rdblue commented on a change in pull request #2877:
URL: https://github.com/apache/iceberg/pull/2877#discussion_r682919095
##########
File path: api/src/main/java/org/apache/iceberg/util/StructProjection.java
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@@ -82,8 +85,31 @@ private StructProjection(StructType structType, StructType
projection) {
dataField.type().asStructType(),
projectedField.type().asStructType());
break;
case MAP:
+ MapType projectedMap = projectedField.type().asMapType();
+ MapType originalMap = dataField.type().asMapType();
+
+ boolean keyProjectable = !projectedMap.keyType().isStructType()
||
+ projectedMap.keyType().equals(originalMap.keyType());
+ boolean valueProjectable =
!projectedMap.valueType().isStructType() ||
+ projectedMap.valueType().equals(originalMap.valueType());
+
+ Preconditions.checkArgument(keyProjectable && valueProjectable,
+ "Cannot perform a projection of a map unless key and value
types are primitive or a " +
+ "struct which is fully projected. Trying to project %s
out of %s", projectedField, dataField);
+ nestedProjections[pos] = null;
+ break;
case LIST:
- throw new IllegalArgumentException(String.format("Cannot project
list or map field: %s", projectedField));
+ ListType projectedList = projectedField.type().asListType();
+ ListType originalList = dataField.type().asListType();
+
+ boolean elementProjectable =
!projectedList.elementType().isStructType() ||
+
projectedList.elementType().equals(originalList.elementType());
+
+ Preconditions.checkArgument(elementProjectable,
+ "Cannot perform a projection of a list unless it's element
is a primitive or a struct which is " +
Review comment:
What about something shorter, like "Cannot project a partial list
element struct: %s from %s"?
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