dynamic linking - Page 2

Rewrite a dynamic URL to a new dynamic URL

- by Jmino14

I am new to the RewriteEngine and have not been able to find an answer to the following issue. I run an ecommerce site with an ever changing catalog of product skus. Our URLs are dynamic. The question is, what if I want to have a dynamic variable redirect to a different dynamic variable. For instance, I want: http://www.mydomain.com/product.jhtm?id=12345 to now go to: www.mydomain.com/product.jhtm?id=78910 How can I do this through the .htaccess? Thanks in advance.

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.NET 4.0 Dynamic object used statically?

- by Kevin Won

I've gotten quite sick of XML configuration files in .NET and want to replace them with a format that is more sane. Therefore, I'm writing a config file parser for C# applications that will take a custom config file format, parse it, and create a Python source string that I can then execute in C# and use as a static object (yes that's right--I want a static (not the static type dyanamic) object in the end). Here's an example of what my config file looks like: // my custom config file format GlobalName: ExampleApp Properties { ExternalServiceTimeout: "120" } Python { // this allows for straight python code to be added to handle custom config def MyCustomPython: return "cool" } Using ANTLR I've created a Lexer/Parser that will convert this format to a Python script. So assume I have that all right and can take the .config above and run my Lexer/Parser on it to get a Python script out the back (this has the added benefit of giving me a validation tool for my config). By running the resultant script in C# // simplified example of getting the dynamic python object in C# // (not how I really do it) ScriptRuntime py = Python.CreateRuntime(); dynamic conf = py.UseFile("conftest.py"); dynamic t = conf.GetConfTest("test"); I can get a dynamic object that has my configuration settings. I can now get my config file settings in C# by invoking a dynamic method on that object: //C# calling a method on the dynamic python object var timeout = t.GetProperty("ExternalServiceTimeout"); //the config also allows for straight Python scripting (via the Python block) var special = t.MyCustonPython(); of course, I have no type safety here and no intellisense support. I have a dynamic representation of my config file, but I want a static one. I know what my Python object's type is--it is actually newing up in instance of a C# class. But since it's happening in python, it's type is not the C# type, but dynamic instead. What I want to do is then cast the object back to the C# type that I know the object is: // doesn't work--can't cast a dynamic to a static type (nulls out) IConfigSettings staticTypeConfig = t as IConfigSettings Is there any way to figure out how to cast the object to the static type? I'm rather doubtful that there is... so doubtful that I took another approach of which I'm not entirely sure about. I'm wondering if someone has a better way... So here's my current tactic: since I know the type of the python object, I am creating a C# wrapper class: public class ConfigSettings : IConfigSettings that takes in a dynamic object in the ctor: public ConfigSettings(dynamic settings) { this.DynamicProxy = settings; } public dynamic DynamicProxy { get; private set; } Now I have a reference to the Python dynamic object of which I know the type. So I can then just put wrappers around the Python methods that I know are there: // wrapper access to the underlying dynamic object // this makes my dynamic object appear 'static' public string GetSetting(string key) { return this.DynamicProxy.GetProperty(key).ToString(); } Now the dynamic object is accessed through this static proxy and thus can obviously be passed around in the static C# world via interface, etc: // dependency inject the dynamic object around IBusinessLogic logic = new BusinessLogic(IConfigSettings config); This solution has the benefits of all the static typing stuff we know and love while at the same time giving me the option of 'bailing out' to dynamic too: // the DynamicProxy property give direct access to the dynamic object var result = config.DynamicProxy.MyCustomPython(); but, man, this seems rather convoluted way of getting to an object that is a static type in the first place! Since the whole dynamic/static interaction world is new to me, I'm really questioning if my solution is optimal or if I'm missing something (i.e. some way of casting that dynamic object to a known static type) about how to bridge the chasm between these two universes.

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dynamic urls and links on one web page

- by John

I am trying to figure out how to create dynamic links and urls on a static webpage. What I want to do is the following: I have a single webpage for example: MYWEBPAGEdotCOM/INDEX.HTML that will always look the same, except for one link on the page. the link would be on the page for example: LINK TO AFFILIATE: affiliatedotCOM/my-affiliate_code_here_DYNAMIC_REFERER the only thing would change is the "DYNAMIC_REFERER" with every dynamic url on this page: MYWEBPAGEdotCOM/INDEX.PHP_id=test1 MYWEBPAGEdotCOM/INDEX.PHP_id=test2 MYWEBPAGEdotCOM/INDEX.PHP_id=test3 MYWEBPAGEdotCOM/INDEX.PHP_id=test4 which would only hange the dynamic link on the page to: affiliatedotCOM/my-affiliate_code_here_test1 affiliatedotCOM/my-affiliate_code_here_test2 affiliatedotCOM/my-affiliate_code_here_test3 affiliatedotCOM/my-affiliate_code_here_test4 Can someone tell me how I could go about doing this? I just dont want to have to make 100's of pages, as this would prevent me from having to do so.

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dynamic urls and links on one web page

- by John

I am trying to figure out how to create dynamic links and urls on a static webpage. What I want to do is the following: I have a single webpage for example: MYWEBPAGEdotCOM/INDEX.HTML that will always look the same, except for one link on the page. the link would be on the page for example: LINK TO AFFILIATE: affiliatedotCOM/my-affiliate_code_here_DYNAMIC_REFERER the only thing would change is the "DYNAMIC_REFERER" with every dynamic url on this page: MYWEBPAGEdotCOM/INDEX.PHP_id=test1 MYWEBPAGEdotCOM/INDEX.PHP_id=test2 MYWEBPAGEdotCOM/INDEX.PHP_id=test3 MYWEBPAGEdotCOM/INDEX.PHP_id=test4 which would only hange the dynamic link on the page to: affiliatedotCOM/my-affiliate_code_here_test1 affiliatedotCOM/my-affiliate_code_here_test2 affiliatedotCOM/my-affiliate_code_here_test3 affiliatedotCOM/my-affiliate_code_here_test4 Can someone tell me how I could go about doing this? I just dont want to have to make 100's of pages, as this would prevent me from having to do so.

