Render items for collection-like properties when deriving $jsonSchema.

Closes #3766
Original pull request: #3837.

Author: christophstrobl

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MappingMongoJsonSchemaCreator.java

@@ -27,11 +27,11 @@
 import org.springframework.data.mapping.PersistentProperty;
 import org.springframework.data.mapping.context.MappingContext;
 import org.springframework.data.mongodb.core.convert.MongoConverter;
-import org.springframework.data.mongodb.core.mapping.BasicMongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.Encrypted;
 import org.springframework.data.mongodb.core.mapping.Field;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
+import org.springframework.data.mongodb.core.schema.IdentifiableJsonSchemaProperty.ArrayJsonSchemaProperty;
 import org.springframework.data.mongodb.core.schema.IdentifiableJsonSchemaProperty.EncryptedJsonSchemaProperty;
 import org.springframework.data.mongodb.core.schema.IdentifiableJsonSchemaProperty.ObjectJsonSchemaProperty;
 import org.springframework.data.mongodb.core.schema.JsonSchemaObject;
@@ -160,15 +160,15 @@ private JsonSchemaProperty computeSchemaForProperty(List<MongoPersistentProperty
 		Class<?> rawTargetType = computeTargetType(property); // target type before conversion
 		Class<?> targetType = converter.getTypeMapper().getWriteTargetTypeFor(rawTargetType); // conversion target type
 
-		if (property.isEntity() && ObjectUtils.nullSafeEquals(rawTargetType, targetType)) {
+		if (!isCollection(property) && property.isEntity() && ObjectUtils.nullSafeEquals(rawTargetType, targetType)) {
 			return createObjectSchemaPropertyForEntity(path, property, required);
 		}
 
 		String fieldName = computePropertyFieldName(property);
 
 		JsonSchemaProperty schemaProperty;
-		if (property.isCollectionLike()) {
-			schemaProperty = createSchemaProperty(fieldName, targetType, required);
+		if (isCollection(property)) {
+			schemaProperty = createSchemaPropertyForCollection(fieldName, property, required);
 		} else if (property.isMap()) {
 			schemaProperty = createSchemaProperty(fieldName, Type.objectType(), required);
 		} else if (ClassUtils.isAssignable(Enum.class, targetType)) {
@@ -180,6 +180,48 @@ private JsonSchemaProperty computeSchemaForProperty(List<MongoPersistentProperty
 		return applyEncryptionDataIfNecessary(property, schemaProperty);
 	}
 
+	private JsonSchemaProperty createSchemaPropertyForCollection(String fieldName, MongoPersistentProperty property,
+			boolean required) {
+
+		ArrayJsonSchemaProperty schemaProperty = JsonSchemaProperty.array(fieldName);
+
+		if (property.getActualType() != Object.class) {
+
+			MongoPersistentEntity<?> persistentEntity = mappingContext
+					.getPersistentEntity(property.getTypeInformation().getComponentType());
+
+			if (persistentEntity == null) {
+
+				if (ClassUtils.isAssignable(Enum.class, property.getActualType())) {
+
+					List<Object> possibleValues = new ArrayList<>();
+
+					for (Object enumValue : EnumSet.allOf((Class) property.getActualType())) {
+						possibleValues.add(converter.convertToMongoType(enumValue));
+					}
+
+					Class targetType = possibleValues.isEmpty() ? property.getActualType()
+							: possibleValues.iterator().next().getClass();
+					schemaProperty = schemaProperty
+							.items(Collections.singleton(JsonSchemaObject.of(targetType).possibleValues(possibleValues)));
+				} else {
+					schemaProperty = schemaProperty.items(Collections.singleton(JsonSchemaObject.of(property.getActualType())));
+				}
+			} else {
+
+				List<JsonSchemaProperty> nestedProperties = computePropertiesForEntity(Collections.emptyList(),
+						persistentEntity);
+
+				if (!nestedProperties.isEmpty()) {
+					schemaProperty = schemaProperty.items(Collections
+							.singleton(JsonSchemaObject.object().properties(nestedProperties.toArray(new JsonSchemaProperty[0]))));
+				}
+			}
+		}
+
+		return createPotentiallyRequiredSchemaProperty(schemaProperty, required);
+	}
+
 	@Nullable
 	private JsonSchemaProperty applyEncryptionDataIfNecessary(MongoPersistentProperty property,
 			JsonSchemaProperty schemaProperty) {
@@ -197,7 +239,6 @@ private JsonSchemaProperty applyEncryptionDataIfNecessary(MongoPersistentPropert
 			enc = enc.keys(property.getEncryptionKeyIds());
 		}
 		return enc;
-
 	}
 
 	private JsonSchemaProperty createObjectSchemaPropertyForEntity(List<MongoPersistentProperty> path,
@@ -268,6 +309,10 @@ private Class<?> computeTargetType(PersistentProperty<?> property) {
 		return mongoProperty.getFieldType() != mongoProperty.getActualType() ? Object.class : mongoProperty.getFieldType();
 	}
 
+	private static boolean isCollection(MongoPersistentProperty property) {
+		return property.isCollectionLike() && !property.getType().equals(byte[].class);
+	}
+
 	static JsonSchemaProperty createPotentiallyRequiredSchemaProperty(JsonSchemaProperty property, boolean required) {
 
 		if (!required) {

Diff for: spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/MappingMongoJsonSchemaCreatorUnitTests.java

@@ -185,6 +185,9 @@ enum JustSomeEnum {
 			"        'arrayProperty' : { 'type' : 'array' }," + //
 			"        'binaryDataProperty' : { 'bsonType' : 'binData' }," + //
 			"        'collectionProperty' : { 'type' : 'array' }," + //
+			"        'simpleTypeCollectionProperty' : { 'type' : 'array', 'items' : { 'type' : 'string' } }," + //
+			"        'complexTypeCollectionProperty' : { 'type' : 'array', 'items' : { 'type' : 'object', 'properties' : { 'field' : { 'type' : 'string'} } } }" + //
+			"        'enumTypeCollectionProperty' : { 'type' : 'array', 'items' : " + JUST_SOME_ENUM + " }" + //
 			"        'mapProperty' : { 'type' : 'object' }," + //
 			"        'objectProperty' : { 'type' : 'object' }," + //
 			"        'enumProperty' : " + JUST_SOME_ENUM + "     }" + //
@@ -203,12 +206,19 @@ static class VariousFieldTypes {
 		Date dateProperty;
 		Object[] arrayProperty;
 		byte[] binaryDataProperty;
-		List<String> collectionProperty;
+		List<Object> collectionProperty;
+		List<String> simpleTypeCollectionProperty;
+		List<SomeDomainType> complexTypeCollectionProperty;
+		List<JustSomeEnum> enumTypeCollectionProperty;
 		Map<String, String> mapProperty;
 		Object objectProperty;
 		JustSomeEnum enumProperty;
 	}
 
+	static class SomeDomainType {
+		String field;
+	}
+
 	// --> NESTED DOMAIN TYPE
 
 	static final String WITH_NESTED_DOMAIN_TYPE = "" + //