Error in LINQ

Aspose.Words Product Family
1

I’m experiencing an issue while using Aspose.Words Reporting Engine with LINQ templates. I have a scenario where I’m working with JSON data that contains nested objects and arrays. Specifically, I’m trying to conditionally display a value (allocationPercentages.ElementAt(0).value) based on its presence and non-nullity.

Here’s the code snippet I’m using in the template:

<<if [p.allocationPercentages.Count() > 0 && p.allocationPercentages.ElementAt(0).value != null]>>
    <<[((decimal)p.allocationPercentages.ElementAt(0).value).ToString("F2")>>
<</if>>

However, I’ve noticed that even when the condition is false (i.e., allocationPercentages is either empty or value is null), the engine still seems to try evaluating the expression, resulting in errors such as:

AsposeDocumentWriter: Error writing values to the template: An error has been encountered at the end of expression \'p.allocationPercentages.Count() \> 0 \&\& p.allocationPercentages.ElementAt(0).value != \'. Can not get the value of member \'value\' on type \'System.Data.DataRow\'.    at dL.d(v d, VL v, Char c)\\n   at dL.dLiFd(VL d, Char v)\\n   at Il.B()\\n   at Vl.P()\\n   at Vl.B()\\n   at Vl.t()\\n   at Vl.d()\\n   at Vl.IliFd()\\n   at Il.d(ZD d, LL v, sL c, Jj t, Boolean n, Ll B, Boolean b)\\n   at Il.IliFd(ZD d, LL v, sL c, Jj t, Boolean n)\\n   at kl.d(String[] d, Object[] v, XL c, ZD t, LL n, sL B)\\n   at kl.d(String[] d, Object[] v, LL c, sL t)\\n   at Aspose.Words.Reporting.ReportingEngine.BuildReport(Document document, Object[] dataSources, String[] dataSourceNames)\\n   at FormEngineCommon.Aspose.Word.LinqReportBuilder.ProcessLinqTemplate(Document doc, JObject fullPayload.
  1. Why does the engine still evaluate the expression even when the first if condition fails?
  2. Is there a recommended way to safely handle null or empty array conditions in LINQ templates to prevent errors like this from occurring?
  3. Can you suggest any improvements in structuring the conditions to prevent this issue from causing performance hits or runtime errors?
2

@vikas_kaushal

LINQ Reporting Engine never evaluates an expression in a branch of an if statement, for which a condition is not met. The error that you have encountered happens during parsing of a template. The engine parses a template document as a whole before evaluating any expression, which corresponds to compile time in terms of programming. 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.

There is the ReportBuildOptions.AllowMissingMembers option designed for scenarios exactly like yours. You can apply the option as follows:

ReportingEngine engine = new ReportingEngine();
engine.Options |= ReportBuildOptions.AllowMissingMembers;
engine.BuildReport(...);

Please see Accessing Missing Members of Data Objects for more information.

If ReportBuildOptions.AllowMissingMembers is applied, the following template snippet should do the job:

<<if [p.allocationPercentages.Count() > 0]>>
    <<[p.allocationPercentages.ElementAt(0)?.value]:"F2">>
<</if>>