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  • Can ElementTree be told to preserve the order of attributes?

    - by dmckee
    I've written a fairly simple filter in python using ElementTree to munge the contexts of some xml files. And it works, more or less. But it reorders the attributes of various tags, and I'd like it to not do that. Does anyone know a switch I can throw to make it keep them in specified order? Context for this I'm working with and on a particle physics tool that has a complex, but oddly limited configuration system based on xml files. Among the many things setup that way are the paths to various static data files. These paths are hardcoded into the existing xml and there are no facilities for setting or varying them based on environment variables, and in our local installation they are necessarily in a different place. This isn't a disaster because the combined source- and build-control tool we're using allows us to shadow certain files with local copies. But even thought the data fields are static the xml isn't, so I've written a script for fixing the paths, but with the attribute rearrangement diffs between the local and master versions are harder to read than necessary. This is my first time taking ElementTree for a spin (and only my fifth or sixth python project) so maybe I'm just doing it wrong. Abstracted for simplicity the code looks like this: tree = elementtree.ElementTree.parse(inputfile) i = tree.getiterator() for e in i: e.text = filter(e.text) tree.write(outputfile) Reasonable or dumb? Related links: How can I get the order of an element attribute list using Python xml.sax? Preserve order of attributes when modifying with minidom

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  • Best way to store sales tax information

    - by Seph
    When designing a stock management database system (sales / purchases) what would be the best way to store the various taxes and other such amounts? A few of the fields that could be saved are: Unit price excluding tax Unit price including tax Tax per item Total excluding tax (rounded to 2 decimals) Total including tax (rounded to 2 decimals) Total tax (rounded to 2 decimals) Currently the most reasonable solution so far is storing down (roughly) item, quantity, total excluding tax (rounded) and the total tax (rounded). Can anyone suggest some better way of storing this details for a generic system? Also, given the system needs to be robust, what should be done if there were multiple tax values (eg: state and city) which might need to be separated, in this case a separate table would be in order, but would it be considered excessive to just have a rowID and some taxID mapping to a totalTax column?

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  • jQuery UI AutoComplete remote json response question

    - by Greg-J
    I was using geonames.org to autocomplete city and state but found it to be far too slow to be reliable. My code is as follows, and does work (wait about 10 seconds to see the autocomplete results) Old (working) code here: http://jsbin.com/umewo3/2/edit Now I am using YQL as they provide a much quicker response. The issue is that I don't seem to understand how to properly map the response. You can see I am sending a well formed request, and getting the response back - but I am somehow not dealing with the response properly. New (broken) code here: http://jsbin.com/aqoke3/2/edit Any and all help appreciated.

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  • cgi.FieldStorage always empty - never returns POSTed form Data

    - by Dan Carlson
    This problem is probably embarrassingly simple. I'm trying to give python a spin. I thought a good way to start doing that would be to create a simple cgi script to process some form data and do some magic. My python script is executed properly by apache using mod_python, and will print out whatever I want it to print out. My only problem is that cgi.FieldStorage() is always empty. I've tried using both POST and GET. Each trial I fill out both form fields. <form action="pythonScript.py" method="POST" name="ARGH"> <input name="TaskName" type="text" /> <input name="TaskNumber" type="text" /> <input type="submit" /> </form> If I change the form to point to a perl script it reports the form data properly. The python page always gives me the same result: number of keys: 0 #!/usr/bin/python import cgi def index(req): pageContent = """<html><head><title>A page from""" pageContent += """Python</title></head><body>""" form = cgi.FieldStorage() keys = form.keys() keys.sort() pageContent += "<br />number of keys: "+str(len(keys)) for key in keys: pageContent += fieldStorage[ key ].value pageContent += """</body></html>""" return pageContent I'm using Python 2.5.2 and Apache/2.2.3. This is what's in my apache conf file (and my script is in /var/www/python): <Directory /var/www/python/> Options FollowSymLinks +ExecCGI Order allow,deny allow from all AddHandler mod_python .py PythonHandler mod_python.publisher </Directory>

