In an ExtJS Grid, how do I get access to the data store fields that are part of the sort set - extjs4

Question

How do I get access to the columns/datastore fields that are part of the sort set.
I am looking to modify the a grid's sort parameters for remote sorting. I need the remote sort param's sort key to match the column's field's mapping property. I need these things to happen though the normal 'column header click sorts the data' functionality.

Answer 1

Remote sorting and field mapping (ExtJS 4.1)
This functionality seems not to be implemented in ExtJS. Here is a solution using the encodeSorters function provided since ExtJS 4. Accessing fields map throught the model's prototype is a bit dirty but it does the job :
var store = Ext.create('Ext.data.Store', {
...,
proxy: {
...,
encodeSorters: function (sorters) {
var model = store.proxy.model,
map = model.prototype.fields.map;
return Ext.encode(Ext.Array.map(sorters, function (sorter) {
return {
property : map[sorter.property].mapping || sorter.property,
direction: sorter.direction
};
}));
}
}
});
However, it would be more relevant to override the original method :
Ext.data.proxy.Server.override({
encodeSorters: function(sorters) {
var min, map = this.model.prototype.fields.map;
min = Ext.Array.map(sorters, function (sorter) {
return {
property : map[sorter.property].mapping || sorter.property,
direction: sorter.direction
};
});
return this.applyEncoding(min);
}
});

Answer 2

Assuming you are using simpleSortMode, you could do something like this in your store.
listeners: {
beforeload: function( store, operation, eOpts ) {
if (store.sorters.length > 0) {
var sorter = store.sorters.getAt(0),
dir = sorter.direction,
prop = sorter.property,
fields = store.model.getFields(),
i,
applyProp = prop;
for (i = 0; i < fields.length; i++) {
if (fields[i].name == prop) {
applyProp = fields[i].mapping || prop;
break;
}
}
//clearing the sorters since the simpleSortMode is true so there will be only one sorter
store.sorters.clear();
store.sorters.insert(0, applyProp, new Ext.util.Sorter({
property : applyProp,
direction: dir
}));
}
}
},