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  • Single Form with Multiple Dynamic Buttons

    - by John Reilly
    I've spent hours/days trying to figure this out and now I'm completely perplexed so I thought I'd give stackoverflow a try. I'm (a newb) working in Java/JSP using Eclipse hosting on Google App Engine trying to develop an app for a volunteer organization I'm a member of. Rather than embarrass myself by showing my current code I'd love just a nudge in the right direction. I have a form (which doubles as a report basically) showing "people" grouped under the "task" they are currently working on. I would like to select multiple people from multiple tasks and reassign them to another task e.g. Bill and Jane are Gardening, Jeff is Painting. I want to select Jane and Jeff (all people have an associated checkbox in the form) and re-assign them to Sweeping (which is a task on the form but has no people assigned to it yet). Ideally, the re-assignment to Sweeping would be via a Sweeping button (each task would have a dynamically-created task button) that would pass the "Sweeping" value to a servlet along with an array or list of people whose checkbox has been checked. The servlet would handle the request (creating an Assignment "object/entity" with timeStamp, personId, taskId) and then re-direct back to the form/report which would then repaint with the current tasks/people generated from the Assignments class in the datastore. All the tasks are user-defined and retrieved from the database when building the form. Ditto the people. I've been trying to keep the jsp for presentation and the servlets for the processing but I'm no purist and would just like to get unstuck. Many thanks in advance for your assistance.

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  • Google App Engine - Spring Security Issue (java.security.AccessControlException)

    - by Taylor L
    I'm currently getting the AccessControlException below when I deploy to app engine (I don't see it when I run in my local environment). I'm using GAE 1.3.1, Spring 3.0.1, and Spring Security 3.0.2. Any ideas how to get around this issue? It appears to be an issue with Spring Security trying to get the system class loader, but I'm not sure how to work around this. Nested in org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.security.filterChainProxy': Initialization of bean failed; nested exception is java.security.AccessControlException: access denied (java.lang.RuntimePermission getClassLoader): java.security.AccessControlException: access denied (java.lang.RuntimePermission getClassLoader) at java.security.AccessControlContext.checkPermission(AccessControlContext.java:355) at java.security.AccessController.checkPermission(AccessController.java:567) at java.lang.SecurityManager.checkPermission(Unknown Source) at com.google.apphosting.runtime.security.CustomSecurityManager.checkPermission(CustomSecurityManager.java:45) at java.lang.ClassLoader.getSystemClassLoader(Unknown Source) at org.springframework.beans.BeanUtils.findEditorByConvention(BeanUtils.java:392) at org.springframework.beans.TypeConverterDelegate.findDefaultEditor(TypeConverterDelegate.java:360) at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:213) at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:104) at org.springframework.beans.BeanWrapperImpl.convertIfNecessary(BeanWrapperImpl.java:419) at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:657) at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:191) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:984) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:888) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:479) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:450) at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveInnerBean(BeanDefinitionValueResolver.java:270) at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:125) at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveManagedMap(BeanDefinitionValueResolver.java:382) at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:161) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1308) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1067) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:511) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:450) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:290) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:287) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:189) at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:562) at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:871) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:423) at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:272) at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:196) at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:47) at org.mortbay.jetty.handler.ContextHandler.startContext(ContextHandler.java:530) at org.mortbay.jetty.servlet.Context.startContext(Context.java:135) at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1218) at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:500) at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:448) at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:40) at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.createHandler(AppVersionHandlerMap.java:191) at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.getHandler(AppVersionHandlerMap.java:168) at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:123) at com.google.apphosting.runtime.JavaRuntime.handleRequest(JavaRuntime.java:235) at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:5485) at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:5483) at com.google.net.rpc.impl.BlockingApplicationHandler.handleRequest(BlockingApplicationHandler.java:24) at com.google.net.rpc.impl.RpcUtil.runRpcInApplication(RpcUtil.java:363) at com.google.net.rpc.impl.Server$2.run(Server.java:837) at com.google.tracing.LocalTraceSpanRunnable.run(LocalTraceSpanRunnable.java:56) at com.google.tracing.LocalTraceSpanBuilder.internalContinueSpan(LocalTraceSpanBuilder.java:536) at com.google.net.rpc.impl.Server.startRpc(Server.java:792) at com.google.net.rpc.impl.Server.processRequest(Server.java:367) at com.google.net.rpc.impl.ServerConnection.messageReceived(ServerConnection.java:448) at com.google.net.rpc.impl.RpcConnection.parseMessages(RpcConnection.java:319) at com.google.net.rpc.impl.RpcConnection.dataReceived(RpcConnection.java:290) at com.google.net.async.Connection.handleReadEvent(Connection.java:474) at com.google.net.async.EventDispatcher.processNetworkEvents(EventDispatcher.java:774) at com.google.net.async.EventDispatcher.internalLoop(EventDispatcher.java:205) at com.google.net.async.EventDispatcher.loop(EventDispatcher.java:101) at com.google.net.rpc.RpcService.runUntilServerShutdown(RpcService.java:251) at com.google.apphosting.runtime.JavaRuntime$RpcRunnable.run(JavaRuntime.java:394) at java.lang.Thread.run(Unknown Source)

