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• Predicting advantages of database denormalization

  - by Janus Troelsen

  I was always taught to strive for the highest Normal Form of database normalization, and we were taught Bernstein's Synthesis algorithm to achieve 3NF. This is all very well and it feels nice to normalize your database, knowing that fields can be modified while retaining consistency. However, performance may suffer. That's why I am wondering whether there is any way to predict the speedup/slowdown when denormalizing. That way, you can build your list of FD's featuring 3NF and then denormalize as little as possible. I imagine that denormalizing too much would waste space and time, because e.g. giant blobs are duplicated or it because harder to maintain consistency because you have to update multiple fields using a transaction. Summary: Given a 3NF FD set, and a set of queries, how do I predict the speedup/slowdown of denormalization? Link to papers appreciated too.

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• How to manage primary key while updating [migrated]

  - by Subin Jacob

  In the following table primaryKeyColumn is primary key. To maintain the data history I always uses the values with WHERE condition(WHERE StatusColumn=1) And will set the StatusColumn to 0 if the data is edited (So that I could keep the previous data). But the problem is, if I update it to 0 , I can't insert the same key to primarykeycolumn since the column validated for primary keys. How can I manage these kind of validations? what the mistake I did in this design? primaryKeyColumn ValueColumn StatusColumn ---------------- ----------- ------------ 2 Name1 1 3 Name2 1 4 Name3 0

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• Design Pattern for Complex Data Modeling

  - by Aaron Hayman

  I'm developing a program that has a SQL database as a backing store. As a very broad description, the program itself allows a user to generate records in any number of user-defined tables and make connections between them. As for specs: Any record generated must be able to be connected to any other record in any other user table (excluding itself...the record, not the table). These "connections" are directional, and the list of connections a record has is user ordered. Moreover, a record must "know" of connections made from it to others as well as connections made to it from others. The connections are kind of the point of this program, so there is a strong possibility that the number of connections made is very high, especially if the user is using the software as intended. A record's field can also include aggregate information from it's connections (like obtaining average, sum, etc) that must be updated on change from another record it's connected to. To conserve memory, only relevant information must be loaded at any one time (can't load the entire database in memory at load and go from there). I cannot assume the backing store is local. Right now it is, but eventually this program will include syncing to a remote db. Neither the user tables, connections or records are known at design time as they are user generated. I've spent a lot of time trying to figure out how to design the backing store and the object model to best fit these specs. In my first design attempt on this, I had one object managing all a table's records and connections. I attempted this first because it kept the memory footprint smaller (records and connections were simple dicts), but maintaining aggregate and link information between tables became....onerous (ie...a huge spaghettified mess). Tracing dependencies using this method almost became impossible. Instead, I've settled on a distributed graph model where each record and connection is 'aware' of what's around it by managing it own data and connections to other records. Doing this increases my memory footprint but also let me create a faulting system so connections/records aren't loaded into memory until they're needed. It's also much easier to code: trace dependencies, eliminate cycling recursive updates, etc. My biggest problem is storing/loading the connections. I'm not happy with any of my current solutions/ideas so I wanted to ask and see if anybody else has any ideas of how this should be structured. Connections are fairly simple. They contain: fromRecordID, fromTableID, fromRecordOrder, toRecordID, toTableID, toRecordOrder. Here's what I've come up with so far: Store all the connections in one big table. If I do this, either I load all connections at once (one big db call) or make a call every time a user table is loaded. The big issue here: the size of the connections table has the potential to be huge, and I'm afraid it would slow things down. Store in separate tables all the outgoing connections for each user table. This is probably the worst idea I've had. Now my connections are 'spread out' over multiple tables (one for each user table), which means I have to make a separate DB called to each table (or make a huge join) just to find all the incoming connections for a particular user table. I've avoided making "one big ass table", but I'm not sure the cost is worth it. Store in separate tables all outgoing AND incoming connections for each user table (using a flag to distinguish between incoming vs outgoing). This is the idea I'm leaning towards, but it will essentially double the total DB storage for all the connections (as each connection will be stored in two tables). It also means I have to make sure connection information is kept in sync in both places. This is obviously not ideal but it does mean that when I load a user table, I only need to load one 'connection' table and have all the information I need. This also presents a separate problem, that of connection object creation. Since each user table has a list of all connections, there are two opportunities for a connection object to be made. However, connections objects (designed to facilitate communication between records) should only be created once. This means I'll have to devise a common caching/factory object to make sure only one connection object is made per connection. Does anybody have any ideas of a better way to do this? Once I've committed to a particular design pattern I'm pretty much stuck with it, so I want to make sure I've come up with the best one possible.

