Get one database record, display it, update it, and save it back to the database - breeze

Question

SOLVED! It was a Knockout issue (wrong binding). But maybe someone likes to argue or comment about the code in general (dataservice, viewmodel, etc).
I tried to build a Breeze sample, where I get one database record (with fetchEntityByKey), display it for updating, then with a save button, write the changes back to the database. I could not figure out how to get it to work.
I was trying to have a dataservice ('class') and a viewmodel ('class'), binding the viewmodel with Knockout to the view.
I very much appreciated if someone could provide a sample or provide some hints.
Thankx, Harry
var dataservice = (function () {
var serviceName = "/api/amms/";
breeze.NamingConvention.camelCase.setAsDefault();
var entityManager = new breeze.EntityManager(serviceName);
var dataservice = {
serviceName: serviceName,
entityManager: entityManager,
init: init,
saveChanges: saveChanges,
getLocation: getLocation
};
return dataservice;
function init() {
return getMetadataStore();
}
function getMetadataStore() {
return entityManager.fetchMetadata()
.then(function (result) { return dataservice; })
.fail(function () { window.alert("fetchMetadata:fail"); })
.fin(function () { });
}
function saveChanges() {
return entityManager.saveChanges()
.then(function (result) { return result; })
.fail(function () { window.alert("fetchEntityByKey:fail"); })
.fin(function () { });
}
function getLocation() {
return entityManager.fetchEntityByKey("LgtLocation", 1001, false)
.then(function (result) { return result.entity; })
.fail(function () { window.alert("fetchEntityByKey:fail"); })
.fin(function () { });
}
})();
var viewmodel = (function () {
var viewmodel = {
location: null,
error: ko.observable(""),
init: init,
saveChanges: null
};
return viewmodel;
function init() {
return dataservice.init().then(function () {
viewmodel.saveChanges = dataservice.saveChanges;
return getLocation();
})
}
function getLocation() {
return dataservice.getLocation().then(function (result) {
return viewmodel.location = result;
})
}
})();
viewmodel.init().then(function () {
ko.applyBindings(viewmodel);
});

Answer 1

Glad you solved it. Can't help noticing that you added a great number of do-nothing callbacks. I can't think of a reason to do that. You also asked for metadata explicitly. But your call to fetchEntityByKey will do that implicitly for you because, as you called it, it will always go to the server.
Also, it is a good idea to re-throw the error in the fail callback within a dataservice so that a caller (e.g., the ViewModel) can add its own fail handler. Without re-throw, the caller's fail callback would not hear it (Q promise machinery acts as if the first fail handler "solved" the problem).
Therefore, your dataservice could be reduced to:
var dataservice = (function () {
breeze.NamingConvention.camelCase.setAsDefault();
var serviceName = "/api/amms/";
var entityManager = new breeze.EntityManager(serviceName);
var dataservice = {
serviceName: serviceName, // why are you exporting this?
entityManager: entityManager,
saveChanges: saveChanges,
getLocation: getLocation
};
return dataservice;
function saveChanges() {
return entityManager.saveChanges()
.fail(function () {
window.alert("saveChanges failed: " + error.message);
throw error; // re-throw so caller can hear it
})
}
function getLocation() {
return entityManager.fetchEntityByKey("LgtLocation", 1001, false)
.then(function (result) { return result.entity; })
.fail(function () {
window.alert("fetchEntityByKey failed: " + error.message);
throw error; // re-throw so caller can hear it
})
}
})();
I don't want to make too much of this. Maybe you're giving us the stripped down version of something more substantial. But, in case you (or a reader) think those methods are always necessary, I wanted to make clear that they are not.