Optionally writing to blob

I am trying to set up an azure function that would write into a blob only if a function is fulfilled. The blob is int he same location as the function, so I am trying to avoid providing a connection string and do this with bindings. I am currently using binding something like the following:

[Blob("folder/myFile.json", FileAccess.Write)]Stream writeBlob

With this binding, I can write into the JSON file using:

if (myCondition)
    using (var writer = new StreamWriter(writeBlob)) 
        writer.Write(myContent);

This works fine when the condition is true. However, when the condition is false, the file gets empty. Since I am not writing to the stream, I expected the file to stay untouched. Right now my workaround is to have another read binding to the same json and rewrite the file contents.

You can use dynamic binding in your case. See this post for more information:

• How do I use Binder to perform dynamic bindings in my C# Function?

So basically you need to:

• Add a IBinder binder parameter in your function definition.
• When your condition is true, write your file:

  if (myCondition)
  {
      var binding= new BlobAttribute(blobPath: "folder/myFile.json");
      using (var writer = binder.Bind<TextWriter>(binding))
      {
          writer.Write(myContent);
      }
  }