jayzhan211 commented on code in PR #14057: URL: https://github.com/apache/datafusion/pull/14057#discussion_r1933220974
########## datafusion-examples/examples/metadata_columns.rs: ########## @@ -0,0 +1,330 @@ +// 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::any::Any; +use std::fmt::{self, Debug, Formatter}; +use std::sync::{Arc, Mutex}; +use std::time::Duration; + +use arrow::array::{ArrayRef, StringArray, UInt64Array}; +use arrow_schema::SchemaBuilder; +use async_trait::async_trait; +use datafusion::arrow::array::{UInt64Builder, UInt8Builder}; +use datafusion::arrow::datatypes::{DataType, Field, Schema, SchemaRef}; +use datafusion::arrow::record_batch::RecordBatch; +use datafusion::datasource::{TableProvider, TableType}; +use datafusion::error::Result; +use datafusion::execution::context::TaskContext; +use datafusion::physical_expr::EquivalenceProperties; +use datafusion::physical_plan::execution_plan::{Boundedness, EmissionType}; +use datafusion::physical_plan::memory::MemoryStream; +use datafusion::physical_plan::{ + project_schema, DisplayAs, DisplayFormatType, ExecutionPlan, Partitioning, + PlanProperties, SendableRecordBatchStream, +}; + +use datafusion::prelude::*; + +use datafusion::catalog::Session; +use datafusion_common::METADATA_OFFSET; +use itertools::Itertools; +use tokio::time::timeout; + +/// This example demonstrates executing a simple query against a custom datasource +#[tokio::main] +async fn main() -> Result<()> { + // create our custom datasource and adding some users + let db = CustomDataSource::default(); + db.populate_users(); + + search_accounts(db.clone(), "select * from accounts", 3).await?; + search_accounts( + db.clone(), + "select _rowid, _file, * from accounts where _rowid > 1", + 1, + ) + .await?; + search_accounts( + db.clone(), + "select _rowid, _file, * from accounts where _file = 'file-0'", + 1, + ) + .await?; + + Ok(()) +} + +async fn search_accounts( + db: CustomDataSource, + sql: &str, + expected_result_length: usize, +) -> Result<()> { + // create local execution context + let ctx = SessionContext::new(); + ctx.register_table("accounts", Arc::new(db)).unwrap(); + let options = SQLOptions::new().with_allow_ddl(false); + + timeout(Duration::from_secs(10), async move { + let dataframe = ctx.sql_with_options(sql, options).await.unwrap(); + let result = dataframe.collect().await.unwrap(); + let record_batch = result.first().unwrap(); + + assert_eq!(expected_result_length, record_batch.column(1).len()); + dbg!(record_batch.columns()); + }) + .await + .unwrap(); + + Ok(()) +} + +/// A User, with an id and a bank account +#[derive(Clone, Debug)] +struct User { + id: u8, + bank_account: u64, +} + +/// A custom datasource, used to represent a datastore with a single index +#[derive(Clone)] +pub struct CustomDataSource { + inner: Arc<Mutex<CustomDataSourceInner>>, + metadata_columns: SchemaRef, +} + +struct CustomDataSourceInner { + data: Vec<User>, +} + +impl Debug for CustomDataSource { + fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result { + f.write_str("custom_db") + } +} + +impl CustomDataSource { + pub(crate) async fn create_physical_plan( + &self, + projections: Option<&Vec<usize>>, + schema: SchemaRef, + ) -> Result<Arc<dyn ExecutionPlan>> { + Ok(Arc::new(CustomExec::new(projections, schema, self.clone()))) + } + + pub(crate) fn populate_users(&self) { + self.add_user(User { + id: 1, + bank_account: 9_000, + }); + self.add_user(User { + id: 2, + bank_account: 100, + }); + self.add_user(User { + id: 3, + bank_account: 1_000, + }); + } + + fn add_user(&self, user: User) { + let mut inner = self.inner.lock().unwrap(); + inner.data.push(user); + } +} + +impl Default for CustomDataSource { + fn default() -> Self { + CustomDataSource { + inner: Arc::new(Mutex::new(CustomDataSourceInner { + data: Default::default(), + })), + metadata_columns: Arc::new(Schema::new(vec![ + Field::new("_rowid", DataType::UInt64, false), + Field::new("_file", DataType::Utf8, false), + ])), + } + } +} + +#[async_trait] +impl TableProvider for CustomDataSource { + fn as_any(&self) -> &dyn Any { + self + } + + fn schema(&self) -> SchemaRef { + SchemaRef::new(Schema::new(vec![ + Field::new("id", DataType::UInt8, false), + Field::new("bank_account", DataType::UInt64, true), + ])) + } + + fn metadata_columns(&self) -> Option<SchemaRef> { + Some(self.metadata_columns.clone()) + } + + fn table_type(&self) -> TableType { + TableType::Base + } + + async fn scan( + &self, + _state: &dyn Session, + projection: Option<&Vec<usize>>, Review Comment: Field related API is also widely used, if we want to make `METADATA_OFFSET` private. We have two options: either introduce a breaking change or add field_with_meta, which could also create confusion for the user ```rust /// Returns an immutable reference of a specific `Field` instance selected using an /// offset within the internal `fields` vector pub fn field(&self, i: usize) -> &Field { if i >= METADATA_OFFSET { if let Some(metadata) = &self.metadata { return metadata.field(i - METADATA_OFFSET); } } self.inner.field(i) } /// Returns an immutable reference of a specific `Field` instance selected using an /// offset within the internal `fields` vector and its qualifier pub fn qualified_field(&self, i: usize) -> (Option<&TableReference>, &Field) { if i >= METADATA_OFFSET { if let Some(metadata) = &self.metadata { return metadata.qualified_field(i - METADATA_OFFSET); } } self.inner.qualified_field(i) } ``` -- 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. 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