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  • MySQL slow query

    - by andrhamm
    SELECT items.item_id, items.category_id, items.title, items.description, items.quality, items.type, items.status, items.price, items.posted, items.modified, zip_code.state_prefix, zip_code.city, books.isbn13, books.isbn10, books.authors, books.publisher FROM ( ( items LEFT JOIN bookitems ON items.item_id = bookitems.item_id ) LEFT JOIN books ON books.isbn13 = bookitems.isbn13 ) LEFT JOIN zip_code ON zip_code.zip_code = items.item_zip WHERE items.rid = $rid` I am running this query to get the list of a user's items and their location. The zip_code table has over 40k records and this might be the issue. It currently takes up to 15 seconds to return a list of about 20 items! What can I do to make this query more efficient?

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  • ASP.NET Web Service - Passing a base object with list/collection?

    - by schooner
    We need to create a simple web service in ASP.NET that can be called from PHP or other languages. This in turn will be used to update records in a database for an item submission. The core part is fairly simple, we have a base set of fields for the object - first name, last name, birth date, city, etc. In addition however we need to accept a list of items associated with that object that can range from 0-n. Jan 1 2009, ABC May 1 2010, 123 Jun 30 2010, XXXXX What would be the best way to structure this so it can be easily passed to the ASP.NET web service and processed as a single call for the entire object? Would passing the list of items as a single delimted string be a wise approach? Ex: Jan 1 2009, ABC|May 1 2010, 123|Jun 30 2010, XXXXX

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  • Unknown user 'app' with capistrano

    - by trobrock
    This is my first time trying to set up capistrano to deploy a rails application. I am deploying from my local machine to my remote server that has the repo, web, app, and mysql servers all on the same machine. I am following this walk through: http://www.capify.org/index.php/From_The_Beginning I get to the command cap deploy:start Then I get this error: *** [err :: example.com] sudo: unknown user: app command finished failed: "sh -c 'cd /var/www/example/current && sudo -p '\\''sudo password: '\\'' -u app nohup script/spin'" on example.com Am I supposed to add an 'app' user, or is there a way of changing what user the command runs as? This is my deploy.rb: set :application, "example" set :repository, "[email protected]:example.git" set :user, "trobrock" set :branch, 'master' set :deploy_to, "/var/www/example" set :scm, :git # Or: `accurev`, `bzr`, `cvs`, `darcs`, `git`, `mercurial`, `perforce`, `subversion` or `none` role :web, "example.com" # Your HTTP server, Apache/etc role :app, "example.com" # This may be the same as your `Web` server role :db, "example.com", :primary => true # This is where Rails migrations will run And obviously everywhere it says example.com is my servers hostname and every it just says example is the app name.

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  • using performSelector

    - by zebra
    Hi all, i've my method that implement a reverseGeocoder - (void)reversing { geoCoder=[[MKReverseGeocoder alloc] initWithCoordinate:locManager.location.coordinate]; geoCoder.delegate=self; [geoCoder start]; } i recall reversing in another method with this: [self performSelector:@selector(reversing) withObject:nil afterDelay:10]; and i receive 2010-04-30 17:44:17.616 high[1167:207] Retrive City Milano 2010-04-30 17:44:17.628 high[1167:207] geocoder released 2010-04-30 17:44:18.723 high[1167:207] Error Domain=MKErrorDomain Code=4 "Operation could not be completed. (MKErrorDomain error 4.)" Program received signal: “EXC_BAD_ACCESS”. Can someone help me? :D

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  • Accessing previous activity instances in a sequence activity

