module Ext_data_Field: sig .. end

Fields are used to define what a Model is. They aren't instantiated directly - instead, when we create a class that extends Ext.data.Model, it will automatically create a Field instance for each field configured in a Model. For example, we might set up a model like this:

Ext.define('User', {
    extend: 'Ext.data.Model',
    fields: [
        'name', 'email',
        {name: 'age', type: 'int'},
        {name: 'gender', type: 'string', defaultValue: 'Unknown'}
    ]
});

Four fields will have been created for the User Model - name, email, age and gender. Note that we specified a couple of different formats here; if we only pass in the string name of the field (as with name and email), the field is set up with the 'auto' type. It's as if we'd done this instead:

Ext.define('User', {
    extend: 'Ext.data.Model',
    fields: [
        {name: 'name', type: 'auto'},
        {name: 'email', type: 'auto'},
        {name: 'age', type: 'int'},
        {name: 'gender', type: 'string', defaultValue: 'Unknown'}
    ]
});

Types and conversion

The type is important - it's used to automatically convert data passed to the field into the correct format. In our example above, the name and email fields used the 'auto' type and will just accept anything that is passed into them. The 'age' field had an 'int' type however, so if we passed 25.4 this would be rounded to 25.

Sometimes a simple type isn't enough, or we want to perform some processing when we load a Field's data. We can do this using a convert function. Here, we're going to create a new field based on another:

Ext.define('User', {
    extend: 'Ext.data.Model',
    fields: [
        {
            name: 'firstName',
            convert: function(value, record) {
                var fullName  = record.get('name'),
                    splits    = fullName.split(" "),
                    firstName = splits[0];

                return firstName;
            }
        },
        'name', 'email',
        {name: 'age', type: 'int'},
        {name: 'gender', type: 'string', defaultValue: 'Unknown'}
    ]
});

Now when we create a new User, the firstName is populated automatically based on the name:

var ed = Ext.create('User', {name: 'Ed Spencer'});

console.log(ed.get('firstName')); //logs 'Ed', based on our convert function

Fields which are configured with a custom convert function are read after all other fields when constructing and reading records, so that if convert functions rely on other, non-converted fields (as in this example), they can be sure of those fields being present.

In fact, if we log out all of the data inside ed, we'll see this:

console.log(ed.data);

//outputs this:
{
    age: 0,
    email: "",
    firstName: "Ed",
    gender: "Unknown",
    name: "Ed Spencer"
}

The age field has been given a default of zero because we made it an int type. As an auto field, email has defaulted to an empty string. When we registered the User model we set gender's defaultValue to 'Unknown' so we see that now. Let's correct that and satisfy ourselves that the types work as we expect:

ed.set('gender', 'Male');
ed.get('gender'); //returns 'Male'

ed.set('age', 25.4);
ed.get('age'); //returns 25 - we wanted an int, not a float, so no decimal places allowed

class type t = object .. end

class type configs = object .. end

class type events = object .. end

class type statics = object .. end

val of_configs : configs Js.t -> t Js.t

val to_configs : t Js.t -> configs Js.t