AppCreator & Use of Keyed Type with Enumeration

Hello Todd,

It is possible to use user-generated types with content filter together in XML App Creator. They are orthogonal features, meaning you can use content filter without type generation, viceversa or both. I don't know what problem you are experiencing, so I would appreciate if you could post the output of your application.

Something that I don't understand though is the "user-defined" enumeration value that you mention. Assuming that you're using SQL, as far as I know there shouldn't be any limitation with enumerated types, and from the XML there shouldn't be any incompability either. However, when specifying a SQL expression through XML we have to be careful with special symbols such as "<" and ">". Before getting there,  I would like to review with you the process of using user-generated types and content filters with XML App Creator. Let's see the two key steps for that:

• User-generated types: A type in XML shall look like this:

<register_type name="registeredTypeName" kind="userGenerated"/>

The key here is to set the kind to "userGenerated" (which in this case this enumeration value is possible) and call DDS_DomainParticipantFactory_register_type_support_exp to supply the registration of the types before you call DDS_DomainParticipantFactory_create_participant_from_config_exp.

• Define a filter within a DataReader tag:

<data_reader name="reader" topic_ref="topic">
	<filter name="filteredTopic" kind="builtin.sql">
		<expression>myField &lt; %0</expression>
		<parameter_list>
			<param>myParam</param>
		</parameter_list>
	</filter>
</data_reader>

In this case, the DataReader will be created from a content filter topic whose filter class is the built-in SQL. So with the "kind" attribute you can specify the filter class to be used, and the two possible values allowed by the schema are builtin.sql and builtin.stringMatch, hence no custom filters are possible.

An important part for the <filter> tag is the <expression> element. This is parsed data, and as such, we cannot use invalid characters that will result in a parsing error. For the SQL case, there are many of those characters. For instance in the example above, we want to use the expression "myField < %0". However this canot be written right away in the XML since "<" is not allowed, and it must be replaced with "&lt;".

For the question of the filter compilation, if you're referring to when the "compile" operation is called, this occurs several times along the lifecycle of the content filter topic, but the first time occurs on ContentFitleredTopic creation. The only requirement for this to work is that a ContentFilter object for a specified filter class must be already registered in the DomainParticipant (similar to type registration).

So in order for XML APP Creation to support custom filter, I would suggest the feature must be able to load a dynamic library containing the filter implemenation, so that it can create a corresponding ContentFilter object to be registered with participants. The library along with the entry point can be specified via XML, and then filter kind could support a "user-generated" value the same way as the <register_type>.

Let me know any other question.

Antonio

Hi Todd,

I have created my own application with your IDL and filter configurations, and I got a compilation error. Even though the error message is little descriptive I figured out that the problem is in the expression: the enumerated value does not have the correct form. I took a look to the user's manual and in section 5.4.6.7 there is the syntax for enumerations. So for this use case, we would need to write it as follows:

key = 'KEY_1'

According to the documentation, only the enumerated value is needed without the fully qualified name as you were setting. This would have been easier to detect with better error messages, but at least we know that if you get an error like this:

[D0000|CREATE CFTopic|T=IDLTypeReader::IDLTypeFilter]PRESParticipant_createContentFilteredTopic:content filter compile error 1

that shows an error code equal to 1, then it is a compilation error due to a malformed expression.

Attached you can find the XML configuration file I used to reproduce your use case but with the correct expression. You can use it to verify if that works in your environment.

Let me know if this solves the problem.

Antonio

You're very welcome Todd! Glad I could help :)

Antonio