How to handle one to many relation ship Knockout-Entity Framework - entity-framework

Question

So I have I have a simple structure where one purchase have a collection of expenses, and each expense have an account(plastic, cash, plastic#2...).
So the json my api gets is similar to this:
[
{"$id":"1","Id":1,"Name":"apple","Value":100.0,"AccountId":1,"Account":
{"$id":"2","Id":1,"Name":"Cash"}},
{"$id":"3","Id":2,"Name":"pear","Value":50.0,"AccountId":1,"Account":
{"$ref":"2"}},
{"$id":"4","Id":3,"Name":"raspberry","Value":10.0,"AccountId":1,"Account":
{"$ref":"2"}}
]
I see my json is not writing my cash account each time it needs it, it is refering it with
{"$ref":"2"}
where
{"$id":"2","Id":1,"Name":"Cash"}
so when I render my table with this html:
<table>
<tbody data-bind="foreach: gastos">
<tr>
<td data-bind="text: $data.id"></td>
<td data-bind="text: $data.name"></td>
<td data-bind="text: $data.value"></td>
<td data-bind="text: $data.account.Name"></td>
<td>
<button type="button" class="btn btn-xs">
<i class="glyphicon glyphicon-trash"></i>
</button>
</td>
</tr>
</tbody>
</table>
I get this, because the account for pear, and raspberry are nulls:
So how do you handle $ref in knockout?
I am mapping to 'gastos' this way:
$.getJSON('#ViewBag.GastosUrl', function (data) {
data.forEach(function(o) {
gastos.push(new gastoVM(o.Id, o.Name, o.Value, o.Account));
});
});
var gastoVM = function(Id, Name, Value, Account) {
var self = this;
self.id = Id;
self.name = Name;
self.value = Value;
self.account = Account;
};
thanks.

Answer 1

I'm not familiar with entity-framework but with the data as provided, a couple options available (JSFiddle):
Build up the account information alongside the gastos. And only provide the $id or $ref for later referencing.
var vm = {
gastos: [],
accounts: {},
accountLookup: function(accountId){
return this.accounts[accountId];
}
}
//... inside AJAX call
var accountId = o.Account["$id"]
if(accountId)
{
vm.accounts[accountId] = o.Account;
}
Use a ko utility method to lookup the account from within your array.
accountLookupByUtil: function(accountId) {
var gasto = ko.utils.arrayFirst(this.gastos, function(item) {
if(item.account['$id'] == accountId)
{
return item
}
});
return gasto.account;
}
From the html:
<td data-bind="text: $root.accountLookup($data.accountId).Name"></td>
<td data-bind="text: $root.accountLookupByUtil($data.accountId).Name"></td>
Note: Both methods are available in the fiddle, thus some properties are provided that would not be necessary depending upon the method used.