    - by Dan Revell
    This has a rather SharePoint spin to it but the problem is straight workflow. I've got a parallel replication activity which contains a sequence activity. The sequence activity contains a CreateTask activity, a CodeActivity, a OnTaskChanged activity and finally a CompleteTask activity. The idea is to create a task for each username passed into the ReplicatorActivity.InitialChildData property. Typically in workflow I bind a field to the CreateTask.TaskId and CreateTask.TaskProperties and inside the CreateTask.MethodInvoking I set these through the local bound fields. This works and my tasks all get created properly. However in the CodeActivity that follows, I want to then access the TaskProperties. The problem I am encountering is that this field holds the values of the final task to be created as the CreateTask runs for all the replications before the CodeActivity gets to runs. From the CodeActivity, here are two ways I've tried to access the CreateTask activity instance from the same context or instance or whatever the terminology is for the replicated sequence. CreateTask task = ((CreateTask)sender.Parent.GetActivityByName("createSoftwareRequestTask", true)); CreateTask createTask = (CreateTask)sender.Parent.Activities[0]; Unfortunately the CreateTask activities both refer back to the last task to be created and not the task from the context that the CodeActivity is executing within. Two reasons why this might be that I can think of. I'm not accessing the correct instance with my code. I am accessing the correct instance, but as the properties I require were bound to and set through local fields then their previous data was overwritten. I'm hitting a brick wall with my understanding of workflow with this and would very much appreciate some assistance here.

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  • Geolocation Null in lat and long

    - by user1706989
    I have had issue today in one application where Geolocation is not working. Even on this page http://slaveryfootprint.org/survey/#where_do_you_live . When you enter a location , its showing null lattiude and longitude. Even though it search for autolocation, it can point the right location. and it happened all if a sudden today which was working fine since yestrday night and when I see in console it is returning null lat and long and null for city and I did not change the code at all. Did google map api changed something. or do I need to update jquery? http://maps.google.com/maps/api/js?v=3.4&sensor=false

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  • Where is the iPhone's Date & Time getting it's time zone list

    - by johnbdh
    I can get a list of time zones with [NSTimeZone knownTimeZoneNames], but that only gives the time zone IDs which include one or 2 cities in each time zone. The Date & Time settings has a great list of cities and I have seen a few other apps that have the same if not similar lookup lists. Where do these lists come from?? I do need to relate a picked city to it's time zone like Date & Time does. Thanks, John

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  • WPF - Why doesn't Microsoft supply a decent set of most-used controls ?

    - by IUsedToBeAPygmy
    I've been playing with WPF for some months now, and I quite like it. But one of the things I don't get is why MS doesn't put a little more effort in helping developers by supplying basic controls, and I need to get this off my chest :) For example, I figure most applications somewhere will need to let you edit some properties - for configuration or whatever. What would be the most used types in a proprety-grid editor ? text numbers (byte, float/double, int, etc) colors ....etc. So why isn't there even something as simple as a control to edit numbers ? Like a generic NumericUpDown control that allows you to type in numbers (no text, no pasting invalid input) or spin them up/down according to some given rules (decimal, floating point, min/maxvalue) ? Why isn't there a generic colorpicker, so people get the same user-experience in every application ? Why isn't there a standard implementation of a SearchTextBox, a BreadCrumb-control, or all these other standard control types users have gotten accustomed to the last 10 years ? (..but at least they DID have the time to implement a generic splashscreen - because everyone knows that greatly increases user-productivity....) The well-known ideal is always to give people the same user-experience over different applications. So even if some of those controls would be easy to make - it would be preferred to have one version over different applications. I see people all over the internet trying to do the same stuff over and over again. Okay, so MS started a WPF Toolkit project on Codeplex that tries to implement some controls, but only did so half-heartedly and is completely dead by now (last update of the roadmap dates back to Mar 21 2009). The result of this is that a lot of people starting a WPF-project end up spending a lot of time on trying to figure out how to create some generic controls and get really frustrated. Wasn't the mantra "Developers, developers, developers!" ..? /Rant

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  • Mysql php error insert statement not working

