Nested loops

[ptemmer]

Hello Bicep community

I was hoping someone could share their thoughts on how he/she would implement the creation of a Service Bus using Bicep, given the following json object, passed as a parameter to the bicep template:

{
  "topics": [
    {
      "name": "agreements",
      "subscriptions": []
    },
    {
      "name": "businessentities",
      "subscriptions": [
        {
          "name": "Affinity"
        },
        {
          "name": "DataWareHouse"
        },
        {
          "name": "Group"
        },
        {
          "name": "HoldingTerminator"
        },
        {
          "name": "Optimum"
        },
        {
          "name": "Path"
        },
        {
          "name": "Pension"
        },
        {
          "name": "Securities"
        },
        {
          "name": "Visis"
        },
        {
          "name": "Zonder"
        }
      ]
    }
  ]
}

I'm able to successfully create all the service bus topics by looping over the "topics" items. However, for each topic I need to create their corresponding subscriptions. This is where I am a bit stuck as subscriptions are defined in Bicep as separate resources. It seems that below snippet is not supported, yielding an error that a nested resource cannot appear in a resource with a for-expression.

resource topic 'Microsoft.ServiceBus/namespaces/topics@2021-01-01-preview' = [for (topic, index) in serviceBusConfig.topics: {
  name: '${servicebusname}/${topic.name}'

  resource sub 'Microsoft.ServiceBus/namespaces/topics/subscriptions@2021-01-01-preview' = [for subscription in ${topic[index].subscriptions}: {
    name: '${servicebusname}/${topic.name}/${subscription.name}'
  }]
}]

[brwilkinson]

Here is another related discussion on this: #3146

The answer is that modules can make this task easier.

[ptemmer]

I managed to get it working using the suggested solution by @brwilkinson. However my for-loop breaks when it comes across an empty array in the parameters I pass in.

Example config:

"topics": [
    {
        "name": "agreements",
        "subscriptions": []
    },
    {
        "name": "businessentities",
        "subscriptions": [
            {
                "name": "Affinity"
            },
            {
                "name": "DataWareHouse"
            },
            {
                "name": "Group"
            }
        ]
    }
]

Module invocation:

module sbsub 'servicebus-subscription.bicep' =  [for sub in servicebustopic.subscriptions: if(!empty(servicebustopic.subscriptions)) {
  name: 'depl-sb-subscription_${sub.name}(${servicebustopic.name}-topic)'
  params: {
    servicebusns: servicebusnamespace
    servicebustopic: sbtopic
    subscription: sub.name
  }
}]

Erorr:

  "error": {
    "code": "InvalidTemplate",
    "message": "Deployment template validation failed: 'The template resource '[format('depl-sb-subscription_{0}({1}-topic)', parameters('servicebustopic').subscriptions[copyIndex()].name, parameters('servicebustopic').name)]' at line '1' and column '1293' is not valid: The language expression property array index '0' is out of bounds.. Please see https://aka.ms/arm-template-expressions for usage details.'.",
    "additionalInfo": [
      {
        "type": "TemplateViolation",
        "info": {
          "lineNumber": 1,
          "linePosition": 1293,
          "path": "properties.template.resources[1]"
        }
      }
    ]
  }
}

[brwilkinson]

This one is also being worked on. However in the meantime, you have to use the exact same logic on your if statement for the name property.

name: 'depl-sb-subscription_${sub.name}(${servicebustopic.name}-topic)'

i.e. since sub.name does not exist, i.e. is not present, that is what needs to be wrapped.

here is an example from the same templates from the other discussion
https://github.com/brwilkinson/AzureDeploymentFramework/blob/2083f3021d86d9865453a1772e9dd7edc28734ec/ADF/bicep/Cosmos-Account.bicep#L74

module CosmosAccountDB 'Cosmos-Account-DB.bicep'= [for (cdb, index) in cosmosAccount.databases : {
  name: 'dp${Deployment}-cosmosDBDeployDB${((length(cosmosAccount.databases) != 0) ? cdb.databaseName : 'na')}'

then yours ... something like below (I didn't test it, however you can see the logic added to wrap the sub.name, or else use empty.).

module sbsub 'servicebus-subscription.bicep' =  [for sub in servicebustopic.subscriptions: if(!empty(servicebustopic.subscriptions)) {
  name: 'depl-sb-subscription_${!empty(servicebustopic.subscriptions) ? sub.name : 'empty'}(${servicebustopic.name}-topic)'

[alex-frankel]

FYI - relevant issue is tracked with #1754

[ptemmer]

Sweet! Works now. LOL, I did notice that in the example you referred to, however I didn't get what that was all about...Thought it was something specific for your deployment :-)

[brwilkinson]

Nice. The deployment creates a resource graph right up front, so that is why the name is required. It will just be too easy once Bicep takes care of that for you, however the code will be much cleaner. 😎