[GitHub] [beam] pabloem commented on a change in pull request #15566: [BEAM-12925] Correct behavior retrieving NULL values from JDBC.

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pabloem commented on a change in pull request #15566:
URL: https://github.com/apache/beam/pull/15566#discussion_r715219964



##########
File path: sdks/java/io/jdbc/src/main/java/org/apache/beam/sdk/io/jdbc/SchemaUtil.java
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@@ -351,7 +351,12 @@ private BeamRowMapper(Schema schema, List<ResultSetFieldExtractor> fieldExtracto
     public Row mapRow(ResultSet rs) throws Exception {
       Row.Builder rowBuilder = Row.withSchema(schema);
       for (int i = 0; i < schema.getFieldCount(); i++) {
-        rowBuilder.addValue(fieldExtractors.get(i).extract(rs, i + 1));
+        Object value = fieldExtractors.get(i).extract(rs, i + 1);
+        if (rs.wasNull() && schema.getField(i).getType().getNullable()) {
+          rowBuilder.addValue(null);
+        } else {
+          rowBuilder.addValue(value);

Review comment:
       if the value was null and the field is not nullable, we would be setting the wrong value, right? (e.g. [for numeric columns, it would be 0](https://docs.oracle.com/javase/7/docs/api/java/sql/ResultSet.html#getShort(int))) - should we be erroring out? perhaps we should:
   
   ```
           if (rs.wasNull()) {
             rowBuilder.addValue(null);
           } else {
             rowBuilder.addValue(value);
           }
   ```
   
   what are your thoughts?
   
   fyi @reuvenlax 




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