    - by DAFFODIL
    I created database using mysql but now,i am unable to insert data,I am getting this error. Notice: Undefined index: Name in C:\wamp\www\customer.php on line 12 Notice: Undefined index: Address in C:\wamp\www\customer.php on line 12 Notice: Undefined index: City in C:\wamp\www\customer.php on line 12 Notice: Undefined index: Pincode in C:\wamp\www\customer.php on line 12 Notice: Undefined index: State in C:\wamp\www\customer.php on line 12 Notice: Undefined index: Country in C:\wamp\www\customer.php on line 12 Notice: Undefined index: Phone in C:\wamp\www\customer.php on line 12 Notice: Undefined index: Mobile in C:\wamp\www\customer.php on line 12 Notice: Undefined index: Fax in C:\wamp\www\customer.php on line 12 Notice: Undefined index: Email in C:\wamp\www\customer.php on line 12 Notice: Undefined index: Website in C:\wamp\www\customer.php on line 12 Notice: Undefined index: Notes in C:\wamp\www\customer.php on line 12 Error: Table 'form.customer' doesn't exist

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  • Aspnet Redirect using location tag

    - by Learner
    <location path="/home/address?city="jcity" allowOverride="true"> <system.webServer> <validation validateIntegratedModeConfiguration="false" /> <httpRedirect enabled="true" httpResponseStatus="Permanent" exactDestination="true" destination="/home/jerseycity" /> </system.webServer> </location> I get an error since location tag can not use "?" tag. What is the best way to do this redirect?

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  • Problem making ant compile my classes present in different Eclipse projects into single destination

    - by KCore
    I have close to about 20 projects in my Eclipse workspace. They are interdependent. Now I want to build all of them in a single war file. The thing is eclipse does it nicely... if I create a Dynamic Web Project and link sources of all the 20 projects. But I want to automate the entire process and want to be able to run a script (ant maybe..) and deploy a war in my app server. My approach: I started with a simple approach. I tried to sequentially build each project (javac task) with destination directory as web-inf of my war. But it is giving me weird errors like : package " ** " not found,when it shows the same all the required classes in classpath (I used verbose) Do you think, a continous integration engine will be better for my case (20 projects..) I saw Team City, but didnt get it the first time...

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  • Google Local Search API

    - by Gublooo
    hey guys couple of quick questions 1) In the local search results - we can get a lot of parameters like street title, address, city, state, lat, long , url etc - In order for me to uniquely identify this record - can I consider URL to be unique to this address or concatenation of latitude and longitude Ref: http://code.google.com/apis/ajaxsearch/documentation/reference.html#_class_GlocalResult 2) In terms of usage, depending upon what user enters, I'm displaying a list of local business for the user to choose. Now when a user selects a particular business address - is it legal for me to store that business address along with lat and longitude information in my database for future look ups. I've seen a lot of blogs talking about storing the lat/long info but just want to be sure that i'm not violating and google rules. Thanks

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  • Proper use of HttpRequestInterceptor and CredentialsProvider in doing preemptive authentication with

    - by Preston
    I'm writing an application in Android that consumes some REST services I've created. These web services aren't issuing a standard Apache Basic challenge / response. Instead in the server-side code I'm wanting to interrogate the username and password from the HTTP(S) request and compare it against a database user to make sure they can run that service. I'm using HttpClient to do this and I have the credentials stored on the client after the initial login (at least that's how I see this working). So here is where I'm stuck. Preemptive authenticate under HttpClient requires you to setup an interceptor as a static member. This is the example Apache Components uses. HttpRequestInterceptor preemptiveAuth = new HttpRequestInterceptor() { @Override public void process( final HttpRequest request, final HttpContext context) throws HttpException, IOException { AuthState authState = (AuthState) context.getAttribute(ClientContext.TARGET_AUTH_STATE); CredentialsProvider credsProvider = (CredentialsProvider) context.getAttribute( ClientContext.CREDS_PROVIDER); HttpHost targetHost = (HttpHost) context.getAttribute(ExecutionContext.HTTP_TARGET_HOST); if (authState.getAuthScheme() == null) { AuthScope authScope = new AuthScope(targetHost.getHostName(), targetHost.getPort()); Credentials creds = credsProvider.getCredentials(authScope); if (creds != null) { authState.setAuthScheme(new BasicScheme()); authState.setCredentials(creds); } } } }; So the question would be this. What would the proper use of this be? Would I spin this up as part of the application when the application starts? Pulling the username and password out of memory and then using them to create this CredentialsProvider which is then utilized by the HttpRequestInterceptor? Or is there a way to do this more dynamically?

