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Expose
parser on DFParser to enable user controlled parsing (apache…
…#9729) * poc: custom parser * play with extension statement * tweak * Revert "tweak" This reverts commit e57006e. * Revert "play with extension statement" This reverts commit 86588e4. * style: cargo fmt * Update datafusion-examples/examples/sql_parsing.rs Co-authored-by: Andrew Lamb <[email protected]> * Apply suggestions from code review Co-authored-by: Andrew Lamb <[email protected]> * style: cargo cmt * refactor: less nesting in parse statement * docs: better example description --------- Co-authored-by: Andrew Lamb <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,134 @@ | ||
| // 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. | ||
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| use std::fmt::Display; | ||
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| use datafusion::error::Result; | ||
| use datafusion_sql::{ | ||
| parser::{CopyToSource, CopyToStatement, DFParser, Statement}, | ||
| sqlparser::{keywords::Keyword, parser::ParserError, tokenizer::Token}, | ||
| }; | ||
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| /// This example demonstrates how to use the DFParser to parse a statement in a custom way | ||
| /// | ||
| /// This technique can be used to implement a custom SQL dialect, for example. | ||
| #[tokio::main] | ||
| async fn main() -> Result<()> { | ||
| let mut my_parser = | ||
| MyParser::new("COPY source_table TO 'file.fasta' STORED AS FASTA")?; | ||
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| let my_statement = my_parser.parse_statement()?; | ||
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| match my_statement { | ||
| MyStatement::DFStatement(s) => println!("df: {}", s), | ||
| MyStatement::MyCopyTo(s) => println!("my_copy: {}", s), | ||
| } | ||
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| Ok(()) | ||
| } | ||
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| /// Here we define a Parser for our new SQL dialect that wraps the existing `DFParser` | ||
| struct MyParser<'a> { | ||
| df_parser: DFParser<'a>, | ||
| } | ||
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| impl MyParser<'_> { | ||
| fn new(sql: &str) -> Result<Self> { | ||
| let df_parser = DFParser::new(sql)?; | ||
| Ok(Self { df_parser }) | ||
| } | ||
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| /// Returns true if the next token is `COPY` keyword, false otherwise | ||
| fn is_copy(&self) -> bool { | ||
| matches!( | ||
| self.df_parser.parser.peek_token().token, | ||
| Token::Word(w) if w.keyword == Keyword::COPY | ||
| ) | ||
| } | ||
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| /// This is the entry point to our parser -- it handles `COPY` statements specially | ||
| /// but otherwise delegates to the existing DataFusion parser. | ||
| pub fn parse_statement(&mut self) -> Result<MyStatement, ParserError> { | ||
| if self.is_copy() { | ||
| self.df_parser.parser.next_token(); // COPY | ||
| let df_statement = self.df_parser.parse_copy()?; | ||
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| if let Statement::CopyTo(s) = df_statement { | ||
| Ok(MyStatement::from(s)) | ||
| } else { | ||
| Ok(MyStatement::DFStatement(Box::from(df_statement))) | ||
| } | ||
| } else { | ||
| let df_statement = self.df_parser.parse_statement()?; | ||
| Ok(MyStatement::from(df_statement)) | ||
| } | ||
| } | ||
| } | ||
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| enum MyStatement { | ||
| DFStatement(Box<Statement>), | ||
| MyCopyTo(MyCopyToStatement), | ||
| } | ||
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| impl Display for MyStatement { | ||
| fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { | ||
| match self { | ||
| MyStatement::DFStatement(s) => write!(f, "{}", s), | ||
| MyStatement::MyCopyTo(s) => write!(f, "{}", s), | ||
| } | ||
| } | ||
| } | ||
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| impl From<Statement> for MyStatement { | ||
| fn from(s: Statement) -> Self { | ||
| Self::DFStatement(Box::from(s)) | ||
| } | ||
| } | ||
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| impl From<CopyToStatement> for MyStatement { | ||
| fn from(s: CopyToStatement) -> Self { | ||
| if s.stored_as == Some("FASTA".to_string()) { | ||
| Self::MyCopyTo(MyCopyToStatement::from(s)) | ||
| } else { | ||
| Self::DFStatement(Box::from(Statement::CopyTo(s))) | ||
| } | ||
| } | ||
| } | ||
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| struct MyCopyToStatement { | ||
| pub source: CopyToSource, | ||
| pub target: String, | ||
| } | ||
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| impl From<CopyToStatement> for MyCopyToStatement { | ||
| fn from(s: CopyToStatement) -> Self { | ||
| Self { | ||
| source: s.source, | ||
| target: s.target, | ||
| } | ||
| } | ||
| } | ||
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| impl Display for MyCopyToStatement { | ||
| fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { | ||
| write!( | ||
| f, | ||
| "COPY {} TO '{}' STORED AS FASTA", | ||
| self.source, self.target | ||
| ) | ||
| } | ||
| } |
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