Only render fields within a IF Statement

Aspose.Words Product Family
1

Hi,

We are using a template with multiple IF conditions to control which sections are rendered based on specific conditions. Ideally, fields should only be rendered if the condition is met. However, in our case, if the fields do not exist in the data source, an error is thrown.

I am aware that enabling AllowMissingMembers can prevent these errors, but I do not want this setting to be enabled by default, as I need to detect missing fields when they are genuinely required.

What we need is:

  • If the condition is met, but a required field within the IF statement is missing, it should throw an error.
  • If the condition is not met, the entire section should be ignored without error.

Could you provide an option or workaround to achieve this behavior?

Thanks!

2

@pphillipsbiz

Can you please specify which version of Aspose.Words you are using and provide a sample template or code snippet that demonstrates the issue?

3

Hi,
Version: 23.8.0
Example template:

<<if [GeneralInfo.PolicyNumber=="ll">>
<<[GeneralInfo.Missing]>>
<</if>>
4

@pphillipsbiz LINQ Reporting Engine parses a template document as a whole before evaluating any expression. The engine does not skip parsing of expressions, which are not going to be evaluated according to template logic and data. This is by design.
You can use ReportBuildOptions.AllowMissingMembers. If this option is set, the engine does not throws an exception when encounters a missing object member. Please see our documentation for more information:
https://docs.aspose.com/words/net/accessing-missing-members-of-data-objects/

5

ok, is there any way to add a custom helper/class that I can access the data?

7

@pphillipsbiz

Of course, you can use an object of any custom type (without violating encapsulation) as a data source or for invocation of its static members. See Accessing Type Members for details.

8

Thank you, I have tried the following:

public static class TemplateSupport
{
    public static int Test { get; set; } = 99;
    public static string Lookup()
    {
        return "Helloer";

…

var engine = new ReportingEngine();
engine.KnownTypes.Add(typeof(Helper));
engine.KnownTypes.Add(typeof(TemplateSupport));

But in the template I have the following but fails:



image.png791×178 6.71 KB

image.png827×164 2.93 KB

9

@pphillipsbiz

A closing bracket is missing for the if tag. It seems like this causes the error.

10

Doh, yes , thanks, I will get my eyes checked :slight_smile:

How do I pass data to the method, for example, I would like to do the following:
<<[TemplateSupport.Lookup(GeneralInfo)]>>
Code:

I can see the data is being passed if the param is an Object, but what is the best way to access the data?

11

@pphillipsbiz

What does GeneralInfo represent? An element of a JSON object? Or an object of a regular type? Or something else, maybe?

12

This is a JSON object via JsonDataSource

13

@pphillipsbiz

Not all JSON elements can be casted to DataRow. However, if such a typecast works in your case, then you can use DataRow as a parameter type for TemplateSupport.Lookup.

14

I tried that but get the following error:

image.png735×130 10.3 KB

15

Then, most likely, data as DataRow would return null in case when TemplateSupport.Lookup’s parameter type is object, would not it?

16

But you can also see that DataRow as a param causes errors in the template.

17

@pphillipsbiz

The reason for this is the same. As I shared earlier:

There is no typecast to DataRow for this JSON element. That is why, neither the typecast works, nor the method is resolved.

18

@pphillipsbiz

Casting JSON elements to DataRow is related to details of JsonDataSource’s internal implementation. Therefore, this is not a recommended technique at all.

This requirement can be fullfilled in another way:

  1. Enable access to missing members of data objects.

  2. For every expression tag that is in a false-branch of an if tag, simply keep it as is.

  3. For every expression tag that is in a true-branch of an if tag, wrap the expression
    like this: <<[Util.Ensure(original_expression)]>>.

  4. Implement the Util class in your code as follows:

public static class Util
{
    public static object Ensure(object value)
    {
        if (value == null) // The value is missing, throw.
            throw ...

        return value;
    }
}
  1. Make the engine aware of the Util class as described at Setting up Known External Types.
20

I thought this would work but this only works for a single element, this will fail if I try to use GeneralInfo.Missing,

You are passing System.Data.DataRow:

963×259 24.4 KB

21

@pphillipsbiz

I am afraid, from the description, it is not clear enough what the problem is. You can process values of different types differently providing special handling of DataRow, if needed.

22

I cannot cast value to System.Data.DataRow, even though as you can see the object is System.Data.DataRow. I believe this is because you have obfuscated your code ({mK}).