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• Should I trust Redis for data integrity?

  - by Jiaji

  In my current project, I have PostgreSQL as my master DB, and Redis as kind of a slave, e.g., when some user adds another as a friend, first the relationship will be stored in PostgreSQL and then a friend list in Redis will be updated. When some user's friend list is requested, it will be pulled out of Redis instead of PostgreSQL. The question is: when I update the friend list in Redis, should I get a fresh copy outof PostgreSQL, and replace the old list in Redis with the new one or should I keep the old list and simply SADD the userid into the list? The latter is of course best for performance, but intuitively the former does a better job in keep the data integrity? And if something like Celery is used, is the second method worth the risk?

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• Choice of programming language for learning data structures and algorithms

  - by bguiz

  Which programming language would you recommend to learn about data structures and algorithms in? Considering the follwing: Personal experience Language features (pointers, OO, etc) Suitability for learning DS & A concepts I ask because there are some books out there that are programming language-agnostic (written from a Mathematical perspective, and use pseudocode). If I learn from one of these I would like to work out the algorithms in a chosen language. Then, there are other books which introduce DS & A concepts with examples in a particular programming laguage - and I would follow these examples as well. Either way, I have to choose a language, and I would like to stick to one throughout. Which one best fits the bill.

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• asp.net Dynamic Data Site with custom own MetaData

  - by loviji

  Hello, I'm searching info about configuring own MetaData in asp.NET Dynamic Site. For example. I have a table in MS Sql Server with structure shown below: CREATE TABLE [dbo].[someTable]( [id] [int] NOT NULL, [pname] [nvarchar](20) NULL, [FullName] [nvarchar](50) NULL, [age] [int] NULL) and I there are 2 Ms Sql tables (I've created), sysTables and sysColumns. sysTables: ID sysTableName TableName TableDescription 1 | someTable |Persons |All Data about Persons in system sysColumns: ID TableName sysColumnName ColumnName ColumnDesc ColumnType MUnit 1 |someTable | sometable_pname| Name | Persona Name(ex. John)| nvarchar(20) | null 2 |someTable | sometable_Fullname| Full Name | Persona Name(ex. John Black)| nvarchar(50) | null 3 |someTable | sometable_age| age | Person age| int | null I want that, in Details/Edit/Insert/List/ListDetails pages use as MetaData sysColumns and sysTableData. Because, for ex. in DetailsPage fullName, it is not beatiful as Full Name . someIdea, is it possible? thanks

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• What would you recommend for a large-scale Java data grid technology: Terracotta, GigaSpaces, Cohere

  - by cliff.meyers

  I've been reading up on so-called "data grid" solutions for the Java platform including Terracotta, GigaSpaces and Coherence. I was wondering if anyone has real-world experience working any of these tools and could share their experience. I'm also really curious to know what scale of deployment people have worked with: are we talking 2-4 node clusters or have you worked with anything significantly larger than that? I'm attracted to Terracotta because of its "drop in" support for Hibernate and Spring, both of which we use heavily. I also like the idea of how it decorates bytecode based on configuration and doesn't require you to program against a "grid API." I'm not aware of any advantages to tools which use the approach of an explicit API but would love to hear about them if they do in fact exist. :) I've also spent time reading about memcached but am more interested in hearing feedback on these three specific solutions. I would be curious to hear how they measure up against memcached in the event someone has used both.

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• Learning Algorithms and Data Structures Fundamentals

  - by valya

  Can you recommend me a book or (better!) a site with many hard problems and exercises about data structures? I'm already answering project Euler questions, but these questions are about interesting, but uncommon algorithms. I hardly used even a simple tree. Maybe there is a site with exercises like: hey, you need to calculate this: ... . Do it using a tree. Now do it using a zipper. Upload your C (Haskell, Lisp, even Pascal or Fortress go) solution. Oh, your solution is so slow! Self-education is very hard then you trying to learn very common, fundamental things. How can I help myself with them without attending to courses or whatever?

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• IN R counting hierarchical data

  - by Alison

  I have a list of counties in each state that received nonattainment status in years 1995-2005. I want to know how many counties in each state each year that received this status. If my data is formatted like this, State1 Country1 YR1 Yr2 Yr3 Yr4... State1 Country2 YR1 Yr2 Yr3 Yr4 State2 County1 Yr1 Yr2..... Each year variable could have a 1 or a zero, since a county may gain or loose this status in a time period. I need to count each year how many counties in each state have nonattainment status (YRx=1), but can't think of how to do it.