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  • Multiple "pages" in GWT with human friendly URLs

    - by Andreas Borglin
    Hi. I'm playing with a GWT/GAE project which will have three different "pages", although it is not really pages in a GWT sense. The top views (one for each page) will have completely different layouts, but some of the widgets will be shared. One of the pages is the main page which is loaded by the default url (http://www.site.com), but the other two needs additional URL information to differentiate the page type. They also need a name parameter, (like http://www.site.com/project/project-name. There are at least two solutions to this that I'm aware of. Use GWT history mechanism and let page type and parameters (such as project name) be part of the history token. Use servlets with url-mapping patterns (like /project/*) The first choice might seem obvious at first, but it has several drawbacks. First, a user should be able to easily remember and type URL directly to a project. It is hard to produce a human friendly URL with history tokens. Second, I'm using gwt-presenter and this approach would mean that we need to support subplaces in one token, which I'd rather avoid. Third, a user will typically stay at one page, so it makes more sense that the page information is part of the "static" URL. Using servlets solves all these problems, but also creates other ones. So my first questions is, what is the best solution here? If I would go for the servlet solution, new questions pop up. It might make sense to split the GWT app into three separate modules, each with an entry point. Each servlet that is mapped to a certain page would then simply forward the request to the GWT module that handles that page. Since a user typically stays at one page, the browser only needs to load the js for that page. Based on what I've read, this solution is not really recommended. I could also stick with one module, but then GWT needs to find out which page it should display. It could either query the server or parse the URL itself. If I stick with one GWT module, I need to keep the page information stored on server side. Naturally I thought about sessions, but I'm not sure if its a good idea to mix page information with user data. A session usually lives between user login and logout, but in this case it would need different behavior. Would it be bad practise to handle this via sessions? The one GWT module + servlet solution also leads to another problem. If a user goes from a project page to the main page, how will GWT know that this has happened? The app will not be reloaded, so it will be treated as a simple state change. It seems rather ineffecient to have to check page info for every state change. Anyone care to guide me out of the foggy darkness that surrounds me? :-)

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  • What is Google Docs' SLA?

    - by Walter White
    Hi all, I am evaluating online storage and for me, that means either Amazon S3 or Google Docs. Amazon very clearly posts there reliability and SLA: http://aws.amazon.com/s3/#protecting Their rates are obviously higher than Google's, but it is really hard to compare without having an SLA. Does anyone know what Google's commitment is for reliability? Is it 99.99% for data, is there anyway to make that more durable? I have to ask too, wouldn't google docs at least be inheritently more reliable than a hard drive? Thanks, Walter

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  • Port a live system from App Engine Helper to App Engine Patch

    - by Alexander
    I am running a live system that is currently serving about 20K pages a day which is based on App Engine Helper (Python) with session support provided by AppEngine utilities. One problem that I have been having is that sessions are occasionally randomly logging out. I would like to try using the App Engine Patch, since it has "native" django session support, but I am worried that this is possibly going to be like doing a brain transplant. Specifically, current database models are all inhereted from BaseModel provided by the App Engine Helper. While, App Engine Patch does not have this inheritance. Does anyone know if it is possible to migrate a live system from App Engine Helper to App Engine Patch? If so, do you have any advice or warnings that I should heed, before attempting this transition? Thank you and kind regards Alex