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• Should all foreign table references use foreign key constraints

  - by TecBrat

  Closely related to: Foreign key restrictions -> yes or no? I asked a question on SO and it led me to ask this here. If I'm faced with a choice of having a circular reference or just not enforcing the restraint, which is the better choice? In my particular case I have customers and addresses. I want an address to have a reference to a customer and I want each customer to have a default billing address id and a default shipping address id. I might query for all addresses that have a certain customer ID or I might query for the address with the ID that matches the default shipping or billing address ids. I'm not sure yet how the constraints (or lack of) will effect the system as my application and it's data age.

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• Relationships in a Chen ERD

  - by Nibroc A Rehpotsirhc

  I am working on a Chen ERD to model our organizations merchandise. Our central entity is a Style. We have supplemental entities of Color and Season. I am defining our assortment as the relationship between these three entities, and this relationship itself will have attributes and is defined by the three entities which participate in the mandatory relationship. The rules are; Many Styles can be offered in a Season, and a Style can be offered in many Seasons. Within a Season, a Style can be offered in Many Colors. I then have 2 other entities, one of which I believe is a weak entity, Climate, and the other may be weak, but I am not sure, this being Transaction Channel. I am thinking of these as relationships off of a relationship? Meaning, for a given Style/Color combination offered in a Season, it can be available through 1 or more Transaction Channels. Additionally, within a season, a given Style/Color combination can be intended for 1 or more Climates. Is it valid to have relationships off of relationships? Or does this requirement dictate that I should think of this Style/Color/Season relationship as an entity itself, and define the relationships to Climate and Transaction Channel off of this entity?

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• Why many designs ignore normalization in RDBMS?

  - by Yosi

  I got to see many designs that normalization wasn't the first consideration in decision making phase. In many cases those designs included more than 30 columns, and the main approach was "to put everything in the same place" According to what I remember normalization is one of the first, most important things, so why is it dropped so easily sometimes? Edit: Is it true that good architects and experts choose a denormalized design while non-experienced developers choose the opposite? What are the arguments against starting your design with normalization in mind?

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• SQL language drawbacks, The Third Manifesto

  - by David Portabella

  Sometime ago I read about SQL language drawbacks (the basic language specification, not vendor specific), and one of the drawbacks was that the language does not allow to create a set of tuples that don't come from a table. For instance, SELECT firstName, lastName from people; this creates a set of tuples coming from the table people. Now, if I don't have this table people, and I want to return a constant, I'd need something like this to return a set of two tuples (this would not require to have a table): SELECT VALUES('james', 'dean'), ('tom', 'cruisse'); Why I would need that? Because of the same reasons that we can define constants (not only basic types, but objects and arrays also) in any advanced programming language. Workarounds, Yes, I could create a temporal table, fill the data, and SELECT from that table. This is a hack, to overcome the drawbacks of the poor SQL language. I think that I read about this somewhere in "The Third Manifesto", but I don't find the paragraph/example talking about this concrete drawback anymore. Do you know a reference about it?

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• How can I implement a database TableView like thing in C++?