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xen 4.1 host priodically dropping network packets of domU

- by Dyutiman Chakraborty

I have xen 4.1 Host running on a ubuntu 12.04 LTS Server with ip 153.x.x.54. I have setup 2 VMs on it, namely, "dev.mydomain.com" and "web.mydomain.com" with ips 195.X.X.2 and 195.x.x.3 respectively. For network the VMs connect through xendbr0 (xen-bridge), and can accces the network properly. I can also login to the VMs with ssh with no issue. However when I ping any of the VMs, there is a high amount of periodic packet drop. If I the ping the xen host (dom0) there is no packet drop. Following is a output of "tcpdump | grep ICMP" on dOM0 while I was pinging one of the domU tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 05:19:55.682493 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 30, length 64 05:19:56.691144 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 31, length 64 05:19:57.698776 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 32, length 64 05:19:58.706784 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 33, length 64 05:19:59.714751 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 34, length 64 05:20:00.723144 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 35, length 64 05:20:01.730349 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 36, length 64 05:20:02.739017 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 37, length 64 05:20:03.746806 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 38, length 64 05:20:06.770326 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 41, length 64 05:20:07.778801 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 42, length 64 05:20:08.786481 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 43, length 64 05:20:09.794720 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 44, length 64 05:20:10.802395 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 45, length 64 05:20:11.810770 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 46, length 64 05:20:12.818511 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 47, length 64 05:20:13.826817 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 48, length 64 05:20:14.835125 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 49, length 64 05:20:15.842138 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3460, seq 50, length 64 05:20:18.274072 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 1, length 64 05:20:19.282347 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 2, length 64 05:20:20.290746 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 3, length 64 05:20:21.297910 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 4, length 64 05:20:22.305656 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 5, length 64 05:20:23.314369 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 6, length 64 05:20:24.322055 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 7, length 64 05:20:25.329782 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 8, length 64 05:20:26.338473 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 9, length 64 05:20:27.346411 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 10, length 64 05:20:28.354175 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 11, length 64 05:20:29.361640 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 12, length 64 05:20:30.370026 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 13, length 64 05:20:31.377696 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 14, length 64 05:20:32.386151 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 15, length 64 05:20:33.394118 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 16, length 64 05:20:34.402058 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 17, length 64 05:20:35.409002 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 18, length 64 05:20:36.417692 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > web.mydomain.com: ICMP echo request, id 3461, seq 19, length 64 05:20:36.496916 IP6 fe80::3285:a9ff:feec:fc69 > ip6-allnodes: HBH ICMP6, multicast listener querymax resp delay: 1000 addr: ::, length 24 05:20:36.499112 IP6 fe80::21c:c0ff:fe6c:c091 > ff02::1:ff6c:c091: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff6c:c091, length 24 05:20:36.507041 IP6 fe80::227:eff:fe11:fa3f > ff02::1:ff00:2: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff00:2, length 24 05:20:36.523919 IP6 fe80::21c:c0ff:fe77:6257 > ff02::1:ff77:6257: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff77:6257, length 24 05:20:36.544785 IP6 fe80::54:ff:fe12:ea9a > ff02::1:ff12:ea9a: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff12:ea9a, length 24 05:20:36.581740 IP6 fe80::5604:a6ff:fef1:6da7 > ff02::1:fff1:6da7: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:fff1:6da7, length 24 05:20:36.600103 IP6 fe80::8a8:8aa0:5e18:917a > ff02::1:ff18:917a: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff18:917a, length 24 05:20:36.601989 IP6 fe80::227:eff:fe11:fa3e > ff02::1:ff11:fa3e: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff11:fa3e, length 24 05:20:36.611090 IP6 fe80::dcad:56ff:fe57:3bbe > ff02::1:ff57:3bbe: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff57:3bbe, length 24 05:20:36.660521 IP6 fe80::54:ff:fe02:1d31 > ff02::1:ff00:6: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff00:6, length 24 05:20:36.698871 IP6 fe80::21e:8cff:feb4:9f89 > ff02::1:ffb4:9f89: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ffb4:9f89, length 24 05:20:36.776548 IP6 fe80::54:ff:fe12:ea9a > ff02::1:ff01:7: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff01:7, length 24 05:20:36.781910 IP6 fe80::54:ff:fe8f:6dd > ff02::1:ff00:3: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff00:3, length 24 05:20:36.865475 IP6 fe80::21c:c0ff:fe4a:ae9f > ff02::1:ff4a:ae9f: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff4a:ae9f, length 24 05:20:36.908333 IP6 fe80::dcad:45ff:fe90:84db > ff02::1:ff90:84db: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff90:84db, length 24 05:20:36.919653 IP6 fe80::54:ff:fe12:ea9a > ff02::1:ff00:7: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff00:7, length 24 05:20:36.924276 IP6 fe80::59a2:2a4a:2082:6dee > ff02::1:ff82:6dee: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff82:6dee, length 24 05:20:37.001905 IP6 fe80::54:ff:fe8f:6dd > ff02::1:ff8f:6dd: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff8f:6dd, length 24 05:20:37.042403 IP6 fe80::54:ff:fe95:54f2 > ff02::1:ff95:54f2: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff95:54f2, length 24 05:20:37.090992 IP6 fe80::21c:c0ff:fe77:62ac > ff02::1:ff77:62ac: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff77:62ac, length 24 05:20:37.098118 IP6 fe80::d63d:7eff:fe01:b67f > ff02::1:ff01:b67f: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff01:b67f, length 24 05:20:37.118784 IP6 fe80::54:ff:fe12:ea9a > ff02::202: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::202, length 24 05:20:37.168548 IP6 fe80::54:ff:fe02:1d31 > ff02::1:ff02:1d31: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff02:1d31, length 24 05:20:41.743286 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 1, length 64 05:20:41.743542 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 1, length 64 05:20:42.743859 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 2, length 64 05:20:42.743952 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 2, length 64 05:20:43.745689 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 3, length 64 05:20:43.745777 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 3, length 64 05:20:44.746706 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 4, length 64 05:20:44.746796 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 4, length 64 05:20:45.747986 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 5, length 64 05:20:45.748082 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 5, length 64 05:20:46.749834 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 6, length 64 05:20:46.749920 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 6, length 64 05:20:47.750838 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 7, length 64 05:20:47.751182 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 7, length 64 05:20:48.751909 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 8, length 64 05:20:48.751991 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 8, length 64 05:20:49.752542 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 9, length 64 05:20:49.752620 IP dev.mydomain.com > ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in: ICMP echo reply, id 3463, seq 9, length 64 05:20:50.754246 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 10, length 64 05:20:51.753856 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 11, length 64 05:20:52.752868 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 12, length 64 05:20:53.754174 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 13, length 64 05:20:54.753972 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 14, length 64 05:20:55.753814 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 15, length 64 05:20:56.753391 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 16, length 64 05:20:57.753683 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 17, length 64 05:20:58.753487 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 18, length 64 05:20:59.754013 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 19, length 64 05:21:00.753169 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 20, length 64 05:21:01.753757 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 21, length 64 05:21:02.753307 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 22, length 64 05:21:03.753021 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 23, length 64 05:21:04.753628 IP ABTS-North-Dynamic-226.X.X.122.airtelbroadband.in > dev.mydomain.com: ICMP echo request, id 3463, seq 24, length 64 ^C479 packets captured 718 packets received by filter 238 packets dropped by kernel 3 packets dropped by interface You see the ping request is not responed to initially, then for a moment it is replied back and then again no reply. I have tried everything (to the best of my knowledge) to fix this, but can't find any answer Any help will be greatly appreciated Thanks.

