common/better way. 1. Separate join tables Would it be wise to have 2 tables for this? Like: users_favorites - user_id - item_id users_blocked - user_id - item_id 2. single table users_marks (or so) - users_id - item_id - type (["fav", "blk"]) Both ways seem to have advantages. Which one would you use and why?

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  • Oracle export problem

    - by Abhiram
    I use exp username/password@servername owner={ownername} file=backuppath; The parameters given are correct but still not able to connect Below is the error trace: EXP-00056: ORACLE error 12545 encountered ORA-12545: Connect failed because target host or object does not exist EXP-00000: Export terminated unsuccessfully What can be the possible reasons?

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  • NoSQL vs Relational Coding Styles

    - by Chris Henry
    When building objects that make use of data stored in a RDBMS, it's normally pretty clear what you're getting back, as dictated by the tables and columns being queried. However, when dealing with NoSQL, document-based systems, it's less clear what is being retrieved. What are common methods of keeping track of structure in which data is stored?

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  • What is a good OO C++ wrapper for sqlite

    - by Foo42
    I'd like to find a good object oriented C++ (as opposed to C) wrapper for sqlite. What do people recommend? If you have several suggestions please put them in separate replies for voting purposes. Also, please indicate whether you have any experience of the wrapper you are suggesting and how you found it to use.

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  • Static selection and Ruby on Rails objects

    - by Dave
    Hi all- I have a simple problem, but am having trouble wrapping my head around it. I have an video object that should have one or more "genres". This list of genres should be prepopulated and then the user should just select one or more using autocomplete or some such. Here is the question: Is it worth creating a table with genres for the static selection? Or should it just be included in the presentation layer? If there is a static table, how do we name it correctly. I envision something like this class Video < ActiveRecord::Base has_many :genres ... end class Genre < ... belongs_to :video ... end But then we get a table called genre, that basically maps all the selected genres to their parent videos. There would need to be some static table to reference the static genres. Is this the best way to do it? Sorry if this was rambl-y a little stream of conciousness. Thanks!

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  • What's the most simple way to retrieve all data from a table and save it back in .NET 3.5?

    - by zoman
    I have a number of tables containing some basic (business related) mapping data. What's the most simple way to load the data from those tables, then save the modified values back. (all data should be replaced in the tables) An ORM is out of question as I would like to avoid creating domain objects for each table. The actual editing of the data is not an issue. (it is exported into Excel where the data is edited, then the file is uploaded with the modified data) The technology is .NET 3.5 (ASP.NET MVC) and SQL Server 2005. Thanks.

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  • How to get only one record for each duplicate rows of the id in oracle?

    - by Psychocryo
    suppose i have this table: group_id | image | image_id | ----------------------------- 23 blob 1 23 blob 2 23 blob 3 21 blob 4 21 blob 5 25 blob 6 25 blob 7 how to get results of only 1 of each group id? in this case,there may be multiple images for one group id, i just want one result of each group_id i tried distinct but i will only get group_id. max for image also would not work.

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  • I built my rails app with sqlite and without specifying any db field sizes, Is my app now foobared for production?

    - by Tim Santeford
    I've been following a lot of good tutorials on building rails apps but I seem to be missing the whole specifying and validating db field sizes part. I love not needing to have to think about it when roughing out an app (I would have never done this with a PHP or ASP.net app). However, now that I'm ready to go to production, I think I might have done myself a disservice by not specifying field sizes as I went. My production db will be MySQL. What is the best practice here? Do I need to go through all of my migration files and specify sizes, update all the models with validation, and update all my form partial views with input max widths? or am I missing a critical step in my development process?

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  • Simple check for SELECT query empty result

    - by den-javamaniac
    Hi. Can anyone point out how to check if a select query returns non empty result set? For example I have next query: SELECT * FROM service s WHERE s.service_id = ?; Should I do something like next: ISNULL(SELECT * FROM service s WHERE s.service_id = ?) to test if result set is not empty?

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  • How to structure data... Sequential or Hierarchical?

    - by Ryan
    I'm going through the exercise of building a CMS that will organize a lot of the common documents that my employer generates each time we get a new sales order. Each new sales order gets a 5 digit number (12222,12223,122224, etc...) but internally we have applied a hierarchy to these numbers: + 121XX |--01 |--02 + 122XX |--22 |--23 |--24 In my table for sales orders, is it better to use the 5 digital number as an ID and populate up or would it be better to use the hierarchical structure that we use when referring to jobs in regular conversation? The only benefit to not populating sequentially seems to be formatting the data later on in my view, but that doesn't sound like a good enough reason to go through the extra work. Thanks

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  • Mysql - Join matches and non-matches

    - by jwzk
    This is related to my other question: http://stackoverflow.com/questions/2579249/managing-foreign-keys I am trying to join the table of matches and non-matches. So I have a list of interests, a list of users, and a list of user interests. I want the query to return all interests, whether the user has the interest or not (should be null in that case), only where the user = x. Every time I get the query working its only matching interests that the user specifically has, instead of all interests whether they have it or not.

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  • Codeigniter: how to track activity w/o using multiple db rows?

    - by Kevin Brown
    I need to track the completion of tasks for users. I started by having a row called "first_login", "profile_complete", "other_thing_complete", etc... I'd like to combine these all into one row "activity_state". I just don't know how to properly store data in this field, and how to retrieve it. What kind of field should it be, and how should I read/write to it?

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  • New replicaset resident memory is larger than the existing sets

    - by eded
    From the mongodb tutorial of how to resync a set, I wipe all the files in /data/db and restart the mongod process to resync the data. Everything looks ok, I get the same number of documents as the existing two sets(primary and one secondary). However, when I check the memory on MMS. it shows me my new resynced set/mongod process has a different memory status value than the other two. For existing twos using db.serverStatus.mem shows like the following: "mem" : { "bits" : 64, "resident" : 239, "virtual" : 66348, "supported" : true, "mapped" : 32865, "mappedWithJournal" : 65730 } however, the new resynced set shows like: "mem" : { "bits" : 64, "resident" : 1239, "virtual" : 52447, "supported" : true, "mapped" : 25700, "mappedWithJournal" : 51400 } the resynced resident memory is 6-10 times more than the existing ones. I wouder if it is normal because all data comes in suddenly during the resyncing?? and even virtual and mapped value are different too. Can anyone explain?? thanks

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  • What is the most efficient way to store and access images

    - by MT
    I am working on a project which has to store tens and thousands of images on a server and let the users access them. I need the most efficient method to store these images and to retrieve them. Also, I need information about which technology I should opt. I haven't started the project yet. So, I am thinking between PHP w/ CodeIgniter and Ruby on Rails. PS: The site is something similar to Flickr except that the images are uploaded only by the Authors of the content, and not by the users.

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  • Beginner SQL question(s)

    - by unit
    I am two months in to an intro sql course, it's late at night, and I am drawing a blank. I have two tables, one customers, and one orders. I have to increase any customers credit limit by twenty five percent for all customers who have made two or more orders in which each order is more than the amount of 250.00. I get how to UPDATE CreditLimit * 1.25 and Cust with an order 250, but how the hell do I get it to check if they have made two orders over 250? Second question, we are just starting to take subqueries, and I am having a difficult time getting it into my skull. Another question posed by the prof of our class is to increase the credit limit of a customer who has an order that exceeds their credit limit. (Credit limit is on a customers table, order and amount are on an orders table). I then take that customer and UPDATE his CreditLimit +1000. Thanks for any help.

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