Submitted form text fields not grouping correctly - grails

Question

In my GSP I have a form with a lot textfields populated by a map that came from the controller, let me put this into an example, because my actual form is a lot more complicated than this:
for example, if I use users to populate a bunch of textfields where I can enter each person's age, I grouped them up into a map called data, and I want to process and save all that information after submitting:
<g:form useToken="true" name='example_form' action='submit'>
<g:each in='${users}' var='user' status='i'>
<g:textField name="data.${user.id}.name" value="${i.name}">
<g:field name="data.${user.id}.age" value="">
</g:each>
<button>Submit</button>
</g:form>
But when I am printing out the params.data in my submit controller, I noticed that not only I am getting the data map that I've created, I am also getting a bunch of garbage within it:
for(i in params.data){
println "key: ${i.key} value: ${i.value}"
}
output:
key: 0.name value: john
key: 0 value: [age: 35, name: john]
key: 1.name value: liz
key: 1 value: [age: 24, name: liz]
key: 2.name value: robert
key: 3.name value: david
key: 0.age value: 35
key: 1.age value: 24
key: 2 value: [age: 44, name: robert]
key: 3 value: [age: 23, name: david]
key: 3.age value: 23
key: 2.age value: 44
Am I doing something wrong?
expected output:
key: 0 value: [age: 35, name: john]
key: 1 value: [age: 24, name: liz]
key: 2 value: [age: 44, name: robert]
key: 3 value: [age: 23, name: david]

Answer 1

It should work exactly this way. When you're submitting data from your form, the body of your POST request looks this way:
data.0.name=john&data.0.age=35&data.1.name=liz&data.1.age=24&data.2.name=robert&data.2.age=44&data.3.name=david&data.3.age=23
So, it's just a plain string, representing a plain key-value map and Grails could parse is just like that:
['data.0.name': 'john', 'data.0.age': '35', 'data.1.name': 'liz', 'data.1.age': '24', 'data.2.name': 'robert', 'data.2.age': '44', 'data.3.name': 'david', 'data.3.age': '23']
But Grails developers wanted to simplify programmers' life, and they decided that if the key contains a dot, the request may represent some kind of structured data. So they decided to put it to the map, in addition to the raw request data. Thus, the dot can be interpreted in two ways - as a plain symbol, or as a separator between map name and map key. And it's up to developer which way the dot should be interpreted.

Answer 2

If you prefer to have clearer params over the easy use like def name = params.data.0.name, then you can use "_" insted of ".". In the controller you can use split("_") in a loop.

Answer 3

In a previous post #Alexander Tokarev explained what happened. The solution is an if statement as shown below:
for(i in params.data){
if( i.key.isNumber() ) {
println "key: ${i.key} value: ${i.value}"
}
}