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Dynamic Class Inheritance For PHP

- by VirtuosiMedia

I have a situation where I think I might need dynamic class inheritance in PHP 5.3, but the idea doesn't sit well and I'm looking for a different design pattern to solve my problem if it's possible. Use Case I have a set of DB abstraction layer classes that dynamically compiles SQL queries, with one DAL class for each DB type (MySQL, MsSQL, Oracle, etc.). Each table in the database has its own class that extends the appropriate DAL class. The idea is that you interact with the table classes, but never directly use the DAL class. If you want to support a different DB type for your app, you don't need to rewrite any queries or even any code, you simply change a setting that swaps one DAL class out for another...and that's it. To give you a better idea of how this is used, you can take a look at the DAL class, the table classes, and how they are used on this StackExchange Code Review page. To really understand what I'm trying to do, please take a look at my implementation first before suggesting a solution. Issues The strategy that I had used previously was to have all of the DAL classes share the same class name. This eliminated autoloading, so I had to manually load the appropriate DAL class in a switch statement. However, this approach presents some problems for testing and documentation purposes, so I'd like to find a different way to solve the problem of loading the correct DAL class more elegantly. Update to clarify the issue The problem basically boils down to inconsistencies in the class name (pre-PHP 5.3) or class namespace (PHP 5.3) and its location in the directory structure. At this point, all of my DAL classes have the same name, DBObject, but reside in different folders, MySQL, Oracle, etc. My table classes all extend DBObject, but which DBObject they extend varies depending on which one has been loaded. Basically, I'm trying to have my cake and eat it too. The table classes act as a stable API and extend a dynamic backend, the DAL (DBObject) classes. It works great, but I outsmarted myself and because of the inconsistencies with the class names and their locations, I can't autoload the DBObject, which makes running unit tests and generating API docs impossible for the DBObject classes because the tests and docs rely on auto-loading. Just loading the appropriate DBObject into memory using a factory method won't work because there will be times when I need to load multiple DBObjects for testing. Because the classes currently share a name, this causes a class is already defined error. I can make exceptions for the DBObjects in my test code, obviously, but I'm looking for something a little less hacky as there may future instances where something similar would need to be done. Solutions? Worst case scenario, I can continue my current strategy, but I don't like it very much, especially as I'll soon be converting my code to PHP 5.3. I suspect that I can use some sort of dynamic inheritance via either namespaces (preferred) or a dynamic class extension, but I haven't been able to find good examples of this implemented in the wild. In your answers, please suggest either an alternate pattern that would work for this use case or an example of dynamic inheritance done right. Please assume PHP 5.3 with namespaced code. Any code examples are greatly encouraged. The preferred constraints for the solution are: DAL class can be autoloaded. DAL classes don't share the same exact same namespace, but share the same class name. As an example, I would prefer to use classes named DbObject that use namespaces like Vm\Db\MySql and Vm\Db\Oracle. Table classes don't have to be rewritten with a change in DB type. The appropriate DB type is determined via a single setting only. That setting is the only thing that should need to change to interchange DB types. Ideally, the setting check should occur only once per page load, but I'm flexible on that.

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Does Java support dynamic method invocation?

- by eSKay

class A { void F() { System.out.println("a"); }} class B extends A { void F() { System.out.println("b"); }} public class X { public static void main(String[] args) { A objA = new B(); objA.F(); } } Here, F() is being invoked dynamically, isn't it? This article says ... the Java bytecode doesn’t support dynamic method invocation. There are three supported invocations modes : invokestatic, invokespecial, invokeinterface or invokevirtual. These modes allows to call methods with known signature. We talk of strongly typed language. This allows to to make some checks directly at compile time. On the other side, the dynamic languages use dynamic types. So we can call a method unknown at the compile time, but that’s completely impossible with the Java bytecode. What am I missing?

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Debugging dynamic sql + dynamic tables in MS SQL Server 2008.

- by Hamish Grubijan

Hi, I have a messy stored procedure which uses dynamic sql. I can debug it in runtime by adding print @sql; where @sql; is the string containing the dynamic SQL, right before I call execute (@sql);. Now, the multi-page stored procedure also creates dynamic tables and uses them in a query. I want to print those tables to the console right before I do an execute, so that I know exactly what the query is trying to do. However, the SQL Server 08 does not like that. When I try: print #temp_table; and try to compile the S.P. I get this error: The name "#temp_table" is not permitted in this context. Valid expressions are constants, constant expressions, and (in some contexts) variables. Column names are not permitted. Please help.

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C++ linking error when linking postgresql

- by Brent Rowswell

When compiling my code I run into an issue as follows: io.cpp:21: undefined reference to `PQconnectdb' as well as all other instances of missing postgres function calls occurring in my code. Obviously this is a linking problem, I'm just not sure what the link issue is. I'm compiling with the following: mpiCC -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ decisioning_mpi.cpp g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ io.cpp g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ calculations.cpp g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ rules.cpp g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ Instrument.cpp g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ Backtest_Parameter_CPO.cpp g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ Backtest_Trade_CPO.cpp g++ -c -O2 -g -Wall -Werror -I /usr/include/postgresql/ Data_Bar.cpp mpiCC -o decisioning_mpi -O2 -g -Wall -Werror -L/usr/lib -lm -lpq decisioning_mpi.o io.o calculations.o rules.o Instrument.o Backtest_Parameter_CPO.o Backtest_Trade_CPO.o Data_Bar.o It should be noted that this is the correct directory for libpq-fe.h and that I'm linking pq, so I'm not exactly sure why the postgres functions aren't linking correctly. I'm running Ubuntu 12.04 and installed psql (PostgreSQL) 9.1.6 from synaptic. As well I'll short circuit this, I am using #include "libpq-fe.h". Any ideas on how I can get this linking issue resolved?

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dynamic, How to test if a property is available

- by Miau

Scenario is very simple somewhere in the code I have this dynamic myVariable = GetDataThatLooksVerySimilarButNotTheSame(); //how to do this? if (myVariable.MyProperty.Exists) //Do stuff So basically the question is how to check (avoiding exceptions) that a certain property is available in my dynamic variable. I could do GetType() but I d rather avoid that, I dont actually want to know the type of the object I want to know if a property (or method if that makes life easier) is available Any pointers? Cheers

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New insights I can learn from the Groovy language

- by Andrea

I realize that, for a programmer coming from the Java world, Groovy contains a lot of new ideas and cool tricks. My situation is different, as I am learning Groovy coming from a dynamic background, mainly Python and Javascript. When learning a new language, I find that it helps me if I know beforehand which features are more or less old acquaintances under a new syntax and which ones are really new, so that I can concentrate on the latter. So I would like to know which traits distinguish Groovy among the dynamic languages. What are the ideas and insights that a programmer well-versed in dynamic languages should pay attention to when learning Groovy?

