在DataTable上构建表达式，设计建议？

Question

I have Questions datatable with columns Question_Id, value, enable. This will be loaded with list of question with answers.

UI controls will be created based on the Questions datatable with question has enable set to true. If user selects / changes answer for any of the question, the value will be updated in the questions table that will result is enable/disable the other related question if any.

This will be defind in an expression like,basically, 'Enable X, if Y == (someValue) AND /OR .....' here X, Y are question.

I would like use Expression tree in Linq.Expression to handle this but new to Expression evaluation and looking for good design approch to implement.

Can some one guide me on this?

Answer 1

If I am understanding the question correctly, you are building a list of questions that should be dynamically updated based on the answers to those questions. For example, if a question #1 is answered, then question #2 should be disabled (or something more complex).

I'm a big fan of dynamic code generation (eg expression trees), but this may actually be addressed more simply with an XML structure since it lends itself to representing relationships much better than a single DataTable .

<question id="1">
    <if valueToCompare="Foo" operator="EqualTo">
        <disable questionId="5" />
        <removeOption questionId="6" optionId="2" />
    </if>
</question>

Whenever the user's answer to a question changes, simply look at the corresponding XML node and act accordingly.

You can evaluate and rebuild your controls in real-time without the need for compiled expressions and the performance will be fine unless you have extremely complex controls.

However, if you want to learn about expressions, you could certainly extrapolate and construct them from an XML structure and create delegates which are invoked whenever a question changes. For example, if answering question #1 should disable question #2, you could turn this logic into a delegate that is fired whenever question #1 changes.

This would require initially parsing your data source (XML or otherwise--you could certainly store simple logic statements in a DataTable as strings or multiple columns and parse those) and turning conditional statement definitions into expression trees. This could be quite simple or complex depending on how complicated your want your decision trees to be.