ExtJS advanced model that is able to update hasMany associations.

gistfile1.js

/**
 * Improved {@link Ext.data.Model}.
 * Can automatically update foreign keys and default filter value for hasMany associations.
 */
Ext.define('App.model.AssocModel', {
    extend: 'Ext.data.Model',

    /**
     * @private
     * Copies data from the passed record into this record. If the passed record is undefined, does nothing.
     *
     * If this is a phantom record (represented only in the client, with no corresponding database entry), and
     * the source record is not a phantom, then this record acquires the id of the source record.
     *
     * ADDED: If this is a phantom record and has hasMany associations, then foreign keys, filter value and `modelDefault` store property
     * for this associations will be updated.
     *
     * @param {Ext.data.Model} sourceRecord The record to copy data from.
     * @return {String[]} The names of the fields which changed value.
     */
    copyFrom: function(sourceRecord) {
        var me = this,
            fields = me.fields.items,
            fieldCount = fields.length,
            modifiedFieldNames = [],
            field, i = 0,
            myData,
            sourceData,
            idProperty = me.idProperty,
            name,
            value;

        if(sourceRecord) {
            myData = me[me.persistenceProperty];
            sourceData = sourceRecord[sourceRecord.persistenceProperty];

            for (; i < fieldCount; i++) {
                field = fields[i];
                name = field.name;

                // Do not use setters.
                // Copy returned values in directly from the data object.
                // Converters have already been called because new Records
                // have been created to copy from.
                // This is a direct record-to-record value copy operation.
                // don't copy the id, we'll do it at the end
                if (name != idProperty) {
                    value = sourceData[name];

                    // If source property is specified, and value is different
                    // copy field value in and build updatedFields
                    if (value !== undefined && !me.isEqual(myData[name], value)) {
                        myData[name] = value;
                        modifiedFieldNames.push(name);
                    }
                }
            }

            // If this is a phantom record being updated from a concrete record, copy the ID in.
            if (me.phantom && !sourceRecord.phantom) {
                // beginEdit to prevent events firing
                // commit at the end to prevent dirty being set
                me.beginEdit();
                me.setId(sourceRecord.getId());

                // update nasMany associations
                me.updateHasManyAssociations(sourceRecord.getId());

                me.endEdit(true);
                me.commit(true);
            }
        }

        return modifiedFieldNames;
    },

    /**
     * @private
     * Update foreign key value for hasMany associations.
     * @param {int} newId
     */
    updateHasManyAssociations: function(newId) {
        var me = this,
            associations = me.associations.items,
            associationCount = associations.length,
            association, associatedStore,
            type, name, foreignKey, filterProperty,
            filters, filter;

        for(var i = 0; i < associationCount; i++) {
            association = associations[i];

            type = association.type;
            name = association.name;
            foreignKey = association.foreignKey;
            filterProperty = association.filterProperty || foreignKey;

            switch(type) {
                case 'hasMany':
                    associatedStore = me[association.storeName];

                    if(associatedStore) {
                        // update store associated foreign key fields
                        // for items are already added to store
                        //
                        if(associatedStore.getCount() > 0) {
                            associatedStore.each(function(item) {
                                item.set(foreignKey, newId);
                            });
                        }

                        // update store `modelDefaults` foreign key property
                        // for future items
                        //
                        associatedStore.modelDefaults[filterProperty] = newId;

                        // update store filter value
                        // for saving/loading store operations
                        //
                        filters = associatedStore.filters;
                        filter = filters.getAt(filters.findIndex('property', filterProperty));

                        if(filter) {
                            filter.setValue(newId);
                        }
                    }

                    break;
            }
        }
    }

});