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What does static linking against a library actually do?

- by Salgar

Say I had a library called libfoo which contained a class, a few static variables, possibly something with 'C' linkage, and a few other functions. Now I have a main program which looks like this: int main() { return 5+5; } When I compile and link this, I link against libfoo. Will this have any effect? Will my executable increase in size? If so, why? Do the static variables or their addresses get copied into my executable? Apologies if there is a similar question to this or if I'm being particularly stupid in any way.

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Creating a dynamic proxy generator – Part 1 – Creating the Assembly builder, Module builder and cach

- by SeanMcAlinden

I’ve recently started a project with a few mates to learn the ins and outs of Dependency Injection, AOP and a number of other pretty crucial patterns of development as we’ve all been using these patterns for a while but have relied totally on third part solutions to do the magic. We thought it would be interesting to really get into the details by rolling our own IoC container and hopefully learn a lot on the way, and you never know, we might even create an excellent framework. The open source project is called Rapid IoC and is hosted at http://rapidioc.codeplex.com/ One of the most interesting tasks for me is creating the dynamic proxy generator for enabling Aspect Orientated Programming (AOP). In this series of articles, I’m going to track each step I take for creating the dynamic proxy generator and I’ll try my best to explain what everything means - mainly as I’ll be using Reflection.Emit to emit a fair amount of intermediate language code (IL) to create the proxy types at runtime which can be a little taxing to read. It’s worth noting that building the proxy is without a doubt going to be slightly painful so I imagine there will be plenty of areas I’ll need to change along the way. Anyway lets get started… Part 1 - Creating the Assembly builder, Module builder and caching mechanism Part 1 is going to be a really nice simple start, I’m just going to start by creating the assembly, module and type caches. The reason we need to create caches for the assembly, module and types is simply to save the overhead of recreating proxy types that have already been generated, this will be one of the important steps to ensure that the framework is fast… kind of important as we’re calling the IoC container ‘Rapid’ – will be a little bit embarrassing if we manage to create the slowest framework. The Assembly builder The assembly builder is what is used to create an assembly at runtime, we’re going to have two overloads, one will be for the actual use of the proxy generator, the other will be mainly for testing purposes as it will also save the assembly so we can use Reflector to examine the code that has been created. Here’s the code: DynamicAssemblyBuilder using System; using System.Reflection; using System.Reflection.Emit; namespace Rapid.DynamicProxy.Assembly { /// <summary> /// Class for creating an assembly builder. /// </summary> internal static class DynamicAssemblyBuilder { #region Create /// <summary> /// Creates an assembly builder. /// </summary> /// <param name="assemblyName">Name of the assembly.</param> public static AssemblyBuilder Create(string assemblyName) { AssemblyName name = new AssemblyName(assemblyName); AssemblyBuilder assembly = AppDomain.CurrentDomain.DefineDynamicAssembly( name, AssemblyBuilderAccess.Run); DynamicAssemblyCache.Add(assembly); return assembly; } /// <summary> /// Creates an assembly builder and saves the assembly to the passed in location. /// </summary> /// <param name="assemblyName">Name of the assembly.</param> /// <param name="filePath">The file path.</param> public static AssemblyBuilder Create(string assemblyName, string filePath) { AssemblyName name = new AssemblyName(assemblyName); AssemblyBuilder assembly = AppDomain.CurrentDomain.DefineDynamicAssembly( name, AssemblyBuilderAccess.RunAndSave, filePath); DynamicAssemblyCache.Add(assembly); return assembly; } #endregion } } So hopefully the above class is fairly explanatory, an AssemblyName is created using the passed in string for the actual name of the assembly. An AssemblyBuilder is then constructed with the current AppDomain and depending on the overload used, it is either just run in the current context or it is set up ready for saving. It is then added to the cache. DynamicAssemblyCache using System.Reflection.Emit; using Rapid.DynamicProxy.Exceptions; using Rapid.DynamicProxy.Resources.Exceptions; namespace Rapid.DynamicProxy.Assembly { /// <summary> /// Cache for storing the dynamic assembly builder. /// </summary> internal static class DynamicAssemblyCache { #region Declarations private static object syncRoot = new object(); internal static AssemblyBuilder Cache = null; #endregion #region Adds a dynamic assembly to the cache. /// <summary> /// Adds a dynamic assembly builder to the cache. /// </summary> /// <param name="assemblyBuilder">The assembly builder.</param> public static void Add(AssemblyBuilder assemblyBuilder) { lock (syncRoot) { Cache = assemblyBuilder; } } #endregion #region Gets the cached assembly /// <summary> /// Gets the cached assembly builder. /// </summary> /// <returns></returns> public static AssemblyBuilder Get { get { lock (syncRoot) { if (Cache != null) { return Cache; } } throw new RapidDynamicProxyAssertionException(AssertionResources.NoAssemblyInCache); } } #endregion } } The cache is simply a static property that will store the AssemblyBuilder (I know it’s a little weird that I’ve made it public, this is for testing purposes, I know that’s a bad excuse but hey…) There are two methods for using the cache – Add and Get, these just provide thread safe access to the cache. The Module Builder The module builder is required as the create proxy classes will need to live inside a module within the assembly. Here’s the code: DynamicModuleBuilder using System.Reflection.Emit; using Rapid.DynamicProxy.Assembly; namespace Rapid.DynamicProxy.Module { /// <summary> /// Class for creating a module builder. /// </summary> internal static class DynamicModuleBuilder { /// <summary> /// Creates a module builder using the cached assembly. /// </summary> public static ModuleBuilder Create() { string assemblyName = DynamicAssemblyCache.Get.GetName().Name; ModuleBuilder moduleBuilder = DynamicAssemblyCache.Get.DefineDynamicModule (assemblyName, string.Format("{0}.dll", assemblyName)); DynamicModuleCache.Add(moduleBuilder); return moduleBuilder; } } } As you can see, the module builder is created on the assembly that lives in the DynamicAssemblyCache, the module is given the assembly name and also a string representing the filename if the assembly is to be saved. It is then added to the DynamicModuleCache. DynamicModuleCache using System.Reflection.Emit; using Rapid.DynamicProxy.Exceptions; using Rapid.DynamicProxy.Resources.Exceptions; namespace Rapid.DynamicProxy.Module { /// <summary> /// Class for storing the module builder. /// </summary> internal static class DynamicModuleCache { #region Declarations private static object syncRoot = new object(); internal static ModuleBuilder Cache = null; #endregion #region Add /// <summary> /// Adds a dynamic module builder to the cache. /// </summary> /// <param name="moduleBuilder">The module builder.</param> public static void Add(ModuleBuilder moduleBuilder) { lock (syncRoot) { Cache = moduleBuilder; } } #endregion #region Get /// <summary> /// Gets the cached module builder. /// </summary> /// <returns></returns> public static ModuleBuilder Get { get { lock (syncRoot) { if (Cache != null) { return Cache; } } throw new RapidDynamicProxyAssertionException(AssertionResources.NoModuleInCache); } } #endregion } } The DynamicModuleCache is very similar to the assembly cache, it is simply a statically stored module with thread safe Add and Get methods. The DynamicTypeCache To end off this post, I’m going to create the cache for storing the generated proxy classes. I’ve spent a fair amount of time thinking about the type of collection I should use to store the types and have finally decided that for the time being I’m going to use a generic dictionary. This may change when I can actually performance test the proxy generator but the time being I think it makes good sense in theory, mainly as it pretty much maintains it’s performance with varying numbers of items – almost constant (0)1. Plus I won’t ever need to loop through the items which is not the dictionaries strong point. Here’s the code as it currently stands: DynamicTypeCache using System; using System.Collections.Generic; using System.Security.Cryptography; using System.Text; namespace Rapid.DynamicProxy.Types { /// <summary> /// Cache for storing proxy types. /// </summary> internal static class DynamicTypeCache { #region Declarations static object syncRoot = new object(); public static Dictionary<string, Type> Cache = new Dictionary<string, Type>(); #endregion /// <summary> /// Adds a proxy to the type cache. /// </summary> /// <param name="type">The type.</param> /// <param name="proxy">The proxy.</param> public static void AddProxyForType(Type type, Type proxy) { lock (syncRoot) { Cache.Add(GetHashCode(type.AssemblyQualifiedName), proxy); } } /// <summary> /// Tries the type of the get proxy for. /// </summary> /// <param name="type">The type.</param> /// <returns></returns> public static Type TryGetProxyForType(Type type) { lock (syncRoot) { Type proxyType; Cache.TryGetValue(GetHashCode(type.AssemblyQualifiedName), out proxyType); return proxyType; } } #region Private Methods private static string GetHashCode(string fullName) { SHA1CryptoServiceProvider provider = new SHA1CryptoServiceProvider(); Byte[] buffer = Encoding.UTF8.GetBytes(fullName); Byte[] hash = provider.ComputeHash(buffer, 0, buffer.Length); return Convert.ToBase64String(hash); } #endregion } } As you can see, there are two public methods, one for adding to the cache and one for getting from the cache. Hopefully they should be clear enough, the Get is a TryGet as I do not want the dictionary to throw an exception if a proxy doesn’t exist within the cache. Other than that I’ve decided to create a key using the SHA1CryptoServiceProvider, this may change but my initial though is the SHA1 algorithm is pretty fast to put together using the provider and it is also very unlikely to have any hashing collisions. (there are some maths behind how unlikely this is – here’s the wiki if you’re interested http://en.wikipedia.org/wiki/SHA_hash_functions) Anyway, that’s the end of part 1 – although I haven’t started any of the fun stuff (by fun I mean hairpulling, teeth grating Relfection.Emit style fun), I’ve got the basis of the DynamicProxy in place so all we have to worry about now is creating the types, interceptor classes, method invocation information classes and finally a really nice fluent interface that will abstract all of the hard-core craziness away and leave us with a lightning fast, easy to use AOP framework. Hope you find the series interesting. All of the source code can be viewed and/or downloaded at our codeplex site - http://rapidioc.codeplex.com/ Kind Regards, Sean.

