BreezeJS + Knockout Not able to set input field to Null

Question

Where a model uses nullable values such as

public Nullable<int> Price { get; set; }

When adding new records all is fine, Price is Not a required field so will be saved as Null value in the database.

If I modify an existing record, let’s say I want to change the value of price from 10 to blank. Then I get a validation error.

Validation error: ‘Price‘ must be an integer between the values of -2147483648 and 2147483647

However this field is not required so I would have expected it to just save a null value?

The Smallest The Smallest · Accepted Answer · 2013-03-17T19:34:52

That happens because empty textbox value is "" (empty string), but not null.

So, before setting new value you should check if value is empty string, if so - assign null manually.

Update for Knockout. You can write custom ko binding, that will do everything for you. Here is example (might be not the best one):

Javascript:

ko.bindingHandlers.nullableValue = {
  init: function (element, valueAccessor, allBindingsAccessor) {
    var underlyingObservable = valueAccessor();
    var interceptor = ko.dependentObservable({
        read: underlyingObservable,
        write: function (value) {
            if (value == '') {
                underlyingObservable(null);
                return;
            }
            underlyingObservable(value);
        }
    });
    ko.bindingHandlers.value.init(element, function () { return interceptor; }, allBindingsAccessor);
  },
  update: ko.bindingHandlers.value.update
};

Html

<input type="text" data-bind="nullableValue: myNullableProperty" />

Hope it helps.

BreezeJS + Knockout Not able to set input field to Null

1 Answers