Parsing and evaluating complex objects using JInt

Question

I have a requirement to evaluate certain expressions, and based on the evaluation choose the next steps. I am trying to use JInt javscript interpreter for this.

For basic evaluations from json, it is working fine. But when I am trying to add additional operations on array, that's where the issue is coming.

My approach, set value for base objects => write a function to evaluate expressions => invoke this function and pass the expression to evaluate => function will use eval to evaluate passed string. Initial objects are already set in previous steps.

Something like this,

inputStart.Reference.CompanyCode == \"ABC\"

In this, inputStart is the base object which I have already set using

engine.SetValue("inputStart", JsonConvert.DeserializeObject(inputStart));

inputStart is json text. Fiddle has the string as well for reference. And finally the function,

engine.Execute("function evaluateExpression(expression) { " +
                       "return eval(expression); " +
                       "}")
            .GetValue("evaluateExpression");

var test = engine.Invoke("evaluateExpression", "inputStart.Reference.CompanyCode == \"ABC\"");

This code works correctly. Now the variation is, I have another json text which has array in it. And I am trying to use filter or find to locate specific array item, and then have some operation on it. Something like this,

inputQuestions.Questions.filter((x) => x.Code == \"INIT_IMP\")[0].Answer.Answer.Code

This gives me below error,

Unhandled exception. System.ArgumentException: Accessed JArray values with invalid key value: "filter". Int32 array index expected.

My complete program for reference,

string inputStart = "{\n\t\"PurposeCode\": \"START\",\n\t\"Reference\": {\n\t\t\"CompanyCode\": \"ABC\"\t\t\n\t}\n}";
string inputQuestions = "{\n\t\"QuestionSetCode\": \"QUES_SET_1\",\n\t\"Version\": 1,\n\t\"Questions\": [{\n\t\t\"Code\": \"INIT_IMP\",\n\t\t\"Text\": \"Impact ?\",\n\t\t\"AnswerType\": 3,\n\t\t\"SequenceNumber\": 1,\n\t\t\"Answer\": {\n\t\t\t\"Answers\": [{\n\t\t\t\t\"Code\": \"INIT_IMP_DO\",\n\t\t\t\t\"Text\": \"A\",\n\t\t\t\t\"SequenceNumber\": 1\n\t\t\t}, {\n\t\t\t\t\"Code\": \"INIT_IMP_DA\",\n\t\t\t\t\"Text\": \"B\",\n\t\t\t\t\"SequenceNumber\": 2\n\t\t\t}, {\n\t\t\t\t\"Code\": \"INIT_IMP_AO\",\n\t\t\t\t\"Text\": \"C\",\n\t\t\t\t\"SequenceNumber\": 3\n\t\t\t}],\n\t\t\t\"Answer\": {\n\t\t\t\t\"Code\": \"INIT_IMP_DO\",\n\t\t\t\t\"Text\": \"A\",\n\t\t\t\t\"SequenceNumber\": 1\n\t\t\t},\n\t\t\t\"Type\": \"ListOfValuesAnswer\"\n\t\t},\n\t\t\"Applicable\": true\n\t}, {\n\t\t\"Code\": \"ENT_ACC_LIQ\",\n\t\t\"Text\": \"Exposure ?\",\n\t\t\"AnswerType\": 3,\n\t\t\"SequenceNumber\": 2,\n\t\t\"Answer\": {\n\t\t\t\"Answers\": [{\n\t\t\t\t\"Code\": \"ENT_ACC_LIQ_Y\",\n\t\t\t\t\"Text\": \"Yes\",\n\t\t\t\t\"SequenceNumber\": 1\n\t\t\t}, {\n\t\t\t\t\"Code\": \"ENT_ACC_LIQ_N\",\n\t\t\t\t\"Text\": \"No\",\n\t\t\t\t\"SequenceNumber\": 2\n\t\t\t}],\n\t\t\t\"Answer\": {\n\t\t\t\t\"Code\": \"ENT_ACC_LIQ_N\",\n\t\t\t\t\"Text\": \"No\",\n\t\t\t\t\"SequenceNumber\": 2\n\t\t\t},\n\t\t\t\"Type\": \"ListOfValuesAnswer\"\n\t\t},\n\t\t\"Applicable\": true\n\t}],\n\t\"ClientId\": null\n}";
        
Engine engine = new Engine();
        
engine.SetValue("inputStart", JsonConvert.DeserializeObject(inputStart));
engine.SetValue("inputQuestions", JsonConvert.DeserializeObject(inputQuestions));
        
engine.Execute("function evaluateExpression(expression) { " +
                       "return eval(expression); " +
                       "}")
            .GetValue("evaluateExpression");

var test = engine.Invoke("evaluateExpression", "inputQuestions.Questions.filter((x) => x.Code == \"INIT_IMP\")[0].Answer.Answer.Code == \"INIT_IMP_DO\" && inputStart.Reference.CompanyCode == \"ABC\"");
        
Console.WriteLine(test);

Here is the complete fiddle for what I am trying to do, https://dotnetfiddle.net/GtamM8

If anyone has come across such issue, or can suggest a solution to this, it will be very helpful.

Answer 1

Because you are using the new language constructs, you should be using 3.x preview release from NuGet. 3.x series contains support for lambda expressions and array filtering against them.