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• Which is a better design pattern for a database wrapper: Save as you go or Save when your done?

  - by izuriel

  I know this is probably a bad way to ask this question. I was unable to find another question that addressed this. The full question is this: We're producing a wrapper for a database and have two different viewpoints on managing data with the wrapper. The first is that all changes made to a data object in code must be persisted in the database by calling a "save" method to actually save the changes. The other side is that these changes should be save as they are made, so if I change a property it's saved, I change another it's save as well. What are the pros/cons of either choice and which is the "proper" way to manage the data?

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• Requring static class setter to be called before constructor, bad design?

  - by roverred

  I have a class, say Foo, and every instance of Foo will need and contain the same List object, myList. Since every class instance will share the same List Object, I thought it would be good to make myList static and use a static function to set myList before the constructor is called. I was wondering if this was bad, because this requires the setter to be called before the constructor? If the person doesn't, the program will crash. Alternative way would be passing myList every time.

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• Advice on database design / SQL for retrieving data with chronological order

  - by Remnant

  I am creating a database that will help keep track of which employees have been on a certain training course. I would like to get some guidance on the best way to design the database. Specifically, each employee must attend the training course each year and my database needs to keep a history of all the dates on which they have attend the course in the past. The end user will use the software as a planning tool to help them book future course dates for employees. When they select a given employee they will see: (a) Last attendance date (b) Projected future attendance date(i.e. last attendance date + 1 calendar year) In terms of my database, any given employee may have multiple past course attendance dates: EmpName AttandanceDate Joe Bloggs 1st Jan 2007 Joe Bloggs 4th Jan 2008 Joe Bloggs 3rd Jan 2009 Joe Bloggs 8th Jan 2010 My question is what is the best way to set up the database to make it easy to retrieve the most recent course attendance date? In the example above, the most recent would be 8th Jan 2010. Is there a good way to use SQL to sort by date and pick the MAX date? My other idea was to add a column called ‘MostRecent’ and just set this to TRUE. EmpName AttandanceDate MostRecent Joe Bloggs 1st Jan 2007 False Joe Bloggs 4th Jan 2008 False Joe Bloggs 3rd Jan 2009 False Joe Bloggs 8th Jan 2010 True I wondered if this would simplify the SQL i.e. SELECT Joe Bloggs WHERE MostRecent = ‘TRUE’ Also, when the user updates a given employee’s attendance record (i.e. with latest attendance date) I could use SQL to: Search for the employee and set the MostRecent value to FALSE Add a new record with MostRecent set to TRUE? Would anybody recommended either method over the other? Or do you have a completely different way of solving this problem?

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• Is this an acceptable UI design decision?

  - by DVK

  OK, while I'm on record as stating that StackExchange UI is pretty much one of the best websites and overall GUIs that I have ever seen as far as usability goes, there's one particular aspect of the trilogy that bugs me. For an example, head on to http://meta.stackoverflow.com . Look at the banner on top (the one that says "reminder -- it's April Fool's Day depending on your time zone!"). Personally, I feel that this is a "make the user do the figuring out work" anti-pattern (whatever it's officially called) - namely, instead of making your app smart enough to only present a certain mode of operations in the conditions when that mode is appropriate, you simply turn on the mode full on and put an explanation to the user of why the mode is on when it should not be (in this particular example, the mode is of course displaying the unicorn gravatars starting with 00:00 in the first timezone, despite the fact that some users still live in March 31st). The Great Recalc was also handled the same way - instead of proactively telling the user "your rep was changed from X to Y" the same nearly invisible banner was displayed on meta. So, the questions are: Is there such an official anti-pattern, and if so,m what the heck do i call it? Do you have any other well-known examples of such design anti-pattern? How would you fix either the SO example I made or you your own example? Is there a pattern of fixing or must it be a case-by-case solution?

