How to see the repository implementation generated by Spring Data MongoDB?

Question

When is the implementation for repositories generated by Spring Data? At compile time or runtime? Can I see the implementation repository implementation generated by Spring Data?

Answer 1

tl;dr

No, for a very simple reason: there's no code generation going on. The implementation is based on proxies and a method interceptor delegating the call executions to the right places.

Details

Effectively, a method execution can be backed by 3 types of code:

1. The store specific implementation of CrudRepository. Have a look for types named Simple(Jpa|Mongo|Neo4|…)Repository (see the JPA specific one here). They have "real" implementations for all of the methods in CrudRepository and PagingAndSortingRepository.

2. Query methods are effectively executed by QueryExecutorMethodInterceptor.doInvoke(…) (see here). It's basically a 3-step-process to find the delegation target and invoke it. The actual execution is done in classes named (Jpa|Mongo|Neo4j…)QueryExecution (see this one for example).

3. Custom implementation code is called directly, also from QueryExecutorMethodInterceptor.

The only thing left is the query derivation, which consists of two major parts: method name parsing and query creation. For the former, have a look at PartTree. It takes a method name and a base type and will return you a parsed AST-like structure or throw an exception if it fails to resolve properties or the like.

The latter is implemented in classes named PartTree(Jpa|Mongo|Neo4j|…)Query and delegates to additional components for actually creating the store specific query. E.g. for JPA the interesting bits are probably in JpaQueryCreator.PredicateBuilder.build() (see here).