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• Core Data table record count

  - by user339633

  I have an entity called Person and it has a relationship called participatingGames, to another entity called GameParticipant. I (apparently) can retrieve the number of matches in the GameParticipant entity using this simple code in the Person object I created from the entity in the model: [self.participatingGames count]; However, I'd just like to retrieve the number of Person records and one might guess the syntax for this is just as simple. I have lots of books including those by Jeff LaMarche, but those sources and what I find around here make me wonder if I need to set up a fetchedResultsController just to know the count of some entity. My background is in SQL, so of course it seems odd that what would take 15 seconds to code in any other environment seems like such a well-guarded secret in Core Data. I'm using iPhone SDK 3.1.4 under OSX 10.5.8 Suggestions?

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• Reverting CoreData data

  - by ndg

  I have an NSTableView which is populated via a CoreData-backed NSArrayController. Users are able to edit any field they choose within the NSTableView. When they select the rows that they have modified and press a button, the data is sent to a third-party webservice. Provided the webservice accepts the updated values, I want to commit those values to my persistent store. If, however, the webservice returns an error (or simply fails to return), I want the edited fields to revert to their original values. To complicate matters, I have a number of other editable controls, backed by CoreData, which do not need to resort to this behaviour. I believe the solution to this problem revolves around the creation of a secondary Managed Object context, which I would use only for values edited within that particularly NSTableView. But I'm confused as to how the two MOC would interact with each other. What's the best solution to this problem?

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• What's the best way to validate EntityFramwork 4.0 classes?

  - by lsb

  Hi! I've done a fair amount of searching but I've yet to find an easy way to validate EntityFramework 4.0 entities passed accross the wire via WCF Data Services. Basically, I want to do something on the client like: Proxy.MyEntities entities = new Proxy.MyEntities( new Uri("http://localhost:2679/Service.svc")); Proxy.Vendor vendor = new Proxy.Vendor(); vendor.Code = "ABC/XYZ"; vendor.Status = "ACTIVE"; // I'd like to do something like the following: vendor.Validate(); entities.AddToVendors(vendor); entities.SaveChanges(); Any help in this regard would be greatly appreciated!

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• What Data structure for Reputation Rules in C# (like stackoverflow)

  - by optician

  I am currently building a system which will have entities that will have scores like reputation etc.. I will have a service that will check for certain rules having been triggered, and will perform certain logic if they are triggered. Previously I have used say an Enum for doing this when I have only had to store an id and a description. public enum ShoppingCratCalculation { PartialCalculation = 1, CompleteCalculation =2 } But in this situation I want to carry more information, such as the modification to reputation, all in one place. I'm essentially asking what data structure would be best suited to storing this information, for each rule in the system. 1. Description = string ("User forgot to write a review") 2. DB id = int (23) 3. Rep score modification = int (-5) Maybe a little class (Rule) with these as properties , and then just a list? Does anyone have any best practice suggestions for this kind of struct?

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• asp.net Dynamic Data Site own MetaData

  - by loviji

  Hello, I'm searching info about configuring own MetaData in asp.NET Dynamic Site. For example. I have a table in MS Sql Server with structure shown below: CREATE TABLE [dbo].[someTable]( [id] [int] NOT NULL, [pname] [nvarchar](20) NULL, [FullName] [nvarchar](50) NULL, [age] [int] NULL) and I have Ms Sql table, sysTables and sysColumns. sysTables: ID sysTableName TableName TableDescription 1 | someTable |Persons |All Data about Persons in system sysColumns ID TableName sysColumnName ColumnName ColumnDesc ColumnType MUnit 1 |someTable | sometable_pname| Name | Persona Name(ex. John)| nvarchar(20) | null 2 |someTable | sometable_Fullname| Full Name | Persona Name(ex. John Black)| nvarchar(50) | null 3 |someTable | sometable_age| age | Person age| int | null

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• implementing feature structures: what data type to use?

  - by Dervin Thunk

  Hello. In simplistic terms, a feature structure is an unordered list of attribute-value pairs. [number:sg, person:3 | _ ], which can be embedded: [cat:np, agr:[number:sg, person:3 | _ ] | _ ], can subindex stuff and share the value [number:[1], person:3 | _ ], where [1] is another feature structure (that is, it allows reentrancy). My question is: what data structure would people think this should be implemented with for later access to values, to perform unification between 2 fts, to "type" them, etc. There is a full book on this, but it's in lisp, which simplifies list handling. So, my choices are: a hash of lists, a list of lists, or a trie. What do people think about this?