  - by Industrial-antidepressant

  How can I implement a TableView like thing in C++? I want to emulating a tiny relation database like thing in C++. I have data tables, and I want to transform it somehow, so I need a TableView like class. I want filtering, sorting, freely add and remove items and transforming (ex. view as UPPERCASE and so on). The whole thing is inside a GUI application, so datatables and views are attached to a GUI (or HTML or something). So how can I identify an item in the view? How can I signal it when the table is changed? Is there some design pattern for this? Here is a simple table, and a simple data item: #include <string> #include <boost/multi_index_container.hpp> #include <boost/multi_index/member.hpp> #include <boost/multi_index/ordered_index.hpp> #include <boost/multi_index/random_access_index.hpp> using boost::multi_index_container; using namespace boost::multi_index; struct Data { Data() {} int id; std::string name; }; struct row{}; struct id{}; struct name{}; typedef boost::multi_index_container< Data, indexed_by< random_access<tag<row> >, ordered_unique<tag<id>, member<Data, int, &Data::id> >, ordered_unique<tag<name>, member<Data, std::string, &Data::name> > > > TDataTable; class DataTable { public: typedef Data item_type; typedef TDataTable::value_type value_type; typedef TDataTable::const_reference const_reference; typedef TDataTable::index<row>::type TRowIndex; typedef TDataTable::index<id>::type TIdIndex; typedef TDataTable::index<name>::type TNameIndex; typedef TRowIndex::iterator iterator; DataTable() : row_index(rule_table.get<row>()), id_index(rule_table.get<id>()), name_index(rule_table.get<name>()), row_index_writeable(rule_table.get<row>()) { } TDataTable::const_reference operator[](TDataTable::size_type n) const { return rule_table[n]; } std::pair<iterator,bool> push_back(const value_type& x) { return row_index_writeable.push_back(x); } iterator erase(iterator position) { return row_index_writeable.erase(position); } bool replace(iterator position,const value_type& x) { return row_index_writeable.replace(position, x); } template<typename InputIterator> void rearrange(InputIterator first) { return row_index_writeable.rearrange(first); } void print_table() const; unsigned size() const { return row_index.size(); } TDataTable rule_table; const TRowIndex& row_index; const TIdIndex& id_index; const TNameIndex& name_index; private: TRowIndex& row_index_writeable; }; class DataTableView { DataTableView(const DataTable& source_table) {} // How can I implement this? // I want filtering, sorting, signaling upper GUI layer, and sorting, and ... }; int main() { Data data1; data1.id = 1; data1.name = "name1"; Data data2; data2.id = 2; data2.name = "name2"; DataTable table; table.push_back(data1); DataTable::iterator it1 = table.row_index.iterator_to(table[0]); table.erase(it1); table.push_back(data1); Data new_data(table[0]); new_data.name = "new_name"; table.replace(table.row_index.iterator_to(table[0]), new_data); for (unsigned i = 0; i < table.size(); ++i) std::cout << table[i].name << std::endl; #if 0 // using scenarios: DataTableView table_view(table); table_view.fill_from_source(); // synchronization with source table_view.remove(data_item1); // remove item from view table_view.add(data_item2); // add item from source table table_view.filter(filterfunc); // filtering table_view.sort(sortfunc); // sorting // modifying from source_able, hot to signal the table_view? // FYI: Table view is atteched to a GUI item table.erase(data); table.replace(data); #endif return 0; }

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• when should a database table be broken into multiple tables with relations?

  - by GSto

  I have an application that needs to store client data, and part of that is some data about their employer as well. Assuming that a client can only have one employer, and that the chance of people having identical employer data is slim to none, which schema would make more sense to use? Schema 1 Client Table: ------------------- id int name varchar(255), email varchar(255), address varchar(255), city varchar(255), state char(2), zip varchar(16), employer_name varchar(255), employer_phone varchar(255), employer_address varchar(255), employer_city varchar(255), employer_state char(2), employer_zip varchar(16) **Schema 2** Client Table ------------------ id int name varchar(255), email varchar(255), address varchar(255), city varchar(255), state char(2), zip varchar(16), Employer Table --------------------- id int name varchar(255), phone varchar(255), address varchar(255), city varchar(255), state char(2), zip varchar(16) patient_id int Part of me thinks that since are clearly two different 'objects' in the real world, seperating them out into two different tables makes sense. However, since a client will always have an employer, I'm also not seeing any real benefits to seperating them out, and it would make querying data about clients more complex. Is there any benefit / reason for creating two tables in a situation like this one instead of one?

