dtenedor commented on a change in pull request #35855: URL: https://github.com/apache/spark/pull/35855#discussion_r827571310
########## File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/DefaultColumns.scala ########## @@ -0,0 +1,266 @@ +/* + * 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. + */ + +package org.apache.spark.sql.catalyst.analysis + +import org.apache.spark.sql.AnalysisException +import org.apache.spark.sql.catalyst.TableIdentifier +import org.apache.spark.sql.catalyst.catalog._ +import org.apache.spark.sql.catalyst.expressions.{Expression, _} +import org.apache.spark.sql.catalyst.optimizer.ConstantFolding +import org.apache.spark.sql.catalyst.parser.{CatalystSqlParser, ParseException} +import org.apache.spark.sql.catalyst.plans.logical._ +import org.apache.spark.sql.types._ + +/** + * This class contains logic for processing DEFAULT columns in statements such as CREATE TABLE. + */ +object DefaultColumns { + val default = "default" + val analysisPrefix = + " has a DEFAULT value which fails to resolve to a valid constant expression: " + val columnDefaultNotFound = "Column 'default' does not exist" + lazy val parser = new CatalystSqlParser() + lazy val analyzer = + new Analyzer(new SessionCatalog(new InMemoryCatalog, FunctionRegistry.builtin)) + + /** + * Finds DEFAULT expressions in CREATE/REPLACE TABLE commands and constant-folds then. + * + * Example: + * CREATE TABLE T(a INT, b INT DEFAULT 5 + 5) becomes + * CREATE TABLE T(a INT, b INT DEFAULT 10) + * + * @param tableSchema represents the names and types of the columns of the statement to process. + * @param statementType name of the statement being processed, such as INSERT; useful for errors. + * @return a copy of `tableSchema` with field metadata updated with the constant-folded values. + */ + def ConstantFoldDefaultExpressions(tableSchema: StructType, statementType: String): StructType = { + // Get the list of column indexes in the CREATE TABLE command with DEFAULT values. + val (fields: Array[StructField], indexes: Array[Int]) = + tableSchema.fields.zipWithIndex.filter { case (f, i) => f.metadata.contains(default) }.unzip + // Extract the list of DEFAULT column values from the CreateTable command. + val colNames: Seq[String] = fields.map { _.name } + val defaults: Seq[String] = fields.map { _.metadata.getString(default) } + // Extract the list of DEFAULT column values from the CreateTable command. + val exprs: Seq[Expression] = colNames.zip(defaults).map { + case (name, text) => Parse(name, text, statementType) + } + // Analyze and constant-fold each parse result. + val analyzed: Seq[Expression] = (exprs, defaults, colNames).zipped.map { + case (expr, default, name) => Analyze(expr, default, name, statementType) + } + // Create a map from the column index of each DEFAULT column to its type. + val indexMap: Map[Int, StructField] = (indexes, fields, analyzed).zipped.map { + case (index, field, expr) => + val newMetadata: Metadata = new MetadataBuilder().withMetadata(field.metadata) + .putString(default, expr.sql).build() + (index, field.copy(metadata = newMetadata)) + }.toMap + // Finally, replace the original struct fields with the new ones. + val newFields: Seq[StructField] = + tableSchema.fields.zipWithIndex.map { case (f, i) => indexMap.getOrElse(i, f) } + StructType(newFields) + } + + /** + * Parses DEFAULT column text to an expression, returning a reasonable error upon failure. + * + * @param colName the name of the DEFAULT column whose text we endeavor to parse. + * @param colText the string contents of the DEFAULT column value. + * @param statementType which type of statement we are running, such as INSERT; useful for errors. + * @return the expression resulting from the parsing step. + */ + private def Parse(colName: String, colText: String, statementType: String): Expression = { + try { + parser.parseExpression(colText) + } catch { + case ex: ParseException => + throw new AnalysisException( + s"Failed to execute $statementType command because the destination table column " + + colName + analysisPrefix + s"$colText yields ${ex.getMessage}") + } + } + + /** + * Analyzes and constant-folds `colExpr`, returning a reasonable error message upon failure. + * + * @param colExpr result of a parsing operation suitable for consumption by analysis. + * @param colText string contents of the DEFAULT column value; useful for errors. + * @param colName string name of the DEFAULT column; useful for errors. + * @param statementType which type of statement we are running, such as INSERT; useful for errors. + * @return Result of the analysis and constant-folding operation. + */ + private def Analyze(colExpr: Expression, colText: String, colName: String, Review comment: Done. -- This is an automated message from the Apache Git Service. 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