"Objects provided via 'anyOf' must not share identical first keys" error in Structured Output

API
1

Our response model anticipates multiple entities: e.g. EntityA or EntityB:

{
   "$defs":{
      "GenerateResponse":{
         "items":{
            "anyOf":[
               {
                  "$ref":"#/$defs/EntityA",
                  "$ref":"#/$defs/EntityB"
               }
            ]
         },
         "title":"GenerateResponse",
         "type":"array"
      },
      "EntityA":{
         "properties":{
            "field_a":{
               "items":{
                  "type":"string"
               },
               "minItems":1,
               "maxItems":4,
               "title":"Field A",
               "type":"array"
            },
         },
         "required":[
            "field_a",
         ],
         "title":"EntityA",
         "type":"object"
      },
      "EntityB":{
         "properties":{
            "field_b":{
               "items":{
                  "type":"string"
               },
               "minItems":1,
               "maxItems":4,
               "title":"Field B",
               "type":"array"
            },
         },
   },
   "properties":{
      "entities":{
         "$ref":"#/$defs/GenerateResponse"
      }
   },
   "required":[
      "entities"
   ],
   "title":"GenerateOpenAiResponse",
   "type":"object"
}

When using gpt4o with structured output, we face “Objects provided via ‘anyOf’ must not share identical first keys. Consider adding a discriminator key or rearranging the properties to ensure the first key is unique.” error.

What would be an appropriate change to the model above to workaround this?

Thanks!

3

your anyOf part seem to be incorrect.
should be like this

"anyOf": [
          {
            "$ref": "#/$defs/EntityA"
          },
          {
            "$ref": "#/$defs/EntityB"
          }
        ]