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• Storing translation data as JSON column

  - by j0ntech

  We're deciding on how to store translations of some descriptions of database items. We could go the traditional way and keep a translations table (and a language table and an object_translation linking table) OR we thought it might be better to just have a Description column that contains JSON like the following: { "EN": "This is the translation in English", "EE" : "See on kirjeldus eesti keeles" } Are there any serious downsides as to why we shouldn't use this? (I haven't seen it being used anywhere else)

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• Type of AI to tackle this problem?

  - by user1154277

  I posted this on stackoverflow but want to get your recommendations as well as a user on overflow recommended I post it here. I'm going to say from the beginning that I am not a programmer, I have a cursory knowledge of different types of AI and am just a businessman building a web app. Anyways, the web app I am investing in to develop is for a hobby of mine. There are many part manufacturers, product manufacturers, upgrade and addon manufacturers etc. for hardware/products in this hobby's industry. Currently, I am in the process of building a crowd sourced platform for people who are knowledgeable to go in and mark up compatibility between those parts as its not always clear cut if they are for example: Manufacturer A makes a "A" class product, and manufacturer B makes upgrade/part that generally goes with class "A" products, but is for one reason or another not compatible with Manufacturer A's particular "A" class product. However, a good chunk (60%-70%) of the products/parts in the database can have their compatibility inferenced by their properties, For example: Part 1 is type "A" with "X" mm receiver and part 2 is also Type "A" with "X" mm interface and thus the two parts are compatible.. or Part 1 is a 8mm gear, thus all bushings of 8mm from any manufacturer is compatible with part 1. Further more, all gears can only have compatibility relationships in the database with bushing and gear boxes, but there can be no meaningful compatibility between a gear and a rail, or receiver since those parts don't interface. Now what I want is an AI to be able to learn from the decisions of the crowdsourced platform community and be able to inference compatibility for new parts/products based on their tagged attributes, what type of part they are etc. What would be the best form of AI to tackle this? I was thinking a Expert System, but explicitly engineering all of the knowledge rules would be daunting because of the complex relations between literally tens of thousands of parts, hundreds of part types and many manufacturers. Would a ANN (neural network) be ideal to learn from the many inputs/decisions of the crowdsource platform users? Any help/input is much appreciated.

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• C# Extend array type to overload operators

  - by Episodex

  I'd like to create my own class extending array of ints. Is that possible? What I need is array of ints that can be added by "+" operator to another array (each element added to each), and compared by "==", so it could (hopefully) be used as a key in dictionary. The thing is I don't want to implement whole IList interface to my new class, but only add those two operators to existing array class. I'm trying to do something like this: class MyArray : Array<int> But it's not working that way obviously ;). Sorry if I'm unclear but I'm searching solution for hours now... UPDATE: I tried something like this: class Zmienne : IEquatable<Zmienne> { public int[] x; public Zmienne(int ilosc) { x = new int[ilosc]; } public override bool Equals(object obj) { if (obj == null || GetType() != obj.GetType()) { return false; } return base.Equals((Zmienne)obj); } public bool Equals(Zmienne drugie) { if (x.Length != drugie.x.Length) return false; else { for (int i = 0; i < x.Length; i++) { if (x[i] != drugie.x[i]) return false; } } return true; } public override int GetHashCode() { int hash = x[0].GetHashCode(); for (int i = 1; i < x.Length; i++) hash = hash ^ x[i].GetHashCode(); return hash; } } Then use it like this: Zmienne tab1 = new Zmienne(2); Zmienne tab2 = new Zmienne(2); tab1.x[0] = 1; tab1.x[1] = 1; tab2.x[0] = 1; tab2.x[1] = 1; if (tab1 == tab2) Console.WriteLine("Works!"); And no effect. I'm not good with interfaces and overriding methods unfortunately :(. As for reason I'm trying to do it. I have some equations like: x1 + x2 = 0.45 x1 + x4 = 0.2 x2 + x4 = 0.11 There are a lot more of them, and I need to for example add first equation to second and search all others to find out if there is any that matches the combination of x'es resulting in that adding. Maybe I'm going in totally wrong direction?

