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  • Is there a best practice for maintaining history in a database?

    - by Pete
    I don't do database work that often so this is totally unfamiliar territory for me. I have a table with a bunch of records that users can update. However, I now want to keep a history of their changes just in case they want to rollback. Rollback in this case is not the db rollback but more like revert changes two weeks later when they realized that they made a mistake. The distinction being that I can't have a transaction do the job. Is the current practice to use a separate table, or just a flag in the current table? It's a small database, 5 tables each with < 6 columns, < 1000 rows total.

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  • O(log n) algorithm for merging lists and computing rank?

    - by Eternal Learner
    Given two sorted lists, each containing n real numbers, is there a O(log?n) time algorithm to compute the element of rank i (where i coresponds to index in increasing order) in the union of the two lists, assuming the elements of the two lists are distinct? I can think of using a Merge procedure to merge the 2 lists and then find the A[i] element in constant time. But the Merge would take O(n) time. How do we solve it in O(log n) time?

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  • A cross-platform application WPF, ASP.NET, Silverlight, WP7, XAML

    - by J. Lennon
    Considering the fact that all applications will interact with the web project (which will use the cloud or web services).. Is there any way to share my class models between applications? If yes, what is the best way to do it? About sending / receiving data from the Webservice, serialize and deserialize, how can I do this in a simple way without having to manually populate the objects? Any information about this applications would be really helpful!

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  • Too many columns to index - use mySQL Partitions?

    - by Christopher Padfield
    We have an application with a table with 20+ columns that are all searchable. Building indexes for all these columns would make write queries very slow; and any really useful index would often have to be across multiple columns increasing the number of indexes needed. However, for 95% of these searches, only a small subset of those rows need to be searched upon, and quite a small number - say 50,000 rows. So, we have considered using mySQL Partition tables - having a column that is basically isActive which is what we divide the two partitions by. Most search queries would be run with isActive=1. Most queries would then be run against the small 50,000 row partition and be quick without other indexes. Only issue is the rows where isActive=1 is not fixed; i.e. it's not based on the date of the row or anything fixed like that; we will need to update isActive based on use of the data in that row. As I understand it that is no problem though; the data would just be moved from one partition to another during the UPDATE query. We do have a PK on id for the row though; and I am not sure if this is a problem; the manual seemed to suggest the partition had to be based on any primary keys. This would be a huge problem for us because the primary key ID has no basis on whether the row isActive.

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  • Does database affect classes?

    - by satyanarayana
    I had created one class User and UserDAOImpl class for querying DB using class User. As there is one table to be queried, these two classes are sufficient for me. What if there is a case where new fields are to be added to that one table is to be divided into 3 tables( user_info, user_profile and user_address) to store user? As new fields are added, I need to change classes User and UserDAOImpl, it seems these two are not sufficient. It seems database changes affect my classes. In this case, do I need to divide class User into 3 classes as tables are changes? Can any one suggest me how can I solve this without making too many changes?

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  • Instantiating and referencing models in MVC

    - by fig-gnuton
    In MVC, should each model be a globally accessible singleton accessible to any view/controller? Or should the models be singletons that are dependency injected into any component that requires them? Or should a new model instance be created for each component that needs one, in which case events would be used to propagate changes across model instances of the same class?

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  • C#, Generic Lists and Inheritance

    - by Andy
    I have a class called Foo that defines a list of objects of type A: class Foo { List<A> Items = new List<A>(); } I have a class called Bar that can save and load lists of objects of type B: class Bar { void Save(List<B> ComplexItems); List<B> Load(); } B is a child of A. Foo, Bar, A and B are in a library and the user can create children of any of the classes. What I would like to do is something like the following: Foo MyFoo = new Foo(); Bar MyBar = new Bar(); MyFoo.Items = MyBar.Load(); MyBar.Save(MyFoo.Items); Obviously this won't work. Is there a clever way to do this that avoids creating intermediate lists? thanks, Andy

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  • Explaining your system to a client

    - by Sir Graystar
    I'm currently developing a small Database Management System for a local company. How would you go about explaining how the system you have designed to a client? If they are non-technical and have no understanding of programming, how would you go about showing what the system will do and how it will do it? I guess some sort of visual representation of the system but this seems very patronising to me.

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  • Instantiate a javascript module only one time.

    - by Cedric Dugas
    Hey guys, I follow a module pattern where I instantiate components, however, a lot of time a component will only be instantiate one time (example: a comment system for an article). For now I instantiate in the same JS file. but I was wondering if it is the wrong approach? It kind of make no sense to instantiate in the same file and always only once. But at the same time, if this file is in the page I want to have access to my module without instantiate from elsewhere, and IF I need another instance, I just create another from elsewhere... Here is the pattern I follow: ApplicationNamespace.Classname = function() { // constructor function privateFunctionInit() { // private } this.privilegedFunction = function() { // privileged privateFunction(); }; privateFunctionInit() }; ApplicationNamespace.Classname.prototype = { Method: function(){} } var class = new ApplicationNamespace.Classname(); What do you think, wrong approach, or is this good?

