castor

Castor code generator has problems with xml schema groups

Details

  • Type: Bug Bug
  • Status: Open Open
  • Priority: Major Major
  • Resolution: Unresolved
  • Affects Version/s: 0.9.4
  • Fix Version/s: None
  • Component/s: XML code generator
  • Labels:
    None
  • Environment:
    Operating System: Windows 2000
    Platform: PC
  • Bugzilla Id:
    1072
  • Number of attachments :
    0

Description

When I try to generate code based on the IMS Global Learning Consortium content
packaging schema (http://www.imsproject.org/xsd/imscp_rootv1p1p2.xsd), I get
problems with the following part of the schema:

<xsd:group name="grp.any">
<xsd:annotation>
<xsd:documentation>Any namespaced element from any namespace may be inc
luded within an "any" element. The namespace for the imported element
must be defined in the instance, and the schema must be imported. </xsd:docume
ntation>
</xsd:annotation>
<xsd:sequence>
<xsd:any namespace="##other" processContents="strict" minOccurs="0" max
Occurs="unbounded"/>
</xsd:sequence>
</xsd:group>

When I try and unmarshall a document, the resulting exception is:

Unmarshalling failed: ValidationException: error-if-this-is-used is a
required field.; - location of error: XPATH:
manifest/organizations/organization/item at
org.exolab.castor.xml.FieldValidator.validate(Unknown Source) at
org.exolab.castor.xml.util.XMLClassDescriptorImpl.validate(Unknown Source) at
org.exolab.castor.xml.util.XMLClassDescriptorImpl.validate(Unknown Source) at
org.exolab.castor.xml.Validator.validate(Unknown Source) at
org.exolab.castor.xml.FieldValidator.validate(Unknown Source) at
org.exolab.castor.xml.util.XMLClassDescriptorImpl.validate(Unknown Source) at
org.exolab.castor.xml.util.XMLClassDescriptorImpl.validate(Unknown Source) at
org.exolab.castor.xml.Validator.validate(Unknown Source) at
org.exolab.castor.xml.FieldValidator.validate(Unknown Source) at
org.exolab.castor.xml.util.XMLClassDescriptorImpl.validate(Unknown Source) at
org.exolab.castor.xml.util.XMLClassDescriptorImpl.validate(Unknown Source) at
org.exolab.castor.xml.Validator.validate(Unknown Source) at
org.exolab.castor.xml.FieldValidator.validate(Unknown Source) at
org.exolab.castor.xml.util.XMLClassDescriptorImpl.validate(Unknown Source) at
org.exolab.castor.xml.util.XMLClassDescriptorImpl.validate(Unknown Source) at
org.exolab.castor.xml.Validator.validate(Unknown Source) at
org.exolab.castor.xml.UnmarshalHandler.endElement(Unknown Source) at
org.apache.xerces.parsers.SAXParser.endElement(SAXParser.java:1392) at
org.apache.xerces.validators.common.XMLValidator.callEndElement
(XMLValidator.java:1550) at
org.apache.xerces.framework.XMLDocumentScanner$ContentDispatcher.dispatch
(XMLDocumentScanner.java:1149) at
org.apache.xerces.framework.XMLDocumentScanner.parseSome
(XMLDocumentScanner.java:381) at org.apache.xerces.framework.XMLParser.parse
(XMLParser.java:1098) at org.exolab.castor.xml.Unmarshaller.unmarshal(Unknown
Source) at org.exolab.castor.xml.Unmarshaller.unmarshal(Unknown Source) at
org.exolab.castor.xml.Unmarshaller.unmarshal(Unknown Source) at
com.sun.elearning.lms_.upload_.schemabinding.imscp.Manifest.unmarshal

It seems that castor generates a 'dummy' XMLFieldDescriptor instance for the
group, with the name 'error-if-this-is-used'. Unfortunately, the
XMLFieldDescriptor has it's 'required' attribute set to true, so during
validation, castor wants there to be an element of that name and complains.