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  • Filtering by entity key name in Google App Engine on Python

    - by Bemmu
    On Google App Engine to query the data store with Python, one can use GQL or Entity.all() and then filter it. So for example these are equivalent gql = "SELECT * FROM User WHERE age >= 18" db.GqlQuery(gql) and query = User.all() query.filter("age >=", 18) Now, it's also possible to query things by key name. I know that in GQL you do it like this gql = "SELECT * FROM User WHERE __key__ >= Key('User', 'abc')" db.GqlQuery(gql) But how would you now use filter to do the same? query = User.all() query.filter("__key__ >=", ?????)

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  • database design in google app engine

    - by iamgopal
    hi , i am designing a simple project based to do list. the idea is to define tasks under project ( no workflow - just "task is completed" or not is required. ) in a hirarchial way. i.e. each task has multiple task and that task may have other multiple task. a project can be said to be completed if all task under that project are completed. , i tought of using refrenceproeperty to create hirarchy , but could not figure out easy way ( which do not take more than 30 seconds to find all the children of a project and check weather it is completed or not ) . to detect if project is complete or not. how to design database for such job ? and also , if i need to copy the project in order to define another project , how to copy hierarchical data ?

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  • How to finish a broken data upload to the production Google App Engine server?

    - by WooYek
    I was uploading the data to App Engine (not dev server) through loader class and remote api, and I hit the quota in the middle of a CSV file. Based on logs and progress sqllite db, how can I select remaining portion of data to be uploaded? Going through tens of records to determine which was and which was not transfered, is not appealing task, so I look for some way to limit the number of record I need to check. Here's relevant (IMO) log portion, how to interpret work item numbers? [DEBUG 2010-03-30 03:22:51,757 bulkloader.py] [Thread-2] [1041-1050] Transferred 10 entities in 3.9 seconds [DEBUG 2010-03-30 03:22:51,757 adaptive_thread_pool.py] [Thread-2] Got work item [1071-1080] <cut> [DEBUG 2010-03-30 03:23:09,194 bulkloader.py] [Thread-1] [1141-1150] Transferred 10 entities in 4.6 seconds [DEBUG 2010-03-30 03:23:09,194 adaptive_thread_pool.py] [Thread-1] Got work item [1161-1170] <cut> [DEBUG 2010-03-30 03:23:09,226 bulkloader.py] [Thread-3] [1151-1160] Transferred 10 entities in 4.2 seconds [DEBUG 2010-03-30 03:23:09,226 adaptive_thread_pool.py] [Thread-3] Got work item [1171-1180] [ERROR 2010-03-30 03:23:10,174 bulkloader.py] Retrying on non-fatal HTTP error: 503 Service Unavailable

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  • QueryReadStore loads JSON into DataGrid, but JsonRestStore does not (from the same source)

    - by labratmatt
    I'm building a Dojo DataGrid from JSON data provided by my REST interface. The DataGrid loads the data fine using a QueryReadStore, but doesn't seem to work with the same same data piped into a JsonRestStore. I'm using the following Dojo libs with Dojo 1.4.1: dojo.require("dojox.data.JsonRestStore"); dojo.require("dojox.grid.DataGrid"); dojo.require("dojox.data.QueryReadStore"); dojo.require("dojo.parser"); I declare my stores in the following manner: var storeJRS = new dojox.data.JsonRestStore({target:"api/collaborations.php/1", idAttribute: 'items[].id'}); var storeQRS = new dojox.data.QueryReadStore({url:"api/collaborations.php/1", requestMethod:"get"}); I create my grid layout like this: var gridLayout = [ new dojox.grid.cells.RowIndex({ name: "Row #", width: 5, styles: "text-align: left;" }), { name: "Name", field: "name", styles: "text-align:right;", width:20 }, { name: "Description", field: "description", width:30 } ]; I create my DataGrid as follows: The above works, but if I use QueryReadStore as my store, the grid is created with the headers (Name, Description), but it isn't populated with any rows: <div dojoType="dojox.grid.DataGrid" jsid="grid3" store="storeQRS" structure="gridLayout" style="height:500px; width:1000px;"></div> Using FireBug, I can see that QueryReadStore is getting my JSON data from my REST interface. It looks like the following: {"numRows":6,"items":[{"name":"My Super Cool Collab","description":"This is for all the super cool people in the super cool group","id":1},{"name":"My Other Super Cool","description":"This is for all the other super cool people","id":3},{"name":"This is another coll","description":"This is just some other collab","id":4},{"name":"some new collab","description":"this is a new collab","id":5},{"name":"yet another new coll","description":"uh huh","id":6},{"name":"asdf","description":"asdf","id":7}]} Any ideas? Thanks.

