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== params



=== Purpose


A mutable multi-dimensional map (hash) of request (CGI) parameters. 
See link:{apiFromRef}grails/web/servlet/mvc/GrailsParameterMap.html[api documentation] for details.


=== Examples


To obtain a request parameter called `id`:
[source,groovy]
----
class BookController {
    def show() {
        def book = Book.get(params.id)
    }
}
----

To perform data binding (see link:{guidePath}theWebLayer.html#dataBinding[data binding] in the user guide):

[source,groovy]
----
def save() {
    def book = new Book(params) // bind request parameters onto properties of book
}
----


=== Description


The standard Servlet API provides access to parameters with the `HttpServletRequest` object. Although Grails provides the same capability through the link:request.html[request] object, it goes a bit further by providing a mutable map of request parameters called `params`.

The `params` object can be indexed into using the array index operator or de-reference operator, so given the URL `/hello?foo=bar` you can access `foo` with

----
println params.foo
----

The params object can also be used to bind request parameters onto the properties of a domain class using either the constructor or the link:{domainClassesRefFromRef}properties.html[properties] property:

[source,groovy]
----
def book = new Book(params)
book = Book.get(1)
book.properties = params
----

For further reading see link:{guidePath}theWebLayer.html#dataBinding[data binding] in the user guide.
