jquery - How can I determine the cause of the Internal Server Error resulting from my Ajax call? -

in asp.net mvc app, ajax call:

$.ajax({     type: 'get',     url: '@url.action("getunitreportpairvals", "home")',     data: { unit: unitval, report: rptval }, // data: model,     contenttype: 'application/json',     cache: false,     success: function (result) {         alert(result);     },     error: function (result) {         alert('failed');         alert(result);     } }); 

...calling controller method:

public jsonresult getunitreportpairvals(string unit, string report) {     int rptid = getreportidforname(report);      datatable unitreportpairemailvalsdt = new datatable();     string qry = string.format(sql.unitreportpairemailquery, unit, rptid);     unitreportpairemailvalsdt = sql.executesqlreturndatatable(         qry,          commandtype.text,         null         );      var model = unitreportpairemailvalsdt;     return json(model); } 

i see "failed" alert, , "result" object has no end of data; here's tip of iceberg:

it seems key thing status of 500, , status text of "internal server error"

so commented out 2 lines , added in "debugger" in stead (as sugged nurdyguy here [why ajaxoned action's return not being seen successful caller?:

$.ajax({     . . .     error: function (result) {         debugger;         //alert('failed');         //alert(result);     } }); 

...yet don't see gets me. putting ajax call through paces shows nothing in browser; using chrome devtools, can step it, once "debugger" line, doesn't me favors. f11 line nothing.

so how can bottom of what's causing 500/internal server error?

update

since have commented out "json" lines jquery ajax call ("var model = json.stringify({})" , "contenttype: 'application/json'"), should change controller return type jsonresult actionresult , "return view(model)"?

update 2

i getting "success" ajax method this, incorporating several suggestions y'all , changing model datatable member generic list of string:

// model (c#) public class unitreportpairmodel {     public list<string> unitreportpairemailvals { get; set; }     . . . }     // controller (c#) public jsonresult getunitreportpairemailaddresses(string unit, string report) {     unitreportpairmodel model = new unitreportpairmodel();     try     {         int rptid = getreportidforname(report);          datatable unitreportpairemailvalsdt = new datatable();         string qry = string.format(sql.unitreportpairemailquery, unit, rptid);         unitreportpairemailvalsdt = sql.executesqlreturndatatable(             qry,             commandtype.text,             null             );          list<string> emailaddresses = unitreportpairemailvalsdt                      .asenumerable()                      .select(row => row.field<string>("emailaddr"))                      .tolist();          model.unitreportpairemailvals = emailaddresses;     }     catch (exception ex)     {         console.writeline(ex.message);     }     return json(model, jsonrequestbehavior.allowget); }  // view (jquery) var model = json.stringify({ unit: unitval, report: rptval });     $.ajax({         type: 'get',             url: '@url.action("getunitreportpairemailaddresses",      "unitreportpair")',             data: { unit: unitval, report: rptval }, // data: model,             contenttype: 'application/json',             cache: false,             success: function (result) {                 alert('success');                 alert(result.data);             },             error: function () {                 alert('failure');             }         }); 

update 2

once pieced several different answers , related questions, wrote tip on how here.

since action method, if returning json data, should explicitly specify jsonrequestbehaviour.allowget.

this should fix it.

return json(model,jsonrequestbehavior.allowget); 

if action method decorated [httppost] , making post call, not need explicitly specify it, return json(model) work fine.

here more detailed explanation same.