[GitHub] [avro] RyanSkraba commented on a change in pull request #1097: AVRO-2872: Fix bug in SpecificCompiler which prevents Logical Types being registered for union fields

[GitBox <gi...@apache.org>]

RyanSkraba commented on a change in pull request #1097:
URL: https://github.com/apache/avro/pull/1097#discussion_r612363711



##########
File path: lang/java/avro/src/main/java/org/apache/avro/LogicalType.java
##########
@@ -89,4 +91,36 @@ public void validate(Schema schema) {
     }
   }
 
+  /**
+   * Utility function to resolve the logical type from the given Schema
+   * 
+   * @param schema a Schema representing a logical type
+   * @return the logical type represented by the schema, or null if the schema
+   *         doesn't represent a logical type, or if the logical type is ambiguous
+   */
+  public static LogicalType resolveLogicalType(Schema schema) {
+    if (schema.getLogicalType() != null) {
+      return schema.getLogicalType();
+    } else if (schema.isUnion()) {
+      List<Schema> types = schema.getTypes();
+      if (types.size() == 1) {
+        // The union has a single branch that may or may not be a logical type - return
+        // it either way
+        return types.get(0).getLogicalType();
+      } else if (types.size() == 2) {
+        // The union has exactly two branches.
+        // If one branch is null and one is a logical type, return the logical type,
+        // else return neither
+        LogicalType t1 = types.get(0).getLogicalType();
+        LogicalType t2 = types.get(1).getLogicalType();
+        if (t1 != null && t2 == null) {

Review comment:
       I don't think this is correct either!
   
   If t1 is an `Schema.Type.STRING` and t2 is a logicalType `timestamp-millis`, for example, this won't return the right answer.




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