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• Object oriented design suggestion

  - by pocoa

  Here is my code: class Soldier { public: Soldier(const string &name, const Gun &gun); string getName(); private: Gun gun; string name; }; class Gun { public: void fire(); void load(int bullets); int getBullets(); private: int bullets; } I need to call all the member functiosn of Gun over a Soldier object. Something like: soldier.gun.fire(); or soldier.getGun().load(15); So which one is a better design? Hiding the gun object as a private member and access it with getGun() function. Or making it a public member? Or I can encapsulate all these functions would make the implementation harder: soldier.loadGun(15); // calls Gun.load() soldier.fire(); // calls Gun.fire() So which one do you think is the best?

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• Autocomplete or Select box? (design problem)

  - by Craig Whitley

  I'm working on a comparison website, so needless to say the search function is the primary feature of the site. I have two input text boxes and a search button. At the moment, the input text boxes use Ajax to query the database and show a drop-down box, but I'm wondering if it would be more intuitive to use a select box instead? The second box is dependant on the first, as when the first is selected theres another ajax query so only the available options for the first selection appear in the autocomplete box. Autocomplete Pros: - "Feels" right? - Looks more appealing than a select box (css design)? Cons: - the user has to be instructed on how to use the search (made to think?) - Only really works off the bat with javascript enabled. - The user may get confused if they type in what they want and no box appears (i.e., no results) Select Box Pros: - Can bring up the list of options / know whats there from the outset. - We use select boxes every day (locations etc.) so we're used to how they work. (more intuitive?) Cons: - Can look a little unaesthetic when theres too many options to choose from. I'm thinking maybe at most around 100 options for my site over time. Any thoughts on how I could go about this would be appreciated!

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• Progress Bar design patterns?

  - by shoosh

  The application I'm writing performs a length algorithm which usually takes a few minutes to finish. During this time I'd like to show the user a progress bar which indicates how much of the algorithm is done as precisely as possible. The algorithm is divided into several steps, each with its own typical timing. For instance- initialization (500 milli-sec) reading inputs (5 sec) step 1 (30 sec) step 2 (3 minutes) writing outputs (7 sec) shutting down (10 milli-sec) Each step can report its progress quite easily by setting the range its working on, say [0 to 150] and then reporting the value it completed in its main loop. What I currently have set up is a scheme of nested progress monitors which form a sort of implicit tree of progress reporting. All progress monitors inherit from an interface IProgressMonitor: class IProgressMonitor { public: void setRange(int from, int to) = 0; void setValue(int v) = 0; }; The root of the tree is the ProgressMonitor which is connected to the actual GUI interface: class GUIBarProgressMonitor : public IProgressMonitor { GUIBarProgressMonitor(ProgressBarWidget *); }; Any other node in the tree are monitors which take control of a piece of the parent progress: class SubProgressMonitor : public IProgressMonitor { SubProgressMonitor(IProgressMonitor *parent, int parentFrom, int parentLength) ... }; A SubProgressMonitor takes control of the range [parentFrom, parentFrom+parentLength] of its parent. With this scheme I am able to statically divide the top level progress according to the expected relative portion of each step in the global timing. Each step can then be further subdivided into pieces etc' The main disadvantage of this is that the division is static and it gets painful to make changes according to variables which are discovered at run time. So the question: are there any known design patterns for progress monitoring which solve this issue?

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• Design/Architecture Advice Needed

  - by Rachel

  Summary: I have different components on homepage and each components shows some promotion to the user. I have Cart as one Component and depending upon content of the cart promotion are show. I have to track user online activities and send that information to Omniture for Report Generation. Now my components are loaded asynchronously basically are loaded when AjaxRequest is fired up and so there is not fix pattern or rather information on when components will appear on the webpages. Now in order to pass information to Omniture I need to call track function on $(document).(ready) and append information for each components(7 parameters are required by Omniture for each component). So in the init:config function of each component am calling Omniture and passing paramters but now no. of Omniture calls is directly proportional to no. of Components on the webpage but this is not acceptable as each call to Omniture is very expensive. Now I am looking for a way where in I can club the information about 7 parameters and than make one Call to Omniture wherein I pass those information. Points to note is that I do not know when the components are loaded and so there is no pre-defined time or no. of components that would be loaded. The thing is am calling track function when document is ready but components are loaded after call to Omniture has been made and so my question is Q: How can I collect the information for all the components and than just make one call to Omniture to send those information ? As mentioned, I do not know when the components are loaded as they are done on the Ajax Request. Hope I am able to explain my challenge and would appreciate if some one can provide from Design/Architect Solutions for the Challenge.

