I'm on Spring boot 1.4.x branch and Spring Data MongoDB.
I want to extend a Pojo from HashMap to give it the possibility to save new properties dynamically.
I know I can create a Map<String, Object> properties in the Entry class to save inside it my dynamics values but I don't want to have an inner structure. My goal is to have all fields at the root's entry class to serialize it like that:
{
"id":"12334234234",
"dynamicField1": "dynamicValue1",
"dynamicField2": "dynamicValue2"
}
So I created this Entry class:
@Document
public class Entry extends HashMap<String, Object> {
@Id
private String id;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
}
And the repository like this:
public interface EntryRepository extends MongoRepository<Entry, String> {
}
When I launch my app I have this error:
Error creating bean with name 'entryRepository': Invocation of init method failed; nested exception is org.springframework.data.mapping.model.MappingException: Could not lookup mapping metadata for domain class java.util.HashMap!
Any idea?
TL; DR;
- Do not use Java collection/map types as a base class for your entities.
- Repositories are not the right tool for your requirement.
- Use
DBObjectwithMongoTemplateif you need dynamic top-level properties.
Explanation
Spring Data Repositories are repositories in the DDD sense acting as persistence gateway for your well-defined aggregates. They inspect domain classes to derive the appropriate queries. Spring Data excludes collection and map types from entity analysis, and that's why extending your entity from a Map fails.
Repository query methods for dynamic properties are possible, but it's not the primary use case. You would have to use SpEL queries to express your query:
public interface EntryRepository extends MongoRepository<Entry, String> {
@Query("{ ?0 : ?1 }")
Entry findByDynamicField(String field, Object value);
}
This method does not give you any type safety regarding the predicate value and only an ugly alias for a proper, individual query.
Rather use DBObject with MongoTemplate and its query methods directly:
List<DBObject> result = template.find(new Query(Criteria.where("your_dynamic_field")
.is(theQueryValue)), DBObject.class);
DBObject is a Map that gives you full access to properties without enforcing a pre-defined structure. You can create, read, update and delete DBObjects objects via the Template API.
A last thing
You can declare dynamic properties on a nested level using a Map, if your aggregate root declares some static properties:
@Document
public class Data {
@Id
private String id;
private Map<String, Object> details;
}