Grails populate g:select from database - grails

Question

I ran into an issue while populating domain object values on a gsp page by using a g:select tag.
<g:select name="demo" id="demo"
value="${dm.id}"
noSelection="${['null':'Select..']}"
from="${dm}"
optionValue="${dm.type}"/>
In my controller, I have an object which gathers values from my domain. I tried writing this object in the controller both as:
def d = Demo.getAll()
and def d = Demo.list()
Both of these returned an exception while trying to use the g:select tag. The error was:
No signature of method: Demo.getAt() is applicable for argument types: (java.util.ArrayList) values: [[One, Two, Three, Four, Five]]
I was able to get my code working by simply removing the g:select tag and writing the following in my gsp:
<select name="demo" id="dm">
<option value="">Select!</option>
<g:each in="${dm}" status="i" var="dm">
<option value="${dm.id}">${dm.name}</option>
</g:each>
</select>
However, I would like to know how to make this work with the g:select tag, for my future reference.
Thanks in advance!

Answer 1

I see two issues in your select:
<g:select name="demo" id="demo"
value="${dm.id}"
noSelection="${['null':'Select..']}"
from="${dm}"
optionValue="${dm.type}"/>
value shouldn't be looking at the collection for the id. I believe this is why you are getting your error. value should be whatever instance's id you've passed into your view.
optionValue doesn't required an expression.
Controller action
def someAction() {
def dm = Demo.get(params.id)
def demos = Demo.list()
[dm: dm, demos: demos]
}
view
<g:select name="demo" id="demo"
value="${dm.id}"
noSelection="${['null':'Select..']}"
from="${demos}"
optionValue="type"/>