[GitHub] [iceberg] slfan1989 commented on pull request #7008: Flink: Replace Flink Tableschema To Resolvedschema

["slfan1989 (via GitHub)" <gi...@apache.org>]

slfan1989 commented on PR #7008:
URL: https://github.com/apache/iceberg/pull/7008#issuecomment-1463014914

   > in the past we haven't added these changes because it is unclear whether Iceberg should produce a resolved schema or an unresolved schema. Can you explain the purpose of both classes, what you plan to use in this PR, and why you've made that choice?
   
   Thank you very much for your question.
   
   We can refer to this document:
   https://cwiki.apache.org/confluence/display/FLINK/FLIP-164%3A+Improve+Schema+Handling+in+Catalogs
   
   `FLIP-164` explains that `Schema` should distinguish between `unresolved` and `resolved` variant, while `TableSchema` is a hybrid between `resolved` and `unresolved` schema.
   
   `TableSchema` is split into 2 parts, `Schema` and `ResolvedSchema`.
   
   1. Schema
   ```
   Contains Unresolved fields, These fields may not be validated, for example, 
   there may be duplicate primary keys.
    Offers convenient methods to adopt columns etc. 
   
   Schema {
       static Schema.Builder newBuilder();
       List<UnresolvedColumn> getColumns();
       List<UnresolvedWatermarkSpec> getWatermarkSpecs();
       Optional<UnresolvedPrimaryKey> getPrimaryKey();
       ResolvedSchema resolve(SchemaResolver);
   }
   ```
   
   2. ResolvedSchema
   ```
   Class that is exposed by the framework at different locations for validated and complete schema.
   It replaces TableSchema
   
   ResolvedSchema {
       int getColumnCount();
       List<Column> getColumns();
       Optional<Column> getColumn(int);
       Optional<Column> getColumn(String);
       List<WatermarkSpec> getWatermarkSpecs();
       Optional<UniqueConstraint> getPrimaryKey();
       DataType toRowDataType();
       DataType toPhysicalRowDataType();
       DataType toPersistedRowDataType();
   .....
   }
   ```
   


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