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Get Fields ?

Drew

Hello,
I am doing a small ESRI JS API project and don't use it too often so the library is new to me..
Anyways.. I cant find anyway to get field information.

I am trying to write a function that will determine what the the OBJECTID field name is based on its data type (esriFieldTypeOID)

The object is in the documentation (Field) but I can't find a way to get a field?

In the Flex API you can call a a function like so...


mapServiceLayer.getLayerDetails(...)

Please help me get a fields array.

Drew

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derekswingley1

Right, properties are available when the layer is loaded. They're not necessarily available immediately after calling calling a layer constructor hence the reason you need to listen to the layer's onLoad event if you want to access layer properties as soon as the layer loads.

This isn't explicitly spelled out in the feature layer documentation you linked to but it is documented for all layers in the Layer class documentation: http://help.arcgis.com/EN/webapi/javascript/arcgis/help/jsapi/layer.htm

When the layer is loaded, the value becomes "true", and layer properties can be accessed. The onLoad event is also fired.

JeffPace1

I get the asynchronous nature of Javascript.

What i do not understand is where in the API

http://help.arcgis.com/EN/webapi/javascript/arcgis/help/jsapi/featurelayer.htm

They say the the Properties of a Feature Layer are not available until it is loaded.

derekswingley1

Glad to help.

I wouldn't say this is a feature or a bug...it's just the asynchronous nature of JavaScript. You can't always assume that because a line of code comes after a variable definition that all properties of that variable are populated and accessible. Reading up on callbacks and how they're used in JavaScript would be a good idea. Here's a good start: Getting comfortable with Javascript callbacks

Money quote:

when you call a method, you know that it has done all of its work and returned something useful. Right? Well�?� not always. Sometimes that method will invoke web requests that need some time to process, or it may call another method that has to do some processing or is waiting for user input�?� These kinds of operations can be implemented asynchronously, and the only way to manage that logic programmatically is with a callback parameter.

I agree on the point about using fields that use domains...there's room for improvement there.

JeffPace1

Wow that works, an undocumented "feature" eh?

The whole reason I am doing this is because queries return coded values and not the "name" value of a domain. Very frustrating.

Thank you for the advise.

derekswingley1

Those properties aren't defined until your feature layer loads...try:

var mapLayer= new esri.layers.FeatureLayer(layer.url,{
  mode: esri.layers.FeatureLayer.MODE_SNAPSHOT,
  outFields: ["*"] 
});
dojo.connect(mapLayer, 'onLoad', function() {
  alert(mapLayer.fields); (undefined)
  alert(mapLayer.version); (undefined)
});

JeffPace1

var mapLayer= new esri.layers.FeatureLayer(layer.url,{
                                   mode: esri.layers.FeatureLayer.MODE_SNAPSHOT,
                                    outFields: ["*"]
                                });
alert(mapLayer.fields); (undefined)
alert(mapLayer.version);   (undefined)

etc...

derekswingley1

@jeff can you post some code that's not working for you?

JeffPace1

I am having a heck of a time with this. I am using javascript api2.2, server 10sp1 for java

have a featureLayer

all the properties return undefined. Cant get fields, version, anything.. very frustrating.

Drew

Thanks for the assistance everyone.
I ended up going with the FeatureLayer to get the information i needed.
I don't think it's the easiest way, but it works....
I would like to see the info come in when the AGSDynamicLayer gets loaded, ArcIMS did that.

I am still looking for better ways if someone else can point me in the right direction.
I feel that I am missing something obvious.....

Anyways.. here is my javascript code to get feature layer information (i.e field names and types)
The GetFeatureLayerInfo function does the work, the other is just sample code to test.

