Make it easier to create custom DataTypes
I've been able to write a custom DataType implementation for Moment.js but am stuck in places where the equality of two instances of the DataType is evaluated.
Currently, there are a number of lines of code which specifically handle Dates differently because of their inability to be compared using ===. For instance, in a35_defaultPropertyInterceptor.js:
// exit if no change - extra cruft is because dateTimes don't compare cleanly.
if (newValue === oldValue || (dataType && dataType.isDate && newValue && oldValue && newValue.valueOf() === oldValue.valueOf())) {
return;
}
However, that means if I want a custom DataType, and need a custom equality operator, I have to edit this portion of the file. Instead, I propose using the `getComparableFn` method already available:
// exit if no change - extra cruft is because dateTimes don't compare cleanly.
var normalize = dataType && DataType.getComparableFn(dataType);
if (newValue === oldValue || (dataType && normalize && normalize(newValue) === normalize(oldValue)) {
return;
}
This would be similar to what you're doing in `getComparer` in `OrderByClause` in a45_entityQuery.js. One could use the same logic for the `coEquals` function in `EntityType` in a40_entityMetadata.js.
The other oddity I found while doing this was the custom code used for Dates in `fromJSON` in `DataProperty`. This function would seem better served by using the `parse` function of the dataType itself, or the static `DataType.parseRawValue`.
Finally, it would be nice to be able to attach a `getConcurrencyValue` function to `DataType` for use in `updateConcurrencyProperty` in `a50_entityManager.js`.
Mike McCaughan
shared this idea
2 comments
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Mike McCaughan
commented
Thanks for taking a look at this!
I was looking at creating a custom datatype for the Moment.js library, as we are trying to use that in our app for easier date handling. I looked at all of the places in breeze.js where there's special handling for Dates, since Moments are obviously very similar.
That's where I noticed the special handling for Dates in `fromJSON`. It would be nice to have an extension point on DataType for that purpose, but maybe I'm not understanding the purpose?
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Steve Schmitt
commented
These are good ideas; it should be easier to create custom datatypes.
We have to be careful in a35_defaultPropertyInterceptor.js, because that's a very hot path (it gets executed every time any property changes on any entity).
DataType.fromJSON is different from the `parse` function because it has different expectations about the incoming format. It's handling the metadata definitions, not arbitrary query responses.