I've tried to fix my own build of castor by modifying the
org.exolab.castor.xml.schema.Group class to set it's 'minOccurs' attribute to
0, rather than the default of 1. This prevents the 'required' attribute from
being set and everything seems to be fine, but I'm not sure if this is really a
valid fix.

This problem appears to be generation time only - the code from my modified
generator works fine with the normal version of castor.

Activity

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Arnaud Blandin added a comment -

accept bug

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Arnaud Blandin added a comment - accept bug
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Permalink
simon.bates added a comment -

I am also using the IMS Content Packaging schema and experiencing the same
problem outlined above. I would like to use Castor and would have some time to
look into fixing this issue.

I am new to Castor and unfamiliar with the code and I was wondering if Arnaud
could give me some pointers as to where I should start and what might be going
wrong?

Thank you very much for your help and for Castor in general! It is a great
piece of work.

Show
simon.bates added a comment - I am also using the IMS Content Packaging schema and experiencing the same problem outlined above. I would like to use Castor and would have some time to look into fixing this issue. I am new to Castor and unfamiliar with the code and I was wondering if Arnaud could give me some pointers as to where I should start and what might be going wrong? Thank you very much for your help and for Castor in general! It is a great piece of work.
Hide
Permalink
simon.bates added a comment -

Is Jack's suggestion of modifying org.exolab.castor.xml.schema.Group to set it's
'minOccurs' attribute to 0 the correct fix?

Thanks!

Show
simon.bates added a comment - Is Jack's suggestion of modifying org.exolab.castor.xml.schema.Group to set it's 'minOccurs' attribute to 0 the correct fix? Thanks!
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Permalink
Arnaud Blandin added a comment -

The proposed fix is incorrect, you cannot set the value to 0 it is only a
workaround.
The main problem comes from the XML Schema design:
<xsd:group name="grp.any">
<xsd:sequence>
<xsd:any namespace="##other" processContents="strict" minOccurs="0"
maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:group>
is a group that can be empty
<xsd:complexType name="metadataType">
<xsd:sequence>
<xsd:group ref="grp.any"/> XXXXXXX
</xsd:sequence>
</xsd:complexType>

XXXX refers to a group that must appear once (minOccurs=1 by default) but it
can be empty by the definition of the group.

This is very bad designed since it is equivalent in OO performance-term that an
Object will hold a reference to an object that can be empty but not null.
I would advise as a workaround to refer to the group as:
<xsd:group ref="grp.any" minOccurs="0"/>

However Castor shouldn't throw an exception when reading valid document but I
am still unclear about what we should do:

1- detect that the group is required
2- detect that the group itself can be empty
3- instantiate a EMPTY vector of AnyNode
...not sure if it is a good solution

Show
Arnaud Blandin added a comment - The proposed fix is incorrect, you cannot set the value to 0 it is only a workaround. The main problem comes from the XML Schema design: <xsd:group name="grp.any"> <xsd:sequence> <xsd:any namespace="##other" processContents="strict" minOccurs="0" maxOccurs="unbounded"/> </xsd:sequence> </xsd:group> is a group that can be empty <xsd:complexType name="metadataType"> <xsd:sequence> <xsd:group ref="grp.any"/> XXXXXXX </xsd:sequence> </xsd:complexType> XXXX refers to a group that must appear once (minOccurs=1 by default) but it can be empty by the definition of the group. This is very bad designed since it is equivalent in OO performance-term that an Object will hold a reference to an object that can be empty but not null. I would advise as a workaround to refer to the group as: <xsd:group ref="grp.any" minOccurs="0"/> However Castor shouldn't throw an exception when reading valid document but I am still unclear about what we should do: 1- detect that the group is required 2- detect that the group itself can be empty 3- instantiate a EMPTY vector of AnyNode ...not sure if it is a good solution
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simon.bates added a comment -

Created an attachment (id=233)
Grp_any.java generated for <xsd:group name="grp.any">

Show
simon.bates added a comment - Created an attachment (id=233) Grp_any.java generated for <xsd:group name="grp.any">
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simon.bates added a comment -

Created an attachment (id=234)
Grp_anyDescriptor.java generated for <xsd:group name="grp.any">

Show
simon.bates added a comment - Created an attachment (id=234) Grp_anyDescriptor.java generated for <xsd:group name="grp.any">
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simon.bates added a comment -

Arnaud,

Thank you very much for your response.