[php]
function TestFeatureLayerInfo(map, serviceURL, layerID)
{

    GetFeatureLayerInfo(map, serviceURL, layerID,
    function (featureLayerInfo)
    {
        alert("ObjectID Field: " + featureLayerInfo.objectIdField);

        var fieldInfos = "";
        for (var i = 0; i < featureLayerInfo.fields.length; i++)
        {
            var field = featureLayerInfo.fields;
            fieldInfos += field.name + "\t=\t" + field.type + "\n";
        }

        alert("Fields: " + fieldInfos);
    });
}

function GetFeatureLayerInfo(map, serviceURL, layerID, callbackFunction)
{

    var featureLayerURL = serviceURL + "/" + layerID;
    var featureLayer = new esri.layers.FeatureLayer(featureLayerURL, { mode: esri.layers.FeatureLayer.MODE_SELECTION });

    var layerAddResult_connect = dojo.connect(map, "onLayerAddResult", function (featureLayerInfo)
    {
        map.removeLayer(featureLayer);
        dojo.disconnect(layerAddResult_connect);

        if (callbackFunction != null)
        {
            callbackFunction(featureLayerInfo);
        }
    });
    map.addLayer(featureLayer);
}
[/php]

Drew

AlexGray

Looks like you can get field dataypes from 'esri.layers.field.type'

type String The data type of the field.

http://help.arcgis.com/en/webapi/javascript/arcgis/help/jsapi_start.htm#jsapi/field.htm#type

timgogl

im new to the esri stuff myself, so this may or may not be of any use to you. have you looked at the task object? inside task is featureset which has the property fieldaliases :

fieldAliases Object Set of name-value pairs for the attribute's field and alias names.

dont know if that is exactly what you are looking for, but maybe it will move you along some more.

Drew

After testing the "FeatureLayer" functionality this morning i realized that its not what i need.
Its more for overlaying the data.

Isn't there a way I can get the Fields and their data types from a specific feature class using the JS API?

Drew

AlexGray

Thanks Alex. I think I can work with this!

Drew

Drew,

Great.. Not a problem..

Alex

Drew

Thanks Alex. I think I can work with this!

Drew

RRubalcava

I'm not too familiar with the Javascript API, so there may be a function for this built in, but you could pull the REST in JSON for any layer in a service like this
http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Petroleum/KGS_OilGasFields_Kansas/MapServer/0?f=json&pretty=true

Than you can iterate through the "fields" element which is an array of objects that has a "type" element that will tell you what type the field is. I find that for some needs, it's just easier for me to make REST requests to get that kind of detailed information.

AlexGray

Drew,

Sorry about that.. I miss read your question..

I did a little research and found a few things.. Although you might have already seen them..

In the JS api there is a property for esri.layers.featurelayer(objectIdField)

There is also a 'fields' property for featurelayer 'Field[]'.. the description for it states "The array of fields in the layer."

http://help.arcgis.com/en/webapi/javascript/arcgis/help/jsapi_start.htm#jsapi/featurelayer.htm

Sorry, I couldn't provide you with any code samples.. as I am just learning programming/javascript now in order to make myself more marketable.. Hope what I provided was of some help..

Alex

Drew

Alex,

I don't quite see any code that is pulling field information from a layer.
Maybe I am missing it just like how I can't find it in the ESRI doc's either..
Can you point me to a line number in your source?

Basically I want to get an array of Fields from a given layer (i.e. Parcels)

Drew

AlexGray

Hello,
I am doing a small ESRI JS API project and don't use it too often so the library is new to me..
Anyways.. I cant find anyway to get field information.

I am trying to write a function that will determine what the the OBJECTID field name is based on its data type (esriFieldTypeOID)

The object is in the documentation (Field) but I can't find a way to get a field?

In the Flex API you can call a a function like so...
mapServiceLayer.getLayerDetails(...)
Please help me get a fields array.

Drew

Drew,

I just learned about that myself not too long ago.. you can try taking a look at my work in progress.. http://www.co.frederick.va.us/planning/newmap1copy2.html

the layer referencing works.. I am a bit stuck on how to get the checkboxes to work properly though.. decided to go with checkboxes instead of link I had before..

Hope that helps..
Alex

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