Custom Data Processing Extension and Parameters

Question

Hello,
I have successfully implemented a custom data processing extension. Now I'm trying to add parameters, but the documentation is very weak on this topic. Also all examples of custam data processing extensions I have found so far are working without parameter support. Using a search engine I have found a custom data processing extension's sequence diagram during report execution. The related article also gives some hints about the IDbCommandAnalysis interface.
The GetParameters implementation creates a parameter collection based on the current command text and returns this collection. So far no problem.
My question is how to implement the IDbCommand's CreateParameter method and Parameters property? In CreateParameter I just return a new instance of my IDataParameter implementation, and the Parameters property returns a new parameter collection based on the current command text.
Is this ok so? At least this is the first implementation which seems to work in the data designer. If I share an instance variable for GetParameters and Parameters I will either get all parameters twice or BIDS will crash when pressing the execute button in the dataset designer - depending on my actual implementation.
What I'm still missing is how to get the parameters added automaticall to the dataset's properties parameter register?
thanx in advance and kind regards, Gerald

Answer 1

I think that finally (after some days of trying) I could make it work. The dataset and report parameters are reflecting the command text's parameters now (BTW: to answer my last question - the dataset's properties are updated after pressing the refresh button only). The road to success was not to use the same member variable for the collections returned by IDbCommandAnalysis:GetParameters() and IDbCommand:Parameter and not to fill the latter one with the command text's parameters (see partial source code below).
public sealed class MyCommand : IDbCommand, IDbCommandAnalysis  
    private string m_commandText;  
    private MyParameterCollection m_parameters = new MyParameterCollection();  
    public string CommandText  
        get { return this.m_commandText; }  
        set { SetCommandText(value); }  
    public IDataParameterCollection Parameters  
        get { return m_parameters; }  
    public IDataParameter CreateParameter()  
        return new MyParameter();  
    public IDataParameterCollection GetParameters()  
        return GetParameterCollection();  
    private void SetCommandText(string commandText)  
        m_commandText = commandText;  
    private MyParameterCollection GetParameterCollection()  
        // ... create parameter collection based on m_commandText  
Still there are some open questions:
How can I update the report parameter's properties? Now the parameter's data type is always string, but I'd like to assign the right data type. I'd also like to tag the parameters as hidden and supply a non-queried default value. Is this possible? How?
Although I my implementation of IDbCommandAnalysis:GetParameters() returns a collection containing the parameter names and values the "prompt query parameters" dialog (after pressing the query designer's execute button in the toolbar) shows a "<blank>" value for the parameters. What could be the problem?
Thanx in advance and regards,
Gerald