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Anomalous (? to me...) behavior using getJSON to make async REST calls in SharePoint 2013

in Using jQuery • 5 years ago

Still accessing SharePoint 2013 lists using REST (_vti_bin/ListData.svc), and $.getJSON. I am seeing a behavior that I cannot explain, and was hoping someone here might have some ideas about what the issue is, or how I can (in the code) gather more information about what the issue is.

What is happening, is that I am able to retrieve the entire list, but I cannot retrieve just a single list item (which would seem much more efficient, once I know which list item I want...). To give a little more information, while respecting the NDA I signed:
this works --
step1 = $.getJSON("https://thesite/this/that/_vti_bin/ListData.svc/TheList", function(data) {...
but not this --
step1 = $.getJSON(""https://thesite/this/that/_vti_bin/ListData.svc/TheList(15)", function(data) {...

The second version, that specifies one particular list item to return, simply returns nothing.

Both of these URLs work as expected when entered in the address bar of IE, so it would not seem to be an issue with the REST service. I have tried stepping through the code in Firebug, but the jQuery code is way too deep for me, especially given the time I have to complete my task... I can see where a variable is getting set to 'cancelled' and 'abort' in the ajax fcn, but I can't say why.

If anyone has ideas they would care to share about what the problem might be, or what I need to include in my .fail function to get useful information about what the problem is, I would be very grateful for any information that might help.

Thank you.

Replies(9)

watusiware

Re: Anomalous (? to me...) behavior using getJSON to make async REST calls in SharePoint 2013

5 years ago

- Learn to use your browser's inspection tools. You can view the exact content sent and received, error codes, timing, etc. etc. etc. It is all there for you to view if you will learn to use the tools. It is essential for debugging REST.

- When you tested from the address bar, did you check the returned JSON to make sure it is valid? JSON is simple, but use a validator anyway. It often trips up developers who make assumptions instead of reading specifications. For example, both keywords and data values need to be enclosed in quotes, and only double-quotes, not single-quotes.

I would guess you have a misunderstanding about JSON and the data returned from the second request is not valid.

what I need to include in my .fail function to get useful information about what the problem is,

See the last example to get the error code programatically. Then Google it. Or, learn to use your browser's inspection tools...

http://api.jquery.com/jquery.getjson/

jakecigar

Re: Anomalous (? to me...) behavior using getJSON to make async REST calls in SharePoint 2013

5 years ago

The second version, that specifies one particular list item to return, simply returns nothing.

Returning nothing (just white space) is not valid JSON. It used to be, but the JSON standards people say it isn’t. So, now, it triggers a fail.

$.getJSON("https://thesite/this/that/_vti_bin/ListData.svc/TheList(15)", function(data) {..})
.fail(function(){ alert('error') })

JΛ̊KE

watusiware

Re: Anomalous (? to me...) behavior using getJSON to make async REST calls in SharePoint 2013

5 years ago

The second version, that specifies one particular list item to return, simply returns nothing.

Obviously, Jake and I interpreted this differently.

My understanding is that the second one "works" (or, at least returns what you expect) if you use it from the browser address bar, but not if you use $.getJSON() . Then you get "nothing" (whatever you mean by that).

Inspect with your browser tools. See what you got.

jakecigar

Re: Anomalous (? to me...) behavior using getJSON to make async REST calls in SharePoint 2013

5 years ago

We’ll never know what nothing is. Unless Michael R.. responds.

JΛ̊KE

Michael R..

Re: Anomalous (? to me...) behavior using getJSON to make async REST calls in SharePoint 2013

5 years ago

You were right; it's not returning nothing (that is to say, it is returning something). And, as a matter of fact, now that I have taken the time to look at the contents of the 'step1' variable after the line shown is executed, it apparently succeeded. Firebug shows these properties:
step1.readyState is 4;
step1.responseText contains all the data from the specified list item (plus a bunch of stuff);
step1.status is 200; and
step1.statusText is "OK".

BUT, the inline call back function is not getting executed, so nothing is getting written to my SharePoint form page -- that is why I thought nothing was being returned. My mistake.

Soooo, the correct question is why is the callback function not being executed? Stepping through the code, if I step over the $.getJSON call, the next line executed is the last line of the inline callback function. It doesn't go into the callback at all.

That is not the behavior I see, when I request the entire list, rather than a single list item. Execution happily goes into the callback, when the entire list is returned.

IE says that there is an error executing Line 3 Char: 5099 of jquery-1.9.1.min.js -- 'length' is null or not an object. Using Firebug to look at the code, it appears that the line is in this code:

        each: function (e, t, n) {
            var r,
            i = 0,
            o = e.length,
            a = M(e);
            if (n) {
                if (a) {
                    for (; o > i; i++) if (r = t.apply(e[i], n), r === !1) break
                } else for (i in e) if (r = t.apply(e[i], n), r === !1) break
            } else if (a) {
                for (; o > i; i++) if (r = t.call(e[i], i, e[i]), r === !1) break
            } else for (i in e) if (r = t.call(e[i], i, e[i]), r === !1) break;
            return e
        },

And it's the o = e.length line that IE complains about.

My code there is:

/* Function to display the fields for the selected product */
function WriteProductFields()
{
    var myURL = "https://thesite/this/that/_vti_bin/ListData.svc/TheList(" + productId + ")";

    step1 = $.getJSON(myURL,function(data) {

        $.each(data.d.results, function(i,result) {
            var src = result.__metadata.media_src;
            /* First, grab values to be stored for later use */
            productLine = result.PL;
            data1       = result.DATA1;
            data2       = result.DATA2; ...

Again, virtually identical code WORKS, if I simply omit the (productId) from the URL. There is an extra 'if' statement, to filter out all list items but the one with the selected productId.

Is this enough information to identify what I am doing wrong?

All assistance is still very welcome... especially since there are such glaring gaps in my understanding (obviously).

Thank you!

Michael R..

Re: Anomalous (? to me...) behavior using getJSON to make async REST calls in SharePoint 2013

5 years ago

BTW, entering those URLs on the address bar of IE returns XML, not JSON. Can a parameter be added to the URL to make it display JSON?

jakecigar

Re: Re: Anomalous (? to me...) behavior using getJSON to make async REST calls in SharePoint 2013

5 years ago

Some programs go both ways. XML when asked for XML and JSON when asked for JSON. It only counts in what you see with the developer tools.

JΛ̊KE

jakecigar

Re: Anomalous (? to me...) behavior using getJSON to make async REST calls in SharePoint 2013

5 years ago

var myURL = " https://thesite/this/that/_vti_bin/ListData.svc/TheList(" + productId + ")";

doesn’t work, it’s your server program that is failing. Your jQuery is probably just fine.

JΛ̊KE

watusiware

Re: Anomalous (? to me...) behavior using getJSON to make async REST calls in SharePoint 2013

5 years ago

Can a parameter be added to the URL to make it display JSON?

You will have to check the Sharepoint REST documentation. It's common to do this, and different APIs have different ways of doing it. You might have to set an HTTP Accept: header, or you might have to add a parameter to the request. Or you might have to use a different endpoint.

In any case, it is up to the API. Check Sharepoint REST documentation.

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