    /**
     * @author Ed Spencer
     * @class Ext.data.Association
     * @extends Object
     *
     * <p>Associations enable you to express relationships between different {@link Ext.data.Model Models}. Let's say we're
     * writing an ecommerce system where Users can make Orders - there's a relationship between these Models that we can
     * express like this:</p>
     *
    <pre><code>
    Ext.define('User', {
        extend: 'Ext.data.Model',
        fields: ['id', 'name', 'email'],

        hasMany: {model: 'Order', name: 'orders'}
    });

    Ext.define('Order', {
        extend: 'Ext.data.Model',
        fields: ['id', 'user_id', 'status', 'price'],

        belongsTo: 'User'
    });
    </code></pre>
     *
     * <p>We've set up two models - User and Order - and told them about each other. You can set up as many associations on
     * each Model as you need using the two default types - {@link Ext.data.HasManyAssociation hasMany} and
     * {@link Ext.data.BelongsToAssociation belongsTo}. There's much more detail on the usage of each of those inside their
     * documentation pages. If you're not familiar with Models already, {@link Ext.data.Model there is plenty on those too}.</p>
     *
     * <p><u>Further Reading</u></p>
     *
     * <ul style="list-style-type: disc; padding-left: 20px;">
     *   <li>{@link Ext.data.HasManyAssociation hasMany associations}
     *   <li>{@link Ext.data.BelongsToAssociation belongsTo associations}
     *   <li>{@link Ext.data.Model using Models}
     * </ul>
     *
     * <b>Self association models</b>
     * <p>We can also have models that create parent/child associations between the same type. Below is an example, where
     * groups can be nested inside other groups:</p>
     * <pre><code>

    // Server Data
    {
        "groups": {
            "id": 10,
            "parent_id": 100,
            "name": "Main Group",
            "parent_group": {
                "id": 100,
                "parent_id": null,
                "name": "Parent Group"
            },
            "child_groups": [{
                "id": 2,
                "parent_id": 10,
                "name": "Child Group 1"
            },{
                "id": 3,
                "parent_id": 10,
                "name": "Child Group 2"
            },{
                "id": 4,
                "parent_id": 10,
                "name": "Child Group 3"
            }]
        }
    }

    // Client code
    Ext.define('Group', {
        extend: 'Ext.data.Model',
        fields: ['id', 'parent_id', 'name'],
        proxy: {
            type: 'ajax',
            url: 'data.json',
            reader: {
                type: 'json',
                root: 'groups'
            }
        },
        associations: [{
            type: 'hasMany',
            model: 'Group',
            primaryKey: 'id',
            foreignKey: 'parent_id',
            autoLoad: true,
            associationKey: 'child_groups' // read child data from child_groups
        }, {
            type: 'belongsTo',
            model: 'Group',
            primaryKey: 'id',
            foreignKey: 'parent_id',
            autoLoad: true,
            associationKey: 'parent_group' // read parent data from parent_group
        }]
    });

    Ext.onReady(function(){

        Group.load(10, {
            success: function(group){
                console.log(group.getGroup().get('name'));

                group.groups().each(function(rec){
                    console.log(rec.get('name'));
                });
            }
        });

    });
     * </code></pre>
     *
     * @constructor
     * @param {Object} config Optional config object
     */
    Ext.define('Ext.data.Association', {
        /**
         * @cfg {String} ownerModel The string name of the model that owns the association. Required
         */

        /**
         * @cfg {String} associatedModel The string name of the model that is being associated with. Required
         */

        /**
         * @cfg {String} primaryKey The name of the primary key on the associated model. Defaults to 'id'.
         * In general this will be the {@link Ext.data.Model#idProperty} of the Model.
         */
        primaryKey: 'id',

        /**
         * @cfg {Ext.data.reader.Reader} reader A special reader to read associated data
         */

        /**
         * @cfg {String} associationKey The name of the property in the data to read the association from.
         * Defaults to the name of the associated model.
         */

        defaultReaderType: 'json',

        statics: {
            create: function(association){
                if (!association.isAssociation) {
                    if (Ext.isString(association)) {
                        association = {
                            type: association
                        };
                    }

                    switch (association.type) {
                        case 'belongsTo':
                            return Ext.create('Ext.data.BelongsToAssociation', association);
                        case 'hasMany':
                            return Ext.create('Ext.data.HasManyAssociation', association);
                        //TODO Add this back when it's fixed
    //                    case 'polymorphic':
    //                        return Ext.create('Ext.data.PolymorphicAssociation', association);
                        default:
                            //<debug>
                            Ext.Error.raise('Unknown Association type: "' + association.type + '"');
                            //</debug>
                    }
                }
                return association;
            }
        },

        constructor: function(config) {
            Ext.apply(this, config);

            var types           = Ext.ModelManager.types,
                ownerName       = config.ownerModel,
                associatedName  = config.associatedModel,
                ownerModel      = types[ownerName],
                associatedModel = types[associatedName],
                ownerProto;

            //<debug>
            if (ownerModel === undefined) {
                Ext.Error.raise("The configured ownerModel was not valid (you tried " + ownerName + ")");
            }
            if (associatedModel === undefined) {
                Ext.Error.raise("The configured associatedModel was not valid (you tried " + associatedName + ")");
            }
            //</debug>

            this.ownerModel = ownerModel;
            this.associatedModel = associatedModel;

            /**
             * The name of the model that 'owns' the association
             * @property ownerName
             * @type String
             */

            /**
             * The name of the model is on the other end of the association (e.g. if a User model hasMany Orders, this is 'Order')
             * @property associatedName
             * @type String
             */

            Ext.applyIf(this, {
                ownerName : ownerName,
                associatedName: associatedName
            });
        },

        /**
         * Get a specialized reader for reading associated data
         * @return {Ext.data.reader.Reader} The reader, null if not supplied
         */
        getReader: function(){
            var me = this,
                reader = me.reader,
                model = me.associatedModel;

            if (reader) {
                if (Ext.isString(reader)) {
                    reader = {
                        type: reader
                    };
                }
                if (reader.isReader) {
                    reader.setModel(model);
                } else {
                    Ext.applyIf(reader, {
                        model: model,
                        type : me.defaultReaderType
                    });
                }
                me.reader = Ext.createByAlias('reader.' + reader.type, reader);
            }
            return me.reader || null;
        }
    });