Apple

This is actually pretty straight forward to do. I don't know if this is the best way to accomplish saving XML objects as EOs, but it works and will hopefully help someone else!

The key is that Apache Digester provides the ability to create and call custom rules that have begin(), body() and end() methods when they hit an XML tag pattern. Use a custom rule instead of the stock ObjectCreateRule to create an EO and add it to an EditingContext BEFORE you start changing property values on the EO with the stock digester rules.

I'm using WOnder so i am using ERXEC for the editing context and when I add the related object with the rule (addToAuthors) I am taking advantage of the WOnder feature that automatically updates my inverse relationship. If you're not using WOnder you'll have to figure out where to addObjectToBothSidesOfRelationship ...

Anyway ....

Here's my example Custom Rule for the main Document object:

public class DocumentECInserterRule extends org.apache.commons.digester.Rule {

private ERXEC ec = (ERXEC) ERXEC.newEditingContext();

private Document doc = new Document();

public void begin(String namespace, String name, org.xml.sax.Attributes attrs) {

digester.push(doc);

ec.insertObject(doc);

}

public void end(String namespace, String name) {

System.out.println("---- Saving out the EO ----");

ec.saveChanges();

}

For any related objects you have to play around with the creation order a bit and not call ec.saveChanges() in the end() method. Here's an example inserter rule for a related object:

package ca.cscw;

import ca.cscw.model.Author;

import ca.cscw.model.Document;

import er.extensions.ERXEC;

public class AuthorECInserterRule extends org.apache.commons.digester.Rule {

public AuthorECInserterRule( ) {

}

public void begin(String namespace, String name, org.xml.sax.Attributes attrs) {

// gets a reference to the top object on the stack, we need this to pass the same editingContext from rule to rule

Document doc = (Document) digester.peek();

// then create your author

Author author = new Author();

// push new author to the top of the stack

digester.push(author);

// get the ec

ERXEC ec = (ERXEC)mc.editingContext();

// insert new author

ec.insertObject(author);

}

public void end(String namespace, String name) {

// remove author from the stack (doc moves to the top once again)

Author author = (Author) digester.pop();

}

Here is the use of my example rules:

DocumentECInserterRule documentECMInserterRule = new DocumentECInserterRule();

digester.addRule("Document", documentECMInserterRule);

// add an attribute property

digester.addSetProperties("Document", "Status", "status" );

AuthorECInserterRule authorECInserterRule = new AuthorECInserterRule();

digester.addRule("Document/AuthorList/Author", authorECInserterRule);

// add a couple example properties

digester.addCallMethod("Document/AuthorList/Author/LastName", "setLastName", 0 );

digester.addCallMethod("Document/AuthorList/Author/FirstName", "setFirstName", 0 );

// call 'addToAuthors' method when the next 'Document/AuthorList/Author' pattern is seen

// this adds the author that is already in the ec from the InserterRule

digester.addSetNext("MedlineCitationSet/MedlineCitation/Article/AuthorList/Author", "addToAuthors" );

The rule firing order is first in, last out. So my custom (ignoring the property setting rules) rules will fire in this order:

documentECMInserterRule.begin() //creates the document and inserts it into a new EditingContext

authorECInserterRule.begin() // create author, get reference to the document's EditingContext, insert author

authorECInserterRule.end() // pops the author off the stack and adds it to the relationship using the default addSetNext rule

documentECMInserterRule.end() // save all changes to the EditingContext

Take care,

David

On 21-Apr-08, at 5:47 PM, Chuck Hill wrote:

On Apr 21, 2008, at 5:28 PM, David Holt wrote:

Hi all,

I have successfully parsed an XML file with the Apache Digester (thanks to Chuck's suggestion) and created EOs using the default rules.

I end up with an array of EOs each of which has several to-many relationships to other created EOs. The xml seems to all be "digested" at once when the file is parsed and I am not sure where to intervene to add an EO to the editing context. Can anyone help me with this?

Offhand, I don't know. I looked at our code using Digester (code which I was not at all involved in, my story, and I am sticking to it), we imported them into intermediate (non-EO) classes and then fetched / created EOs (as appropriate for update / create). We then copied the needed values from the intermediate classes. I think that was necessary as the XML represented EOs getting inserted into an existing, complex graph of objects. Your case is probably simpler, but I don't have a simple solution at hand.

Chuck

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Practical WebObjects - for developers who want to increase their overall knowledge of WebObjects or who are trying to solve specific problems.
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References:
	>Digester and EOs (From: David Holt <email@hidden>)
	>Re: Digester and EOs (From: Chuck Hill <email@hidden>)