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  • Blackberry - application settings save/load

    - by Max Gontar
    Hi! I know two ways to save/load application settings: use PersistentStore use filesystem (store, since SDCard is optional) I'd like to know what are you're practicies of working with application settings? Using PersistentStore to save/load application settings The persistent store provides a means for objects to persist across device resets. A persistent object consists of a key-value pair. When a persistent object is committed to the persistent store, that object's value is stored in flash memory via a deep copy. The value can then be retrieved at a later point in time via the key. Example of helper class for storing and retrieving settings: class PSOptions { private PersistentObject mStore; private LongHashtableCollection mSettings; private long KEY_URL = 0; private long KEY_ENCRYPT = 1; private long KEY_REFRESH_PERIOD = 2; public PSOptions() { // "AppSettings" = 0x71f1f00b95850cfeL mStore = PersistentStore.getPersistentObject(0x71f1f00b95850cfeL); } public String getUrl() { Object result = get(KEY_URL); return (null != result) ? (String) result : null; } public void setUrl(String url) { set(KEY_URL, url); } public boolean getEncrypt() { Object result = get(KEY_ENCRYPT); return (null != result) ? ((Boolean) result).booleanValue() : false; } public void setEncrypt(boolean encrypt) { set(KEY_ENCRYPT, new Boolean(encrypt)); } public int getRefreshPeriod() { Object result = get(KEY_REFRESH_PERIOD); return (null != result) ? ((Integer) result).intValue() : -1; } public void setRefreshRate(int refreshRate) { set(KEY_REFRESH_PERIOD, new Integer(refreshRate)); } private void set(long key, Object value) { synchronized (mStore) { mSettings = (LongHashtableCollection) mStore.getContents(); if (null == mSettings) { mSettings = new LongHashtableCollection(); } mSettings.put(key, value); mStore.setContents(mSettings); mStore.commit(); } } private Object get(long key) { synchronized (mStore) { mSettings = (LongHashtableCollection) mStore.getContents(); if (null != mSettings && mSettings.size() != 0) { return mSettings.get(key); } else { return null; } } } } Example of use: class Scr extends MainScreen implements FieldChangeListener { PSOptions mOptions = new PSOptions(); BasicEditField mUrl = new BasicEditField("Url:", "http://stackoverflow.com/"); CheckboxField mEncrypt = new CheckboxField("Enable encrypt", false); GaugeField mRefresh = new GaugeField("Refresh period", 1, 60 * 10, 10, GaugeField.EDITABLE|FOCUSABLE); ButtonField mLoad = new ButtonField("Load settings", ButtonField.CONSUME_CLICK); ButtonField mSave = new ButtonField("Save settings", ButtonField.CONSUME_CLICK); public Scr() { add(mUrl); mUrl.setChangeListener(this); add(mEncrypt); mEncrypt.setChangeListener(this); add(mRefresh); mRefresh.setChangeListener(this); HorizontalFieldManager hfm = new HorizontalFieldManager(USE_ALL_WIDTH); add(hfm); hfm.add(mLoad); mLoad.setChangeListener(this); hfm.add(mSave); mSave.setChangeListener(this); loadSettings(); } public void fieldChanged(Field field, int context) { if (field == mLoad) { loadSettings(); } else if (field == mSave) { saveSettings(); } } private void saveSettings() { mOptions.setUrl(mUrl.getText()); mOptions.setEncrypt(mEncrypt.getChecked()); mOptions.setRefreshRate(mRefresh.getValue()); } private void loadSettings() { mUrl.setText(mOptions.getUrl()); mEncrypt.setChecked(mOptions.getEncrypt()); mRefresh.setValue(mOptions.getRefreshPeriod()); } }