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• how to retrieve data in image uri in sd card to read data in byte convertion

  - by narasimha

  hi sir i am implementing upload image click upload button then select into sdcard images i am getting uri File Img = new File(selectedImage.getPath()); System.out.println("2............."+Img); FileInputStream is = null; try { is = new FileInputStream(Img); is.read(buffer); BufferedInputStream bis = new BufferedInputStream(is); Bitmap bm = BitmapFactory.decodeStream(is); bis.close(); is.close(); i got in image uri how can retrieve data in particular image uri in image path above code Img i am new in android then some suggition give me some reply

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• Data truncation when retrieving data from MySQL database with prepared statements

  - by KSiimson

  I have a script that retrieves multiple products using prepared statements. Like putting loops into loops, I have prepared statements in prepared statements - so there is a prepared statement for retrieving all products, a prepared statement to retrieve all images for that product, a prepared statement to get all attributes for that products, and so on. This does not work with one MySQLi instance, so I use multiple MySQLi objects that are opened and closed when needed. It usually works fine, but sometimes, especially when displaying multiple products, some data is truncated. For example - MicoLoans becomes MicoLoa. There was an actual spelling mistake here - now when I changed MicoLoans to MicroLoans, the same page displayed MicroLoa... So the same number of characters was truncated from the end. It is sort of consistent where it appears - for example there can be descriptions for 8 products, and description of 1 product is heavily truncated. When I add 9th product, the short description is still truncated for that same product as before. Any ideas?

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• How to handle concurrency control in dynamic data?

  - by Andrew

  I've been quite impressed with dynamic data and how easy and quick it is to get a simple site up and running. I'm planning on using it for a simple internal HR admin site for registering people's skills/degrees/etc. I've been watching the intro videos at www.asp.net/dynamicdata and one thing they never mention is how to handle concurrency control. It seems that DD does not handle it right out of the box (unless there is some setting I haven't seen) as I manually generated a change conflict exception and the app failed without any user friendly message. Anybody know if DD handles it out of the box? Or do you have to somehow build it into the site?

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• net c# lock statement in data access layer

  - by Pedro Rivera

  I saw a code where they have the data access layer like this: public class CustomerDA{ private static readonly object _sync = new object(); private static readonly CustomerDA _mutex = new CustomerDA(); private CustomerDA(){ } public CustomerDA GetInstance(){ lock(_sync){ return _mutex; } } public DataSet GetCustomers(){ //database SELECT //return a DataSet } public int UpdateCustomer(some parameters){ //update some user } } public class CustomerBO{ public DataSet GetCustomers(){ //some bussiness logic return CustomerDA.GetInstance().GetCustomers(); } } I was using it, but start thinking... "and what if had to build a facebook like application where there are hundreds of thousands of concurrent users? would I be blocking each user from doing his things until the previous user ends his database stuff? and for the Update method, is it useful to LOCK THREADS in the app when database engines already manage concurrency at database server level?" Then I started to think about moving the lock to the GetCustomers and UpdateCustomer methods, but think again: "is it useful at all?"

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• iphone core data loop array and save each

  - by Matt Facer

  I have a core data model with two tables (meal and ingredients). I am trying to save ONE meal with MANY ingredients. I have the code below which loops through an array of ingredients. I'm trying to save it, but I cannot redeclare the "entity" below. How do I do it? I've tried releasing it, but that didn't work! Thanks for any help. for (x=0;x<ingredients;x++) { NSEntityDescription *entity = [NSEntityDescription insertNewObjectForEntityForName:@"Ingredient" inManagedObjectContext:managedObjectContext]; entity.name = @"test"; } (this method does work saving ONE record out of the loop.. so that's not the problem)

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• Whats the proper way of accessing a database through an assembly?

  - by H4mm3rHead

  Hi, I have a ASP.NET MVC application which is build up as an assembly that queries the database and a asp.net frontend that references this assembly and this assembly abstracts the underlying database. This means that my Assembly contains a app.config file that contains the connectionstring to the database (Linq to Sql data model). How do I go about making this more flexible? Should i make a "initialize()" method somewhere in my assembly which takes the connection string from the asp.net mvc application and then that controls which database to use? or how is this done?

