topic Re: Multiple query tasks in ArcGIS JavaScript Maps SDK Questions

Multiple query tasks

OliviaGill1 — Sun, 12 Dec 2021 01:03:10 GMT

Hi, I have carried out a queryTask on a map service that returns a polygon when I input a postcode. Within the same service, there is an additional layer where I want to query a local authority name on. I would like to carry out a querytask on this layer at the same time so that the map returns a polygon relating to the postcode input and also tells me what local authority it is contained within. I will ultimately show the local authority as text in a separate widget. Can anyone help please? Here's my code so far with the second queryTask cancelled out near the middle as I'm not sure where it should go??

var query = new Query();
  query.returnGeometry = true;
  query.outFields = [
  "POSTCODE"
  ];

  on(dom.byId("execute"), "click", execute);

  function execute() {
  query.text = dom.byId("Postcode").value;
  queryTask.execute(query, showResults);
  }
  function showResults(results) {
  var resultItems = [];
  var resultCount = results.features.length;
  for (var i = 0; i < resultCount; i++) {
  var featureAttributes = results.features.attributes;

  var graphic = results.features;
  graphic.setSymbol(symbol);
  map.graphics.add(graphic);

  //var queryTask2 = new QueryTask("http://rest/services/live/SEARCH/MapServer/15");
  //query2 = new.esri.tasks.Query();
  //query2.returnGeometry - false;
  //query2.where = ""
var strNum = 100;
  var newExtent = graphic.geometry.getExtent();
  newExtent.xmin = newExtent.xmin - strNum;
  newExtent.ymin = newExtent.ymin - strNum;
  newExtent.xmax = newExtent.xmax + strNum;
  newExtent.ymax = newExtent.ymax + strNum;
  map.setExtent(newExtent);

  for (var attr in featureAttributes) {
  resultItems.push("<b>" + attr + ":</b> " + featureAttributes[attr] + "<br>");
  }
  resultItems.push("<br>");
  }
  dom.byId("info").innerHTML = resultItems.join("");

  }
  dom.byId("results")

  function addToMap(result) {
  debugger;
  }
 });

Re: Multiple query tasks

RobertScheitlin__GISP — Sun, 12 Dec 2021 01:03:12 GMT

Olivia,

This is a perfect situation to use dojo/promise/all

        var promises = [];
        promises.push(queryTask.execute(query));
        promises.push(queryTask2.execute(query2));
        var allPromises = new all(promises); 
        allPromises.then(function (taskResults) {
            // results will be an Array 
            for (var i=0;i<taskResults.length;i++){
                var taskResult = taskResults;
                showResults(taskResult);
            }
        });

Re: Multiple query tasks

thejuskambi — Mon, 06 Jul 2015 13:59:37 GMT

I dont understand your problem, do you want to use the result of one querytask to make a query on another layer. is that what you are asking for?

Re: Multiple query tasks

thejuskambi — Mon, 06 Jul 2015 14:02:57 GMT

Not necessarily, you could easily build a whereClause within the loop or get a Union of all the geometries and than use it in the query after the looping.

Re: Multiple query tasks

OliviaGill1 — Mon, 06 Jul 2015 14:05:51 GMT

Yes, I have carried out an initial queryTask on the first services layer, here:

var queryTask = new QueryTask("http://rest/services/live/SEARCH/MapServer/2");

This returns a polygon. Within the same service but within another layer I want to use this polygon geometry to carry out another query so that it will return the name of the local authority where that postcode is found..

I hope this make sense??

Re: Multiple query tasks

OliviaGill1 — Mon, 06 Jul 2015 14:07:02 GMT

Thank you - so do I just need to add this to the end of a the 2 consecutive queryTasks that I carry out?? Sorry but I'm stuck!

Re: Multiple query tasks

RobertScheitlin__GISP — Mon, 06 Jul 2015 14:26:02 GMT

Olivia,

Sorry I misunderstood your needs. I thought you needed to execute both queries then work with the results of both, I did not understand that the second query was dependent on the result of the first.

I sounds like you need to take the geometry of the first query result and use that as the Query geometry for the second Query. Is this the use case?

It also sounds like you are wanting to add a single attribute from the second query to the resultItems object that you are creating from the first query Is this correct?