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how to dinamically add controls in asp.net Dynamic Data

- by loviji

Hello, i'm trying to work with asp.NET Dynamic Data. So, I see Dynamic Data not well learned by people as other technologies. now, to my question. Lets us work with Details.aspx page that located on ~\DynamicData\PageTemplates I need to add <asp:DynamicControl runat="server" to page into Form1.detailsTable. i've tried like this: protected DynamicControl myC=new DynamicControl(); protected void Page_Load(object sender, EventArgs e) { foreach(var c in table.Columns) { myC.DataField=c.DisplayName; FormView1.Controls.Add(myC); } } but I can not see the desired result. where is the problem. thanks

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How to dynamically add controls in asp.net Dynamic Data

- by loviji

Hello, i'm trying to work with asp.NET Dynamic Data. So, I see asp.NET Dynamic Data not well learned by people as other technologies. now, to my question. Lets us work with Details.aspx page that located on ~\DynamicData\PageTemplates I need to add <asp:DynamicControl runat="server" to page into Form1.detailsTable. i've tried like this: protected DynamicControl myC=new DynamicControl(); protected void Page_Load(object sender, EventArgs e) { foreach(var c in table.Columns) { myC.DataField=c.DisplayName; FormView1.Controls.Add(myC); } } but I can not see the desired result. where is the problem. thanks

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Dynamic DNS at freedns.afraid.org using a Fritz!Box

- by kai

I am having some trouble setting up Dynamic DNS with my Fritz!Box 7360. I have set up the Dynamic DNS page with (this is translated from German, so might be worded a bit differently): [x] Use dynamic DNS Dynamic DNS Provider: User defined Update-URL: https://freedns.afraid.org/dynamic/update.php?MY-DIRECT-URL-KEY Domain Name: mydomain.crabdance.com User Name: myusername Password: mypassword Now on the FritzBox status page, it says: Dynamic DNS: activated, mydomain.crabdance.com, Status: Account temprarily deactivated When I check back on http://freedns.afraid.org, my IP address never changes. Is there any way to fix this? Note my router is on an IPv6 network (m-net), with IPv4 only through DS-Lite. I'm not sure whether this affects anything. Update: Following the guide here (putting myusername instead of MY-DIRECT-URL-KEY) hasn't given any succes. However, the status field has changed slightly: Dynamic DNS: activated, mydomain.crabdance.com, Status: unknown

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What can I do with dynamic typing that I can not do with static typing

- by Justin984

I've been using python for a few days now and I think I understand the difference between dynamic and static typing. What I don't understand is why it's useful. I keep hearing about its "flexibility" but it seems like it just moves a bunch of compile time checks to runtime, which means more unit tests. This seems like an awfully big tradeoff to make for small advantages like readability and "flexibility". Can someone provide me with a real world example where dynamic typing allows me to do something I can't do with static typing?

