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• Where to ask a question about startups?

  - by Wolfpack'08

  I've got some questions about how to better run my web application development business, which has only been running for a little more than two years. It's still in its early phases, as I consider the first five years the 'early years'. Being inexperienced with business in general, I always have a lot of questions as to whether I am making the right decisions (for example, I often worry about my hiring practices, and I often worry that I may have priced new products wrongly). Is there a good site on the Stack Exchange to ask questions about things like this (for example, this site, the Project Management site, the Salesforce site, or perhaps the Personal Finance site)? I'm combing through questions and answers on each of these sites, now, and I can see questions that mimic my own. Nothing precisely the same, but things that are similar on all sites. Apart from just reading through previously asked questions, what is a good way to get a sense of whether or not my question fits on a site in the exchange? If you recommend going out of the exchange, please also let me know.

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• what's a good approach to working with multiple databases?

  - by Riz

  I'm working on a project that has its own database call it InternalDb, but also it queries two other databases, call them ExternalDb1 and ExternalDb2. Both ExternalDb1 and ExternalDb2 are actually required by a few other projects. I'm wondering what the best approach for dealing with this is? Currently, I've just created a project for each of these external databases and then generated Edmx and entities using the entity-framework approach. My thought was that I could then include these projects in any of my solutions that require access to these databases. Also, I don't have any separate business layers. I just have a solution like below: Project.Domain ExternalDb1Project.Domain ExternalDb2Project.Domain Project.Web So my Domain projects contain the data access as well as the POCOs generated by Entity Framework and any business logic. But I'm not sure if this is a good approach. For example if I want to do Validation in my Project.Domain on the entities in the InternalDb, it's fine. But if I want to do Validation for entities from either of the ExternalDbs, then I wonder where it should go? To be more specific, I retrieve Employees from ExternalDb1Project.Domain. However, I want to make sure they are Active. Where should this Validation go? How to architect a project like this at a high level? Also, I want to make sure that I use IoC for my data contexts so I can create Fakes when writing tests. I wonder where the interfaces for these various data contexts would reside?

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• Should business objects be able to create their own DTOs?

  - by Sam

  Suppose I have the following class: class Camera { public Camera( double exposure, double brightness, double contrast, RegionOfInterest regionOfInterest) { this.exposure = exposure; this.brightness = brightness; this.contrast = contrast; this.regionOfInterest = regionOfInterest; } public void ConfigureAcquisitionFifo(IAcquisitionFifo acquisitionFifo) { // do stuff to the acquisition FIFO } readonly double exposure; readonly double brightness; readonly double contrast; readonly RegionOfInterest regionOfInterest; } ... and a DTO to transport the camera info across a service boundary (WCF), say, for viewing in a WinForms/WPF/Web app: using System.Runtime.Serialization; [DataContract] public class CameraData { [DataMember] public double Exposure { get; set; } [DataMember] public double Brightness { get; set; } [DataMember] public double Contrast { get; set; } [DataMember] public RegionOfInterestData RegionOfInterest { get; set; } } Now I can add a method to Camera to expose its data: class Camera { // blah blah public CameraData ToData() { var regionOfInterestData = regionOfInterest.ToData(); return new CameraData() { Exposure = exposure, Brightness = brightness, Contrast = contrast, RegionOfInterestData = regionOfInterestData }; } } or, I can create a method that requires a special IReporter to be passed in for the Camera to expose its data to. This removes the dependency on the Contracts layer (Camera no longer has to know about CameraData): class Camera { // beep beep I'm a jeep public void ExposeToReporter(IReporter reporter) { reporter.GetCameraInfo(exposure, brightness, contrast, regionOfInterest); } } So which should I do? I prefer the second, but it requires the IReporter to have a CameraData field (which gets changed by GetCameraInfo()), which feels weird. Also, if there is any even better solution, please share with me! I'm still an object-oriented newb.

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• Creating an object that is ready to be used & unset properties - with IoC

  - by GetFuzzy

  I have a question regarding the specifics of object creation and the usage of properties. A best practice is to put all the properties into a state such that the object is useful when its created. Object constructors help ensure that required dependencies are created. I've found myself following a pattern lately, and then questioning its appropriateness. The pattern looks like this... public class ThingProcesser { public List<Thing> CalculatedThings { get; set; } public ThingProcesser() { CalculatedThings = new List<Thing>(); } public double FindCertainThing() { CheckForException(); foreach (var thing in CalculatedThings) { //do some stuff with things... } } public double FindOtherThing() { CheckForException(); foreach (var thing in CalculatedThings) { //do some stuff with things... } } private void CheckForException() { if (CalculatedThings.Count < 2) throw new InvalidOperationException("Calculated things must have more than 2 items"); } } The list of items is not being changed, just looked through by the methods. There are several methods on the class, and to avoid having to pass the list of things to each function as a method parameter, I set it once on the class. While this works, does it violate the principle of least astonishment? Since starting to use IoC I find myself not sticking things into the constructor, to avoid having to use a factory pattern. For example, I can argue with myself and say well the ThingProcessor really needs a List to work, so the object should be constructed like this. public class ThingProcesser { public List<Thing> CalculatedThings { get; set; } public ThingProcesser(List<Thing> calculatedThings) { CalculatedThings = calculatedThings; } } However, if I did this, it would complicate things for IoC, and this scenario hardly seems appropriate for something like the factory pattern. So in summary, are there some good guidelines for when something should be part of the object state, vs. passed as a method parameter? When using IoC, is the factory pattern the best way to deal with objects that need created with state? If something has to be passed to multiple methods in a class, does that render it a good candidate to be part of the objects state?

