extjs 4 : get store record values

Question

my json data looks like this :

({"success": "true", "message" : "OK","data":[{"id_metric":"1","name_filter":"doc filter","type_guicomp":"combobox"},{"id_metric":"1","name_filter":"severity","type_guicomp":"combobox"}]})

I'd like to be able to retrieve the "type_guicomp" field value for the "id_metric" = 1 , so the result would be : "type_guicomp":"combobox" and "type_guicomp":"combobox".

I do this because I need the value "combobox" to assign it to a variable. I've tried several things including :

myStore.load({
        scope: this,
        callback : function(record, operation, success) {
            console.log(record);
            console.log(record.data);
            }

And :

var index = Ext.StoreMgr.lookup("myStore").findExact('id_metric',1);
var rec = Ext.StoreMgr.lookup("myStore").getAt(index);
console.log(rec);

These solutions return undefined or null. So when I did this in the callback :

var i = myStore.getCount();
console.log(i);

It returned 0. But when I check the json output, it's not empty and there's actually data in it.

What am I doing wrong? Please any help would be appreciated.

EDIT

My store looks like this :

Ext.define('Metrics.store.MyStore', {
extend: 'Ext.data.Store',
model: 'Metrics.model.MyModel',
autoLoad: true,
idProperty: 'id_metric',
proxy : {
    type : 'ajax',
    actionMethods : 'POST',
    node : 'id_metric',
    api : {
    read : 'gui_comp_items.php' //the php script that gets data from db
    },
    reader: {
        type: 'json',
        successProperty: 'success',
        messageProperty: 'message',
        root: 'data'
    }
}
});

My Model :

Ext.define('Metrics.model.MyModel', {
extend: 'Ext.data.Model',
fields: [
{name : 'id_metric', type : 'int'},
{name : 'name_filter', type : 'string'},
{name : 'type_guicomp', type : 'string'},
{name : 'value', type : 'string'}]  
});

Solution

What i don't get is the way you have used myStore. You have used it both ways as a string as well as a variable. Which is it? If its a string, then myStore.load() will not work. If its a variable, you need to lose the quotes on Ext.StoreMgr.lookup(myStore). Where is the store variable being declared?

Comments

[salamey]

I have declared : var myStore = this.getMyStore();

[Aashray]

Have you created the store and model using Ext.create? From my understanding, these are just definitions, you need to create them once they have been defined.

[salamey]

I'm using the Extjs 4 MVC architecture, the store and model are defined then used by the controller. I don't think that's the problem.