jamesfredley commented on code in PR #16532:
URL: https://github.com/apache/grails-core/pull/16532#discussion_r4210586173
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grails-data-hibernate7/core/src/main/groovy/org/grails/orm/hibernate/cfg/domainbinding/binder/CollectionBinder.java:
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@@ -212,6 +217,34 @@ private void bindCollectionTable(HibernateToManyProperty
property, Collection co
collection.setCollectionTable(
mappings.addTable(schemaName, catalogName, tableName, null,
false, metadataBuildingContext, false));
collection.setInverse(property.isBidirectional() &&
!property.isOwningSide());
+ if (collection.isInverse()) {
+ warnIfManyToManyHasNoOwningSide(property);
+ }
+ }
+
+ /**
+ * A bidirectional many-to-many is written by its owning side, which
{@code belongsTo} designates. When neither
+ * side declares {@code belongsTo}, both sides are inverse and the
relationship is never stored, so warn about it
+ * once per relationship.
+ */
+ private void warnIfManyToManyHasNoOwningSide(HibernateToManyProperty
property) {
+ if (!(property instanceof HibernateManyToManyProperty manyToMany) ||
+ !manyToMany.isBidirectional() || manyToMany.isCircular()) {
+ return;
+ }
+ Association<?> otherSide = manyToMany.getInverseSide();
+ if (otherSide == null || otherSide.isOwningSide()) {
+ return;
+ }
+ if
(manyToMany.getOwner().getName().compareTo(otherSide.getOwner().getName()) > 0)
{
+ return;
+ }
+ LOG.warn("Neither side of the many-to-many between [{}.{}] and [{}.{}]
declares belongsTo, so the relationship " +
Review Comment:
For a Map-valued many-to-many this warning runs from `bindCollectionTable`
while `isOwningSide()` is still false. `MapSecondPassBinder` then calls
`map.setInverse(false)`, so that side writes the join table anyway. The text
says the relationship is not stored, which is not true for a map.
Skip map-valued sides, or emit the warning only after the second pass has
set the final inverse flags. Please add a regression for a bidirectional Map
many-to-many with no `belongsTo`.
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