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• DDD principlers and ASP.NET MVC project design

  - by kaivalya

  Two part questions I have a product aggregate that has; Prices PackagingOptions ProductDescriptions ProductImages etc I have modeled one product repository and did not create individual repositories for any of the child classes. All db operations are handled through product repository. Am I understanding the DDD concept correctly so far? Sometimes the question comes to my mind that having a repository for lets say packaging options could make my life easier by directly fetching a the packaging option from the DB by using its ID instead of asking the product repository to find it in its PackagingOptions collection and give it to me.. Second part is managing the edit create operations using ASP.MVC frame work I am currently trying to manage all add edit remove of these child collections of product through product controller(sound right?). One challenge I am now facing is; If I edit a specific packaging option of product through mydomain/product/editpackagingoption/10 I have access to the id of the packaging option But I don't have the ID of the product it self and this forces me to write a query to first find the product that has this specific packaging option then edit that product and the revelant packaging option. I can do this as all packaging option have their unique ID but this would fail if I have collections that don't have unique ID. That feels very wrong.. The next option I thought of is sending both the product and packaging option IDs on the url like; mydomain/product/editpackagingoption/3/10 But I am not sure if that is a good design either. So I am at a point that I am a bit confused. might be having fundamental misunderstandings around all of this... I would appreciate if you bear with the long question and help me put this together. thanks!

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• Mutability design patterns in Objective C and C++

  - by Mac

  Having recently done some development for iPhone, I've come to notice an interesting design pattern used a lot in the iPhone SDK, regarding object mutability. It seems the typical approach there is to define an immutable class NSFoo, and then derive from it a mutable descendant NSMutableFoo. Generally, the NSFoo class defines data members, getters and read-only operations, and the derived NSMutableFoo adds on setters and mutating operations. Being more familiar with C++, I couldn't help but notice that this seems to be a complete opposite to what I'd do when writing the same code in C++. While you certainly could take that approach, it seems to me that a more concise approach is to create a single Foo class, mark getters and read-only operations as const functions, and also implement the mutable operations and setters in the same class. You would then end up with a mutable class, but the types Foo const*, Foo const& etc all are effectively the immutable equivalent. I guess my question is, does my take on the situation make sense? I understand why Objective-C does things differently, but are there any advantages to the two-class approach in C++ that I've missed? Or am I missing the point entirely? Not an overly serious question - more for my own curiosity than anything else.

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• C# Static constructors design problem - need to specify parameter

  - by Neil Dobson

  I have a re-occurring design problem with certain classes which require one-off initialization with a parameter such as the name of an external resource such as a config file. For example, I have a corelib project which provides application-wide logging, configuration and general helper methods. This object could use a static constructor to initialize itself but it need access to a config file which it can't find itself. I can see a couple of solutions, but both of these don't seem quite right: 1) Use a constructor with a parameter. But then each object which requires corelib functionality should also know the name of the config file, so this has to be passed around the application. Also if I implemented corelib as a singleton I would also have to pass the config file as a parameter to the GetInstance method, which I believe is also not right. 2) Create a static property or method to pass through the config file or other external parameter. I have sort of used the latter method and created a Load method which initializes an inner class which it passes through the config file in the constructor. Then this inner class is exposed through a public property MyCoreLib. public static class CoreLib { private static MyCoreLib myCoreLib; public static void Load(string configFile) { myCoreLib = new MyCoreLib(configFile); } public static MyCoreLib MyCoreLib { get { return myCoreLib; } } public class MyCoreLib { private string configFile; public MyCoreLib(string configFile) { this.configFile = configFile; } public void DoSomething() { } } } I'm still not happy though. The inner class is not initialized until you call the load method, so that needs to be considered anywhere the MyCoreLib is accessed. Also there is nothing to stop someone calling the load method again. Any other patterns or ideas how to accomplish this?

