Generate unions from oneOf return type

Author: ftatzky

packages/openapi-to-graphql/src/oas_3_tools.ts

@@ -406,6 +406,13 @@ export function getSchemaTargetGraphQLType<TSource, TContext, TArgs>(
   schema: SchemaObject,
   data: PreprocessingData<TSource, TContext, TArgs>
 ): string | null {
+  if (schema.oneOf) {
+    return 'union'
+  }
+
+  if (schema.allOf) {
+    return 'object'
+  }
   // CASE: object
   if (schema.type === 'object' || typeof schema.properties === 'object') {
     // TODO: additionalProperties is more like a flag than a type itself

packages/openapi-to-graphql/src/preprocessor.ts

@@ -1504,14 +1504,10 @@ function createDataDefFromOneOf<TSource, TContext, TArgs>(
     if (
       oneOfData.allTargetGraphQLTypes.every(memberTargetGraphQLType => {
         return memberTargetGraphQLType === 'object'
-      }) &&
-      oneOfData.allProperties.length > 0 // Redundant check
+      })
     ) {
       // Ensure that parent schema is compatiable with oneOf
-      if (
-        def.targetGraphQLType === null ||
-        def.targetGraphQLType === 'object'
-      ) {
+      if (def.targetGraphQLType === 'union') {
         def.subDefinitions = []
 
         collapsedSchema.oneOf.forEach(memberSchema => {