JSF: Update and add new request params - jsf-2

Question

I have a page with the following params:
<f:metadata>
<f:event type="preRenderView" listener="#{busquedaBean.init}" />
<f:viewParam name="k" value="#{busquedaBean.keyword}" />
<f:viewParam name="categoryId" value="#{busquedaBean.categoryId}" />
<f:viewParam name="minprice" value="#{busquedaBean.minPrice}" />
<f:viewParam name="maxprice" value="#{busquedaBean.maxPrice}" />
</f:metadata>
All of them are optional. I need to do 2 things, which I wasn't able to do so far:
1) Add new params (keeping the previous params). This is what I tried for adding price params:
<h:outputText value="Precio diario" />
<o:form includeRequestParams="true">
<h:outputText value="min: " />
<p:inputText id="min" value="#{busquedaBean.minPrice}" />
<h:outputText value="max: " />
<p:inputText id="max" value="#{busquedaBean.maxPrice}" />
<p:commandButton icon="ui-icon-search" ajax="false">
<f:param name="minprice" value="#{busquedaBean.minPrice}" />
<f:param name="maxprice" value="#{busquedaBean.maxPrice}" />
</p:commandButton>
</o:form>
This basically works but the problem is that the URL is not updated. if the params in the URL were ?minprice=10&maxprice=200 and I update those values, the url remains the same. if these params were not included in the url, they won't be added and the filter won't work.
2) Updating the value of a param:
When categoryId is not empty, I want to show a button that will clear this param. This is what I tried:
<p:button outcome="/busqueda" includeViewParams="true" >
<f:param name="categoryId=" value="" />
</p:button>
But this button makes a GET to this URL: /busqueda/?categoryId=%3D&categoryId=1
The categoryId param appears twice. How can I just update the existing param?
I'm using MyFaces 2.1.14, Tomcat 7, Primefaces 4.0, Omnifaces
Thanks!

Answer 1

I was looking at this in the wrong way. includeViewParams=true will make the request include all the params declared in f:metadata with the current values. if such value is null, then the parameter is not included.
So.. to add price params:
<h:form >
<h:outputText value="$ " />
<p:inputText id="min" value="#{busquedaBean.minPrice}"/>
<h:outputText value=" a $ " />
<p:inputText id="max" value="#{busquedaBean.maxPrice}"/>
<p:commandButton icon="ui-icon-search" ajax="false" action="/busqueda?faces-redirect=true&includeViewParams=true" />
</h:form>
And to remove a param:
<p:commandButton action="#{busquedaBean.removeCategory}" ajax="false" icon="ui-icon-close" />
In the backing bean:
public String removeCategory() {
categoryId = null;
return "/busqueda?faces-redirect=true&includeViewParams=true";
}