Terraform validation for optional variables and for list of object variables - terraform-provider-azure

Question

I am using the monitor autoscale setting resource for Terraform and I am trying to validate attributes of a complex object.
https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/monitor_autoscale_setting
The "trigger" block has been made optional so I have added a step to check if a value exists before checking for validation. Below is the scaling profile:
`
variable "scaling_profile" {
type = list(object({
name = optional(string, "Profile 1")
capacity = number
min_capacity = optional(number)
max_capacity = optional(number)
trigger = optional(list(object({
metric_name = string
operator = string
threshold = number
scale_action = string
scale_instance_count = number
time_window = number
scale_cooldown = number
})), [])
schedule = list(object({
days = list(string)
start_hour = number
start_minute = number
end_hour = number
end_minute = number
}))
}))
default = [{
capacity = 1
min_capacity = 1
max_capacity = 3
trigger = [
{
metric_name = "Percentage CPU"
operator = "GreaterThan"
threshold = 60
scale_action = "Increase"
scale_instance_count = 1
time_window = 5
scale_cooldown = 5
},
{
metric_name = "Percentage CPU"
operator = "LessThan"
threshold = 20
scale_action = "Decrease"
scale_instance_count = 1
time_window = 5
scale_cooldown = 5
}
]
schedule = []
}]
validation {
condition = ! contains([
for profile in var.scaling_profile :
[for trigger in profile.trigger :
profile.trigger != [] ?
contains(["GreaterThan", "LessThan", "GreaterThanOrEqual", "NotEquals", "Equals", "LessThanOrEqual"], trigger.operator)
: true]
], false)
error_message = "Threshold operator must be one of following values: GreaterThan, LessThan,GreaterThanOrEqual, NotEquals, Equals, LessThanOrEqual."
}
validation {
condition = ! contains([
for profile in var.scaling_profile :
[for trigger in profile.trigger :
profile.trigger != [] ?
contains(["Increase", "Decrease"], trigger.scale_action)
: true]
], false)
error_message = "Scale action must be one of the following: Increase or Decrease."
}
}
`
The module is being called as below. I have taken out the trigger block and I am only accounting for the schedule block. I want to be able to check for the existence of the trigger block before validation.
`
module "autoscale_vmss_linux" {
source = "../../"
resource_group_name = var.resource_group_name
target_resource_id = module.vmss_linux.id
default_scaling_profile = {
capacity = 1
}
scaling_profile = var.scaling_profile_vmss
depends_on = [
module.vmss_linux
]
}
variable "scaling_profile_vmss" {
description = "set of rules used to determine when autoscale triggers"
default = [{
capacity = 3
schedule = [{
days = ["Monday"],
start_hour = 12,
start_minute = 20,
end_hour = 12,
end_minute = 30
}]
}]
}
`
Below is the error I am receiving when running the apply.
╷ │ Error: Unsupported attribute │ │ on ..\..\variables.tf line 70, in variable "default_scaling_profile": │ 70: [for trigger in profile.trigger : │ │ Can't access attributes on a primitive-typed value (number). ╵ ╷ │ Error: Attempt to get attribute from null value │ │ on ..\..\variables.tf line 70, in variable "default_scaling_profile": │ 70: [for trigger in profile.trigger : │ │ This value is null, so it does not have any attributes. ╵ ╷ │ Error: Unsupported attribute │ │ on ..\..\variables.tf line 70, in variable "default_scaling_profile": │ 70: [for trigger in profile.trigger : │ │ Can't access attributes on a list of objects. Did you mean to access an attribute for a specific element of the list, or across all elements of the list? ╵ ╷ │ Error: Unsupported attribute │ │ on ..\..\variables.tf line 80, in variable "default_scaling_profile": │ 80: [for trigger in profile.trigger : │ │ Can't access attributes on a primitive-typed value (number). ╵ ╷ │ Error: Attempt to get attribute from null value │ │ on ..\..\variables.tf line 80, in variable "default_scaling_profile": │ 80: [for trigger in profile.trigger : │ │ This value is null, so it does not have any attributes. ╵ ╷ │ Error: Unsupported attribute │ │ on ..\..\variables.tf line 80, in variable "default_scaling_profile": │ 80: [for trigger in profile.trigger : │ │ Can't access attributes on a list of objects. Did you mean to access an attribute for a specific element of the list, or across all elements of the list?
I've rearranged the validation step several times but I continue to run into the issue of accessing attributes from a list of objects. I've nested the validation in such a way that it should be able to iterate through the trigger options. I have also created an optional default for the trigger block to allow for an empty list such that when the validation step checks for trigger not equal to an empty list, the validation proceeds as normal. However, I have the resulting errors. Any insight would be greatly appreciated.