Re: Multiple query tasks

thejuskambi — Sun, 12 Dec 2021 01:03:15 GMT

you code should be something like this. It has not been tested. The example shows using the geometry, you could also build where clause as well

function showResults(results) {
    var resultItems = [];
    var inBuffer= [];
    var resultCount = results.features.length; 
    for (var i = 0; i < resultCount; i++) {
        inBuffer.push(results.features.geometry);

        var featureAttributes = results.features.attributes; 

        var graphic = results.features; 
        graphic.setSymbol(symbol); 
        map.graphics.add(graphic); 
     
        var strNum = 100; 
       
        var newExtent = graphic.geometry.getExtent(); 
        newExtent.xmin = newExtent.xmin - strNum; 
        newExtent.ymin = newExtent.ymin - strNum; 
        newExtent.xmax = newExtent.xmax + strNum; 
        newExtent.ymax = newExtent.ymax + strNum; 
        map.setExtent(newExtent); 
     
        for (var attr in featureAttributes) {
            resultItems.push("<b>" + attr + ":</b> " + featureAttributes[attr] + "<br>"); 
        } 
            resultItems.push("<br>"); 
    }
   
    var query = new Query();         
    query.geometry = geometryEngine.union(inBuffer);     
    //your second query should come here
    //var queryTask2 = new QueryTask("http://rest/services/live/SEARCH/MapServer/15"); 
    //query2 = new.esri.tasks.Query(); 
    //query2.returnGeometry - false; 
    //query2.where = "" 
    dom.byId("info").innerHTML = resultItems.join(""); 
}

Re: Multiple query tasks

OliviaGill1 — Mon, 06 Jul 2015 15:29:39 GMT

It work to an extent although I still don't get the local authority name back?? I've attached my code for info...Perhaps I've been staring at it for too long??

Re: Multiple query tasks

Steveway1 — Mon, 06 Jul 2015 15:30:40 GMT

You can do this in the code, your second query at the end of your first showResults function. But the simpler option is if you have access to the data, then to modify your feature classes to hold that information as an attribute of the polygon, then republish your map service.

That will provide you better performance, and reliability then executing dependant query Tasks.

What ever approach you take, you should ensure that the postcode area (polygon) you are retrieving, is fully contained within the local authority area (polygon) you are querying.

Are you UK based? Just guessing from your terminology this is a possibility - there is a free data product from OS called codepoint that has postcode unit points which could return you a safer results than postcode polygon.

Re: Multiple query tasks

OliviaGill1 — Mon, 06 Jul 2015 15:44:43 GMT

I'm using an OS services layer so there is no opportunity for me to amend the features in the layer unfortunately. I really need a layer that includes the postcode and the local authority but unfortunately they are held separately. I will keep plodding on and also have a look at codepoint as you suggest. Thank you.

Re: Multiple query tasks

RobertScheitlin__GISP — Sun, 12 Dec 2021 01:03:17 GMT

Olivia,

See if this helps:

         function showResults(results) {
            var resultItems = [];
            var inBuffer = [];
            var resultCount = results.features.length;
            for (var i = 0; i < resultCount; i++) {
                inBuffer.push(results.features.geometry);
                var featureAttributes = results.features.attributes;
                var graphic = results.features;
                graphic.setSymbol(symbol);
                map.graphics.add(graphic);
               
                var strNum = 100;
                var newExtent = graphic.geometry.getExtent();
                newExtent.xmin = newExtent.xmin - strNum;
                newExtent.ymin = newExtent.ymin - strNum;
                newExtent.xmax = newExtent.xmax + strNum;
                newExtent.ymax = newExtent.ymax + strNum;
                map.setExtent(newExtent);

                for (var attr in featureAttributes) {
                    resultItems.push("<b>" + attr + ":</b>  " + featureAttributes[attr] + "<br>");
                }
                resultItems.push("<br>");
            }
            var query2 = new Query();
            query2.geometry = geometryEngine.union(inBuffer);
            query2.returnGeometry = false;
            query2.outFields = ["NAME"];
            var queryTask2 = new QueryTask("http://rest/services/live/SEARCH/MapServer/15");
            queryTask2.execute(query2, function(results2){
              for (var j = 0; j < results2.features.length; j++) {
                resultItems.push("<b>Local Authority:</b>  " + results2.features.attributes.NAME + "<br>");
              }
            });
            dom.byId("info").innerHTML = resultItems.join("");
        }

Re: Multiple query tasks

Steveway1 — Mon, 06 Jul 2015 15:50:33 GMT

It doesn't look like you are executing your second query task

Re: Multiple query tasks

thejuskambi — Sun, 12 Dec 2021 01:03:20 GMT

you need the execute the second query task. Please make sure geometryEngine and array are part of the require/define modules.