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Java Dynamic Binding

- by Chris Okyen

I am having trouble understanding the OOP Polymorphic principl of Dynamic Binding ( Late Binding ) in Java. I looked for question pertaining to java, and wasn't sure if a overall answer to how dynamic binding works would pertain to Java Dynamic Binding, I wrote this question. Given: class Person { private String name; Person(intitialName) { name = initialName; } // irrelevant methods is here. // Overides Objects method public void writeOutput() { println(name); } } class Student extends Person { private int studentNumber; Student(String intitialName, int initialStudentNumber) { super(intitialName); studentNumber = initialStudentNumber; } // irrellevant methods here... // overides Person, Student and Objects method public void writeOutput() { super.writeOutput(); println(studentNumber); } } class Undergaraduate extends Student { private int level; Undergraduate(String intitialName, int initialStudentNumber,int initialLevel) { super(intitialName,initialStudentNumber); level = initialLevel; } // irrelevant methods is here. // overides Person, Student and Objects method public void writeOutput() { super.writeOutput(); println(level); } } I am wondering. if I had an array called person declared to contain objects of type Person: Person[] people = new Person[2]; person[0] = new Undergraduate("Cotty, Manny",4910,1); person[1] = new Student("DeBanque, Robin", 8812); Given that person[] is declared to be of type Person, you would expect, for example, in the third line where person[0] is initialized to a new Undergraduate object,to only gain the instance variable from Person and Persons Methods since doesn't the assignment to a new Undergraduate to it's ancestor denote the Undergraduate object to access Person - it's Ancestors, methods and isntance variables... Thus ...with the following code I would expect person[0].writeOutput(); // calls Undergraduate::writeOutput() person[1].writeOutput(); // calls Student::writeOutput() person[0] to not have Undergraduate's writeOutput() overidden method, nor have person[1] to have Student's overidden method - writeOutput(). If I had Person mikeJones = new Student("Who?,MikeJones",44,4); mikeJones.writeOutput(); The Person::writeOutput() method would be called. Why is this not so? Does it have to do with something I don't understand about relating to arrays? Does the declaration Person[] people = new Person[2] not bind the method like the previous code would?

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Dynamic obstacles avoidance in navigation mesh system

- by Variable

I've built my path finding system with unreal engine, somehow the path finding part works just fine while i can't find a proper way to solve dynamic obstacles avoidance problem. My characters are walking allover the map and collide with each other while they moving. I try to steering them when collision occurs, but this doesn't work well. For example, two characters block on the road while the third one's path is right in the middle of them and he'll get stuck. Can someone tell me the most popular way of doing dynamic avoidance? Thanks a lot.

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Creating a Dynamic DataRow for easier DataRow Syntax

