Extending Ext.data.Store

Here is the super class:

Ext.define('My.store.Direct', {

extend: 'Ext.store.Direct',

paramsAsHash: true,

proxy: {

reader: {

type: 'json',

root: 'data',

totalProperty: 'total'

},

type: 'direct',

}

});

In subclasses I only need to set the API config. I tried:

Ext.define('My.store.User', {

extend: 'My.store.Direct',

model: 'My.model.User',

storeId: 'user',

constructor: function () {

this.callParent(arguments);

this.getProxy().api.read = RPC.UserApi.read;

}}

);

Ext.define('My.store.Post', {

extend: 'My.store.Direct',

model: 'Mehr.model.Post',

storeId: 'post',

constructor: function () {

this.callParent(arguments);

this.getProxy().api.read = RPC.PostApi.read;

}}

);

Unfortunately, after executing the code both store will have the `api.read` of the first subclass. What is wrong with it? What is proper method of extending stroes?