return value from Ajax callback

[eribla]

Hi

I watched all the nice movies (66) about Ajax callbacks but all these steps show how to get data TO the server.


I want to do an SQL query from the page. I don't know if an SQL query is possible at all directly through Java script, so I try to do it with
an Ajax callback. (similar to Video 91).

But how do I get any results from the query back into a grid. I am not even talking about many data sets in an array, but only a True/False that
shows me if a Phone number already exists. (I don't want to do this with the field validation, because I want a real time validation and not onSubmit).

So the function declaration is:

function Does_Phone_Nbr_Exist as c (e as p)

...Do the query...

Does_Phone_Nbr_Exist = "Y"
end function


It is defined to return a character, but where can I get the return value from?

Thanks a lot!

[Steve Wood]

Re: return value from Ajax callback

You have to return javascript to the browser, not just a value. This had me stumped for a long time as well. Say you did return a value of "Y" to the browser, the browser would not know what to do that that value -- the browser is just sitting there, idle really. So you cause your callback to return javascript and it can update your screen, insert values in any field, popup an alert, etc.

So in your example:

Does_Phone_Nbr_Exist = "alert('Y');" - this would popup an alert with the letter "Y"
Does_Phone_Nbr_Exist = "alert('Yes the number exists');" - this would popup an alert with that message
Does_Phone_Nbr_Exist = "{grid.object}.setValue('D','HASNUMBER','Y');" - would put "Y" in the field named hasNumber, assuming the request came from a Detail View.

You can get the exact syntax for js like the last one by going to any onClick event, add a New Action, pick in-line Javascript, pick Insert method...

If you are new to this, you will need to expirement or ask more questions after you get a start.

[iRadiate]

Re: return value from Ajax callback

Hi Eriks,

Have you seen Bob Moore's videos on calling stored procedures? http://www.screencast.com/users/remo...re%20Tutorials
Not sure if it's exactly what you're trying to do but it may also be helpful.

Stephen

[eribla]

Re: return value from Ajax callback

Thanks Steve, that did help, and I also looked at the movie Stephen!

One more thing though to this issue:

My call to the Ajax callback looks like:

var Phone_Exists='N';
alert(Phone_Exists);

{grid.Object}.ajaxCallback('G','{Grid.RowNumber}:all','Does_Phone_Nbr_Exist','','_getData=true');

alert(Phone_Exists);

My Server side XBasic function is:

function Does_Phone_Nbr_Exist as c (e as p)

// figure out if phone number exists code ( SQL query)

// If Yes, return:
Does_Phone_Nbr_Exist = "Phone_Exists='Y'"
end function

it runs without errors, but I get the alert "N" twice.

Why is Phone_Exists='Y' not executed?

Thanks

Eriks

[kingcarol]

Re: return value from Ajax callback

I'm no expert, but don't you need an if statement in your javascript?

[Clipper87]

Re: return value from Ajax callback

You need to add a semicolon e.g. "Phone_Exists='Y';" to make it a valid javascript expression

[Steve Wood]

Re: return value from Ajax callback

Why is Phone_Exists='Y' not executed?

It won't do anything, but what do you expect it to do? What do you mean by not executed?

[Clipper87]

Re: return value from Ajax callback

I think he means the value 'Y' is not being assigned to the variable 'Phone_exists' but I wonder if that is possible because of the variable scope ? 'Phone_exists' is declared in the function thus it is local. I need to test this.

[Steve Wood]

Re: return value from Ajax callback

What you want is this (this is not exactly how I would write the callback but it illustrates a point):

onClick event: {grid.Object}.ajaxCallback('G','{Grid.RowNumber}','Does_Phone_Nbr_Exist','','_getData=true');

Callback:
function Does_Phone_Nbr_Exist as c (e as p)

dim Phone_Exists as L = .f. ' default to No

// figure out if phone number exists code ( SQL query)
//set Phone_Exists to true or false

If Phone_Exists = .t.
Does_Phone_Nbr_Exist = "alert('Yes Phone Exists');"
else
Does_Phone_Nbr_Exist = "alert('No Phone does not exists');"
end if
end function

You DO NOT return a value for Phone_Exists to browser. The javascript alert is handled as part of the callback function.

I don't know why you had ":all" following the the Grid.Rownumber, I assume this is on a button on a grid row and you want to inquire about a number on THAT row.

[eribla]

Re: return value from Ajax callback

Hi Steve,

Clipper is correct.

the alert is clear to me but I not just want to alert the user but also do something if duplicates exist. (Opening another window to show him the duplicate customer entries in another grid).
So I need to get a variable or something back that will allow me to take action beyond an alert.

(The same would be true for another problem I am having:

If you do a callback to do a server side XB SQL query, how do you get the result(s) back into the local Java program)

Thanks

Eriks

[Steve Wood]

Re: return value from Ajax callback

I've never been successful taking the results of a callback and using them in a subsequent task in the Action Javascript window, I don't know if you can. Everyone I work with does all of that in the return from the callback, just like the Alert example. There is an inherent problem in making a callback and then trying to run some additional task. The problem is the callback will finish and return control to the browser BEFORE the xbasic or sql script in the callback is complete. This has been proven over and over.

Using your example, if you tried to send back the results of the callback and then fire the alert as a subsequent task, it will never work because the alert will fire before the xbasic script determined the value for your variable.

[Clipper87]

Re: return value from Ajax callback

Steve is right, that's why they call it ajax; asynchronous. I keep forgetting that all the time.

[eribla]

Re: return value from Ajax callback

Great.

Now that this is clear:

How can I find out if a certain Phone number is already in the database and base some actions onto the result?

[kingcarol]

Re: return value from Ajax callback

I think the videos in section 85 here (http://news.alphasoftware.com/V10Preview/videos.htm) will help you, Eriks. These were some videos made after Selwyn helped me quite a bit with doing a lookup to my database to see if a record existed in a table before I deleted something in a parent table.

[eribla]

Re: return value from Ajax callback

Thanks Carol,

that helped a lot!