LLDay commented on code in PR #20222: URL: https://github.com/apache/datafusion/pull/20222#discussion_r2782203472
########## datafusion-examples/examples/udf/main.rs: ########## Review Comment: ```suggestion //! cargo run --example udf -- [all|adv_udaf|adv_udf|adv_udwf|async_udf|udaf|udf|udtf|udwf|table_list_udtf] ``` ########## docs/source/library-user-guide/functions/adding-udfs.md: ########## @@ -1388,15 +1388,16 @@ in the CLI to read the metadata from a Parquet file. The simple UDTF used here takes a single `Int64` argument and returns a table with a single column with the value of the argument. To create a function in DataFusion, you need to implement the `TableFunctionImpl` trait. This trait has a -single method, `call`, that takes a slice of `Expr`s and returns a `Result<Arc<dyn TableProvider>>`. +single method, `call_with_args`, that takes a `TableFunctionArgs` struct and returns a `Result<Arc<dyn TableProvider>>`. +Passed struct includes function arguments as a slice of `Expr`s. -In the `call` method, you parse the input `Expr`s and return a `TableProvider`. You might also want to do some +In the `call_with_args` method, you parse the input `Expr`s and return a `TableProvider`. You might also want to do some Review Comment: Here we can mention that UDTF can use session state. ########## datafusion-examples/examples/udf/table_list_udtf.rs: ########## @@ -0,0 +1,128 @@ +// 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. + +//! See `main.rs` for how to run it. + +use std::sync::{Arc, LazyLock}; + +use arrow::array::{RecordBatch, StringArray}; +use arrow_schema::{DataType, Field, Schema, SchemaRef}; +use datafusion::{ + catalog::{MemTable, TableFunctionArgs, TableFunctionImpl, TableProvider}, + common::Result, + execution::SessionState, + prelude::SessionContext, +}; +use datafusion_common::{DataFusionError, plan_err}; +use tokio::{runtime::Handle, task::block_in_place}; + +const FUNCTION_NAME: &str = "table_list"; + +// The example shows, how to create UDTF that depends on the session state. +// Defines a `table_list` UDTF that returns a list of tables within the provided session. + +pub async fn table_list_udtf() -> Result<()> { + let ctx = SessionContext::new(); + ctx.register_udtf(FUNCTION_NAME, Arc::new(TableListUdtf)); + + // Register different kinds of tables. + ctx.sql("create view v as select 1") + .await? + .collect() + .await?; + ctx.sql("create table t(a int)").await?.collect().await?; + + // Print results. + ctx.sql("select * from table_list()").await?.show().await?; + + Ok(()) +} + +#[derive(Debug, Default)] +struct TableListUdtf; + +static SCHEMA: LazyLock<SchemaRef> = LazyLock::new(|| { + SchemaRef::new(Schema::new(vec![ + Field::new("catalog", DataType::Utf8, false), + Field::new("schema", DataType::Utf8, false), + Field::new("table", DataType::Utf8, false), + Field::new("type", DataType::Utf8, false), + ])) +}); + +impl TableFunctionImpl for TableListUdtf { + fn call_with_args(&self, args: TableFunctionArgs) -> Result<Arc<dyn TableProvider>> { + if !args.args.is_empty() { + return plan_err!( + "{}: unexpected number of arguments: {}, expected: 0", + FUNCTION_NAME, + args.args.len() + ); + } + let state = args + .session + .as_any() + .downcast_ref::<SessionState>() + .ok_or_else(|| { + DataFusionError::Internal("failed to downcast state".into()) + })?; + + let mut catalogs = vec![]; + let mut schemas = vec![]; + let mut tables = vec![]; + let mut types = vec![]; Review Comment: Could you use `StringBuilder`? -- 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] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