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• Routing static IP traffic on a Comcast Business Class IP Gateway (SMCD3G-CCR)

  - by Jakobud

  We are in the process of replacing our firewall, which is currently the only thing connected to our Comcast Business Class modem. Comcast gives us 5 static IP addresses. Currently, all traffic to all 5 static IPs goes directly to the existing firewall. Eventually, obviously all traffic will goto the new firewall, once the old firewall is removed from the network. But in the meantime, as we will have two firewalls plugged into the same Comcast modem, I need to route certain traffic to the new firewall instead of the old one. The firewall switchover is going to be slow and gradual as I am testing it, so I can't simply unplug the existing firewall and plug in the new one. So my question is, how do I tell the modem to route all traffic that goes to a specific IP to goto the new firewall instead of the old one? I've logged into the web interface for the modem, but the available options aren't very clear. There is a 1-to-1 NAT option (which I can't seem to get the interface for it to work properly) but I also see a "Static Routing" section. I always understood Static Routing to refer to routing data within the LAN though, so I'm not sure if that's what I'm looking for or not. Keep in mind, I'm not looking to do simple port forwarding. I'm wanting 100% of traffic to certain public static IPs to go to the specified connected firewall (I'll deal with service policies there). The modem is an SMC SMCD3G-CCR and is labeled as a Comcast Business Class Business IP Gateway. Any help or direction would be greatly appreciated.

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• Elfsign Object Signing on Solaris