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  • How to get Jquery form plugin and Jquery validation to work together.

    - by Matthew
    Hello guys, I was hoping someone can shed some light on what might be occurring on my page. Okay what I currently have on my page is a simple form that collects first name, last name, city, state and email. Once submitted it will hit a PHP page that updates our DB and echo's back to the designted div with a class of .response. I am using jquery.validation and placing that dynamic function within the submitHandler like so: submitHandler: function(form) { $(form).ajaxSubmit({ target: '.response', // target element(s) to be updated with server response resetForm: true, success: function() { $('#commentform').hide(); $('.response').show(); } }); So what I am getting is a div that is not being populated with the echo from my php file in FF and in IE I am getting the message of thank you but the page is taking me to the update.php script in which I have the form action pointing to. I am not sure what I am missing... Thanks, Matt

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  • Spooling data to CSV truncates

    - by Steve
    Hi, I am using the below script to output data to a csv file: set heading off set linesize 10000 set pagesize 0 set echo off set verify off spool D:\OVERNIGHT\TEMP_FILES\PFRA_DETAIL_VIXEN_OUTPUT.txt SELECT TRIM(T4.S_ORG_ID)||','|| TRIM(T4.NAME)||','|| TRIM(T3.CREATION_TIME)||','|| TRIM(T5.X_HOUSE_NUMBER)||','|| TRIM(T5.X_FLAT_NUMBER)||','|| TRIM(T5.ADDRESS)||','|| TRIM(T5.CITY)||','|| TRIM(T5.ZIPCODE)||','|| TRIM(T3.NOTES) FROM TABLE_CASE T1 INNER JOIN TABLE_QUEUE T2 ON T1.CASE_CURRQ2QUEUE = T2.OBJID INNER JOIN TABLE_PHONE_LOG T3 ON T1.OBJID = T3.CASE_PHONE2CASE INNER JOIN TABLE_BUS_ORG T4 ON T1.X_CASE2X_BUS_ORG = T4.OBJID INNER JOIN TABLE_ADDRESS T5 ON T1.CASE2ADDRESS = T5.OBJID WHERE case_currq2queue IN(422); / spool off; exit; However the data is being truncated to 80 characters. The t3.notes field is in CLOB format. Does anyone know how I can spool this out to csv? I only have access to SQL*Plus. Thanks in advance, Steve

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  • SELLER REPORT FORM

    - by jack
    how to produce seller ID :xxxxx name :xxxxx address :xxxxxx phone : xxxxxx identification : passport identificatio : drivers licence identification : birth certificate xml file KS0000001 Mr. Clive Owen 14 Fifth Street Sin City NSW 2480 0455555551 &p; &dl; </seller> </sellers> dtd file <!ENTITY p "passport."> <!ENTITY dl "drivers licence."> <!ENTITY bc "birth certificate."> <!ENTITY mc "medicare card.">

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  • Repopulating a collection of Backbone forms with previously submitted data

