ASP.NET MVC2 ModelMetadataProviders: What's the difference between overriding CreateMetadata() and GetMetadataForProperty()? -

i'm statring explore framework's extension points, starting metadataproviders. i've implemented populating modelmetadata.isrequired property using requiredattribute succesfully, can't seem find difference between overriding createmetadata() or getmetadataforproperty(), since both options seem work.

in general, examples i've seen override createmetadata().

• what pro , cons of using either options?
• are there scenarios 1 of these preferred options?

as extra: there resources (blogs, books) learn extension point?

the getmetadataforproperty() declared on class modelmetadataprovider.

associatedmetadataprovider derives modelmetadataprovider. createmetadata() declared on associatedmetadataprovider. dataannotationsmetadataprovider overridden in link provide derived associatedmetadataprovider.

the mvc framework makes calls modelmetadataprovider's getmetadataforproperty() method.

the reason overriding createmetadata() working because associatedmodelmetadataprovider's default implementation of getmetadataforproperty() makes call createmetadata(). looks this:

public override modelmetadata getmetadataforproperty(func<object> modelaccessor, type containertype, string propertyname) {    if (containertype == null)    {        throw new argumentnullexception("containertype");    }    if (string.isnullorempty(propertyname))    {        throw new argumentexception(mvcresources.common_nullorempty, "propertyname");    }    propertydescriptor propertydescriptor = this.gettypedescriptor(containertype).getproperties().find(propertyname, true);    if (propertydescriptor == null)    {        throw new argumentexception(string.format(cultureinfo.currentculture, mvcresources.common_propertynotfound, new object[] { containertype.fullname, propertyname   }));    } return this.getmetadataforproperty(modelaccessor, containertype, propertydescriptor); 

}

protected virtual modelmetadata getmetadataforproperty(func<object> modelaccessor, type containertype, propertydescriptor propertydescriptor)  {    ienumerable<attribute> attributes = this.filterattributes(containertype, propertydescriptor, propertydescriptor.attributes.cast<attribute>());    return this.createmetadata(attributes, containertype, modelaccessor, propertydescriptor.propertytype, propertydescriptor.name); } 

if subclassing associatedmetadataprovider in link provided, preferred extensibility point createmetadata method, because associatedmetadataprovider.getmetadataforproperty() method pre-validates contract of createmetadata() method. way, know if there error in createmetadata() method, know source of error in method , not in arguments passed it.

also, here source of filterattributes() method, in case wondering:

protected virtual ienumerable<attribute> filterattributes(type containertype, propertydescriptor propertydescriptor, ienumerable<attribute> attributes) { if (!typeof(viewpage).isassignablefrom(containertype) && !typeof(viewusercontrol).isassignablefrom(containertype))     {         return attributes;     }     return attributes.where<attribute>(delegate (attribute a) {         return !(a readonlyattribute);     }); }