  - by danx

  Elfsign Object Signing on Solaris Don't let this happen to you—use elfsign! Solaris elfsign(1) is a command that signs and verifies ELF format executables. That includes not just executable programs (such as ls or cp), but other ELF format files including libraries (such as libnvpair.so) and kernel modules (such as autofs). Elfsign has been available since Solaris 10 and ELF format files distributed with Solaris, since Solaris 10, are signed by either Sun Microsystems or its successor, Oracle Corporation. When an ELF file is signed, elfsign adds a new section the ELF file, .SUNW_signature, that contains a RSA public key signature and other information about the signer. That is, the algorithm used, algorithm OID, signer CN/OU, and time stamp. The signature section can later be verified by elfsign or other software by matching the signature in the file agains the ELF file contents (excluding the signature). ELF executable files may also be signed by a 3rd-party or by the customer. This is useful for verifying the origin and authenticity of executable files installed on a system. The 3rd-party or customer public key certificate should be installed in /etc/certs/ to allow verification by elfsign. For currently-released versions of Solaris, only cryptographic framework plugin libraries are verified by Solaris. However, all ELF files may be verified by the elfsign command at any time. Elfsign Algorithms Elfsign signatures are created by taking a digest of the ELF section contents, then signing the digest with RSA. To verify, one takes a digest of ELF file and compares with the expected digest that's computed from the signature and RSA public key. Originally elfsign took a MD5 digest of a SHA-1 digest of the ELF file sections, then signed the resulting digest with RSA. In Solaris 11.1 then Solaris 11.1 SRU 7 (5/2013), the elfsign crypto algorithms available have been expanded to keep up with evolving cryptography. The following table shows the available elfsign algorithms: Elfsign Algorithm Solaris Release Comments elfsign sign -F rsa_md5_sha1   S10, S11.0, S11.1 Default for S10. Not recommended* elfsign sign -F rsa_sha1 S11.1 Default for S11.1. Not recommended elfsign sign -F rsa_sha256 S11.1 patch SRU7+   Recommended ___ *Most or all CAs do not accept MD5 CSRs and do not issue MD5 certs due to MD5 hash collision problems. RSA Key Length. I recommend using RSA-2048 key length with elfsign is RSA-2048 as the best balance between a long expected "life time", interoperability, and performance. RSA-2048 keys have an expected lifetime through 2030 (and probably beyond). For details, see Recommendation for Key Management: Part 1: General, NIST Publication SP 800-57 part 1 (rev. 3, 7/2012, PDF), tables 2 and 4 (pp. 64, 67). Step 1: create or obtain a key and cert The first step in using elfsign is to obtain a key and cert from a public Certificate Authority (CA), or create your own self-signed key and cert. I'll briefly explain both methods. Obtaining a Certificate from a CA To obtain a cert from a CA, such as Verisign, Thawte, or Go Daddy (to name a few random examples), you create a private key and a Certificate Signing Request (CSR) file and send it to the CA, following the instructions of the CA on their website. They send back a signed public key certificate. The public key cert, along with the private key you created is used by elfsign to sign an ELF file. The public key cert is distributed with the software and is used by elfsign to verify elfsign signatures in ELF files. You need to request a RSA "Class 3 public key certificate", which is used for servers and software signing. Elfsign uses RSA and we recommend RSA-2048 keys. The private key and CSR can be generated with openssl(1) or pktool(1) on Solaris. Here's a simple example that uses pktool to generate a private RSA_2048 key and a CSR for sending to a CA: $ pktool gencsr keystore=file format=pem outcsr=MYCSR.p10 \ subject="CN=canineswworks.com,OU=Canine SW object signing" \ outkey=MYPRIVATEKEY.key $ openssl rsa -noout -text -in MYPRIVATEKEY.key Private-Key: (2048 bit) modulus: 00:d2:ef:42:f2:0b:8c:96:9f:45:32:fc:fe:54:94: . . . [omitted for brevity] . . . c9:c7 publicExponent: 65537 (0x10001) privateExponent: 26:14:fc:49:26:bc:a3:14:ee:31:5e:6b:ac:69:83: . . . [omitted for brevity] . . . 81 prime1: 00:f6:b7:52:73:bc:26:57:26:c8:11:eb:6c:dc:cb: . . . [omitted for brevity] . . . bc:91:d0:40:d6:9d:ac:b5:69 prime2: 00:da:df:3f:56:b2:18:46:e1:89:5b:6c:f1:1a:41: . . . [omitted for brevity] . . . f3:b7:48:de:c3:d9:ce:af:af exponent1: 00:b9:a2:00:11:02:ed:9a:3f:9c:e4:16:ce:c7:67: . . . [omitted for brevity] . . . 55:50:25:70:d3:ca:b9:ab:99 exponent2: 00:c8:fc:f5:57:11:98:85:8e:9a:ea:1f:f2:8f:df: . . . [omitted for brevity] . . . 23:57:0e:4d:b2:a0:12:d2:f5 coefficient: 2f:60:21:cd:dc:52:76:67:1a:d8:75:3e:7f:b0:64: . . . [omitted for brevity] . . . 06:94:56:d8:9d:5c:8e:9b $ openssl req -noout -text -in MYCSR.p10 Certificate Request: Data: Version: 2 (0x2) Subject: OU=Canine SW object signing, CN=canineswworks.com Subject Public Key Info: Public Key Algorithm: rsaEncryption Public-Key: (2048 bit) Modulus: 00:d2:ef:42:f2:0b:8c:96:9f:45:32:fc:fe:54:94: . . . [omitted for brevity] . . . c9:c7 Exponent: 65537 (0x10001) Attributes: Signature Algorithm: sha1WithRSAEncryption b3:e8:30:5b:88:37:68:1c:26:6b:45:af:5e:de:ea:60:87:ea: . . . [omitted for brevity] . . . 06:f9:ed:b4 Secure storage of RSA private key. The private key needs to be protected if the key signing is used for production (as opposed to just testing). That is, protect the key to protect against unauthorized signatures by others. One method is to use a PIN-protected PKCS#11 keystore. The private key you generate should be stored in a secure manner, such as in a PKCS#11 keystore using pktool(1). Otherwise others can sign your signature. Other secure key storage mechanisms include a SCA-6000 crypto card, a USB thumb drive stored in a locked area, a dedicated server with restricted access, Oracle Key Manager (OKM), or some combination of these. I also recommend secure backup of the private key. Here's an example of generating a private key protected in the PKCS#11 keystore, and a CSR. $ pktool setpin # use if PIN not set yet Enter token passphrase: changeme Create new passphrase: Re-enter new passphrase: Passphrase changed. $ pktool gencsr keystore=pkcs11 label=MYPRIVATEKEY \ format=pem outcsr=MYCSR.p10 \ subject="CN=canineswworks.com,OU=Canine SW object signing" $ pktool list keystore=pkcs11 Enter PIN for Sun Software PKCS#11 softtoken: Found 1 asymmetric public keys. Key #1 - RSA public key: MYPRIVATEKEY Here's another example that uses openssl instead of pktool to generate a private key and CSR: $ openssl genrsa -out cert.key 2048 $ openssl req -new -key cert.key -out MYCSR.p10 Self-Signed Cert You can use openssl or pktool to create a private key and a self-signed public key certificate. A self-signed cert is useful for development, testing, and internal use. The private key created should be stored in a secure manner, as mentioned above. The following example creates a private key, MYSELFSIGNED.key, and a public key cert, MYSELFSIGNED.pem, using pktool and displays the contents with the openssl command. $ pktool gencert keystore=file format=pem serial=0xD06F00D lifetime=20-year \ keytype=rsa hash=sha256 outcert=MYSELFSIGNED.pem outkey=MYSELFSIGNED.key \ subject="O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com" $ pktool list keystore=file objtype=cert infile=MYSELFSIGNED.pem Found 1 certificates. 