Overriding Controllers and Actions in Magento
In my previous post, I had explained a way to add extra controllers to existing route. Here I am going to explain another method which is used for overriding controllers and actions. Like my each post on tips & tricks, I am going to first explain where the trick is applicable! I am considering that readers of this post are aware of MVC architecture in Magento.
Let me explain the difference between the both tricks. The trick explained in previous post is used when we need additional URLs in same route i.e. additional controllers and actions. I have already explained an example there. Here we need to change the behavior of existing controller and action. For example, when a customer adds a product to shopping cart,
Of course, this too can be done just by simple XML configuration (apart from creating custom controllers and actions) but without using route rewriting approach! Let's take a same example above where we want to override action for
Simple isn't it? Now let's understand how it works. The work flow of this rewrite process is little bit tricky.
Let me explain the difference between the both tricks. The trick explained in previous post is used when we need additional URLs in same route i.e. additional controllers and actions. I have already explained an example there. Here we need to change the behavior of existing controller and action. For example, when a customer adds a product to shopping cart,
addAction of CartController of Mage_Checkout module is called. If we want to override this by My_Checkout, MycartController, myaddAction as similarly as we can override Models and Blocks in our own modules. So the the trick in previous post is used for overloading while the trick here is used for overriding.Of course, this too can be done just by simple XML configuration (apart from creating custom controllers and actions) but without using route rewriting approach! Let's take a same example above where we want to override action for
checkout/cart/add. First create My_Checkout module with MycartController class and myaddAction method defined within it. The way to do this is better explained in this wiki. Then the configuration required in etc/config.xml of My_Checkout module is like below:<global>
<routers>
<checkout> <!-- Mage_Checkout module -->
<rewrite>
<cart> <!-- CartController -->
<to>mycheckout/mycart</to> <!-- My_Checkout module, MycartController -->
<override_actions>true</override_actions>
<actions>
<add> <!-- addAction -->
<to>mycheckout/mycart/myadd<to> <!-- My_Checkout/MycartController/myaddAction -->
</add>
</actions>
</cart>
</rewrite>
</checkout>
</routers>
</global>
Here we also need configuration to define module front name for My_Checkout module as below:<frontend> <!-- It will be admin for overriding admin controller -->
<routers>
<mycheckout>
<use>admin</use>
<args>
<module>My_Checkout</module>
<frontName>mycheckout</frontName>
</args>
</mycheckout>
</routers>
</frontend> <!-- It will be admin for overriding admin controller -->Note: The above configuration examples only display portions of config.xml file. Please do not consider it as a complete configuration.Simple isn't it? Now let's understand how it works. The work flow of this rewrite process is little bit tricky.
- When an
checkout/cart/addaction is going to be dispatched, first it is passed through rewrite process. - Rewrite process tries to find
global/routers/checkout/rewrite/cartnode is found in configuration, wherecheckoutis front name ofMage_Checkoutmodule andcartindicatesMage_Checkout_CartController - If this node is not found, rewrite process is not be continued and returned to dispatch process. So the action is executed normally. Otherwise, rewrite process is continued.
- Now, under this node, it tries to find whether
override_actionsnode istrueorfalse. By default value ofoverride_actionsis true. So if it is not added in configuration, it is considered as true. - If
override_actionsistrue, it overrides all actions ofMage_Checkout_CartControllerwith same actions ofMy_Checkout_MycartControlleras defined bytonode valuemycheckout/mycart. For example, if we have definedaddActionandindexActionmethods insideMy_Checkout_MycartController, then it automatically overrides bothaddActionandindexActionofMage_Checkout_CartController. In short usingtonode andoverride_actionsnode we can override whole controller instead of individual actions. - If
actions/addnode is defined where,addindicatesaddActionofMage_Checkout_CartController, thenoverride_actionsnode value is not considered and overrides action by value ofactions/add/tonode which ismycheckout/mycart/myaddi.e.My_Checkoutmodule, My_Checkout_MycontrollerandmyaddAction. So we can also override individual actions by this type of configuration.
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