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• 48-bit bitwise operations in Javascript?

  - by randomhelp

  I've been given the task of porting Java's Java.util.Random() to JavaScript, and I've run across a huge performance hit/inaccuracy using bitwise operators in Javascript on sufficiently large numbers. Some cursory research states that "bitwise operators in JavaScript are inherently slow," because internally it appears that JavaScript will cast all of its double values into signed 32-bit integers to do the bitwise operations (see https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Operators/Bitwise_Operators for more on this.) Because of this, I can't do a direct port of the Java random number generator, and I need to get the same numeric results as Java.util.Random(). Writing something like this.next = function(bits) { if (!bits) { bits = 48; } this.seed = (this.seed * 25214903917 + 11) & ((1 << 48) - 1); return this.seed >>> (48 - bits); }; (which is an almost-direct port of the Java.util.Random()) code won't work properly, since Javascript can't do bitwise operations on an integer that size.) I've figured out that I can just make a seedable random number generator in 32-bit space using the Lehmer algorithm, but the trick is that I need to get the same values as I would with Java.util.Random(). What should I do to make a faster, functional port?

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• Why is it called NoSQL?

  - by beef jerky

  I've recently worked with MongoDB and learned about its schemaless design. However, I'm confused with the term NoSQL? Why is it called that? Doesn't it use SQL or SQL-like queries? I've also read from an article that the main difference lies in how data is stored. In the case of MongoDB, it's stored like JSON documents. Is this true? Also, I'm confused why I always see 'NoSQL vs relational databases'. Aren't NoSQL databases relational? I believe documents in MongoDB are still related/linked through some keys (please correct me if I'm wrong). So why is it labeled as non-relational? Thanks in advance!

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• Purpose of overloading operators in C++?

  - by Geo Drawkcab

  What is the main purpose of overloading operators in C++? In the code below, << and >> are overloaded; what is the advantage to doing so? #include <iostream> #include <string> using namespace std; class book { string name,gvari; double cost; int year; public: book(){}; book(string a, string b, double c, int d) { a=name;b=gvari;c=cost;d=year; } ~book() {} double setprice(double a) { return a=cost; } friend ostream& operator <<(ostream& , book&); void printbook(){ cout<<"wignis saxeli "<<name<<endl; cout<<"wignis avtori "<<gvari<<endl; cout<<"girebuleba "<<cost<<endl; cout<<"weli "<<year<<endl; } }; ostream& operator <<(ostream& out, book& a){ out<<"wignis saxeli "<<a.name<<endl; out<<"wignis avtori "<<a.gvari<<endl; out<<"girebuleba "<<a.cost<<endl; out<<"weli "<<a.year<<endl; return out; } class library_card : public book { string nomeri; int raod; public: library_card(){}; library_card( string a, int b){a=nomeri;b=raod;} ~library_card() {}; void printcard(){ cout<<"katalogis nomeri "<<nomeri<<endl; cout<<"gacemis raodenoba "<<raod<<endl; } friend ostream& operator <<(ostream& , library_card&); }; ostream& operator <<(ostream& out, library_card& b) { out<<"katalogis nomeri "<<b.nomeri<<endl; out<<"gacemis raodenoba "<<b.raod<<endl; return out; } int main() { book A("robizon kruno","giorgi",15,1992); library_card B("910CPP",123); A.printbook(); B.printbook(); A.setprice(15); B.printbook(); system("pause"); return 0; }

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• Details of 5GB and 50GB SQL Azure databases have now been released, along with new price points