1. (X.509 certificate) Filename: MYSELFSIGNED.pem ID: c8:24:59:08:2b:ae:6e:5c:bc:26:bd:ef:0a:9c:54:de:dd:0f:60:46 Subject: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com Issuer: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com Not Before: Oct 17 23:18:00 2013 GMT Not After: Oct 12 23:18:00 2033 GMT Serial: 0xD06F00D0 Signature Algorithm: sha256WithRSAEncryption $ openssl x509 -noout -text -in MYSELFSIGNED.pem Certificate: Data: Version: 3 (0x2) Serial Number: 3496935632 (0xd06f00d0) Signature Algorithm: sha256WithRSAEncryption Issuer: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com Validity Not Before: Oct 17 23:18:00 2013 GMT Not After : Oct 12 23:18:00 2033 GMT Subject: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com Subject Public Key Info: Public Key Algorithm: rsaEncryption Public-Key: (2048 bit) Modulus: 00:bb:e8:11:21:d9:4b:88:53:8b:6c:5a:7a:38:8b: . . . [omitted for brevity] . . . bf:77 Exponent: 65537 (0x10001) Signature Algorithm: sha256WithRSAEncryption 9e:39:fe:c8:44:5c:87:2c:8f:f4:24:f6:0c:9a:2f:64:84:d1: . . . [omitted for brevity] . . . 5f:78:8e:e8 $ openssl rsa -noout -text -in MYSELFSIGNED.key Private-Key: (2048 bit) modulus: 00:bb:e8:11:21:d9:4b:88:53:8b:6c:5a:7a:38:8b: . . . [omitted for brevity] . . . bf:77 publicExponent: 65537 (0x10001) privateExponent: 0a:06:0f:23:e7:1b:88:62:2c:85:d3:2d:c1:e6:6e: . . . [omitted for brevity] . . . 9c:e1:e0:0a:52:77:29:4a:75:aa:02:d8:af:53:24: c1 prime1: 00:ea:12:02:bb:5a:0f:5a:d8:a9:95:b2:ba:30:15: . . . [omitted for brevity] . . . 5b:ca:9c:7c:19:48:77:1e:5d prime2: 00:cd:82:da:84:71:1d:18:52:cb:c6:4d:74:14:be: . . . [omitted for brevity] . . . 5f:db:d5:5e:47:89:a7:ef:e3 exponent1: 32:37:62:f6:a6:bf:9c:91:d6:f0:12:c3:f7:04:e9: . . . [omitted for brevity] . . . 97:3e:33:31:89:66:64:d1 exponent2: 00:88:a2:e8:90:47:f8:75:34:8f:41:50:3b:ce:93: . . . [omitted for brevity] . . . ff:74:d4:be:f3:47:45:bd:cb coefficient: 4d:7c:09:4c:34:73:c4:26:f0:58:f5:e1:45:3c:af: . . . [omitted for brevity] . . . af:01:5f:af:ad:6a:09:bf Step 2: Sign the ELF File object By now you should have your private key, and obtained, by hook or crook, a cert (either from a CA or use one you created (a self-signed cert). The next step is to sign one or more objects with your private key and cert. Here's a simple example that creates an object file, signs, verifies, and lists the contents of the ELF signature. $ echo '#include <stdio.h>\nint main(){printf("Hello\\n");}'>hello.c $ make hello cc -o hello hello.c $ elfsign verify -v -c MYSELFSIGNED.pem -e hello elfsign: no signature found in hello. $ elfsign sign -F rsa_sha256 -v -k MYSELFSIGNED.key -c MYSELFSIGNED.pem -e hello elfsign: hello signed successfully. format: rsa_sha256. signer: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com. signed on: October 17, 2013 04:22:49 PM PDT. $ elfsign list -f format -e hello rsa_sha256 $ elfsign list -f signer -e hello O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com $ elfsign list -f time -e hello October 17, 2013 04:22:49 PM PDT $ elfsign verify -v -c MYSELFSIGNED.key -e hello elfsign: verification of hello failed. format: rsa_sha256. signer: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com. signed on: October 17, 2013 04:22:49 PM PDT. Signing using the pkcs11 keystore To sign the ELF file using a private key in the secure pkcs11 keystore, replace "-K MYSELFSIGNED.key" in the "elfsign sign" command line with "-T MYPRIVATEKEY", where MYPRIVATKEY is the pkcs11 token label. Step 3: Install the cert and test on another system Just signing the object isn't enough. You need to copy or install the cert and the signed ELF file(s) on another system to test that the signature is OK. Your public key cert should be installed in /etc/certs. Use elfsign verify to verify the signature. Elfsign verify checks each cert in /etc/certs until it finds one that matches the elfsign signature in the file. If one isn't found, the verification fails. Here's an example: $ su Password: # rm /etc/certs/MYSELFSIGNED.key # cp MYSELFSIGNED.pem /etc/certs # exit $ elfsign verify -v hello elfsign: verification of hello passed. format: rsa_sha256. signer: O=Canine Software Works, OU=Self-signed CA, CN=canineswworks.com. signed on: October 17, 2013 04:24:20 PM PDT. After testing, package your cert along with your ELF object to allow elfsign verification after your cert and object are installed or copied. Under the Hood: elfsign verification Here's the steps taken to verify a ELF file signed with elfsign. The steps to sign the file are similar except the private key exponent is used instead of the public key exponent and the .SUNW_signature section is written to the ELF file instead of being read from the file. Generate a digest (SHA-256) of the ELF file sections. This digest uses all ELF sections loaded in memory, but excludes the ELF header, the .SUNW_signature section, and the symbol table Extract the RSA signature (RSA-2048) from the .SUNW_signature section Extract the RSA public key modulus and public key exponent (65537) from the public key cert Calculate the expected digest as follows:     signaturepublicKeyExponent % publicKeyModulus Strip the PKCS#1 padding (most significant bytes) from the above. The padding is 0x00, 0x01, 0xff, 0xff, . . ., 0xff, 0x00. If the actual digest == expected digest, the ELF file is verified (OK). Further Information elfsign(1), pktool(1), and openssl(1) man pages. "Signed Solaris 10 Binaries?" blog by Darren Moffat (2005) shows how to use elfsign. "Simple CLI based CA on Solaris" blog by Darren Moffat (2008) shows how to set up a simple CA for use with self-signed certificates. "How to Create a Certificate by Using the pktool gencert Command" System Administration Guide: Security Services (available at docs.oracle.com)

