azure-webjobs-sdk-extensions: Function app settings not read when a function is developed in portal using Cosmos DB Trigger

From @baskar3078 on November 1, 2017 2:49

When we develop a function using Cosmos DB Trigger in azure portal, the database and collection names are not read from function application settings in function.json file.

Investigative information

https://stackoverflow.com/questions/47043182/azure-functions-function-json-cosmos-trigger

Repro steps

1. Create a function using CosmosDB Trigger portal
2. Add an function application setting with Key - “cosmos-triggers-database-name” and any value
3. Update the function.json as below

{
  "bindings": [
    {
      "type": "cosmosDBTrigger",
      "name": "inputDocs",
      "direction": "in",
      "leaseDatabaseName": "leases",
      "leaseCollectionName": "MyCosmosCollection-myFunction",
      "connectionStringSetting": "CosmosTriggers-SourceAdapter",
      "databaseName": "%cosmos-triggers-database-name%",
      "collectionName": "MyCosmosCollection",
      "createLeaseCollectionIfNotExists": true
    }
  ],
  "disabled": false
}

1. Save and run the function

Expected behavior

Expected behavior is to read the document from Cosmos DB.

Actual behavior

Function ($myFunction) Error: The listener for function 'Functions.myFunction' was unable to start.
 Microsoft.Azure.WebJobs.Extensions.DocumentDB: Either the source collection 'MyCosmosCollection' (in database '%cosmos-triggers-database-name%') or the lease collection 'MyCosmosCollection-myFunction' (in database 'leases') does not exist. Both collections must exist before the listener starts. To automatically create the lease collection, set 'CreateLeaseCollectionIfNotExists' to 'true'. Microsoft.Azure.Documents.Client: Message: {"Errors":["Resource Not Found"]}
 ActivityId: b00f7802-fccb-47eb-972d-0bd70ec896c1, Request URI: rntbd://bn6prdddc05-docdb-1.documents.azure.com:14639/apps/6628b461-75d4-4e4a-9897-ada4076dc30c/services/1b0fc27a-de15-45cf-a1b2-ebfce044d1e2/partitions/34cfee55-54aa-4e31-81f4-08cf1bfdf62f/replicas/131523094168492638s/.
 Session Id: 092ccb7ce9104407bf56c26a5cc8b119
 Timestamp: 2017-10-31T19:13:03.914Z

Known workarounds

We need to explicitly mention the database and collection name in function.json file.

Related information

https://stackoverflow.com/questions/47043182/azure-functions-function-json-cosmos-trigger

Copied from original issue: Azure/azure-webjobs-sdk-script#2086