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  • How to model a social news feed on Google App Engine

    - by PEZ
    We want to implement a "News feed" where a user can see messages broadcasted by her friends, sorted with newest message first. But the feed should reflect changes in her friends list. (If she adds new friends, messages from those should be included in the feed, and if she removes friends their messages should not be included.) If we use the pubsub-test example and attach a recipient list to each message this means a lot of manipulation of the message recipients lists when users connect and disconnect friends. We first modeled publish-subscribe "fan out" using conventional RDBMS thinking. It seemed to work at first, but then, since the IN operator works the way it does, we quickly realized we couldn't continue on that path. We found Brett Slatkin's presentation from last years Google I/O and we have now watched it a few times but it isn't clear to us how to do it with "dynamic" recipient lists. What we need are some hints on how to "think" when modeling this.

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  • What's faster Model.get(keys) or Model.get_by_id(ids, parent=None)

    - by WooYek
    I'm wondering is there a difference in terms of computing cost for the Model.get(keys) and Model.get_by_id(ids, parent=None) methods? Is there a server side computing advantage of using numeric id's over encoded string keys, or other way around? How big is the difference? PS. Sorry, if it's a dupe. I'm sure I read an article about it, but I cannot find it now.

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  • DataNucleus Enhancer flakey?

    - by KevMo
    I'm creating a GWT app in Google App Engine, and using Google data store. Does anybody else have the problem of the DataNucleus being flakey as all get out? I can save a class, and DataNucleus will do it's thing just fine. If I change ANYTHING in the class (even adding whitespace) and then save, I get the following error: DataNucleus Enhancer completed with success for 0 classes. Timings : input=37 ms, enhance=0 ms, total=37 ms. Consult the log for full details DataNucleus Enhancer completed and no classes were enhanced. Consult the log for full details Once I clean my project, DataNucleus is happy again. Is this common when using eclipse? Is there a workaround?

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  • Can't wrap my head around appengine data store persistence

    - by aloo
    Hi, I've run into the "can't operate on multiple entity groups in a single transaction." problem when using APPENGINE FOR JAVA w/ JDO with the following code: PersistenceManager pm = PMF.get().getPersistenceManager(); Query q = pm.newQuery("SELECT this FROM " + TypeA.class.getName() + " WHERE userId == userIdParam "); q.declareParameters("String userIdParam"); List<TypeA> poos = (List<TypeA>) q.execute(userIdParam); for (TypeA a : allTypeAs) { a.setSomeField(someValue); } pm.close(); } The problem it seems is that I can't operate on a multiple entities at the same time b/c they arent in the same entity group while in a transaction. Even though it doesn't seem like I'm in a transaction, appengine generates one because I have the following set in my jdoconfig.xml: <property name="datanucleus.appengine.autoCreateDatastoreTxns" value="true"/> Fine. So far I think I understand. BUT - if I replace TypeA in the above code, with TypeB - I don't get the error. I don't believe there is anything different between type a and type b - they both have the same key structure. They do have different fields but that shouldn't matter, right? My question is - what could possible be different between TypeA and TypeB that they give this different behavior? And consequently what do you I fundamentally misunderstand that this behavior could even exist.... Thanks.

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  • How to think in data stores instead of databases?

    - by Jim
    As an example, Google App Engine uses data stores, not a database, to store data. Does anybody have any tips for using data stores instead of databases? It seems I've trained my mind to think 100% in object relationships that map directly to table structures, and now it's hard to see anything differently. I can understand some of the benefits of data stores (e.g. performance and the ability to distribute data), but some good database functionality is sacrificed (e.g. joins). Does anybody who has worked with data stores like BigTable have any good advice to working with them?

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  • Why is only the suffix of work_index hashed?

