Persisting date and nested with JSON - grails

Question

I'm trying to save nested person, which is json array and complains about requiring a Set.
Another problem I encountered, is that another field date cannot be null, but contains value already.
What I need to do before for adding params into my object or I have to change my json is built? I'm trying to save json post like this:
// relationship of Test
//static hasMany = [people: Person, samples: Sample]
def jsonParams= JSON.parse(request.JSON.toString())
def testInstance= new Test(jsonParams)
//Error requiring a Set
[Failed to convert property value of type 'org.codehaus.groovy.grails.web.json.JSONArray' to required type 'java.util.Set' for property 'people'; nested exception is java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type [com.Person] for property 'people[0]': no matching editors or conversion strategy found]]
//error saying its null
Field error in object 'com.Test' on field 'samples[2].dateTime': rejected value [null]; codes [com.Sample]
//...
"samples[0].dateTime_hour":"0",
"samples[0].dateTime_minute":"0",
"samples[0].dateTime_day":"1",
"samples[0].dateTime_month":"0",
"samples[0].dateTime_year":"-1899",
"samples[0]":{
"dateTime_minute":"0",
"dateTime_day":"1",
"dateTime_year":"-1899",
"dateTime_hour":"0",
"dateTime_month":"0"
},
"people":[
"1137",
"1141"
], //...

Answer 1

First off, ths line is unnecessary:
def jsonParams= JSON.parse(request.JSON.toString())
The request.JSON can be directly passed to the Test constructor:
def testInstance = new Test(request.JSON)
I'm not sure what your Person class looks like, but I'm assuming those numbers (1137, 1141) are ids. If that is the case, then your json should work - there's a chance that passing the request.JSON directly could help. I tested your JSON locally and it has no problem associating the hasMany collection. I also used:
// JSON numbers rather than strings
"people": [1137, 1141]
// using Person map with the id
"people: [{
"id": 1137
}, {
"id": 1141
}]
Both of these worked as well and are worth trying.
Concerning the null dateTime, I would rework your JSON. I would send the dateTime in a single field, instead of splitting the value into hour/minute/day/etc. The default formats are yyyy-MM-dd HH:mm:ss.S and yyyy-MM-dd'T'hh:mm:ss'Z', but these can be defined by the grails.databinding.dateFormats config setting (config.groovy). There are other ways to do the binding as well (#BindingFormat annotation) but it's going to be easiest to just send the date in a way that grails can handle without additional configuration.
If you are dead set on splitting the dateTime into pieces, then you could use the #BindUsing annotation:
class Sample{
#BindUsing({obj, source ->
def hour = source['dateTime_hour']
def minute = source['dateTime_minute']
...
// set obj.dateTime based on these pieces
})
Date dateTime
}
An additional comment on your JSON, you seem to have samples[0] defined twice and are using 2 syntaxes for your internal collections (JSON arrays and indexed keys). I personally would stick with a single syntax to clean it up:
"samples": [
{"dateTime": "1988-01-01..."}
{"dateTime": "2015-10-21..."}
],"people": [
{"id": "1137"},
{"id": "1141"}
],