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• Database warehouse design: fact tables and dimension tables

  - by morpheous

  I am building a poor man's data warehouse using a RDBMS. I have identified the key 'attributes' to be recorded as: sex (true/false) demographic classification (A, B, C etc) place of birth date of birth weight (recorded daily): The fact that is being recorded My requirements are to be able to run 'OLAP' queries that allow me to: 'slice and dice' 'drill up/down' the data and generally, be able to view the data from different perspectives After reading up on this topic area, the general consensus seems to be that this is best implemented using dimension tables rather than normalized tables. Assuming that this assertion is true (i.e. the solution is best implemented using fact and dimension tables), I would like to seek some help in the design of these tables. 'Natural' (or obvious) dimensions are: Date dimension Geographical location Which have hierarchical attributes. However, I am struggling with how to model the following fields: sex (true/false) demographic classification (A, B, C etc) The reason I am struggling with these fields is that: They have no obvious hierarchical attributes which will aid aggregation (AFAIA) - which suggest they should be in a fact table They are mostly static or very rarely change - which suggests they should be in a dimension table. Maybe the heuristic I am using above is too crude? I will give some examples on the type of analysis I would like to carryout on the data warehouse - hopefully that will clarify things further. I would like to aggregate and analyze the data by sex and demographic classification - e.g. answer questions like: How does male and female weights compare across different demographic classifications? Which demographic classification (male AND female), show the most increase in weight this quarter. etc. Can anyone clarify whether sex and demographic classification are part of the fact table, or whether they are (as I suspect) dimension tables.? Also assuming they are dimension tables, could someone elaborate on the table structures (i.e. the fields)? The 'obvious' schema: CREATE TABLE sex_type (is_male int); CREATE TABLE demographic_category (id int, name varchar(4)); may not be the correct one.

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• C++ design question on traversing binary trees

  - by user231536

  I have a binary tree T which I would like to copy to another tree. Suppose I have a visit method that gets evaluated at every node: struct visit { virtual void operator() (node* n)=0; }; and I have a visitor algorithm void visitor(node* t, visit& v) { //do a preorder traversal using stack or recursion if (!t) return; v(t); visitor(t->left, v); visitor(t->right, v); } I have 2 questions: I settled on using the functor based approach because I see that boost graph does this (vertex visitors). Also I tend to repeat the same code to traverse the tree and do different things at each node. Is this a good design to get rid of duplicated code? What other alternative designs are there? How do I use this to create a new binary tree from an existing one? I can keep a stack on the visit functor if I want, but it gets tied to the algorithm in visitor. How would I incorporate postorder traversals here ? Another functor class?

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• SQL Server 2005 database design - many-to-many relationships with hierarchy

  - by Remnant

  Note I have completely re-written my original post to better explain the issue I am trying to understand. I have tried to generalise the problem as much as possible. Also, my thanks to the original people who responded. Hopefully this post makes things a little clearer. Context In short, I am struggling to understand the best way to design a small scale database to handle (what I perceive to be) multiple many-to-many relationships. Imagine the following scenario for a company organisational structure: Textile Division Marketing Division | | ---------------------- ---------------------- | | | | HR Dept Finance Dept HR Dept Finance Dept | | | | ---------- ---------- ---------- --------- | | | | | | | | Payroll Hiring Audit Tax Payroll Hiring Audit Accounts | | | | | | | | Emps Emps Emps Emps Emps Emps Emps Emps NB: Emps denotes a list of employess that work in that area When I first started with this issue I made four separate tables: Divisions - Textile, Marketing (PK = DivisionID) Departments - HR, Finance (PK = DeptID) Functions - Payroll, Hiring, Audit, Tax, Accounts (PK = FunctionID) Employees - List of all Employees (PK = EmployeeID) The problem as I see it is that there are multiple many-to-many relationships i.e. many departments have many divisions and many functions have many departments. Question Giving the database structure above, suppose I wanted to do the following: Get all employees who work in the Payroll function of the Marketing Division To do this I need to be able to differentiate between the two Payroll departments but I am not sure how this can be done? I understand that I could build a 'Link / Junction' table between Departments and Functions so that I can retrieve which Functions are in which Departments. However, I would still need to differentiate the Division they belong to. Research Effort As you can see I am an abecedarian when it comes to database deisgn. I have spent the last two days resaerching this issue, traversing nested set models, adjacency models, reading that this issue is known not to be NP complete etc. I am sure there is a simple solution?