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• My Right-to-Left Foot (T-SQL Tuesday #13)

  - by smisner

  As a business intelligence consultant, I often encounter the situation described in this month's T-SQL Tuesday, hosted by Steve Jones ( Blog | Twitter) – “What the Business Says Is Not What the  Business Wants.” Steve posed the question, “What issues have you had in interacting with the business to get your job done?” My profession requires me to have one foot firmly planted in the technology world and the other foot planted in the business world. I learned long ago that the business never says exactly what the business wants because the business doesn't have the words to describe what the business wants accurately enough for IT. Not only do technological-savvy barriers exist, but there are also linguistic barriers between the two worlds. So how do I cope? The adage "a picture is worth a thousand words" is particularly helpful when I'm called in to help design a new business intelligence solution. Many of my students in BI classes have heard me explain ("rant") about left-to-right versus right-to-left design. To understand what I mean about these two design options, let's start with a picture: When we design a business intelligence solution that includes some sort of traditional data warehouse or data mart design, we typically place the data sources on the left, the new solution in the middle, and the users on the right. When I've been called in to help course-correct a failing BI project, I often find that IT has taken a left-to-right approach. They look at the data sources, decide how to model the BI solution as a _______ (fill in the blank with data warehouse, data mart, cube, etc.), and then build the new data structures and supporting infrastructure. (Sometimes, they actually do this without ever having talked to the business first.) Then, when they show what they've built to the business, the business says that is not what we want. Uh-oh. I prefer to take a right-to-left approach. Preferably at the beginning of a project. But even if the project starts left-to-right, I'll do my best to swing it around so that we’re back to a right-to-left approach. (When circumstances are beyond my control, I carry on, but it’s a painful project for everyone – not because of me, but because the approach just doesn’t get to what the business wants in the most effective way.) By using a right to left approach, I try to understand what it is the business is trying to accomplish. I do this by having them explain reports to me, and explaining the decision-making process that relates to these reports. Sometimes I have them explain to me their business processes, or better yet show me their business processes in action because I need pictures, too. I (unofficially) call this part of the project "getting inside the business's head." This is starting at the right side of the diagram above. My next step is to start moving leftward. I do this by preparing some type of prototype. Depending on the nature of the project, this might mean that I simply mock up some data in a relational database and build a prototype report in Reporting Services. If I'm lucky, I might be able to use real data in a relational database. I'll either use a subset of the data in the prototype report by creating a prototype database to hold the sample data, or select data directly from the source. It all depends on how much data there is, how complex the queries are, and how fast I need to get the prototype completed. If the solution will include Analysis Services, then I'll build a prototype cube. Analysis Services makes it incredibly easy to prototype. You can sit down with the business, show them the prototype, and have a meaningful conversation about what the BI solution should look like. I know I've done a good job on the prototype when I get knocked out of my chair so that the business user can explore the solution further independently. (That's really happened to me!) We can talk about dimensions, hierarchies, levels, members, measures, and so on with something tangible to look at and without using those terms. It's not helpful to use sample data like Adventure Works or to use BI terms that they don't really understand. But when I show them their data using the BI technology and talk to them in their language, then they truly have a picture worth a thousand words. From that, we can fine tune the prototype to move it closer to what they want. They have a better idea of what they're getting, and I have a better idea of what to build. So right to left design is not truly moving from the right to the left. But it starts from the right and moves towards the middle, and once I know what the middle needs to look like, I can then build from the left to meet in the middle. And that’s how I get past what the business says to what the business wants.

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• Class design issue

  - by user2865206

  I'm new to OOP and a lot of times I become stumped in situations similar to this example: Task: Generate an XML document that contains information about a person. Assume the information is readily available in a database. Here is an example of the structure: <Person> <Name>John Doe</Name> <Age>21</Age> <Address> <Street>100 Main St.</Street> <City>Sylvania</City> <State>OH</State> </Address> <Relatives> <Parents> <Mother> <Name>Jane Doe</Name> </Mother> <Father> <Name>John Doe Sr.</Name> </Father> </Parents> <Siblings> <Brother> <Name>Jeff Doe</Name> </Brother> <Brother> <Name>Steven Doe</Name> </Brother> </Siblings> </Relatives> </Person> Ok lets create a class for each tag (ie: Person, Name, Age, Address) Lets assume each class is only responsible for itself and the elements directly contained Each class will know (have defined by default) the classes that are directly contained within them Each class will have a process() function that will add itself and its childeren to the XML document we are creating When a child is drawn, as in the previous line, we will have them call process() as well Now we are in a recursive loop where each object draws their childeren until all are drawn But what if only some of the tags need to be drawn, and the rest are optional? Some are optional based on if the data exists (if we have it, we must draw it), and some are optional based on the preferences of the user generating the document How do we make sure each object has the data it needs to draw itself and it's childeren? We can pass down a massive array through every object, but that seems shitty doesnt it? We could have each object query the database for it, but thats a lot of queries, and how does it know what it's query is? What if we want to get rid of a tag later? There is no way to reference them. I've been thinking about this for 20 hours now. I feel like I am misunderstanding a design principle or am just approaching this all wrong. How would you go about programming something like this? I suppose this problem could apply to any senario where there are classes that create other classes, but the classes created need information to run. How do I get the information to them in a way that doesn't seem fucky? Thanks for all of your time, this has been kicking my ass.