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  • Parallelizing L2S Entity Retrieval

    - by MarkB
    Assuming a typical domain entity approach with SQL Server and a dbml/L2S DAL with a logic layer on top of that: In situations where lazy loading is not an option, I have settled on a convention where getting a list of entities does not also get each item's child entities (no loading), but getting a single entity does (eager loading). Since getting a single entity also gets children, it causes a cascading effect in which each child then gets its children too. This sounds bad, but as long as the model is not too deep, I usually don't see performance problems that outweigh the benefits of the ease of use. So if I want to get a list in which each of the items is fully hydrated with children, I combine the GetList and GetItem methods. So I'll get a list and then loop through it getting each item with the full cascade. Even this is generally acceptable in many of the projects I've worked on - but I have recently encountered situations with larger models and/or more data in which it needs to be more efficient. I've found that partitioning the loop and executing it on multiple threads yields excellent results. In my first experiment with a list of 50 items from one particular project, I did 5 threads of 10 items each and got a 3X improvement in time. Of course, the mileage will vary depending on the project but all else being equal this is clearly a big opportunity. However, before I go further, I was wondering what others have done that have already been through this. What are some good approaches to parallelizing this type of thing?

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  • Is Embed Resource a good approach for a read only xml database?

    - by Nasser Hajloo
    I have an open source application (here) This application get a character or a sentence and give some unicode information about it. Iuse Unicode Character Database which provided by Unicode.org this is a XML document (130MB) At first I embed this XML to my DLL but I don't know is it a good approach or no. because DLL size growth just because of this XML document. I can use it like any other resources but usercan see it. What Should I do? What is the best pattern for this? and Why ? TIA

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  • What do you call a generalized (non-GUI-related) "Model-View-Controller" architecture?

    - by dcuccia
    I am currently refactoring code that coordinates multiple hardware components for data acquisition, and feeling a bit like I'm recreating the wheel. In particular, an MVC-like pattern seems to be emerging. Except, this has nothing to do with a GUI and I'm worried that I'm forcing this particular pattern where another might be more appropriate. Here's my scenario: Individual hardware "component" classes obey interface contracts for each hardware type. Previously, component instances were orchestrated by a single monolithic InstrumentController class, which relied heavily on configuration + branching logic for executing a specific acquisition sequence. After an iteration, I have a separate controller for each component, with these controllers all managed by a small InstrumentControllerBase (or its derivatives). The composite system will receive "input" either programmatically or via inter-hardware component triggering - in either case these interactions are routed to, and handled by, the appropriate controller. So, I have something that feels MVC-esque, but I don't know if that's because I'm forcing the point. With little direct MVC experience in application development, it's hard to know if I'm just trying to make my scenario fit MVC, where another pattern might be a good alternative or complimentary. My problem is, search results and wiki documentation of these family of patterns seems to immediately drop me into GUI-specific discussions. I understand "M means Model data and the V means View" - but do you call the superset pattern? Component-Commander-Controller? Whence can I exhume examples exemplary?

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  • Entities used to serialize data have changed. How can the serialized data be upgraded for the new entities?

    - by i8abug
    Hi, I have a bunch of simple entity instances that I have serialized to a file. In the future, I know that the structure of these entities (ie, maybe I will rename Name to Header or something). The thing is, I don't want to lose the data that I have saved in all these old files. What is the proper way to either load the data from the old entities into new entities upgrade the old files so that they can be used with new entities Note: I think I am stuck with binary serialization, not xml serialization. Thanks in advance! Edit: So I have an answer for the case I have described. I can use a dataContractSerializer and do something like [DataMember("bar")] private string foo; and change the name in the code and keep the same name that was used for serialization. But what about the following additional cases: The original entity has new members which can be serialized Some serialized members that were in the original entity are removed Some members have actually changed in function (suppose that the original class had a FirstName and LastName member and it has been refactored to have only a FullName member which combines the two) To handle these, I need some sort of interpreter/translator deserialization class but I have no idea what I should use

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  • Creating DB views in Ruby on Rails

    - by Zigu
    Hey guys, I'm building a "reports" functionality to a project. 3 roles here: 1) Volunteers (they report what hours they volunteered) 2) Supervisors (they look at the reported stuff, note: one supervisor can view all projects) 3) Projects (Represents a work project that some collection of volunteers work on) To explain what it does: A report will be specified by the supervisor to generate based on a query of what he needs. These could be plausible reports: 1) The total number of volunteers, and the total amount of volunteer hours on this project 2) All the volunteer's names and emails associated with a project 3) The number of active projects vs. the total number of projects I was thinking maybe that creating a view in rails and storing the name of that view so Rails will just check the view whenever a supervisor wants to pull up the "report". Is a view really the answer or is it better to just save a query? Can Rails do this or is there an even better or more simple way of achieving this functionality? Cheers, -Jeremiah Tantongco

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  • Decorator that can take both init args and call args?