    - by Brian Wheat
    I am able to post my forms to my database and I have stepped through my back end function to check and see that my Get function is returning the same data I submitted. However I am having trouble understanding how to have this data rendered upon visiting the page again. What am I missing? The intention is to be able to create, read, update, or delete (CRUD) some personal contact data for a variable collection of individuals. //Model var PersonItem = Backbone.Model.extend({ url: "/Application/PersonList", idAttribute: "PersonId", schema: { Title: { type: 'Select', options: function (callback) { $.getJSON("/Application/GetTitles/").done(callback); } }, Salutation: { type: 'Select', options: ['Mr.', 'Mrs.', 'Ms.', 'Dr.'] }, FirstName: 'Text', LastName: 'Text', MiddleName: 'Text', NameSuffix: 'Text', StreetAddress: 'Text', City: 'Text', State: { type: 'Select', options: function (callback) { $.getJSON("/Application/GetStates/").done(callback); } }, ZipCode: 'Text', PhoneNumber: 'Text', DateOfBirth: 'Date', } }); Backbone.Form.setTemplates(template, PersonItem); //Collection var PersonList = Backbone.Collection.extend({ model: PersonItem , url: "/Application/PersonList" }); //Views var PersonItemView = Backbone.Form.extend({ tagName: "li", events: { 'click button.delete': 'remove', 'change input': 'change' }, initialize: function (options) { console.log("ItemView init"); PersonItemView.__super__.initialize.call(this, options); _.bindAll(this, 'render', 'remove'); console.log("ItemView set attr = " + options); }, render: function () { PersonItemView.__super__.render.call(this); $('fieldset', this.el).append("<button class=\"delete\" style=\"float: right;\">Delete</button>"); return this; }, change: function (event) { var target = event.target; console.log('changing ' + target.id + ' from: ' + target.defaultValue + ' to: ' + target.value); }, remove: function () { console.log("delete button pressed"); this.model.destroy({ success: function () { alert('person deleted successfully'); } }); return false; } }); var PersonListView = Backbone.View.extend({ el: $("#application_fieldset"), events: { 'click button#add': 'addPerson', 'click button#save': 'save2db' }, initialize: function () { console.log("PersonListView Constructor"); _.bindAll(this, 'render', 'addPerson', 'appendItem', 'save'); this.collection = new PersonList(); this.collection.bind('add', this.appendItem); //this.collection.fetch(); this.collection.add([new PersonItem()]); console.log("collection length = " + this.collection.length); }, render: function () { var self = this; console.log(this.collection.models); $(this.el).append("<button id='add'>Add Person</button>"); $(this.el).append("<button id='save'>Save</button>"); $(this.el).append("<fieldset><legend>Contact</legend><ul id=\"anchor_list\"></ul>"); _(this.collection.models).each(function (item) { self.appendItem(item); }, this); $(this.el).append("</fieldset>"); }, addPerson: function () { console.log("addPerson clicked"); var item = new PersonItem(); this.collection.add(item); }, appendItem: function (item) { var itemView = new PersonItemView({ model: item }); $('#anchor_list', this.el).append(itemView.render().el); }, save2db: function () { var self = this; console.log("PersonListView save"); _(this.collection.models).each(function (item) { console.log("item = " + item.toJSON()); var cid = item.cid; console.log("item.set"); item.set({ Title: $('#' + cid + '_Title').val(), Salutation: $('#' + cid + '_Salutation').val(), FirstName: $('#' + cid + '_FirstName').val(), LastName: $('#' + cid + '_LastName').val(), MiddleName: $('#' + cid + '_MiddleName').val(), NameSuffix: $('#' + cid + '_NameSuffix').val(), StreetAddress: $('#' + cid + '_StreetAddress').val(), City: $('#' + cid + '_City').val(), State: $('#' + cid + '_State').val(), ZipCode: $('#' + cid + '_ZipCode').val(), PhoneNumber: $('#' + cid + '_PhoneNumber').val(), DateOfBirth: $('#' + cid + '_DateOfBirth').find('input').val() }); if (item.isNew()) { console.log("item.isNew"); self.collection.create(item); } else { console.log("!item.isNew"); item.save(); } }); return false; } }); var personList = new PersonList(); var view = new PersonListView({ collection: personList }); personList.fetch({ success: function () { $("#application_fieldset").append(view.render()); } });

