Hi JB, The Java objects you mentioned should either belong to the service/business layer or be unnecessary. Apart from the business entities in Polaris, each backend will maintain its own set of persistence-layer entities. The backend implementations (whether Postgres, FDB, or MongoDB) will be responsible for mapping between these persistence-layer entities and the business entities. Currently, the business entity set is tightly coupled with FDB, which is not ideal for supporting multiple backends. While we can refactor them, creating an entirely new set of business entities is not required.
Regarding the PolarisStore you mentioned, it functions similarly to the DAO layer in the POC. It'd make more sense to split its responsibilities into separate interfaces rather than combining them into a single one. A single interface violates the Single Responsibility Principle and may lead to maintenance challenges as we introduce new data access patterns. For instance, we would be forced to continuously add new methods to accommodate additional entities like Policy and Volume, or to support new query patterns for existing entities. As for choosing between record or immutable classes, either is fine. But I'd prefer to use any native Java feature if possible. Yufei On Mon, Feb 17, 2025 at 9:10 AM Michael Collado <collado.m...@gmail.com> wrote: > I prefer native Java constructs over third party libraries and compiler > plugins, whenever possible. I’m a fan of Java records. > > Mike > > On Mon, Feb 17, 2025 at 6:55 AM Jean-Baptiste Onofré <j...@nanthrax.net> > wrote: > > > Hi Robert, > > > > Yes, my intention about Java records (e.g. > > https://openjdk.org/jeps/395) is to leverage: > > - Devise an object-oriented construct that expresses a simple > > aggregation of values. > > - Focus on modeling immutable data rather than extensible behavior. > > - Automatically implement data-driven methods such as equals and > accessors. > > - Preserve long-standing Java principles such as nominal typing and > > migration compatibility. > > - Provide inner builder, optionally with technical validation > > (Objects.NotNull, etc), for instance: > > > > public record CatalogDAO(String id, String name, ...) { > > > > public static final class Builder { > > String id; > > String name; > > public Builder() {} > > public Builder id(String id) { > > this.id = id; > > return this; > > } > > public Builder name(String name) { > > this.name = name; > > return this; > > } > > public CatalogDAO build() { > > return new CatalogDAO(id, name); > > } > > } > > > > } > > NB: that's just a "raw" example :) > > > > That could help us for the "DAO" layer, with clean isolation and data > > "transport". The "conversion" from Polaris Entity to DAO could be > > performed by the intermediate logic layer (e.g. > > PolarisMetaStoreManager), the pure persistence layer can deal with DAO > > only (e.g. PolarisStore). > > > > Good point about immutable collections. In some projects, I "force" > > the copy of a collection to ensure immutability, something like: > > > > record NamespaceDAO(Set<String> children) { > > public NamespaceDAO { > > children = Set.copyOf(children); > > } > > } > > > > OK, that's not super elegant :) but it does the trick ;) > > > > Regards > > JB > > > > On Mon, Feb 17, 2025 at 5:28 PM Robert Stupp <sn...@snazy.de> wrote: > > > > > > Agree with JB, except I think "immutables" serves the need much better. > > > Java records are okay, but do not ensure that all fields are immutable > - > > > especially collections. The other pro of immutables is that there are > > > proper, descriptive builders - hence no need to constructors with a > > > gazillion parameters. > > > > > > On 17.02.25 11:42, Jean-Baptiste Onofré wrote: > > > > Hi Yufei > > > > > > > > I left comments in the PR. > > > > > > > > Thanks for that. That's an interesting approach but slightly > different > > > > to what I had in mind. > > > > > > > > My proposal was: > > > > > > > > 1. The DAOs are Java records clearly descriptive, without "storage > > operations". > > > > For instance, we can imagine: > > > > > > > > public record CatalogDao(String id, String name, String location, > ...) > > { > > > > ... > > > > } > > > > > > > > public record NamespaceDao(String id, String name, String parent, > ...) > > {} > > > > > > > > public record TableDao(String id, String name, ...) {} > > > > > > > > etc > > > > > > > > The advantages are: > > > > - very simple and descriptive > > > > - common to any backend implementation > > > > > > > > 2. The PolarisStore defines the DAO backend operations and mapping to > > > > "internal" Polaris entities. Each persistence adapter implements the > > > > PolarisStore. > > > > For the persistence adapter implementer, he just has to implement the > > > > DAO persistence (no need to understand other Polaris parts). > > > > Each persistence adapter is in its own module (for isolation and > > dependencies). > > > > > > > > During the Polaris Persistence Meeting last week, we already got > > > > consensus on the approach proposed by Dennis and I. I propose to do a > > > > new sync/review with Dennis. > > > > > > > > Regards > > > > JB > > > > > > > > On Mon, Feb 17, 2025 at 9:40 AM Yufei Gu <flyrain...@gmail.com> > wrote: > > > >> Hi Folks: > > > >> > > > >> Here is a POC for persistence layer refactor. Please check it out > and > > let > > > >> me know what you think. Please note this is a POC, we still need a > > lot of > > > >> effort to complete the refactor. > > > >> > > > >> PR: https://github.com/apache/polaris/pull/1011. > > > >> Design doc: > > > >> > > > https://docs.google.com/document/d/1Vuhw5b9-6KAol2vU3HUs9FJwcgWtiVVXMYhLtGmz53s/edit?tab=t.0 > > > >> > > > >> Experiment: > > > >> > > > >> - Added a DAO layer for the business entity namespace(except the > > read). > > > >> - Integrated with existing DAO components > > (PolarisMetaStoreManager and > > > >> PolarisMetaStoreSession). > > > >> - All tests passed successfully, including a manual local run > > with Spark > > > >> sql. > > > >> > > > >> Benefits: > > > >> > > > >> - Compatible with the existing backend(FDB), as we hide it > behind > > the > > > >> new DAO. > > > >> - Adding new backends(Postgres/MongoDB) is much easier now, esp > > for > > > >> Postgres, we could be able to use a similar model as Iceberg > Jdbc > > catalog. > > > >> - Allows gradual refactoring to remove old DAO dependencies > > > >> (PolarisMetaStoreManager and PolarisMetaStoreSession). > > > >> - Enables parallel development of new backend implementations. > > > >> > > > >> Next Steps: > > > >> > > > >> - Define business entities one by one to decouple them from FDB. > > > >> - Create DAO interfaces for each entity to standardize > operations > > (e.g., > > > >> CRUD, ID generation). > > > >> - Expand DAO implementations to support additional backends over > > time. > > > >> > > > >> > > > >> > > > >> > > > >> Yufei > > > > > > -- > > > Robert Stupp > > > @snazy > > > > > >
