Declaring Ember Data Model Defaults in Open Event Frontend

This article will illustrate the ways to declare the model defaults for JavaScript data types ‘boolean’, ‘string’, ‘number’, ‘object’ and ‘array’ as used in Open Event frontend project.

While working with ember-data models which define the properties and behaviour of data, in Open Event frontend project, we needed to preset the values for certain attributes if they are not supplied along with data. To preset the values in ember-data we need to specify the default values to the attribute. The process of setting the default values is very much similar to the way we handle it in other databases like MySQL and we might have certainly done it many times there. In ember, we set the values like this.

export default Model.extend({
 type : attr('string', { defaultValue: 'text' }),
 isRequired : attr('boolean', { defaultValue: false })

This way we could set values for attributes having data types, ‘boolean’, ‘string’ and ‘number’. But when it came to data types, ‘object’ and ‘array’ we were unable to set the default values in similar way reason being ember data does not provide support for ‘array’ and ‘object’ data types. Also, we tried to play around by not providing the first argument to the DS.attr() method, then Ember does not remain the value for that particular attribute empty or unhandled rather it forced to matching JavaScript type. The other and the obvious way which clicked to us was this.The attributes are properties defined to convert the JSON data coming from our server into a record, and serializing a record to save back to the server after it has been modified. In above code we defined that ‘type’  has a default value of ‘text’ and ‘isRequired’ has default value ‘false’ which will be present at the time of model’s creation.

export default Model.extend({
 startTime : attr('object', { defaultValue: {} })

But soon after executing the code, we got a warning which can be seen below.The above code implies that whenever we create a new
event model then it would be expected to have an attribute startTime with value {}.

Non primitive defaultValues are deprecated because they are shared between all instances. If you would like to use a complex object as a default value please provide a function that returns the complex object.

The warning explains that ember-data model extends from Ember.Object, which means that arrays and objects will be shared among all instances of that model hence the use of non-primitive (apart from boolean, number & string) default values are deprecated.

Now again we thought of something that can handle ‘array’ and ‘object’ data types. We thought of adding a function which would convert them to the custom type. To add that we needed to provide proper serialize and deserialize methods for processing the data properly which was a bit tedious process and increase the overall complexity of code both in terms of execution as well as understanding.

After reading the available resources, we got to know that the defaultValue accepts the function as well. So what we finally did was passed a function which will add the months and days to the date object based on the current time which can be calculated using moment.

export default Model.extend({
 startTime : attr('date', { defaultValue: () => moment().add(1, 'months').startOf('day').toDate() }) 

The ability to pass afunction to defaultValue proved very helpful. It suits best if we want to set custom defaults.That’s it! Passing the function will ensure that every
startTime attribute contains it’s own date instance.

Additional Resources:

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