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• to-many Core Data fetch request behaves oddly with a new store

  - by Giao

  I have two entities, Department and Person. Department has a to-many relationship to Person. The Person entity has a hireDate property. I'm using the predicate "count(person) = 0 OR none person.hireDate %@" to find Departments without any Persons in them or Departments that haven't hired anyone since a recent date. When the app first starts up (new user experience) and Departments are inserted and no Person have been inserted, the fetch request with this predicate returns nothing. However, if I create insert a new Person entity and delete it, then save the store, the fetch request will return all the Departments. I've found a work around where, I just insert a new Person and delete it, then save the store, the fetch request as I expected it to work. I've found that inserting a new Person and deleting it without saving will not correct the problem. Is this a bug with Core Data or is this a bug with how I've designed my app?

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• Declaring STL Data Structures such as Vector in the .h

  - by sc_ray

  I am trying to declare a private Data Structure such as the Vector in my C++ header file which I want to eventually use within the method implementation of my .cpp. An example would be my header "SomeClass.h" where I have: class SomeClass { private: Vector<T> myVector; public: void AddTtoMyVector(T add); } And in my .cpp which is "SomeClass.cpp", I have the following: #include "SomeClass.h" SomeClass::AddTtoMyVector(T add) { myVector.Push_back(add); } Would the syntax here work? Or is there a different way of declaring and populating such structures?

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• How to manually manage Core Data relationships when deleting

  - by Simon

  I have a Core Data entity, which contains a relationship to another entity. Under certain circumstances, I need to delete the managed objects in the relationship, and at other times no action needs to be taken. I have the Delete Rule on the entity is No Action because of this manual management. The problem I have is, where is the best place to enforce these rules? I cannot see any suitable messages to override on NSManagedObject (something that might notify the object it has been deleted and should clear up its relationships). I would rather not do it higher up in the application logic, because the entity objects can get deleted from array controllers and at different points in the applications, making it necessary to stuff relationship update code at all those levels.

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• Updating/Inserting multiple rows using jQuery and OData (WCF Data Services)

  - by Pieter

  I have three tables, Template, Fields and TemplateFields. TemplateFields holds the selected fields for each template. I need to update TemplateFields when the user is finished selecting the fields. The only way I can see to do this is by deleting all the TemplateFields for that Template and then add them one by one in separate requests. This is really bad because there is not transaction to fall back onto and there will also be MANY requests. Is there a way of adding multiple 'objects' at once using WCF Data Services? I can then use an Interceptor to update the database.

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• How do I query/filter a to-many relationship in Core Data

  - by Kris Bixler

  I have Customer, Event and Address objects in my data model. Both Customer and Address have a one-to-many relationship to Event. I can get the distinct list of addresses for a customer's events for by doing this: NSSet *addressSet = [customer valueForKeyPath:@"events.address"]; For the part of the UI I'm working on now, I need to display the address from the most recent event prior to now that has an address. I'm starting to go down the path of creating a NSFetchRequest, setting it's entity, sort descriptors, predicate and then looping through the results, but it seems like a lot of code. Am I missing some obvious way of filtering/sorting on the "events" relationship of the Customer object or is creating the NSFetchRequest the best solution?

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• Determining Connections between data in a single table

  - by user1689749

  Hi I'm a BA / programmer type doing data analysis on a legacy system. I've been teaching myself SQL to help, but I've appeared to hit upon a problem bigger than my abilities. I have two tables (generalized for simplicity): Table Objects Object_PK Table Components Component_PK Object_FK Component_Type There are 100+ distinct values in Component_Type_Code. Given that any object can have N number of Components, how can I see which Component_Type(s) appear with other Component_Type(s)? For example, the following query tells me what component_types appear with the component_type 'Component_type_1': select component_type_code, count(*) from components where object_fk in ( select object_fk from components where component_type_code = 'component_type_1' ) group by component_type_code I'd like to get a query to show me all connections My apologies for the formatting. Any help is appreciated. I've looked at cube and rollup, but didn't know how to apply to this situtation.

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• Core Data - Relationship to dissimilar entities

  - by carotene

  Suppose I have the following data model: Entity Person Attribute name String Attribute personType String Attribute dailyRecords Entity CarpenterDailyRecord Attribute numberOfNailsHammered Int Attribute picNameOfFinishedCabinet String Entity WindowWasherDailyRecord Attribute nameOfBuildingWashed String Attribute numberOfWindowsWashed Int I would like to establish a to-many relationship between the Person.dailyRecords and 1 of the daily record entities (which changes depending on the person type). Of course, i could create a CarpenterPerson and WindowWasher entity which each points to it's unique daily record structure, but i have to group people together in my app somehow. so if i do a Group Entity: Entity Group Attribute people array i'm still stuck. how do i point to multiple & different Person entities? There must be an obvious answer, it's just i'm so new to all of this. thanks!

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