Unwrap nested collections in default Querydsl binding.

When binding values to collection-like paths, we now unwrap potentially double-wrapped collections as QuerydslPredicateBuilder attempts to convert the binding value to the type of the path.

Our default is a contains binding for single elements.

Closes #2834

src/main/java/org/springframework/data/querydsl/binding/QuerydslDefaultBinding.java

@@ -59,7 +59,16 @@ class QuerydslDefaultBinding implements MultiValueBinding<Path<? extends Object>
 			BooleanBuilder builder = new BooleanBuilder();
 
 			for (Object element : value) {
-				builder.and(((CollectionPathBase) path).contains(element));
+
+				if (element instanceof Collection<?> nestedCollection) {
+
+					for (Object nested : nestedCollection) {
+						builder.and(((CollectionPathBase) path).contains(nested));
+					}
+				} else {
+					builder.and(((CollectionPathBase) path).contains(element));
+				}
+
 			}
 
 			return Optional.of(builder.getValue());

src/test/java/org/springframework/data/querydsl/binding/QuerydslDefaultBindingUnitTests.java

@@ -22,13 +22,15 @@ import java.util.Collections;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
-
 import org.springframework.data.querydsl.QUser;
 
 /**
+ * Unit tests for {@link QuerydslDefaultBinding}.
+ *
  * @author Christoph Strobl
  * @author Oliver Gierke
  * @author Colin Gao
+ * @author Mark Paluch
  */
 class QuerydslDefaultBindingUnitTests {
 
@@ -64,6 +66,14 @@ class QuerydslDefaultBindingUnitTests {
 		assertThat(predicate).hasValue(QUser.user.nickNames.contains("dragon reborn"));
 	}
 
+	@Test // GH-2834
+	void shouldUnwrapNestedCollectionsWithContainingWhenPropertyIsCollectionLike() {
+
+		var predicate = binding.bind(QUser.user.nickNames, Collections.singleton(Collections.singleton("dragon reborn")));
+
+		assertThat(predicate).hasValue(QUser.user.nickNames.contains("dragon reborn"));
+	}
+
 	@Test // DATACMNS-669
 	void shouldCreatePredicateWithInWhenPropertyIsAnObjectAndValueIsACollection() {
 
@@ -73,7 +83,7 @@ class QuerydslDefaultBindingUnitTests {
 	}
 
 	@Test
-	void testname() {
+	void shouldNotBindEmptyParameterCollection() {
 		assertThat(binding.bind(QUser.user.lastname, Collections.emptySet())).isNotPresent();
 	}
 

src/test/java/org/springframework/data/querydsl/binding/QuerydslPredicateBuilderUnitTests.java

@@ -19,12 +19,10 @@ import static org.assertj.core.api.Assertions.*;
 import static org.assertj.core.api.Assumptions.*;
 import static org.springframework.test.util.ReflectionTestUtils.*;
 
-import java.util.Arrays;
 import java.util.List;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
-
 import org.springframework.data.querydsl.Address;
 import org.springframework.data.querydsl.QSpecialUser;
 import org.springframework.data.querydsl.QUser;
@@ -189,9 +187,7 @@ class QuerydslPredicateBuilderUnitTests {
 
 		var predicate = builder.getPredicate(USER_TYPE, values, DEFAULT_BINDINGS);
 
-		var constant = (Constant<Object>) ((List<?>) getField(getField(predicate, "mixin"), "args")).get(0);
-
-		assertThat(constant.getConstant()).isEqualTo(Arrays.asList("Walt", "Heisenberg"));
+		assertThat(predicate).hasToString("Walt in user.nickNames && Heisenberg in user.nickNames");
 	}
 
 	@Test // GH-2649
@@ -200,9 +196,8 @@ class QuerydslPredicateBuilderUnitTests {
 		values.add("user.nickNames", "Walt,Heisenberg");
 
 		var predicate = builder.getPredicate(TypeInformation.of(UserWrapper.class), values, DEFAULT_BINDINGS);
-		var constant = (Constant<Object>) ((List<?>) getField(getField(predicate, "mixin"), "args")).get(0);
 
-		assertThat(constant.getConstant()).isEqualTo(Arrays.asList("Walt", "Heisenberg"));
+		assertThat(predicate).hasToString("Walt in userWrapper.user.nickNames && Heisenberg in userWrapper.user.nickNames");
 	}
 
 	@Test // DATACMNS-883