- by Rick Strahl

I've been thrown back into an older project that uses DataSets and DataRows as their entity storage model. I have several applications internally that I still maintain that run just fine (and I sometimes wonder if this wasn't easier than all this ORM crap we deal with with 'newer' improved technology today - but I disgress) but use this older code. For the most part DataSets/DataTables/DataRows are abstracted away in a pseudo entity model, but in some situations like queries DataTables and DataRows are still surfaced to the business layer. Here's an example. Here's a business object method that runs dynamic query and the code ends up looping over the result set using the ugly DataRow Array syntax:public int UpdateAllSafeTitles() { int result = this.Execute("select pk, title, safetitle from " + Tablename + " where EntryType=1", "TPks"); if (result < 0) return result; result = 0; foreach (DataRow row in this.DataSet.Tables["TPks"].Rows) { string title = row["title"] as string; string safeTitle = row["safeTitle"] as string; int pk = (int)row["pk"]; string newSafeTitle = this.GetSafeTitle(title); if (newSafeTitle != safeTitle) { this.ExecuteNonQuery("update " + this.Tablename + " set safeTitle=@safeTitle where pk=@pk", this.CreateParameter("@safeTitle",newSafeTitle), this.CreateParameter("@pk",pk) ); result++; } } return result; } The problem with looping over DataRow objecs is two fold: The array syntax is tedious to type and not real clear to look at, and explicit casting is required in order to do anything useful with the values. I've highlighted the place where this matters. Using the DynamicDataRow class I'll show in a minute this code can be changed to look like this:public int UpdateAllSafeTitles() { int result = this.Execute("select pk, title, safetitle from " + Tablename + " where EntryType=1", "TPks"); if (result < 0) return result; result = 0; foreach (DataRow row in this.DataSet.Tables["TPks"].Rows) { dynamic entry = new DynamicDataRow(row); string newSafeTitle = this.GetSafeTitle(entry.title); if (newSafeTitle != entry.safeTitle) { this.ExecuteNonQuery("update " + this.Tablename + " set safeTitle=@safeTitle where pk=@pk", this.CreateParameter("@safeTitle",newSafeTitle), this.CreateParameter("@pk",entry.pk) ); result++; } } return result; } The code looks much a bit more natural and describes what's happening a little nicer as well. Well, using the new dynamic features in .NET it's actually quite easy to implement the DynamicDataRow class. Creating your own custom Dynamic Objects .NET 4.0 introduced the Dynamic Language Runtime (DLR) and opened up a whole bunch of new capabilities for .NET applications. The dynamic type is an easy way to avoid Reflection and directly access members of 'dynamic' or 'late bound' objects at runtime. There's a lot of very subtle but extremely useful stuff that dynamic does (especially for COM Interop scenearios) but in its simplest form it often allows you to do away with manual Reflection at runtime. In addition you can create DynamicObject implementations that can perform custom interception of member accesses and so allow you to provide more natural access to more complex or awkward data structures like the DataRow that I use as an example here. Bascially you can subclass DynamicObject and then implement a few methods (TryGetMember, TrySetMember, TryInvokeMember) to provide the ability to return dynamic results from just about any data structure using simple property/method access. In the code above, I created a custom DynamicDataRow class which inherits from DynamicObject and implements only TryGetMember and TrySetMember. Here's what simple class looks like:/// <summary> /// This class provides an easy way to turn a DataRow /// into a Dynamic object that supports direct property /// access to the DataRow fields. /// /// The class also automatically fixes up DbNull values /// (null into .NET and DbNUll to DataRow) /// </summary> public class DynamicDataRow : DynamicObject { /// <summary> /// Instance of object passed in /// </summary> DataRow DataRow; /// <summary> /// Pass in a DataRow to work off /// </summary> /// <param name="instance"></param> public DynamicDataRow(DataRow dataRow) { DataRow = dataRow; } /// <summary> /// Returns a value from a DataRow items array. /// If the field doesn't exist null is returned. /// DbNull values are turned into .NET nulls. /// /// </summary> /// <param name="binder"></param> /// <param name="result"></param> /// <returns></returns> public override bool TryGetMember(GetMemberBinder binder, out object result) { result = null; try { result = DataRow[binder.Name]; if (result == DBNull.Value) result = null; return true; } catch { } result = null; return false; } /// <summary> /// Property setter implementation tries to retrieve value from instance /// first then into this object /// </summary> /// <param name="binder"></param> /// <param name="value"></param> /// <returns></returns> public override bool TrySetMember(SetMemberBinder binder, object value) { try { if (value == null) value = DBNull.Value; DataRow[binder.Name] = value; return true; } catch {} return false; } } To demonstrate the basic features here's a short test: [TestMethod] [ExpectedException(typeof(RuntimeBinderException))] public void BasicDataRowTests() { DataTable table = new DataTable("table"); table.Columns.Add( new DataColumn() { ColumnName = "Name", DataType=typeof(string) }); table.Columns.Add( new DataColumn() { ColumnName = "Entered", DataType=typeof(DateTime) }); table.Columns.Add(new DataColumn() { ColumnName = "NullValue", DataType = typeof(string) }); DataRow row = table.NewRow(); DateTime now = DateTime.Now; row["Name"] = "Rick"; row["Entered"] = now; row["NullValue"] = null; // converted in DbNull dynamic drow = new DynamicDataRow(row); string name = drow.Name; DateTime entered = drow.Entered; string nulled = drow.NullValue; Assert.AreEqual(name, "Rick"); Assert.AreEqual(entered,now); Assert.IsNull(nulled); // this should throw a RuntimeBinderException Assert.AreEqual(entered,drow.enteredd); } The DynamicDataRow requires a custom constructor that accepts a single parameter that sets the DataRow. Once that's done you can access property values that match the field names. Note that types are automatically converted - no type casting is needed in the code you write. The class also automatically converts DbNulls to regular nulls and vice versa which is something that makes it much easier to deal with data returned from a database. What's cool here isn't so much the functionality - even if I'd prefer to leave DataRow behind ASAP - but the fact that we can create a dynamic type that uses a DataRow as it's 'DataSource' to serve member values. It's pretty useful feature if you think about it, especially given how little code it takes to implement. By implementing these two simple methods we get to provide two features I was complaining about at the beginning that are missing from the DataRow: Direct Property Syntax Automatic Type Casting so no explicit casts are required Caveats As cool and easy as this functionality is, it's important to understand that it doesn't come for free. The dynamic features in .NET are - well - dynamic. Which means they are essentially evaluated at runtime (late bound). Rather than static typing where everything is compiled and linked by the compiler/linker, member invokations are looked up at runtime and essentially call into your custom code. There's some overhead in this. Direct invocations - the original code I showed - is going to be faster than the equivalent dynamic code. However, in the above code the difference of running the dynamic code and the original data access code was very minor. The loop running over 1500 result records took on average 13ms with the original code and 14ms with the dynamic code. Not exactly a serious performance bottleneck. One thing to remember is that Microsoft optimized the DLR code significantly so that repeated calls to the same operations are routed very efficiently which actually makes for very fast evaluation. The bottom line for performance with dynamic code is: Make sure you test and profile your code if you think that there might be a performance issue. However, in my experience with dynamic types so far performance is pretty good for repeated operations (ie. in loops). While usually a little slower the perf hit is a lot less typically than equivalent Reflection work. Although the code in the second example looks like standard object syntax, dynamic is not static code. It's evaluated at runtime and so there's no type recognition until runtime. This means no Intellisense at development time, and any invalid references that call into 'properties' (ie. fields in the DataRow) that don't exist still cause runtime errors. So in the case of the data row you still get a runtime error if you mistype a column name:// this should throw a RuntimeBinderException Assert.AreEqual(entered,drow.enteredd); Dynamic - Lots of uses The arrival of Dynamic types in .NET has been met with mixed emotions. Die hard .NET developers decry dynamic types as an abomination to the language. After all what dynamic accomplishes goes against all that a static language is supposed to provide. On the other hand there are clearly scenarios when dynamic can make life much easier (COM Interop being one place). Think of the possibilities. What other data structures would you like to expose to a simple property interface rather than some sort of collection or dictionary? And beyond what I showed here you can also implement 'Method missing' behavior on objects with InvokeMember which essentially allows you to create dynamic methods. It's all very flexible and maybe just as important: It's easy to do. There's a lot of power hidden in this seemingly simple interface. Your move…© Rick Strahl, West Wind Technologies, 2005-2011Posted in CSharp .NET Tweet (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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Dynamic mod_rewrite or how to plan a dynamic website

- by Sophia Gavish

Hi, I'm trying to make a clean url for a blog on a dynamic website, but I think that the problem is that I don't know how to plan the website schema. I read about how to use mod_rewrite and all I found is how to make "http://www.website.com/?category&date&post-title" to "http://www.website.com/category/date/post-title". that's works o.k for me. The problem is that If my url looks like "http://www.website.com/blog/?id=34" this method won't work as far as I got it. So, I have two questions: 1. Is there a way to use mod_rewrite (maybe read from a txt file) to read the post title of my blog and rewrite my url by date and post-title? 2. Should I rewrite my website to query the data from one index file in the homepage and use mod_rewrite to write the nice url? should I query also the date and the title of the post instead just the post ID?

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Is there a modified LGPL license that allows static linking?

- by Petr Pudlák

úLGPL requires that it if a program uses LGPL-ed library, users must be able to re-link the program with a different version of the library: ... d) Do one of the following: 0) Convey the Minimal Corresponding Source under the terms of this License, and the Corresponding Application Code in a form suitable for, and under terms that permit, the user to recombine or relink the Application with a modified version of the Linked Version to produce a modified Combined Work, in the manner specified by section 6 of the GNU GPL for conveying Corresponding Source. 1) Use a suitable shared library mechanism for linking with the Library. A suitable mechanism is one that (a) uses at run time a copy of the Library already present on the user's computer system, and (b) will operate properly with a modified version of the Library that is interface-compatible with the Linked Version. ... However in some cases, this can pose considerable difficulties. In particular, Haskell programs are almost always statically compiled. Moreover, the compiler does cross-module optimizations so it's very hard to satisfy this condition. (See this link at Haskell Wiki.) Therefore, I'm looking for a standard LGPL-like license that wouldn't require the possibility of re-linking. Some projects use their own modification of LGPL, for example wxWidgets. But I'd rather use some standard license that is somewhat more official, perhaps checked by some law experts, and (L)GPL compatible. Is there some like that? (Also I'd be interested to know if are there some unforeseen consequences of such a modification of LGPL.)

