topic Extract field of featurelayer as object in ArcGIS JavaScript Maps SDK Questions

Extract field of featurelayer as object

RabinSubedi — Fri, 08 Jan 2021 18:56:51 GMT

Hello Everyone,

How do we extract all fields of featurelayer as an object? I tried this but didn't worked:

var fieldslist = featureLayer.fields;

document.getElementById("List").innerHTML = fieldslist[0].NLFID;

I require this to perform computations only using some of the fields.

Thank you in advance!

Re: Extract field of featurelayer as object

BlakeTerhune — Fri, 08 Jan 2021 19:48:06 GMT

The fields property of FeatureLayer will return an array of field objects, each having a field's properties. I found this only to be available once the FeatureLayer's layerview-create event has fired.

featureLayer.on("layerview-create", function(event){ console.log(featureLayer.fields); console.log(featureLayer.getField("NLFID")); });

Re: Extract field of featurelayer as object

RabinSubedi — Fri, 08 Jan 2021 22:57:47 GMT

Thanks @BlakeTerhune for your reply. I used layerview-create event and tried to test the result by printing NLFID value of the first feature, but it didn't work. Can you please take a look at it? Does the 'fieldsList' variable contain all the fields (let's say the whole attribute table)?

Thanks much!

<html> <head> <meta charset="utf-8"> <meta name="viewport" content="initial-scale=1, maximum-scale=1, user-scalable=no"> <title>High Injury Network</title> <style> html, body, #viewDiv { padding: 0; margin: 0; height: 50%; width: 100%; } </style> <link rel="stylesheet" href="https://js.arcgis.com/4.18/esri/themes/light/main.css"> <script src="https://js.arcgis.com/4.18/"></script> <script> require([ "esri/Map", "esri/views/MapView", "esri/layers/FeatureLayer", "esri/layers/GraphicsLayer", "esri/geometry/geometryEngine", "esri/Graphic" ], function ( Map, MapView, FeatureLayer, GraphicsLayer, geometryEngine, Graphic ) { var Crashes = [1,2]; var HINLayer = new FeatureLayer({ url: "https://services1.arcgis.com/wb4Og4gH5mvzQAIV/arcgis/rest/services/HIN_Columbus/FeatureServer", outFields: ["*"], visible: true }); var resultsLayer = new GraphicsLayer(); var map = new Map({ basemap: "topo-vector", layers: [HINLayer, resultsLayer] }); var view = new MapView({ container: "viewDiv", map: map, center: [-82.9, 39.99], // longitude, latitude zoom: 10 }); HINLayer.on("layerview-create", function(event){ var fieldsList= HINLayer.fields; document.getElementById("List").innerHTML = fieldsList[0].NLFID; }); var sortedList = Crashes.sort(); var sortedString = sortedList.join("','"); var whereClause = "VehCrashCo IN ('" + sortedString + "')"; var query = HINLayer.createQuery(); query.where = whereClause ; // query.outStatistics = [ sumCost]; query.returnGeometry= true; return HINLayer.queryFeatures(query).then(function(results){ resultsLayer.removeAll(); var features = results.features.map(function (graphic) { graphic.symbol = { color: "darkorange" }; return graphic; }); resultsLayer.addMany(features); }); }); </script> </head> <body> <div id="viewDiv"></div> <div id="List"></div> </body> </html>

Re: Extract field of featurelayer as object

BlakeTerhune — Fri, 08 Jan 2021 23:29:25 GMT

Oh, you want field values, not field names? You'll have to query the FeatureLayer and then do something with the result. In your case, if you only want to display a single value from the first feature returned. Something like this maybe? And you don't need the layerview-create event listener for query.

HINLayer.queryFeatures({ start: 0, num: 1, returnGeometry: false, outFields: ["NLFID"], }) .then(function(featureSet) { let listContent; if(featureSet.features.length > 0) { listContent = featureSet.features[0].attributes.NLFID; } else { listContent = "There are no records in HINLayer"; } document.getElementById("List").textContent = listContent; });

Re: Extract field of featurelayer as object

RabinSubedi — Sat, 09 Jan 2021 00:45:21 GMT

Actually, I need to do a tradeoff analysis with the data of this layer and present the resulting features in map and charts. I need to perform multiple queries and filtering according to my task requirement, which might be possible with ArcGIS JS API but I am not familiar with it, so it will take me a lot of time. I was hoping to extract the whole attribute table in the form of an object like this:

attributeData = [ { "OBJECTID": 1, "NLFID": "CFRACR00125**C", "SUM_c_segm": 6.0, "SUM_w_segm": 11.0, "STREET_NAM": "FRANK RD"},
{ "OBJECTID": 2, "NLFID": "CFRACR00114**C", "SUM_c_segm": 5.0, "SUM_w_segm": 6.0, "STREET_NAM": "COURTRIGHT RD"},
{ "OBJECTID": 3, "NLFID": "CFRACR00602**C", "SUM_c_segm": 5.0, "SUM_w_segm": 7.0, "STREET_NAM": "TOWN ST"}
...
...
...

}]

After the analysis, I plan to pass the array of OBJECTID of resulting features to the query to display them in the map. Is it possible to extract all data in this way?

I am sorry I couldn't make it clear earlier and I apologize for your trouble.

Thank You!

Re: Extract field of featurelayer as object

JohnGrayson — Sat, 09 Jan 2021 00:58:10 GMT

Blake's response gets you almost there:

// LAYER QUERY // const query = HIMLayer.createQuery(); query.set({ where: "1=1", returnGeometry: false }); // RETRIEVE ALL FEATURES FROM LAYER // HINLayer.queryFeatures(query).then((featureSet) => { // FEATURES THAT SATISFY THE ABOVE QUERY // const features = featureSet.features; // CREATE LIST OF ATTRIBUTES FROM THE FEATURES // const attributeData = features.map(feature => { return feature.attributes; }); // DO SOMETHING WITH LIST OF ATTRIBUTES // document.getElementById("List").textContent = attributeData; });

If you're only interested in the OBJECTIDS, then check out the queryObjectIds() method.

Re: Extract field of featurelayer as object

RabinSubedi — Sat, 09 Jan 2021 01:04:18 GMT

It works, Thank you very Much @BlakeTerhune @JohnGrayson