Getting exception in MappingMongoConverter while trying to map array of string into string

[packageman]

When I upgrade spring-data-mongodb from 3.1.8 to 3.3.5, I encountered below exception:

org.springframework.data.mapping.MappingException: Cannot convert [a, b, c] of type class java.util.ArrayList into an instance of class java.lang.String! Implement a custom Converter<class java.util.ArrayList, class java.lang.String> and register it with the CustomConversions. Parent object was: MemberGroup(id=6271f70e87d74d524481a418, accountId=5b036b566e2bdaa2074b0101, proposedGroupId=null, name=byron-test-9, description=Byron Test 18, type=portal, conditionGroups=[MemberGroup.MemberGroupConditionGroup(name=null, conjunction=OR, conditions=[MemberGroup.MemberGroupCondition(type=EVENT, filters=[Filter(type=STRING, field=properties.channelId, operator=IN, value=[5ad411ab6f82dc001f2420f0], caseSensitive=null, aggregation=null, expression=null, isEditable=null, editableFields=null, extra=null, fieldForSql=null), Filter(type=STRING, field=name, operator=EQUALS, value=maievent-subscribe, caseSensitive=false, aggregation=null, expression=null, isEditable=null, editableFields=null, extra=null, fieldForSql=null)])], isEditable=null, editableFields=null)], memberCount=7, computingAt=null, computedAt=2022-05-27T20:44:04.858, editedAt=null, isEnabled=true, dontCompute=false, inDeveloperMode=false, isDeleted=false, dataSource=null, distributorId=null, distributorIds=null, createdBy=null, events=null) -> null
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter$ConversionContext.convert(MappingMongoConverter.java:2044)
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter$MongoDbPropertyValueProvider.getPropertyValue(MappingMongoConverter.java:1779)
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.readProperties(MappingMongoConverter.java:512)
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.populateProperties(MappingMongoConverter.java:425)
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.read(MappingMongoConverter.java:394)
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.readDocument(MappingMongoConverter.java:356)
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.read(MappingMongoConverter.java:292)
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.read(MappingMongoConverter.java:288)
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.read(MappingMongoConverter.java:107)
	at org.springframework.data.mongodb.core.MongoTemplate$ReadDocumentCallback.doWith(MongoTemplate.java:3207)
	at org.springframework.data.mongodb.core.MongoTemplate.executeFindOneInternal(MongoTemplate.java:2822)
	at org.springframework.data.mongodb.core.MongoTemplate.doFindOne(MongoTemplate.java:2529)
	at org.springframework.data.mongodb.core.MongoTemplate.findOne(MongoTemplate.java:811)
	at org.springframework.data.mongodb.core.MongoTemplate.findOne(MongoTemplate.java:798)
	at com.xxx.bigdata.repository.BaseRepository.getOneById(BaseRepository.java:102)
	at java.lang.invoke.MethodHandle.invokeWithArguments(MethodHandle.java:627)

Checked MappingMongoConverter.java commit history, I found out that this commit caused the above exception. It seems that this commit is just doing refactoring, not to change the program execution behavior.

So is the above exception an intentional change or a bug caused by refactoring?

[christophstrobl]

It is hard to tell what actually causes the problem by just looking at the exception message without the context the conversion is running in. Please take the time to provide a complete minimal sample (something that we can unzip or git clone, build, and deploy) that reproduces the problem.

[packageman]

I wrote a demo application, you may need:

• update mongo uri accordingly in config/MongoConfig.java.
• insert test data (db.user.insert({"_id" : ObjectId("644755d3e3e11b27f1997ff5"), "name" : "test", "age" : 20, "favorites" : ["swimming", "football"]})) in mongodb.
• run ./mvnw spring-boot:run
• run curl localhost:8080/test to see the result (it will succeed because currently the app is running with spring-data-mongodb-3.1.8).
• add spring-data-mongodb-3.3.5 dependency in pom.xml to make the newer version take effect and test again, you will see an exception occurs.

spring-mongodb-test.tar.gz

[christophstrobl]

@packageman thanks for the reproducer.