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Dynamic Code for type casting Generic Types 'generically' in C#

- by Rick Strahl

C# is a strongly typed language and while that's a fundamental feature of the language there are more and more situations where dynamic types make a lot of sense. I've written quite a bit about how I use dynamic for creating new type extensions: Dynamic Types and DynamicObject References in C# Creating a dynamic, extensible C# Expando Object Creating a dynamic DataReader for dynamic Property Access Today I want to point out an example of a much simpler usage for dynamic that I use occasionally to get around potential static typing issues in C# code especially those concerning generic types. TypeCasting Generics Generic types have been around since .NET 2.0 I've run into a number of situations in the past - especially with generic types that don't implement specific interfaces that can be cast to - where I've been unable to properly cast an object when it's passed to a method or assigned to a property. Granted often this can be a sign of bad design, but in at least some situations the code that needs to be integrated is not under my control so I have to make due with what's available or the parent object is too complex or intermingled to be easily refactored to a new usage scenario. Here's an example that I ran into in my own RazorHosting library - so I have really no excuse, but I also don't see another clean way around it in this case. A Generic Example Imagine I've implemented a generic type like this: public class RazorEngine<TBaseTemplateType> where TBaseTemplateType : RazorTemplateBase, new() You can now happily instantiate new generic versions of this type with custom template bases or even a non-generic version which is implemented like this: public class RazorEngine : RazorEngine<RazorTemplateBase> { public RazorEngine() : base() { } } To instantiate one: var engine = new RazorEngine<MyCustomRazorTemplate>(); Now imagine that the template class receives a reference to the engine when it's instantiated. This code is fired as part of the Engine pipeline when it gets ready to execute the template. It instantiates the template and assigns itself to the template: var template = new TBaseTemplateType() { Engine = this } The problem here is that possibly many variations of RazorEngine<T> can be passed. I can have RazorTemplateBase, RazorFolderHostTemplateBase, CustomRazorTemplateBase etc. as generic parameters and the Engine property has to reflect that somehow. So, how would I cast that? My first inclination was to use an interface on the engine class and then cast to the interface. Generally that works, but unfortunately here the engine class is generic and has a few members that require the template type in the member signatures. So while I certainly can implement an interface: public interface IRazorEngine<TBaseTemplateType> it doesn't really help for passing this generically templated object to the template class - I still can't cast it if multiple differently typed versions of the generic type could be passed. I have the exact same issue in that I can't specify a 'generic' generic parameter, since there's no underlying base type that's common. In light of this I decided on using object and the following syntax for the property (and the same would be true for a method parameter): public class RazorTemplateBase :MarshalByRefObject,IDisposable { public object Engine {get;set; } } Now because the Engine property is a non-typed object, when I need to do something with this value, I still have no way to cast it explicitly. What I really would need is: public RazorEngine<> Engine { get; set; } but that's not possible. Dynamic to the Rescue Luckily with the dynamic type this sort of thing can be mitigated fairly easily. For example here's a method that uses the Engine property and uses the well known class interface by simply casting the plain object reference to dynamic and then firing away on the properties and methods of the base template class that are common to all templates:/// <summary> /// Allows rendering a dynamic template from a string template /// passing in a model. This is like rendering a partial /// but providing the input as a /// </summary> public virtual string RenderTemplate(string template,object model) { if (template == null) return string.Empty; // if there's no template markup if(!template.Contains("@")) return template; // use dynamic to get around generic type casting dynamic engine = Engine; string result = engine.RenderTemplate(template, model); if (result == null) throw new ApplicationException("RenderTemplate failed: " + engine.ErrorMessage); return result; } Prior to .NET 4.0 I would have had to use Reflection for this sort of thing which would have a been a heck of a lot more verbose, but dynamic makes this so much easier and cleaner and in this case at least the overhead is negliable since it's a single dynamic operation on an otherwise very complex operation call. Dynamic as a Bailout Sometimes this sort of thing often reeks of a design flaw, and I agree that in hindsight this could have been designed differently. But as is often the case this particular scenario wasn't planned for originally and removing the generic signatures from the base type would break a ton of other code in the framework. Given the existing fairly complex engine design, refactoring an interface to remove generic types just to make this particular code work would have been overkill. Instead dynamic provides a nice and simple and relatively clean solution. Now if there were many other places where this occurs I would probably consider reworking the code to make this cleaner but given this isolated instance and relatively low profile operation use of dynamic seems a valid choice for me. This solution really works anywhere where you might end up with an inheritance structure that doesn't have a common base or interface that is sufficient. In the example above I know what I'm getting but there's no common base type that I can cast to. All that said, it's a good idea to think about use of dynamic before you rush in. In many situations there are alternatives that can still work with static typing. Dynamic definitely has some overhead compared to direct static access of objects, so if possible we should definitely stick to static typing. In the example above the application already uses dynamics extensively for dynamic page page templating and passing models around so introducing dynamics here has very little additional overhead. The operation itself also fires of a fairly resource heavy operation where the overhead of a couple of dynamic member accesses are not a performance issue. So, what's your experience with dynamic as a bailout mechanism? © Rick Strahl, West Wind Technologies, 2005-2012Posted in CSharp Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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Drupal - no self-linking

- by pygorex1

So, I've added several pages to my Drupal install and linking to the pages using URL aliases via the Path module. So far so good - http://mydrupal/node/1 becomes http://mydrupal/about which is exactly what I'm looking for. Then I'm adding these links to the primary navigation and outputting the primary links via a custom theme (copy and paste the primary link code from the Chameleon theme). Here's the problem: when viewing http://mydrupal/about the page links to itself - that is the "About" link at http://mydrupal/about is still linking to http://mydrupal/about - the behavior I'm looking for is to have the "About" text display without a link. In summary: how do I prevent self-linking of pages when displaying the primary navigation?

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Convert Dynamic to Type and convert Type to Dynamic

- by Jon Canning

public static class DynamicExtensions { public static T FromDynamic<T>(this IDictionary<string, object> dictionary) { var bindings = new List<MemberBinding>(); foreach (var sourceProperty in typeof(T).GetProperties().Where(x => x.CanWrite)) { var key = dictionary.Keys.SingleOrDefault(x => x.Equals(sourceProperty.Name, StringComparison.OrdinalIgnoreCase)); if (string.IsNullOrEmpty(key)) continue; var propertyValue = dictionary[key]; bindings.Add(Expression.Bind(sourceProperty, Expression.Constant(propertyValue))); } Expression memberInit = Expression.MemberInit(Expression.New(typeof(T)), bindings); return Expression.Lambda<Func<T>>(memberInit).Compile().Invoke(); } public static dynamic ToDynamic<T>(this T obj) { IDictionary<string, object> expando = new ExpandoObject(); foreach (var propertyInfo in typeof(T).GetProperties()) { var propertyExpression = Expression.Property(Expression.Constant(obj), propertyInfo); var currentValue = Expression.Lambda<Func<string>>(propertyExpression).Compile().Invoke(); expando.Add(propertyInfo.Name.ToLower(), currentValue); } return expando as ExpandoObject; } }

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