Develop Reference

how to pass complicated data between mvc and javascript

I'm trying to build a UI with two dropdowns. The first one is "category", the second one is "sub-category". I can build a static list of "category" in my razor view. I want the "sub-category" item list to be dynamically updated when "category" is changed. I'm trying to pass all category information from server side to client side since the list is not big and there is no security issue. But I cannot find a good way to format my data and transfer it to client side. I can generate a json object with all of my category trees using the following code:
ExpandoObject catToSubcatMap = new ExpandoObject();
foreach (var cat in repository.Categories)
{
var subcats = repository.SubCategories.Where(s => s.ParentID == cat.CategoryID);
List<Object> subcatNameList = new List<object>();
foreach(var subcat in subcats)
{
subcatNameList.Add(new { Name = subcat.Name });
}
AddProperty(catToSubcatMap, cat.Name, subcatNameList);
}
Session["CatToSubcatMap"] = JsonConvert.SerializeObject(catToSubcatMap, Newtonsoft.Json.Formatting.Indented, new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore });
The json itself looks perfect. But when I tried to read the value from my jQuery function, it failed:
var sss = '#Session["CatToSubcatMap"]';
It seems like there are too many special characters in the json string. My generic question is: how should I format and pass complicated data between server and client. Using Viewbag or Session, which one is preferred?
Thanks
Chris

You can do what you are trying to do; what you have should be formatted correctly, but you just have to include Html.Raw.
var sss = #(
Html.Raw(Session["CatToSubcatMap"].ToString())
);
Raw will essentially write out directly to the response without encoding the contents, which is what likely was happening.

object has no method push in node js

I am trying to append the user details from the registration form to the json file so that the user-details can be used for authentication. the problem is i am not able append to the json file in correct format.The code i have tried so far is,
var filename= "./user_login.json";
var contents = fs.readFileSync(filename);
var jsonContent = JSON.parse(contents);
//sample data
var data =[
{
"try" : "till success"
}
];
jsonContent.push(data);
fs.writeFileSync(filename,jsonContent);
I have tried different methods that i found by googling and nothing worked so far. I want the data to be stored in correct format. Most of the times i got this error like object has no push function. So what is the alternative to that?
The correct format i am looking for is ,
[
user1-details : {
//user1 details
},
user2-deatils : {
}//So on
]

Object has no push function, arrays do. Your json is invalid too, it should be an array:
[ // here
{
//user1 details
},
{
//So on
}
] // and here
Now, you can use push(). However, data is an array, if you want an array of objects in your json file, it should be a simple object:
var data = {
"try" : "till success"
};
You also have to stringify the object before writing it back to the file:
fs.writeFileSync(filename, JSON.stringify(jsonContent));
You should consider using something like node-json-db, it will take care of reading/writing the file(s) and it gives you helper functions (save(), push()...).

Is it possible to retrieve a record from parse.com without knowing the objectId

See the sample code below - in this case, the objectId for the record I am trying to retrieve is known.
My question is, if I don't know the Parse.com objectId, how would I implement the code below?
var Artwork = Parse.Object.extend("Artwork");
var query = new Parse.Query(Artwork);
query.get(objectId, {
success: function(artwork) {
// The object was retrieved successfully.
// do something with it
},
error: function(object, error) {
// The object was not retrieved successfully.
// warn the user
}
});

Query.get() is used when you already know the Parse object id.
Otherwise, one can use query.find() to get objects based on the query parameters.

Sure, you can use Parse Query to search for objects based on their properties.

The thing that wasn't clear to me in the documentation is that once you get the object in the query, you would need to do:
With Query (can return multiple objects):
artwork[0].get('someField');
With 'first' or 'get':
artwork.get('someField');
You cannot do something like artwork.someField like I assumed you would

How to insert data, in key value pairs, into HTML

I have returned a form with some key value pairs populated. Depending on user interaction I want to insert some of them into my HTML. I have found some answers using AJAX but could not workout how to access the key value pairs via javascript. I do not want to use jquery yet as I want understand how javascript and the DOM works first. Below is an idea of what I want to do
<script>
function changeanchor(urlitem) {
document.getElementById("urlanchor").innerHTML = "";
while ($urls as $url) {
if (urlitem == $url->item) {
document.getElementById("urlanchor").innerHTML .= $url->urlanchor;
}
}
</script>
I know "$urls as $url" etc is PHP but I thought it was the easiest way to explain what I need to do.
I use PHP to generate the function call but I am unable to get it to display here it (pieces of code do not display)

Like so?
<script>
function changeanchor(urlitem) {
document.getElementById("urlanchor").innerHTML = "";
for (i in urls) {
var url = urls[i];
if (urlitem == url.item) {
document.getElementById("urlanchor").innerHTML += url.urlanchor;
}
}
</script>
urls was never defined so this code won't execute unless urls stores a bunch of url objects with those properties.
In order to create a url object that acts like the one you try to use, either use JSON to pipe it to the JavaScript or make an object:
var urls = [
{
'item': 100,
'urlanchor': 'foo'
}, {
'item': 200,
'urlanchor': 'bar'
}
];

are you asking about the setting key value pair data in a dome object then,
$('body').data('foo', 52);
link for help:-
http://api.jquery.com/data/

SQLike - understanding the basics

I'm trying to use the query engine
SQLike and am struggling with the basic concept.
The JSON I'm using as my data source comes from my PHP code, like so:
var placesJSON=<? echo json_encode($arrPlaces) ?>;
Here's a sample JSON:
var placesJSON=[{"id":"100","name":"Martinique","type":"CTRY"},{"id":"101","name":"Mauritania","type":"CTRY"},{"id":"102","name":"Mauritius","type":"CTRY"},{"id":"103","name":"Mexico","type":"CTRY"},{"id":"799","name":"Northern Mexico","type":"SUBCTRY"},{"id":"800","name":"Southern Mexico","type":"SUBCTRY"},{"id":"951","name":"Central Mexico","type":"SUBCTRY"},{"id":"104","name":"Micronesia, Federated States","type":"CTRY"},{"id":"105","name":"Moldova","type":"CTRY"}];
I understand (via this reference) that I first need to unpack my JSON like so:
var placesData = SQLike.q(
{
Unpack: placesJSON,
Columns: ['id','name','type']
}
)
And the next step would be to query the results like so:
var selectedPlaces = SQLike.q(
{
Select: ['*'],
From: placesData,
OrderBy: ['name','|desc|']
}
Lastly, to display the results in the browser I should use something like:
document.getElementById("myDiv").innerHTML=selectedPlaces[0].name
This doesn't work. The error I get is: selectedPlaces[0].name is undefined.
I'm pretty sure I'm missing out on something very simple. Any hints?

"Unpack" converts an array of arrays, like [["John", "Peterson", 38, 28000], ["Vicki", "Smith", 43, 89000]] into an array of objects. Since your Json is already in this format, there's no need to unpack it.