    - by Jaroslav Záruba
    I'm reading through the PDF that Brett Slatkin has published for Google I/O 2010: "Data pipelines with Google App Engine": http://tinyurl.com/3523mej In the video (the Fan-in part) Brett says that the work_index has to be a hash, so that 'you distribute the load across the BigTable': http://www.youtube.com/watch?v=zSDC_TU7rtc#t=48m44 ...and this is how work_index is created: work_index = '%s-%d' % (sum_name, knuth_hash(index)) ...which I guess creates something like 'mySum-54657651321987' I do understand the basic idea, but is why only one half of work_index is hashed? Is it important to hash only part of it leaving the suffix out? Would it be wrong to do md5('%s-%d' % (sum_name, index)) so that the hash would be like '6gw8....hq6' ? I'm Java guy so I would use md5 to hash, which means I get id like 'mySum' + 32 characters. (Obviously I want my ids/keys to be as short as possible here.) If I could hash the whole string my id would be just 32 chars. Or would you suggest to use something else to do the hashing with?

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  • How to change order in ordered+persisted collection?

    - by Jaroslav Záruba
    I just need to change order of items in a (previously persisted) ordered collection... I tried simply passing the re-arranged collection to a setter: after committing a transaction the collection is gone. Then I tried to clear() the existing collection and addAll() afterwards: clear() makes persistent manager to mark all the elements as deleted. (But obviously I would like to be able to work with the collection items in the very transaction.) (The collection is not in a default fetch group, so I tried the above also with the named fetch group added into the fetch plan. No luck.) This must be the most stupid question, but I ran out of ideas and I'm stuck here two days already. I swear I googled. :(

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  • Show users a list of unique items on Java Google App Engine

    - by James
    I've been going round in circles with what must be a very simple challenge but I want to do it the most efficient way from the start. So, I've watched Brett Slatkin's Google IO videos (2008 & 2009) about building scalable apps including http://www.youtube.com/watch?v=AgaL6NGpkB8 and read the docs but as a n00b, I'm still not sure. I'm trying to build an app on GAEJ similar to the original 'hotornot' where a user is presented with an item which they rate. Once they rate it, they are presented with another one which they haven't seen before. My question is this; is it most efficient to do a query up front to grab x items (say 100) and put them in a list (stored in memcache?) or is it better to simply make a query for a new item after each rating. To keep track of the items a user has seen, I'm planning to keep those items' keys in a list property of the user's entity. Does that sound sensible? I've really got myself confused about this so any help would be much appreciated.

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  • unable to set fields of a collection-property elements after changing their order (elements becoming

    - by Jaroslav Záruba
    Hello I want to change order of objects in a collection, and then to access+modify fields of those items. Unfortunately the items somehow become 'deleted'. This is what I do... if(someCondition) { MainEvent mainEvent = pm.getObjectById(MainEvent.class, mainEventKey); /* * events in the original order * MainEvent.subEvents field is not in default fetch group, * therefore I also tried to add the named group into the * persistenceManeger fetch plan, no difference * (mainEvent is not instance of the Event sub/class BTW) */ List<Event> subEvents = mainEvent.getSubEvents(); // re-arrange the events according to keysOrdered { Map<Key, Event> eventMap = new HashMap<Key, Event>(); for(Event event : subEvents) eventMap.put(event.getKey(), event); List<Event> eventsOrdered = new LinkedList<Event>(); for(Key eventKey : keysOrdered) eventsOrdered.add(eventMap.put(eventKey, eventMap.get(eventKey))); // } // put the re-arranged items back into the collection property { subEvents.clear(); subEvents.addAll(eventsOrdered); // } pm.makePersistent(mainEvent); eventsOrdered = subEvents; } else eventsOrdered = getEventsUsingAlternateApproach(); /* * so by now the mainEvent variable does not exist; * could it be this lead the persistence manager to mark * my events as abandoned/obsolete/invalid/deleted...? */ for(Event event : eventsOrdered) event.setDate(new Date()); // -> "Cannot write fields to a deleted object" What am I doing wrong please?

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  • Google App Engine - DELETE JPQL Query and Cascading

    - by Taylor Leese
    I noticed that the children of PersistentUser are not deleted when using the JPQL query below. However, the children are deleted if I perform an entityManager.remove(object). Is this expected? Why doesn't the JPQL query below also perform a cascaded delete? @OneToMany(mappedBy = "persistentUser", cascade = CascadeType.ALL) private Collection<PersistentLogin> persistentLogins; ... @Override @Transactional public final void removeUserTokens(final String username) { final Query query = entityManager.createQuery( "DELETE FROM PersistentUser p WHERE username = :username"); query.setParameter("username", username); query.executeUpdate(); }

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