paul-rogers commented on a change in pull request #1383: DRILL-6613: Refactor
MaterializedField
URL: https://github.com/apache/drill/pull/1383#discussion_r204166252
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File path:
exec/vector/src/main/java/org/apache/drill/exec/record/MaterializedField.java
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@@ -49,39 +54,79 @@ private MaterializedField(String name, MajorType type,
LinkedHashSet<Materialize
this.children = children;
}
+ private MaterializedField(String name, MajorType type, int size) {
+ this(name, type, new LinkedHashSet<>(size));
+ }
+
+ private <T> void copyFrom(Collection<T> source, Function<T,
MaterializedField> transformation) {
+ Preconditions.checkState(children.isEmpty());
+ source.forEach(child -> children.add(transformation.apply(child)));
+ }
+
+ public static MaterializedField create(String name, MajorType type) {
+ return new MaterializedField(name, type, 0);
+ }
+
public static MaterializedField create(SerializedField serField) {
- LinkedHashSet<MaterializedField> children = new LinkedHashSet<>();
- for (SerializedField sf : serField.getChildList()) {
- children.add(MaterializedField.create(sf));
+ MaterializedField field = new
MaterializedField(serField.getNamePart().getName(), serField.getMajorType(),
serField.getChildCount());
+ if (OFFSETS_FIELD.equals(field)) {
+ return OFFSETS_FIELD;
}
- return new MaterializedField(serField.getNamePart().getName(),
serField.getMajorType(), children);
+ field.copyFrom(serField.getChildList(), MaterializedField::create);
+ return field;
}
- /**
- * Create and return a serialized field based on the current state.
- */
- public SerializedField getSerializedField() {
- SerializedField.Builder serializedFieldBuilder = getAsBuilder();
- for(MaterializedField childMaterializedField : getChildren()) {
-
serializedFieldBuilder.addChild(childMaterializedField.getSerializedField());
+ public MaterializedField copy() {
+ return copy(getName(), getType());
+ }
+
+ public MaterializedField copy(MajorType type) {
+ return copy(name, type);
+ }
+
+ public MaterializedField copy(String name) {
+ return copy(name, getType());
+ }
+
+ public MaterializedField copy(String name, final MajorType type) {
+ if (this == OFFSETS_FIELD) {
+ return this;
}
- return serializedFieldBuilder.build();
+ MaterializedField field = new MaterializedField(name, type,
getChildren().size());
+ field.copyFrom(getChildren(), MaterializedField::copy);
Review comment:
My point is not how things are implemented. The point is: we almost never
want to copy children when copying a `MaterializedField`. Why? Because the
consumer of that copy may be code that creates a new vector. When it does, it
will add child vectors (copies of the source vectors), and that action will add
new child fields.
This is why I said that "copy" is misleading: we need to understand the
context in which we make the copy, and possibly name the method accordingly:
"copyForNewVector", "fullCopy", "copyIfNeeded", and so on. All of these should
have comments that explain the use case that they serve.
Sorry that this is so complex; it is just the way the code has evolved. As I
recently found, it is quite hard to change entrenched code behavior, even when
it is not quite right.
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