site_archiver@lists.apple.com Delivered-To: webobjects-dev@lists.apple.com Hi all, The second exception we get is: Can anyone point me in the right direction on this? Marek Wawrzyczny software engineer --------------------------> ish group pty ltd http://www.ish.com.au 7 Darghan St Glebe 2037 Australia phone +61 2 9660 1400 fax +61 2 9660 7400 <<< Code follows >>> package ish.common.webobjects.utilities; import com.webobjects.foundation.*; import com.webobjects.eocontrol.*; import com.webobjects.eoaccess.*; public class EOFetchCounting extends Object { private static EOAttribute _objectCountAttribute = null; if (fetchSpecification != null) { EOFetchSpecification rawFetchspecification; if ((results != null) && (results.count() == 1)) { NSDictionary row = (NSDictionary) results.lastObject(); return (Number)row.objectForKey(attribute.name()); } } return null; } /** * Returns the number of rows metching the fetch specifivation. * * @param editingContext - editing context to perform the fetch in * @param entityName - the entity to perform the count on * @param fetchSpecification - the fetch specification * @param bindings - the fetch bindings */ public static Number objectCountWithFetchSpecificationAndBindings( EOEditingContext editingContext, String entityName, String fetchSpecName, NSDictionary bindings) { /** * <p>Private.</p> */ private static EOAttribute objectCountAttribute() { return _objectCountAttribute; } } _______________________________________________ Do not post admin requests to the list. They will be ignored. Webobjects-dev mailing list (Webobjects-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/webobjects-dev/site_archiver%40lists.... A long time ago I came across Eric Noyau's famous BugTracker, and the useful FetchCounting class. Since then we used something similar to perform counts in our application, however recently it has become the source of a problem. The source is at the end of the file. I have to admit, I don't fully understand how it works, but essentially it appears that the target entity is retrieved from the fetch specification. Then a additional "count" attribute is added to the model to perform the count. There are two problems with that solution we have encountered, the first one results in the following exception: "Exception while trying to save the EOEditingContext during the processing of transaction... Stack trace: java.lang.IllegalArgumentException: addAttribute: duplicated attribute name: p_objectCountAttribute at com.webobjects.eoaccess.EOEntity.addAttribute(EOEntity.java:2153) at ish.common.webobjects.utilities.EOFetchCounting.objectCountWithFetchSpec ification(EOFetchCounting.java:61) <...>" I believe that this is caused due to the variable "_objectCountAttribute" being static. I think that two different threads are attempting to perform the fetch count 'simultaneously' on the same entity. One has already added the "count" attribute when the other attempts to do this again. "java.lang.IllegalArgumentException: addAttribute: attribute has a different entity at com.webobjects.eoaccess.EOEntity.addAttribute(EOEntity.java:2149) at ish.common.webobjects.utilities.EOFetchCounting.objectCountWithFetchSpec ification(EOFetchCounting.java:61) <...>" Here I believe two threads are attempting to perform fetch counts on different entities. Since the static "_objectCountAttribute" can only be linked to one entity at a time, we get the exception when the second thread attempts to add the attribute before the first thread had the opportunity to remove it from its entity. This is actually where I am stuck. I don't understand the EOModel and EOAttribute mechanism very well. One solution I tried was to add the count attribute permanently, that crashed the application. So I tried creating the attributes on the fly and removing them once finished this worked. However, it doesn't appear I can make this thread-safe since there is no locking mechanism on the EOModel (I think this is why Eric's solution used a static var) and I cannot easily test this concept under duress (when the exceptions actually start occurring). /** * <p>This class impements methods that allow us to count the number of * rows for a user defined fetch specification.</p> * * <p>The count is performed directly on the database source without having to load * them into memory.</p> * * <p>Original code by Eric Noyau. This class has been taken from Eric's Bugtracker application.</p> * * @author Eric Noyau * @author Marek Wawrzyczny * @version 1.1 */ /** * <p>Returns the number of rows metching the fetch specifivation.</p> * * @param editingContext - editing context to perform the fetch in * @param fetchSpecification - the fetch specification */ public static Number objectCountWithFetchSpecification( EOEditingContext editingContext, EOFetchSpecification fetchSpecification) { try { rawFetchspecification = (EOFetchSpecification)fetchSpecification.clone(); } catch (Exception e) { System.out.println("\nException in objectCountWithFetchSpecification :\n"+e); return null; } EOEntity entity = EOModelGroup.defaultGroup().entityNamed(rawFetchspecification.entityName ()); EOQualifier schemaBasedQualifier = entity.schemaBasedQualifier(rawFetchspecification.qualifier()); EOAttribute attribute = EOFetchCounting.objectCountAttribute(); NSArray results = null; entity.addAttribute(attribute); // Fix to ensure that fetch counting does not trip the site when // the fetch fails for some reason try { rawFetchspecification.setQualifier(schemaBasedQualifier); rawFetchspecification.setRawRowKeyPaths(new NSArray(attribute.name())); results = editingContext.objectsWithFetchSpecification(rawFetchspecification); } finally { // IMPORTANT!!! // This needs to run every time, exception or not entity.removeAttribute(attribute); } EOModelGroup modelGroup = EOModelGroup.defaultGroup(); EOFetchSpecification unboundFetchSpec; EOFetchSpecification boundFetchSpec; unboundFetchSpec = modelGroup.fetchSpecificationNamed(fetchSpecName, entityName); if (unboundFetchSpec == null) { return null; } boundFetchSpec = unboundFetchSpec.fetchSpecificationWithQualifierBindings(bindings); return objectCountWithFetchSpecification(editingContext, boundFetchSpec); } if ( _objectCountAttribute == null ) { _objectCountAttribute = new EOAttribute(); _objectCountAttribute.setName("p_objectCountAttribute"); _objectCountAttribute.setColumnName("p_objectCountAttribute"); _objectCountAttribute.setClassName("Number"); _objectCountAttribute.setValueType("i"); _objectCountAttribute.setReadFormat("count(*)"); } This email sent to site_archiver@lists.apple.com