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• Lifetime issue of IDisposable unmanaged resources in a complex object graph?

  - by stakx

  This question is about dealing with unmanaged resources (COM interop) and making sure there won't be any resource leaks. I'd appreciate feedback on whether I seem to do things the right way. Background: Let's say I've got two classes: A class LimitedComResource which is a wrapper around a COM object (received via some API). There can only be a limited number of those COM objects, therefore my class implements the IDisposable interface which will be responsible for releasing a COM object when it's no longer needed. Objects of another type ManagedObject are temporarily created to perform some work on a LimitedComResource. They are not IDisposable. To summarize the above in a diagram, my classes might look like this: +---------------+ +--------------------+ | ManagedObject | <>------> | LimitedComResource | +---------------+ +--------------------+ | o IDisposable (I'll provide example code for these two classes in just a moment.) Question: Since my temporary ManagedObject objects are not disposable, I obviously have no control over how long they'll be around. However, in the meantime I might have Disposed the LimitedComObject that a ManagedObject is referring to. How can I make sure that a ManagedObject won't access a LimitedComResource that's no longer there? +---------------+ +--------------------+ | managedObject | <>------> | (dead object) | +---------------+ +--------------------+ I've currently implemented this with a mix of weak references and a flag in LimitedResource which signals whether an object has already been disposed. Is there any better way? Example code (what I've currently got): LimitedComResource: class LimitedComResource : IDisposable { private readonly IUnknown comObject; // <-- set in constructor ... void Dispose(bool notFromFinalizer) { if (!this.isDisposed) { Marshal.FinalReleaseComObject(comObject); } this.isDisposed = true; } internal bool isDisposed = false; } ManagedObject: class ManagedObject { private readonly WeakReference limitedComResource; // <-- set in constructor ... public void DoSomeWork() { if (!limitedComResource.IsAlive()) { throw new ObjectDisposedException(); // ^^^^^^^^^^^^^^^^^^^^^^^ // is there a more suitable exception class? } var ur = (LimitedComResource)limitedComResource.Target; if (ur.isDisposed) { throw new ObjectDisposedException(); } ... // <-- do something sensible here! } }

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• What makes the availability of both primitive and object-wrapped values in JavaScript useful?

  - by Delan Azabani

  I wrote a blog post a while ago detailing how the availability of both primitive and object-wrapped value types in JavaScript (for things such as Number, String and Boolean) causes trouble, including but not limited to type-casting to a boolean (e.g. object-wrapped NaN, "" and false actually type-cast to true). My question is, with all this confusion and problems, is there any benefit to JavaScript having both types of values for the built-in classes?

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• How can you make a variable/Object read only in Javascript?

  - by codeninja

  I have an Object that I only want to be defined when constructed. How can I prevent the Object reference from being changed?

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• In java what is the diference between an object and a class?

  - by David

  In java what is the diference between an object and a class? The book i'm working from made it seem as though once a class is created it also exists as an object.

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• In java what is the difference between an object and a class?

  - by David

  In java what is the difference between an object and a class? The book I'm working from made it seem as though once a class is created it also exists as an object.

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• How would I create an object that uses String type behaviour for creation?

  - by Zachary Spencer

  I'd like to be able to create an object that is created like a String object, and when created verifies that the String value is an appropriate option. I.E. SpecificString can be "Bob" or "Jim". SpecificString BadName = "Sam" //Throws exception SpecificString GoodName = "Bob" //Does not throw exception. Is this possible?

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• Object Building in ActionScript

  - by kumar

  I am getting an object structure like Object-- --- Object STRING1:VALUE STRING2:VALUE STRING3:VALUE ---- OBJECT STRING1:VALUE STRING2:VALUE STRING3:VALUE Now I want to filter this object because i need only STRING2:VALUE in the same object structure and need to a an structure similar to: Object STRING2:VALUE Object STRING2:VALUE and I need to do it in runtime can somebody please let me know ..

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• C++ is it possible to set an object to null?

  - by John

  Further in my code, I check to see check if an object is null/empty. Is there a way to set an object to null?

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• Detect when a new property is added to a Javascript object?

  - by UICodes

  A simple example using a built-in javascript object: navigator.my_new_property = "some value"; //can we detect that this new property was added? I don't want to constantly poll the object to check for new properties. Is there some type of higher level setter for objects instead of explicitly stating the property to monitor? Again, I don't want to detect if the property value changed, but rather when a new property is added. Ideas? thanks

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• Looping through a SimpleXML object, or turning the whole thing into an array.