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  • not including null values in sql join

    - by Ashanti
    Hi, I have two tables CustomerAddress(CustomerId, City, Country) and CustomerTransactions(TransactionId, CustomerId, CustomerContact). Here are the values in the tables: For CustomerAddress: 1001, El Paso, USA 1002, Paris, France 1003, Essen, Germany For CustomerTransactions: 98, 1001, Phillip 99, 1001, NULL 100, 1001, NULL 101, 1003, Carmen 102, 1003, Carmen 103, 1003, Lola 104, 1003, NULL 105, 1002, NULL I'm trying to join both tables and have the following result set: 1001, El Paso, USA, Phillip 1002, Paris, France, (empty string) 1003, Essen, Germany, Carmen 1003, Essen, Germany, Lola It seems like a simple join but I'm having trouble coming up with the above result set. Please help. Thanks.

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  • Not able to update contact name in emulator 2.1

    - by Rishabh
    Hi, I am tring to update name of existing contact in android 2.1 emulator with the following code but always getting "java.lang.IllegalArgumentException: Emplty values" Exception. ContentValues contactValues = new ContentValues(); contactValues.put(People.NAME, "rishabh"); getContentResolver().update(UpdateContactUri, contactValues, null, null); UpdateContactUri is the uri of existing contact with id 4. It is working on emulator 1.6 but not on 2.1. One more thing i need to ask how can i access indivisual fields of Name(first, middle, last) and Address(Street, city, state, zip, country) in 2.1

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  • proper use of volatile keyword

    - by luke
    I think i have a pretty good idea about the volatile keyword in java, but i'm thinking about re-factoring some code and i thought it would be a good idea to use it. i have a class that is basically working as a DB Cache. it holds a bunch of objects that it has read from a database, serves requests for those objects, and then occasionally refreshes the database (based on a timeout). Heres the skeleton public class Cache { private HashMap mappings =....; private long last_update_time; private void loadMappingsFromDB() { //.... } private void checkLoad() { if(System.currentTimeMillis() - last_update_time > TIMEOUT) loadMappingsFromDB(); } public Data get(ID id) { checkLoad(); //.. look it up } } So the concern is that loadMappingsFromDB could be a high latency operation and thats not acceptable, So initially i thought that i could spin up a thread on cache startup and then just have it sleep and then update the cache in the background. But then i would need to synchronize my class (or the map). and then i would just be trading an occasional big pause for making every cache access slower. Then i thought why not use volatile i could define the map reference as volatile private volatile HashMap mappings =....; and then in get (or anywhere else that uses the mappings variable) i would just make a local copy of the reference: public Data get(ID id) { HashMap local = mappings; //.. look it up using local } and then the background thread would just load into a temp table and then swap the references in the class HashMap tmp; //load tmp from DB mappings = tmp;//swap variables forcing write barrier Does this approach make sense? and is it actually thread-safe?

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  • Atomic int writes on file

    - by Waneck
    Hello! I'm writing an application that will have to be able to handle many concurrent accesses to it, either by threads as by processes. So no mutex'es or locks should be applied to this. To make the use of locks go down to a minimum, I'm designing for the file to be "append-only", so all data is first appended to disk, and then the address pointing to the info it has updated, is changed to refer to the new one. So I will need to implement a small lock system only to change this one int so it refers to the new address. How is the best way to do it? I was thinking about maybe putting a flag before the address, that when it's set, the readers will use a spin lock until it's released. But I'm afraid that it isn't at all atomic, is it? e.g. a reader reads the flag, and it is unset on the same time, a writer writes the flag and changes the value of the int the reader may read an inconsistent value! I'm looking for locking techniques but all I find is either for thread locking techniques, or to lock an entire file, not fields. Is it not possible to do this? How do append-only databases handle this? Thanks! Cauê

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