zmlcc commented on code in PR #62: URL: https://github.com/apache/paimon-rust/pull/62#discussion_r1748306164
########## crates/paimon/src/catalog/mod.rs: ########## @@ -0,0 +1,254 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +use std::collections::HashMap; +use std::fmt; +use std::hash::Hash; + +use async_trait::async_trait; +use chrono::Duration; + +use crate::error::Result; +use crate::io::FileIO; +use crate::spec::{RowType, SchemaChange, TableSchema}; + +/// This interface is responsible for reading and writing metadata such as database/table from a paimon catalog. +/// +/// Impl References: <https://github.com/apache/paimon/blob/release-0.8.2/paimon-core/src/main/java/org/apache/paimon/catalog/Catalog.java#L42> +#[async_trait] +pub trait Catalog: Send + Sync { + const DEFAULT_DATABASE: &'static str = "default"; + const SYSTEM_TABLE_SPLITTER: &'static str = "$"; + const SYSTEM_DATABASE_NAME: &'static str = "sys"; + + /// Returns the warehouse root path containing all database directories in this catalog. + fn warehouse(&self) -> &str; + + /// Returns the catalog options. + fn options(&self) -> &HashMap<String, String>; + + /// Returns the FileIO instance. + fn file_io(&self) -> &FileIO; + + /// Lists all databases in this catalog. + async fn list_databases(&self) -> Result<Vec<String>>; + + /// Checks if a database exists in this catalog. + async fn database_exists(&self, database_name: &str) -> Result<bool>; + + /// Creates a new database. + async fn create_database( + &self, + name: &str, + ignore_if_exists: bool, + properties: Option<HashMap<String, String>>, + ) -> Result<()>; + + /// Loads database properties. + async fn load_database_properties(&self, name: &str) -> Result<HashMap<String, String>>; + + /// Drops a database. + async fn drop_database( + &self, + name: &str, + ignore_if_not_exists: bool, + cascade: bool, + ) -> Result<()>; + + /// Returns a Table instance for the specified identifier. + async fn get_table(&self, identifier: &Identifier) -> Result<impl Table>; Review Comment: > > In the java version，`Table` interface represents various specialized table types. Is it possible to define a simple `Table` struct in rust ? What about returning `Box<dyn Table>` instead? > > Maybe we will not use `dyn`, when returning `Box<dyn Table>` has some error like `error[E0404]: expected trait, found struct Table`. In Rust, `dyn` is used for dynamic dispatch with trait objects. Why `Box<dyn Table>` would give `error[E0404]` ? It should not when using properly. I think in many cases, the return value of `get_table` needs to be downcast to a concrete type, so it makes sense to use `dyn Table`. Alternatively, maybe using `enum Table` is feasible -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