  - by Eric Nelson

  Like many others signed up to the Windows Azure Platform, I received an email overnight detailing the upcoming database size changes for SQL Azure. I know from our work with early adopters over the last 12 months that the 1GB and 10GB limits were sometimes seen as blockers, especially when migrating existing application to SQL Azure. On June 28th 2010, we will be increasing the size limits: SQL Azure Web Edition database from 1 GB to 5 GB SQL Azure Business Edition database will go from 10 GB to 50 GB Along with these changes comes new price points, including the option to increase in increments of 10GB: Web Edition: Up to 1 GB relational database = $9.99 / month Up to 5 GB relational database = $49.95 / month Business Edition: Up to 10 GB relational database = $99.99 / month Up to 20 GB relational database = $199.98 / month Up to 30 GB relational database = $299.97 / month Up to 40 GB relational database = $399.96 / month Up to 50 GB relational database = $499.95 / month Check out the full SQL Azure pricing. Related Links: http://ukazure.ning.com UK community site Getting started with the Windows Azure Platform

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• Use cases for NoSQL

  - by seengee

  NoSQL has been getting a lot of attention in the industry recently. Really interested in peoples thoughts on the best use-cases for its use over relational database storage. What should trigger a developer into thinking that particular datasets are more suited to a NoSQL solution like Redis/CouchDB/MongoDB/Cassandra etc. Would also be really interested to hear what people have ported from relational db's to NoSQL and what improvements they have seen.

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• VIM: created syntax not showing up?

  - by joxnas

  HI people I recently changed to VIM for coding in C. I'd like to hightlight the operators +-<=& ... etc I searched in google how should i do it, and i found the answer in this website: I was suppose to do something like: syntax match Operadores /[][><()&!|+*={}-]/ hi Operadores guifg=#000000 gui=BOLD Those characters were supposed to appear as black, bold characters. However, that doesn't happen when I open my .C files. However, if I create a newfile, (where there the C syntax doesn't show up), I am able to see the black, bolded operators. How can i correct this situation, and why is this happening (it seams like if my syntax is beeing overwrided by the C syntax). I'm using gvim, and this is my vimrc: colorscheme nicotine set smartindent set number set guifont=Inconsolata\ Medium\ 11 set numberwidth=5 noremap j jzz noremap k kzz Thanks, any help is appreciated. (And dont forget I'm a novice in VIM, and ..sorry for my English)

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• Consistency in placing operator functions

  - by wrongusername

  I have a class like this: class A { ...private functions, variables, etc... public: ...some public functions and variables... A operator * (double); A operator / (double); A operator * (A); ...and lots of other operators } However, I want to also be able to do stuff like 2 * A instead of only being allowed to do A * 2, and so I would need functions like these outside of the class: A operator * (double, A); A operator / (double, A); ...etc... Should I put all these operators outside of the class for consistency, or should I keep half inside and half outside?

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• Are there real world applications where the use of prefix versus postfix operators matters?

  - by Kenneth

  In college it is taught how you can do math problems which use the ++ or -- operators on some variable referenced in the equation such that the result of the equation would yield different results if you switched the operator from postfix to prefix or vice versa. Are there any real world applications of using postfix or prefix operator where it makes a difference as to which you use? It doesn't seem to me (maybe I just don't have enough experience yet in programming) that there really is much use to having the different operators if it only applies in math equations. EDIT: Suggestions so far include: function calls //f(++x) != f(x++) loop comparison //while (++i < MAX) != while (i++ < MAX)

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• Is learning the Caché database hard coming from relational databases and object oriented programming

  - by Edelcom

  I am currently running the local version of Caché on my system in order to determine if I can (and will) take on a new possible project. The current project uses Delphi 7 as a front end calling a Caché dll where the business logic is stored in the database. I have a background of Sqlserver and Firebird (and before Access and Paradox) as databases. I use Delphi 7 for 95% of my Windows development, so I know about object programming. I would like to recieve opinions from persons having used Caché and either SqlServer, Firebird or Oracle and having developed in Delphi (or C++ or C# - an object oriented language). I have read the pro's and con's from other questions, but I am not asking for this, I need input from Caché developers. Thanks in advance.