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• Does my API design violate RESTful principles?

  - by peta

  Hello everybody, I'm currently (I try to) designing a RESTful API for a social network. But I'm not sure if my current approach does still accord to the RESTful principles. I'd be glad if some brighter heads could give me some tips. Suppose the following URI represents the name field of a user account: people/{UserID}/profile/fields/name But there are almost hundred possible fields. So I want the client to create its own field views or use predefined ones. Let's suppose that the following URI represents a predefined field view that includes the fields "name", "age", "gender": utils/views/field-views/myFieldView And because field views are kind of higher logic I don't want to mix support for field views into the "people/{UserID}/profile/fields" resource. Instead I want to do the following: utils/views/field-views/myFieldView/{UserID} Though Leonard Richardson & Sam Ruby state in their book "RESTful Web Services" that a RESTful design is somehow like an "extreme object oriented" approach, I think that my approach is object oriented and therefore accords to RESTful principles. Or am I wrong? When not: Are such "object oriented" approaches generally encouraged when used with care and in order to avoid query-based REST-RPC hybrids? Thanks for your feedback in advance, peta

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• Database warehoue design: fact tables and dimension tables

  - by morpheous

  I am building a poor man's data warehouse using a RDBMS. I have identified the key 'attributes' to be recorded as: sex (true/false) demographic classification (A, B, C etc) place of birth date of birth weight (recorded daily): The fact that is being recorded My requirements are to be able to run 'OLAP' queries that allow me to: 'slice and dice' 'drill up/down' the data and generally, be able to view the data from different perspectives After reading up on this topic area, the general consensus seems to be that this is best implemented using dimension tables rather than normalized tables. Assuming that this assertion is true (i.e. the solution is best implemented using fact and dimension tables), I would like to see some help in the design of these tables. 'Natural' (or obvious) dimensions are: Date dimension Geographical location Which have hierarchical attributes. However, I am struggling with how to model the following fields: sex (true/false) demographic classification (A, B, C etc) The reason I am struggling with these fields is that: They have no obvious hierarchical attributes which will aid aggregation (AFAIA) - which suggest they should be in a fact table They are mostly static or very rarely change - which suggests they should be in a dimension table. Maybe the heuristic I am using above is too crude? I will give some examples on the type of analysis I would like to carryout on the data warehouse - hopefully that will clarify things further. I would like to aggregate and analyze the data by sex and demographic classification - e.g. answer questions like: How does male and female weights compare across different demographic classifications? Which demographic classification (male AND female), show the most increase in weight this quarter. etc. Can anyone clarify whether sex and demographic classification are part of the fact table, or whether they are (as I suspect) dimension tables.? Also assuming they are dimension tables, could someone elaborate on the table structures (i.e. the fields)? The 'obvious' schema: CREATE TABLE sex_type (is_male int); CREATE TABLE demographic_category (id int, name varchar(4)); may not be the correct one.