function showResults(results) {
            var resultItems = [];
            var inBuffer = [];
            var resultCount = results.features.length;
            for (var i = 0; i < resultCount; i++) {
                inBuffer.push(results.features.geometry);

                var featureAttributes = results.features.attributes;

                var graphic = results.features;
                graphic.setSymbol(symbol);
                map.graphics.add(graphic);
               
                var strNum = 100;
                var newExtent = graphic.geometry.getExtent();
                newExtent.xmin = newExtent.xmin - strNum;
                newExtent.ymin = newExtent.ymin - strNum;
                newExtent.xmax = newExtent.xmax + strNum;
                newExtent.ymax = newExtent.ymax + strNum;
                map.setExtent(newExtent);

                for (var attr in featureAttributes) {
                    resultItems.push("<b>" + attr + ":</b>  " + featureAttributes[attr] + "<br>");
                }
                resultItems.push("<br>");
            }
            var query2 = new Query();
            query.geometry = geometryEngine.union(inBuffer);
            query2.returnGeometry = false;
            query2.outFields = [ "NAME" ];

            var resultNames = [];
            var queryTask2 = new QueryTask("http://rest/services/live/SEARCH/MapServer/15");
            queryTask2.execute(query2, function(result){
                if(result && result.features.length > 0){
                    array.forEach(result.features, function(feature){
                        resultNames.push(feature.attributes.NAME);
                    }
                }
            });
           
            dom.byId("info").innerHTML = resultItems.join("") + "<BR>" + resultNames.join(",");
}

Re: Multiple query tasks

OliviaGill1 — Tue, 07 Jul 2015 10:23:10 GMT

Hi Robert

I added the geometryEngine module but I am still not getting back a local authority. I'm wondering if it's something to do with my html now?? The attached code returns the polygon showing the postcode polygon but still no local authority??

Re: Multiple query tasks

Steveway1 — Tue, 07 Jul 2015 10:48:17 GMT

Hi Olivia,

Robert's code should work. Can you try this, on the line directly after

dom.byId("info").innerHTML = resultItems.join("");

Add the following line:

console.log(resultItems);

On the line in your query2 execute callback function,before the FOR loop, add:

console.log(results2);

Then, using chrome or IE, press F12, go to console and look through the Object that has been logged.

Re: Multiple query tasks

OliviaGill1 — Tue, 07 Jul 2015 11:48:38 GMT

Hi Steve

Thank you for the help. I added the console.log as you suggested and I got this:

Hopefully you can make out the attributes: Object

NAME: Glasgow City' so yes it works. Just need to work out how to get that onto the screen as a widget now! Lots to learn...

Olivia

Re: Multiple query tasks

Steveway1 — Tue, 07 Jul 2015 11:59:20 GMT

OK I think what is happening, is that the results are being put into the div before the seconds query has finished executing (JS is asynchronous).

Replace your callback function for the query2 execute with this one:

queryTask2.execute(query2, function (results2) {

for (var j = 0; j < results2.features.length; j++) {

resultItems.push("<b>Local Authority:</b> " + results2.features.attributes.NAME + "<br>");

}

dom.byId("info").innerHTML = resultItems.join("");

});

Also noticed in the console, there is an exception being thrown, but cannot see what line that is happening.

Re: Multiple query tasks

OliviaGill1 — Tue, 07 Jul 2015 12:40:45 GMT

Afraid it doesn't seem to return anything?:

var query2 = new Query();

query2.geometry = geometryEngine.union(inBuffer);

query2.returnGeometry = false;

query2.outFields = ["NAME"];

var queryTask2 = new QueryTask("http://rest/services/live/SEARCH/MapServer/15");

queryTask2.execute(query2, function (results2) {

for (var j = 0; j < results2.features.length; j++) {

resultItems.push("<b>Local Authority:</b> " + results2.features.attributes.NAME + "<br>");

}

dom.byId("info").innerHTML = resultItems.join("");

console.log();

});

dom.byId("results")

function addToMap(result) {

}

my html:

<body>

Postcode :

<br />

</div>

</table>

</div>

</body>

Re: Multiple query tasks

Steveway1 — Tue, 07 Jul 2015 13:42:24 GMT

Hi Olivia,

The code I sent you works for me (I am using County and region polygon data in my case).

However, i see from the code you pasted, you have an erraneous console.log() in your query 2 call back function - just remove this. That should do it.

Also, if you are looking to add the polygon to the map, I recommend adding the graphics to a graphics layer, then adding the graphics layer to the map. Early in your showResults function you are trying to add graphics directly to the map graphics object - this wont work.

Steve