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• MySQL Relational Database Foreign Key

  - by user623879

  To learn databasing, I am creating a movie database. To associate multiple directors with a movie, I have the following schema: movie(m_ID, ....) m_director(dirID, dirName)//dirID is a autoincrement primary key m_directs(dirID, m_ID) //dirID, m_ID are set as foreign Keys in the mysql database(InnoDB engine) I have a program that connects to the db that needs to add a movie to the database. I can easily add a new entry to the movie table and the m_director table, but I am having trouble adding a entry in the m_directs table. INSERT INTO m_director (dirName) VALUES("Jason Reitman"); INSERT INTO m_directs (dirID, m_ID) VALUES(LAST_INSERT_ID(), "tt0467406"); I am using this sql statement to insert a new director and add the association to the movie. I know the primary key of the movie, but I don't know the dirID, so I use LAST_INSERT_ID() to get the last id of the director just inserted. The problem I am having is that I get the following error: MySql.Data.MySqlClient.MySqlException (0x80004005): Cannot add or update a child row: a foreign key constraint fails (`siteproducts`. `m_directs`, CONSTRAINT `m_directs_ibfk_2` FOREIGN KEY (`dirID`) REFERENCES `m_directs` (`dirID`) ON DELETE CASCADE ON UPDATE CASCADE) Any ideas?

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• Pros/Cons of document based database vs relational database

  - by damian

  I've been trying to see if I can accomplish some requirements with a document based database, in this case CouchDB. Two generic requirements: CRUD of entities with some fields which have unique index on it ecommerce web app like eBay (better description here). And I'm begining to think that a Document-based database isn't the best choice to address these requirements. Furthermore, I can´t imagine a use for a Document based database (maybe my imagination is too little). Can you explain me if I am asking pears to an elm when I try to use a Document based database for this requirements?

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• Overloading the QDataStream << and >> operators for a user-defined type

  - by Alex Wood

  I have a an object I'd like to be able to read and write to/from a QDataStream. The header is as follows: class Compound { public: Compound(QString, QPixmap*, Ui::MainWindow*); void saveCurrentInfo(); void restoreSavedInfo(QGraphicsScene*); void setImage(QPixmap*); QString getName(); private: QString name, homeNotes, addNotes, expText; Ui::MainWindow *gui; QPixmap *image; struct NMRdata { QString hnmrText, cnmrText, hn_nmrText, hn_nmrNucl, notes; int hnmrFreqIndex, cnmrFreqIndex, hn_nmrFreqIndex, hnmrSolvIndex, cnmrSolvIndex, hn_nmrSolvIndex; }*nmr_data; struct IRdata { QString uvConc, lowResMethod, irText, uvText, lowResText, highResText, highResCalc, highResFnd, highResFrmla, notes; int irSolvIndex, uvSolvIndex; }*ir_data; struct PhysicalData { QString mpEdit, bpEdit, mpParensEdit, bpParensEdit, rfEdit, phyText, optAlpha, optConc, elemText, elemFrmla, notes; int phySolvIndex, optSolvIndex; }*physical_data; }; For all intensive purposes, the class just serves as an abstraction for a handful of QStrings and a QPixmap. Ideally, I would be able to write a QList to a QDataStream but I'm not exactly sure how to go about doing this. If operator overloading is a suitable solution, would writing code like friend QDataStream& operator << (QDataStream&,Compound) { ... } be a potential solution? I'm very open to suggestions! Please let me know if any further clarification is needed.

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• relational database: how to design this table

  - by donpal

  I'm a database newbie designing a database. I'll use SO to ask my question because it's easier to ask it on something that you can see already, but it's not the same, it will just help me understand the right approach. As you can see, there are many questions here and each can have many answers. How should I store the answers in a table? Should I store all the answers in the SAME table with a unique id (make it the key) and just a new field for the question id? What if there are 100,000 answers like there is here? Do I still store them in 1 table? What keys should I use to minimize search time when I want to search for the answers of a specific question? The database is both read and write if that makes any difference in this case.

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