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• GAE python database object design for simple list of values

  - by Joey

  I'm really new to database object design so please forgive any weirdness in my question. Basically, I am use Google AppEngine (Python) and contructing an object to track user info. One of these pieces of data is 40 Achievement scores. Do I make a list of ints in the User object for this? Or do I make a separate entity with my user id, the achievement index (0-39) and the score and then do a query to grab these 40 items every time I want to get the user data in total? The latter approach seems more object oriented to me, and certainly better if I extend it to have more than just scores for these 40 achievements. However, considering that I might not extend it, should I even consider just doing a simple list of 40 ints in my user data? I would then forgo doing a query, getting the sorted list of achievements, reading the score from each one just to process a response etc. Is doing this latter approach just such a common practice and hand-waved as not even worth batting an eyelash at in terms of thinking it might be more costly or complex processing wise?

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• Which design is better?

  - by Tattat

  I have an "Enemy" object, that have many "gun" . Each "gun" can fire "bullet". Storing "gun" is using an array. when the "gun" is fired, the "bullet" will be created. And the enemy object will have an array to store the "bullet". So, I am thinking about the fire method. I am think making a firebulletFromGun in the "enemy". It need have a parameter: "gun". while this method is called. The "enemy" 's bullet will be added in the Array. Another design is writing the fire method in the "gun". The "enemy" use the "gun"'s fire method. And the "gun" will return a "bullet" object, and it will be added in the Array of "enemy". Both method can work, but which way is better? or they are similar the same? plx drop ur ideas/suggestions. thz.

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• python: how to design a container with elements that must reference their container

  - by Luke404

  (the title is admittedly not that great. Please forgive my English, this is the best I could think of) I'm writing a python script that will manage email domains and their accounts, and I'm also a newby at OOP design. My two (related?) issues are: the Domain class must do special work to add and remove accounts, like adding/removing them to the underlying implementation how to manage operations on accounts that must go through their container To solve the former issue I'd add a factory method to the Domain class that'll build an Account instance in that domain, and a 'remove' (anti-factory?) method to handle deletions. For the latter this seems to me "anti-oop" since what would logically be an operation on an Account (eg, change password) must always reference the containing Domain. Seems to me that I must add to the Account a reference back to the Domain and use that to get data (like the domain name) or call methods on the Domain class. Code example (element uses data from the container) that manages an underlying Vpopmail system: class Account: def __init__(self, name, password, domain): self.name = name self.password = password self.domain = domain def set_password(self, password): os.system('vpasswd %s@%s %s' % (self.name, self.domain.name, password) self.password = password class Domain: def __init__(self, domain_name): self.name = domain_name self.accounts = {} def create_account(self, name, password): os.system('vadduser %s@%s %s' % (name, self.name, password)) account = Account(name, password, self) self.accounts[name] = account def delete_account(self, name): os.system('vdeluser %s@%s' % (name, self.name)) del self.accounts[name] another option would be for Account.set_password to call a Domain method that would do the actual work - sounds equally ugly to me. Also note the duplication of data (account name also as dict key), it sounds logical (account names are "primary key" inside a domain) but accounts need to know their own name.

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• Design: Website calling a webservice on the same machine

  - by Chris L

  More of a design/conceptual question. At work the decision was made to have our data access layer be called through webservices. So our website would call the webservices for any/all data to and from the database. Both the website & the webservices will be on the same machine(so no trip across the wire), but the database is on a separate machine(so that would require a trip across the wire regardless). This is all in-house, the website, webservice, and database are all within the same company(AFAIK, the webservices won't be reused by another other party). To the best of my knowledge: the website will open a port to the webservices, and the webservices will in turn open another port and go across the wire to the database server to get/submit the data. The trip across the wire can't be avoided, but I'm concerned about the webservices standing in the middle. I do agree there needs to be distinct layers between the functionality(such as business layer, data access layer, etc...), but this seems overly complex to me. I'm also sensing there will be some performance problems down the line. Seems to me it would be better to have the (DAL)assemblies referenced directly within the solution, thus negating the first port to port connection. Any thoughts(or links) both for and against this idea would be appreciated P.S. We're a .NET shop(migrating from vb to C# 3.5)

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• DIY intellisense on XPath - design approach? (WinForms app)

