[jira] [Created] (FLINK-38122) Creating structured types with no fully defining constructor results in wrong results

["Ramin Gharib (Jira)" <ji...@apache.org>]

Ramin Gharib created FLINK-38122:
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             Summary: Creating structured types with no fully defining constructor results in wrong results
                 Key: FLINK-38122
                 URL: https://issues.apache.org/jira/browse/FLINK-38122
             Project: Flink
          Issue Type: Sub-task
            Reporter: Ramin Gharib


When using the OBJECT_OF function or CAST with STRUCTURED types in Flink SQL, if the target Java class does not have a fully defining constructor, the field ordering is incorrectly determined, leading to corrupted data reads from the wrong memory segments.
h4. Root Cause:


Flink's structured type extraction logic (in DataTypeExtractor.createStructuredTypeAttributes()) falls back to alphabetical field ordering when no constructor is present, rather than preserving the order of field declarations. This causes a mismatch between the expected field layout and the actual memory layout when creating structured objects.
h4. Current Behavior:

 
{code:java}
// Without constructor - fields are ordered alphabetically: [age, name] public static class User {    
    public String name;  // Declared first    
    public int age;      // Declared second
} {code}
When using:
{code:java}
SELECT OBJECT_OF('com.example.User', 'name', 'Alice', 'age', 30) {code}
The system creates a structured type with field order [age, name] (alphabetical), but assigns values in the order [name, age] (as specified), resulting in memory corruption. It outputs:
{code:java}
User info: +I[User{name='                Alice  �             ', age=1667853377}]{code}
 

 
h4. Workaround:

Add a fully defining constructor that explicitly defines field order:


 
{code:java}
public static class User {
    public String name;
    public int age;
    
    // Fully defining constructor enforces field order
    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }
} {code}
 

 
h4. Analysis:

The issue is in [flink-table-common/src/main/java/org/apache/flink/table/types/extraction/DataTypeExtractor.java at lines 655-668|https://github.com/raminqaf/flink/blob/master/flink-table/flink-table-common/src/main/java/org/apache/flink/table/types/extraction/DataTypeExtractor.java#L669-L669]:

 
{code:java}
private DataTypes.Field[] createStructuredTypeAttributes(
        ExtractionUtils.AssigningConstructor constructor,
        Map<String, DataType> fieldDataTypes) {
    return Optional.ofNullable(constructor)
            .map(c -> c.parameterNames.stream())  // Uses constructor order
            .orElseGet(() -> fieldDataTypes.keySet().stream().sorted())  // ← PROBLEM: Alphabetical sort
            .map(name -> DataTypes.FIELD(name, fieldDataTypes.get(name)))
            .toArray(DataTypes.Field[]::new);
} {code}
 

 
 
 
 
 



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