  - by Coffee Cup

  I'm trying to work out how to iterate though a returned SimpleXML object. I'm using a toolkit called Tarzan AWS, which connects to Amazon Web Services (SimpleDB, S3, EC2, etc). I'm specifically using SimpleDB. I can put data into the Amazon SimpleDB service, and I can get it back. I just don't know how to handle the SimpleXML object that is returned. The Tarzan AWS documentation says this: Look at the response to navigate through the headers and body of the response. Note that this is an object, not an array, and that the body is a SimpleXML object. Here's a sample of the returned SimpleXML object: [body] = SimpleXMLElement Object ( [QueryWithAttributesResult] = SimpleXMLElement Object ( [Item] = Array ( [0] = SimpleXMLElement Object ( [Name] = message12413344443260 [Attribute] = Array ( [0] = SimpleXMLElement Object ( [Name] = active [Value] = 1 ) [1] = SimpleXMLElement Object ( [Name] = user [Value] = john ) [2] = SimpleXMLElement Object ( [Name] = message [Value] = This is a message. ) [3] = SimpleXMLElement Object ( [Name] = time [Value] = 1241334444 ) [4] = SimpleXMLElement Object ( [Name] = id [Value] = 12413344443260 ) [5] = SimpleXMLElement Object ( [Name] = ip [Value] = 10.10.10.1 ) ) ) [1] = SimpleXMLElement Object ( [Name] = message12413346907303 [Attribute] = Array ( [0] = SimpleXMLElement Object ( [Name] = active [Value] = 1 ) [1] = SimpleXMLElement Object ( [Name] = user [Value] = fred ) [2] = SimpleXMLElement Object ( [Name] = message [Value] = This is another message ) [3] = SimpleXMLElement Object ( [Name] = time [Value] = 1241334690 ) [4] = SimpleXMLElement Object ( [Name] = id [Value] = 12413346907303 ) [5] = SimpleXMLElement Object ( [Name] = ip [Value] = 10.10.10.2 ) ) ) ) So what code do I need to get through each of the object items? I'd like to loop through each of them and handle it like a returned mySQL query. For example, I can query SimpleDB and then loop though the SimpleXML so I can display the results on the page. Alternatively, how do you turn the whole shebang into an array? I'm new to SimpleXML, so I apologise if my questions aren't specific enough.

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• C# using the "this" keyword in this situation?

  - by Alex

  Hi, I've completed a OOP course assignment where I design and code a Complex Number class. For extra credit, I can do the following: Add two complex numbers. The function will take one complex number object as a parameter and return a complex number object. When adding two complex numbers, the real part of the calling object is added to the real part of the complex number object passed as a parameter, and the imaginary part of the calling object is added to the imaginary part of the complex number object passed as a parameter. Subtract two complex numbers. The function will take one complex number object as a parameter and return a complex number object. When subtracting two complex numbers, the real part of the complex number object passed as a parameter is subtracted from the real part of the calling object, and the imaginary part of the complex number object passed as a parameter is subtracted from the imaginary part of the calling object. I have coded this up, and I used the this keyword to denote the current instance of the class, the code for my add method is below, and my subtract method looks similar: public ComplexNumber Add(ComplexNumber c) { double realPartAdder = c.GetRealPart(); double complexPartAdder = c.GetComplexPart(); double realPartCaller = this.GetRealPart(); double complexPartCaller = this.GetComplexPart(); double finalRealPart = realPartCaller + realPartAdder; double finalComplexPart = complexPartCaller + complexPartAdder; ComplexNumber summedComplex = new ComplexNumber(finalRealPart, finalComplexPart); return summedComplex; } My question is: Did I do this correctly and with good style? (using the this keyword)?

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• jQuery accessing objects

  - by user1275268

  I'm trying to access the values of an object from a function I created with a callback, but have run into some trouble. I'm still fairly new at jQuery/javascript. I call the function as follows: siteDeps(id,function(data){ $.each(data,function(key,val) { console.log(key); console.log(val); }); }); The function runs 5 ajax queries from XML data and returns data as an multidimensional object; here is a excerpt showing the meat of it: function siteDeps(id,callback) { var result = { sitecontactid : {}, siteaddressid : {}, sitephoneid : {}, contactaddressid : {}, contactphoneid : {} }; ...//.... var url5 = decodeURIComponent("sql2xml.php?query=xxxxxxxxxxx"); $.get(url5, function(data){ $(data).find('ID').each(function(i){ result.delsitephoneid[i] = $(this).text(); }); }); callback(result); } The console.log output shows this: sitecontactid Object 0: "2" 1: "3" __proto__: Object siteaddressid Object 0: "1" __proto__: Object sitephoneid Object 0: "1" 1: "5" 2: "54" __proto__: Object contactaddressid Object 0: "80" __proto__: Object contactphoneid Object 0: "6" __proto__: Object How can I extract the callback data in a format I can use, for instance sitephoneid: "1","5","54" Or is there a better/simpler way to do this? Thanks in advance.

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• Can static methods be called using object/instance in .NET