  - by Cheeso

  I read the DIY Intellisense article on code project, which was referenced from the Mimic Intellisense? question here on SO. I wanna do something similar, DIY intellisense, but for XPath not C#. The design approach used there makes sense to me: maintain a tree of terms, and when the "completion character" is pressed, in the case of C#, a dot, pop up the list of possible completions in a textfield. Then allow the user to select a term from the textfield either through typing, arrow keys, or double-click. How would you apply this to XPath autocompletion? should there be an autocomplete key? In XPath there is no obvious separator key like "dot" in C#. should the popup be triggered explicitly in some other way, let's say ctrl-. ? or should the parser try to autocomplete continuously? If I do the autocomplete continuously, how to scale it properly? There are 93 xpath functions, not counting overloads. I certainly don't want to popup a list of 93 choices. How do I decide when I've narrowed it enough to offer a useful lsit of possible completions? How to populate the tree of possible completions? For C#, it's easy: walk the type space via reflection. At a first level, the "syntax tree" for C# seems like a single tree, and the list of completions at any point depends on the graph of nodes you've traversed to that point. Typing System.Console. traverses to a certain node in that tree, and the list of completions is the set of child nodes available at that node in the tree. On the other hand, the xpath syntax seems like it is a "flatter" tree - function names, axis names, literals. Does this make sense? what have I not considered?

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• Database Design Question regaurding duplicate information.

  - by galford13x

  I have a database that contains a history of product sales. For example the following table CREATE TABLE SalesHistoryTable ( OrderID, // Order Number Unique to all orders ProductID, // Product ID can be used as a Key to look up product info in another table Price, // Price of the product per unit at the time of the order Quantity, // quantity of the product for the order Total, // total cost of the order for the product. (Price * Quantity) Date, // Date of the order StoreID, // The store that created the Order PRIMARY KEY(OrderID)); The table will eventually have millions of transactions. From this, profiles can be created for products in different geographical regions (based on the StoreID). Creating these profiles can be very time consuming as a database query. For example. SELECT ProductID, StoreID, SUM(Total) AS Total, SUM(Quantity) QTY, SUM(Total)/SUM(Quantity) AS AvgPrice FROM SalesHistoryTable GROUP BY ProductID, StoreID; The above query could be used to get the Information based on products for any particular store. You could then determine which store has sold the most, has made the most money, and on average sells for the most/least. This would be very costly to use as a normal query run anytime. What are some design descisions in order to allow these types of queries to run faster assuming storage size isn’t an issue. For example, I could create another Table with duplicate information. Store ID (Key), Product ID, TotalCost, QTY, AvgPrice And provide a trigger so that when a new order is received, the entry for that store is updated in a new table. The cost for the update is almost nothing. What should be considered when given the above scenario?

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• Bus Timetable database design

  - by paddydub

  hi, I'm trying to design a db to store the timetable for 300 different bus routes, Each route has a different number of stops and different times for Monday-Friday, Saturday and Sunday. I've represented the bus departure times for each route as follows, I'm not sure if i should have null values in the table, does this look ok? route,Num,Day, t1, t2, t3, t4 t5 t6 t7 t8 t9 t10 117, 1, Monday, 9:00, 9:30, 10:50, 12:00, 14:00 18:00 19:00 null null null 117, 2, Monday, 9:03, 9:33, 10:53, 12:03, 14:03 18:03 19:03 null null null 117, 3, Monday, 9:06, 9:36, 10:56, 12:06, 14:06 18:06 19:06 null null null 117, 4, Monday, 9:09, 9:39, 10:59, 12:09, 14:09 18:09 19:09 null null null . . . 117, 20, Monday, 9:39, 10.09, 11:39, 12:39, 14:39 18:39 19:39 null null null 119, 1, Monday, 9:00, 9:30, 10:50, 12:00, 14:00 18:00 19:00 20:00 21:00 22:00 119, 2, Monday, 9:03, 9:33, 10:53, 12:03, 14:03 18:03 19:03 20:03 21:03 22:03 119, 3, Monday, 9:06, 9:36, 10:56, 12:06, 14:06 18:06 19:06 20:06 21:06 22:06 119, 4, Monday, 9:09, 9:39, 10:59, 12:09, 14:09 18:09 19:09 20:09 21:09 22:09 . . . 119, 37, Monday, 9:49, 9:59, 11:59, 12:59, 14:59 18:59 19:59 20:59 21:59 22:59 139, 1, Sunday, 9:00, 9:30, 20:00 21:00 22:00 null null null null null 139, 2, Sunday, 9:03, 9:33, 20:03 21:03 22:03 null null null null null 139, 3, Sunday, 9:06, 9:36, 20:06 21:06 22:06 null null null null null 139, 4, Sunday, 9:09, 9:39, 20:09 21:09 22:09 null null null null null . . . 139, 20, Sunday, 9:49, 9:59, 20:59 21:59 22:59 null null null null null