    - by digitala
    Is it possible to create a decorator which can be __init__'d with a set of arguments, then later have methods called with other arguments? For instance: from foo import MyDecorator bar = MyDecorator(debug=True) @bar.myfunc(a=100) def spam(): pass @bar.myotherfunc(x=False) def eggs(): pass If this is possible, can you provide a working example?

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  • Many tables for many users?

    - by Seagull
    I am new to web programming, so excuse the ignorance... ;-) I have a web application that in many ways can be considered to be a multi-tenant environment. By this I mean that each user of the application gets their own 'custom' environment, with absolutely no interaction between those users. So far I have built the web application as a 'single user' environment. In other words, I haven't actually done anything to support multi-users, but only worked on the functionality I want from the app. Here is my problem... What's the best way to build a multi-user environment: All users point to the same 'core' backend. In other words, I build the logic to separate users via appropriate SQL queries (eg. select * from table where user='123' and attribute='456'). Each user points to a unique tablespace, which is built separately as they join the system. In this case I would simply generate ALL the relevant SQL tables per user, with some sort of suffix for the user. (eg. now a query would look like 'select * from table_ where attribute ='456'). In short, it's a difference between "select * from table where USER=" and "select * from table_USER".

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  • Change object on client side or on server side

    - by Polina Feterman
    I'm not sure what is the best practice. I have some big and complex objects (NOT flat). In that object I have many related objects - for example Invoice is the main class and one of it's properties is invoiceSupervisor - a big class by it's own called User. User can also be not flat and have department property - also an object called Department. For example I want create new Invoice. First way: I can present to client several fields to fill in. Some of them will be combos that I will need to fill with available values. For example available invoiceSupervisors. Then all the chosen values I can send to server and on server I can create new Invoice and assign all chosen values to that new Invoice. Then I will need to assign new supervisor I will pull the chosen User by id that user picked up on server from combobox. I might do some verification on the User such as does the user applicable to be invoice supervisor. Then I will assign the User object to invoiceSupervisor. Then after filling all properties I will save the new invoice. Second way: In the beginning I can call to server to get a new Invoice. Then on client I can fill all chosen values , for example I can call to server to get new User object and then fill it's id from combobox and assign the User as invoiceSupervisor. After filling the Invoice object on client I can send it to server and then the server will save the new invoice. Before saving server can run some validations as well. So what is the best approach - to make the object on client and send it to server or to collect all values from client and to make a new object on server using those values ?

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  • How to represent a 3-way relation with JPA?

    - by simpatico
    A user may have several labels, and links. Then, a user associates a label (or more) to a link. How does one represent the later relationship? A solution could be a many-to-many relationship btw user and link with the optional attribute label. http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany#Mapping_a_Join_Table_with_Additional_Columns In this case the relationship btw user and label may better be 'virtual'. Any alternative I'm not seeing? PS: I've used google bookmarks terminology, as it matches my case quite well.

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  • Foreign keys and NULL in mySQL

    - by Industrial
    Hi everyone, Can I have a column in my values table (value) referenced as a foreign key to knownValues table, and let it be NULL whenever needed, like in the example: Table: values product type value freevalue 0 1 NULL 100 1 2 NULL 25 3 3 1 NULL Table: types id name prefix 0 length cm 1 weight kg 2 fruit NULL Table: knownValues id Type name 0 2 banana Note: The types in the table values & knownValues are of course referenced into the types table. Thanks!

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  • Entering large amounts of text data in HTML form

    - by MakkyNZ
    Hi I have a web page that has a requirement to allow users to paste large amounts of text data from an Excel spreadsheet directly into the input controls of the page. Typically the user would be pasting anywhere between 150 to 300 spreadsheet cells that are all in one column. What are some good ways i could use to capture this data on the web page? thanks

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  • When/Why to use Cascading in SQL Server?

    - by Joel Coehoorn
    When setting up foreign keys in SQL Server, under what circumstances should you have it cascade on delete or update, and what is the reasoning behind it? This probably applies to other databases as well. I'm looking most of all for concrete examples of each scenario, preferably from someone who has used them successfully.

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  • Storing information for drop-down menus

    - by Mark
    Suppose you're building an HTML form and you want to have 2 or more drop-down menus, where after picking an option from the first, the 2nd menu is populated, and so forth. For example, choosing a country would bring up a list of provinces for that country, which would in turn list the cities. How would you store that sort of information in a database? Would you have a table Countries(id, name), Provinces(id, country_id, name), Cities(id, province_id, name) or would you have just one big denormalized table Entries(country, province, city)? (Why?)

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