[GitHub] [iceberg] rdblue commented on a change in pull request #1353: Core: check that cannot project schema when selected columns is specified

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

rdblue commented on a change in pull request #1353:
URL: https://github.com/apache/iceberg/pull/1353#discussion_r472550187



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File path: core/src/main/java/org/apache/iceberg/BaseTableScan.java
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@@ -159,6 +159,10 @@ public TableScan option(String property, String value) {
 
   @Override
   public TableScan project(Schema projectedSchema) {
+    if (context.selectedColumns() != null) {
+      throw new IllegalStateException("Cannot project schema when selected columns is specified.");
+    }

Review comment:
       We would normally use a `Precondition` check here:
   
   ```java
   Preconditions.checkState(context.selectedColumns() == null, "Cannot ...");
   ```
   
   I was also going to say that I think we should check the reverse as well, in case `project` is called before `select`, but it looks like the projection is tracked outside of the context for some reason. I don't think that's quite right. We probably want to move `project` to the context as well.
   
   @edgarRd, do you know why `project` doesn't use the scan context?




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