  Ans is Yes and No   Yes in C++, Java and VB.NET No in C#   This is only compiler restriction in c#. You might see in some websites that we can break this restriction using reflection and delegates, but we can’t, according to my little research J I shall try to explain you…   Following is code sample to break this rule using reflection, it seems that it is possible to call a static method using an object, p1 using System; namespace T {     class Program     {         static void Main()         {             var p1 = new Person() { Name = "Smith" };             typeof(Person).GetMethod("TestStatMethod").Invoke(p1, new object[] { });                     }         class Person         {             public string Name { get; set; }             public static void TestStatMethod()             {                 Console.WriteLine("Hello");             }         }     } } but I do not think so this method is being called using p1 rather Type Name “Person”. I shall try to prove this… look at another example…  Test2 has been inherited from Test1. Let’s see various scenarios… Scenario1 using System; namespace T {     class Program     {         static void Main()         {             Test1 t = new Test1();            typeof(Test2).GetMethod("Method1").Invoke(t,                                  new object[] { });         }     }     class Test1     {         public static void Method1()         {             Console.WriteLine("At test1::Method1");         }     }       class Test2 : Test1     {         public static void Method1()         {             Console.WriteLine("At test1::Method2");         }     } } Output:   At test1::Method2 Scenario2         static void Main()         {             Test2 t = new Test2();            typeof(Test2).GetMethod("Method1").Invoke(t,                                          new object[] { });         }   Output:   At test1::Method2   Scenario3         static void Main()         {             Test1 t = new Test2();            typeof(Test2).GetMethod("Method1").Invoke(t,                             new object[] { });         }   Output: At test1::Method2 In all above scenarios output is same, that means, Reflection also not considering the object what you pass to Invoke method in case of static methods. It is always considering the type which you specify in typeof(). So, what is the use passing instance to “Invoke”. Let see below sample using System; namespace T {     class Program     {         static void Main()         {            typeof(Test2).GetMethod("Method1").                Invoke(null, new object[] { });         }     }       class Test1     {         public static void Method1()         {             Console.WriteLine("At test1::Method1");         }     }     class Test2 : Test1     {         public static void Method1()         {             Console.WriteLine("At test1::Method2");         }     } }   Output is   At test1::Method2   I was able to call Invoke “Method1” of Test2 without any object.  Yes, there no wonder here as Method1 is static. So we may conclude that static methods cannot be called using instances (only in c#) Why Microsoft has restricted it in C#? Ans: Really there Is no use calling static methods using objects because static methods are stateless. but still Java and C++ latest compilers allow calling static methods using instances. Java sample class Test {      public static void main(String str[])      {            Person p = new Person();            System.out.println(p.GetCount());      } }   class Person {   public static int GetCount()   {      return 100;   } }   Output          100 span.fullpost {display:none;}

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• Unity3d: calculate the result of a transform without modifying transform object itself

  - by Heisenbug

  I'm in the following situation: I need to move an object in some way, basically rotating it around its parent local position, or translating it in its parent local space (I know how to do this). The amount of rotation and translation is know at runtime (it depends on several factors, the speed of the object, enviroment factors, etc..). The problem is the following: I can perform this transformation only if the result position of the transformed object fit some criterias. An example could be this: the distance between the position before and after the transformation must be less than a given threshold. (Actually the conditions could be several and more complex) The problem is that if I use Transform.Rotate and Transform.Translate methods of my GameObject, I will loose the original Transform values. I think I can't copy the original Transform using instantiate for performance issues. How can I perform such a task? I think I have more or less 2 possibilities: First Don't modify the GameObject position through Transform. Calculate which will be the position after the transform. If the position is legal, modify transform through Translate and Rotate methods Second Store the original transform someway. Transform the object using Translate and Rotate. If the transformed position is illegal, restore the original one.

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• How to write constructors which might fail to properly instantiate an object

  - by whitman

  Sometimes you need to write a constructor which can fail. For instance, say I want to instantiate an object with a file path, something like obj = new Object("/home/user/foo_file") As long as the path points to an appropriate file everything's fine. But if the string is not a valid path things should break. But how? You could: 1. throw an exception 2. return null object (if your programming language allows constructors to return values) 3. return a valid object but with a flag indicating that its path wasn't set properly (ugh) 4. others? I assume that the "best practices" of various programming languages would implement this differently. For instance I think ObjC prefers (2). But (2) would be impossible to implement in C++ where constructors must have void as a return type. In that case I take it that (1) is used. In your programming language of choice can you show how you'd handle this problem and explain why?

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• Object pools for efficient resource management

  - by GameDevEnthusiast

  How can I avoid using default new() to create each object? My previous demo had very unpleasant framerate hiccups during dynamic memory allocations (usually, when arrays are resized), and creating lots of small objects which often contain one pointer to some DirectX resource seems like an awful lot of waste. I'm thinking about: Creating a master look-up table to refer to objects by handles (for safety & ease of serialization), much like EntityList in source engine Creating a templated object pool, which will store items contiguously (more cache-friendly, fast iteration, etc.) and the stored elements will be accessed (by external systems) via the global lookup table. The object pool will use the swap-with-last trick for fast removal (it will invoke the object's ~destructor first) and will update the corresponding indices in the global table accordingly (when growing/shrinking/moving elements). The elements will be copied via plain memcpy(). Is it a good idea? Will it be safe to store objects of non-POD types (e.g. pointers, vtable) in such containers? Related post: Dynamic Memory Allocation and Memory Management

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• Scrolling though objects then creating a new instace of this object

  - by gopgop

  In my game when pressing the right mouse button you will place an object on the ground. all objects have the same super class (GameObject). I have a field called selected and will be equal to one certain gameobject at a time. when clicking the right mouse button it checks whats the instance of selected and that how it determines which object to place on the ground. code exapmle: t is the "slot" for which the object will go to. if (selected instanceof MapleTree) { t = new MapleTree(game,highLight); } else if (selected instanceof OakTree) { t = new OakTree(game,highLight); } Now it has to be a "new" instance of the object. Eventually my game will have hundreds of GameObjects and I don't want to have a huge if else statement. How would I make it so it scrolls though the possible kinds of objects and if its the correct type then create a new instance of it...? When pressing E it will switch the type of selected and is an if else statement as well. How would I do it for this too? here is a code example: if (selected instanceof MapleTree) { selected = new OakTree(game); } else if (selected instanceof OakTree) { selected = new MapleTree(game); }

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