Referencing items from other resources in loops (copy index)

[fluffy-cakes]

Does anyone know if it's possible to reference another resource that's looped over an array, which then allows a parameter field to be dynamically generated?

Looking at my reference code below; essentially I'm dynamically building out both resources via loops (copy indexing), and I would like to reference one field from the other, if it contains 'something'. Looking at routeTable in the 2nd resource.

param p_vnetObject  array
param p_routeTables array


resource myRoutes 'Microsoft.Network/routeTables@2020-06-01' = [for item in p_routeTables: {
    name              : item.name
    location          : resourceGroup().location
    properties        : {
        routes        : [for subitem in item.routes: {
            name      : subitem.name
            properties: subitem.properties
        }]
    }
}]

resource vnet 'Microsoft.Network/virtualNetworks@2020-08-01' = [for (item, i) in p_vnetObject: if (item.deploy == true) {
    name                     : '${item.name}${i}'
    location                 : resourceGroup().location
    properties               : {
        addressSpace         : {
            addressPrefixes  : item.cidr
        }
        subnets              : [for subitem in item.subnets: {
            name             : subitem.name
            properties       : {
                addressPrefix: subitem.addressPrefix
                routeTable: {
                    id: myRoutes[].name == 'asdf'
                }
            }
        }]
    }
}]

[majastrz]

You can use the local loop's index i in the myRoutes[i].name expression. If i exceeds the range of the myRoutes array, you will get a failure at deployment time, though.

I feel like something is missing from the expression at:

routeTable: {
  id: myRoutes[].name == 'asdf'
}

id properties are usually strings and that expression above returns a bool type. Are you trying to conditionally set different IDs? Or something else?

[fluffy-cakes]

I think I might reference something "similar" to how I've done it in Terraform

resource "azurerm_route_table" "route_tables" {
    for_each                       = var.route_tables

    name                           = "${module.names.standard["route-table"]}-${each.value.name}"
    location                       = var.ARM_LOCATION
    resource_group_name            = "${module.names.standard["resource-group"]}-${each.value.resource_group_name}"
    disable_bgp_route_propagation  = each.value.disable_bgp_route_propagation
    tags                           = var.global_settings.tags

    dynamic "route" {
        for_each                   = each.value.route_entries

        content {
            name                   = route.value.name
            address_prefix         = route.value.prefix
            next_hop_type          = (
                contains(var.build_route_tables,each.key) &&
                local.build_mode == true && route.value.prefix == "0.0.0.0/0"
            ) ? "Internet" : route.value.next_hop_type

            next_hop_in_ip_address = (
                    contains(var.build_route_tables, each.key) && local.build_mode == true && route.value.prefix != "0.0.0.0/0" && route.value.next_hop_type == "VirtualAppliance"
                ) || (
                    contains(var.build_route_tables, each.key) && local.build_mode == false && route.value.next_hop_type == "VirtualAppliance"
                )  || (
                    contains(var.build_route_tables, each.key) == false && route.value.next_hop_type == "VirtualAppliance"
                ) ? route.value.next_hop_in_ip_address: null
        }
    }
    depends_on                     = [module.resource_groups_networking]
}

resource "azurerm_subnet_route_table_association" "special_subnets" {
    for_each = {
        for key, value in var.vnet_transit_object.specialsubnets:
            key => value
            if value.route != null
    }

    subnet_id                      = (
        each.value.name == "AzureFirewallSubnet" ||
        each.value.name == "GatewaySubnet"
    ) ? lookup(module.vnet_transit.vnet_subnets, each.value.name, null) : lookup(module.vnet_transit.vnet_subnets, "${module.names.standard["subnet"]}-${each.value.name}", null)

    route_table_id                 = azurerm_route_table.route_tables[lookup(each.value, "route", null)].id
}

Here we're using objects to iterate over, and the great thing about that is that the objects are given names (not indexes) for which we can reference. The very last line route_table_id is the important part, where we use the name of a azurerm_route_table object to link it together. Might I also add, please can we have something like lookup for Bicep? I am not too sure if the current Bicep will fall over if you're referencing a value that doesn't exist in an object, but as you can see with TF you can save that by passing a value if none found.

I know this is not the same, but conceptually I want to link one resource with another, or null the parameter if it doesn't exist.

This code block and the types of functions used is a good comparison for how advanced/matures Bicep is.

[majastrz]

I think adding something like lookup to both the runtime and Bicep is a great suggestion. Could you open an issue to request it? (It makes it easier for us to track and prioritize.) I think in general we're lacking some find/search/check existence functions that make things like your example harder than they need to be.

[fluffy-cakes]

Raised :)
#2065

[majastrz]

Awesome. Thank you!

[brwilkinson]

@fluffy-cakes based on you raising a new issue, I will mark this one as answered for now.