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• How can I improve this design?

  - by klausbyskov

  Let's assume that our system can perform actions, and that an action requires some parameters to do its work. I have defined the following base class for all actions (simplified for your reading pleasure): public abstract class BaseBusinessAction<TActionParameters> : where TActionParameters : IActionParameters { protected BaseBusinessAction(TActionParameters actionParameters) { if (actionParameters == null) throw new ArgumentNullException("actionParameters"); this.Parameters = actionParameters; if (!ParametersAreValid()) throw new ArgumentException("Valid parameters must be supplied", "actionParameters"); } protected TActionParameters Parameters { get; private set; } protected abstract bool ParametersAreValid(); public void CommonMethod() { ... } } Only a concrete implementation of BaseBusinessAction knows how to validate that the parameters passed to it are valid, and therefore the ParametersAreValid is an abstract function. However, I want the base class constructor to enforce that the parameters passed are always valid, so I've added a call to ParametersAreValid to the constructor and I throw an exception when the function returns false. So far so good, right? Well, no. Code analysis is telling me to "not call overridable methods in constructors" which actually makes a lot of sense because when the base class's constructor is called the child class's constructor has not yet been called, and therefore the ParametersAreValid method may not have access to some critical member variable that the child class's constructor would set. So the question is this: How do I improve this design? Do I add a Func<bool, TActionParameters> parameter to the base class constructor? If I did: public class MyAction<MyParameters> { public MyAction(MyParameters actionParameters, bool something) : base(actionParameters, ValidateIt) { this.something = something; } private bool something; public static bool ValidateIt() { return something; } } This would work because ValidateIt is static, but I don't know... Is there a better way? Comments are very welcome.

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• Erlang OTP application design

  - by Toby Hede

  I am struggling a little coming to grips with the OTP development model as I convert some code into an OTP app. I am essentially making a web crawler and I just don't quite know where to put the code that does the actual work. I have a supervisor which starts my worker: -behaviour(supervisor). -define(CHILD(I, Type), {I, {I, start_link, []}, permanent, 5000, Type, [I]}). init(_Args) -> Children = [ ?CHILD(crawler, worker) ], RestartStrategy = {one_for_one, 0, 1}, {ok, {RestartStrategy, Children}}. In this design, the Crawler Worker is then responsible for doing the actual work: -behaviour(gen_server). start_link() -> gen_server:start_link(?MODULE, [], []). init([]) -> inets:start(), httpc:set_options([{verbose_mode,true}]), % gen_server:cast(?MODULE, crawl), % ok = do_crawl(), {ok, #state{}}. do_crawl() -> % crawl! ok. handle_cast(crawl}, State) -> ok = do_crawl(), {noreply, State}; do_crawl spawns a fairly large number of processes and requests that handle the work of crawling via http. Question, ultimately is: where should the actual crawl happen? As can be seen above I have been experimenting with different ways of triggering the actual work, but still missing some concept essential for grokering the way things fit together. Note: some of the OTP plumbing is left out for brevity - the plumbing is all there and the system all hangs together

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