I think the solution that would match the schema most closely to my mind would
be that an instance of Grp_any is created at unmarshalling and that
Grp_any.getAnyObjectCount() returns 0. For example:

Manifest manifest = Manifest.unmarshal(someReader);
Metadata metadata = manifest.getMetadata();
Grp_any a = metadata.getGrp_any();

for the following XML:

<manifest>
<metadata>
</metadata>
</manifest>

a.getAnyObjectCount() would return 0.

I would be happy to have a go at implementing this is you think it is the
correct approach and if you could maybe give me a pointer to how this might be done.

Regards,
Simon.

Show
simon.bates added a comment - Arnaud, Thank you very much for your response. I think the solution that would match the schema most closely to my mind would be that an instance of Grp_any is created at unmarshalling and that Grp_any.getAnyObjectCount() returns 0. For example: Manifest manifest = Manifest.unmarshal(someReader); Metadata metadata = manifest.getMetadata(); Grp_any a = metadata.getGrp_any(); for the following XML: <manifest> <metadata> </metadata> </manifest> a.getAnyObjectCount() would return 0. I would be happy to have a go at implementing this is you think it is the correct approach and if you could maybe give me a pointer to how this might be done. Regards, Simon.
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simon.bates added a comment -

Created an attachment (id=235)
Descriptor generated for metadataType that references a grp.any group

Show
simon.bates added a comment - Created an attachment (id=235) Descriptor generated for metadataType that references a grp.any group
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Permalink
simon.bates added a comment -

Is a possible solution to modify the source code generator so that:

In the case that a class contains a group with a minOccurs of 1 and that group
itself can be empty
then
the containing class creates an instance of the class representing the group in
its constructor?

For example rather than:

public ManifestType()

{ super(); _manifestList = new Vector(); }

could we generate:

public ManifestType()

{ super(); _manifestList = new Vector(); _grp_any = new ca.utoronto.atrc.tile.imscp.Grp_any(); }

and if so is this a good solution?

I started looking into this. It looks like the "_manifestList = new Vector();"
line is added by
org.exolab.castor.builder.CollectionInfo.generateInitializerCode which is called
by org.exolab.castor.builder.SourceFactory.handleField

Is it feasible to modify the source generator so that SourceFactory.handleField
adds a line to the constructor that creates a instance of a group as for
_manifestList above when it is called on a group with minOccurs=1 that can be empty?

Thanks a lot.

Show
simon.bates added a comment - Is a possible solution to modify the source code generator so that: In the case that a class contains a group with a minOccurs of 1 and that group itself can be empty then the containing class creates an instance of the class representing the group in its constructor? For example rather than: public ManifestType() { super(); _manifestList = new Vector(); } could we generate: public ManifestType() { super(); _manifestList = new Vector(); _grp_any = new ca.utoronto.atrc.tile.imscp.Grp_any(); } and if so is this a good solution? I started looking into this. It looks like the "_manifestList = new Vector();" line is added by org.exolab.castor.builder.CollectionInfo.generateInitializerCode which is called by org.exolab.castor.builder.SourceFactory.handleField Is it feasible to modify the source generator so that SourceFactory.handleField adds a line to the constructor that creates a instance of a group as for _manifestList above when it is called on a group with minOccurs=1 that can be empty? Thanks a lot.
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simon.bates added a comment -

Created an attachment (id=245)
ManifestType.java that contains a Grp_any

Show
simon.bates added a comment - Created an attachment (id=245) ManifestType.java that contains a Grp_any

People

  • Assignee:
    Unassigned
    Reporter:
    Jack Honeghan-Bates
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  • Created:
    Updated: