How to Handel large data like 50 lac characters support in Base64 binary in Binary FHIR Resource ? i

The issue arises from attempting to deserialize large data in a FHIR Binary resource that exceeds the maximum local string length (3641144 characters). InterSystems IRIS signals a <MAXSTRING> error when object string data exceeds this limit but commonly offers solutions as follows:

1. ObjectStream Usage:
   You can use the %Stream class (e.g., %Stream.DynamicBinary for binary data or %Stream.DynamicCharacter for characters) to handle very large strings. Change the Binary class property that currently holds data using %String format to %Stream. This avoids exceeding the maximum length in memory and limits signal triggers caused by JSONAdapter calling deprecated %FromStream at dynamic fields.[1]

   Re-creation example:

   • Conversion workaround steps:
     Appropriate substitution methods e.g.:

   -For managing the actual parsed content:

     zConvertStream+ INSTEAD workaround binary first parsing+:

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To address the issue with <MAXSTRING> in the FHIR Binary resource involving Base64 encoded content, the following solutions are recommended:

1. Use Streams Instead of Strings:
   Update your code to use stream classes (%Stream.DynamicBinary or %Stream.DynamicCharacter) for handling large data fields instead of %Binary (which maps to %String). Using streams allows handling strings that exceed the maximum length allocated for ObjectScript strings [2][3].

   This can be implemented by defining a method to set the Binary resource using streams, as shown:

   ClassMethod SetBinaryR4(json As %DynamicObject) {
      Set obj = ##class(HS.FHIR.DTL.vR4.Model.Resource.Binary).%New()
      Set obj.contentType = json.contentType
      // Convert large data field to stream
      Set dataAsStrm = json.%Get("data",,"stream")
      Set obj.data = dataAsStrm
      Set obj.id = json.id
   }
   

   This approach bypasses <MAXSTRING> errors by storing the large content (Base64 encoded) in memory-efficient streams [3].

2. Refactor %GetNext Usage:
   Modify all usages of the %GetNext method in your adapter classes. The %GetNext(.key, .value) method triggers a <MAXSTRING> error if the value exceeds the string length limit. Instead, use the three-argument form %GetNext(.key, .value, .type). This ensures that the returned value is a %Stream object when the content type is "string" [2][3].

   Example Update:

   While iter.%GetNext(.Name, .Value, .Type) {
      If .Type="string" {
          // Handle value as stream
      }
   }
   

3. Workflow for Transformations:
   Create a workaround where:

   • You replace large Base64 strings in the JSON with placeholders.
   • Perform DTL transformations excluding large strings.
   • Reintroduce Base64 strings using %Stream just before submission to the FHIR server [3].

Implementing the above adjustments would eliminate the likelihood of encountering the <MAXSTRING> error while handling large FHIR Binary resources containing Base64 data.

Sources:

`Hi Rutvik

You can handle this error with below code. Some sample code

swt datatype "stream"
While iter.%GetNext(.key, .value, .datatype) {
}

If you want to get the values as a stream from DynamicObject Use %Get(key,,"stream") 

set stream = dao.%Get(key,,"stream")

This 3rd parameter support in %GetNext() and %Get()  from 2022 version

There is a specific reason for using this custom code instead of relying on the built-in %FromJSON() method. The third argument is currently not implemented in the following ##class(HS.FHIR.DTL.vR4.Model.Resource.Binary).%FromJSON(fhirresourceStream)

ClassMethod SetBinaryR4(json As %DynamicObject) {
   Set obj = ##class(HS.FHIR.DTL.vR4.Model.Resource.Binary).%New()
   Set obj.contentType = json.contentType
   // Convert large data field to stream
   Set dataAsStrm = json.%Get("data",,"stream")
   Set obj.data = dataAsStrm
   Set obj.id = json.id
}

Thank you!