From 9bd7c1b431f3c345ce277ccfb6a97605d4071339 Mon Sep 17 00:00:00 2001 From: Michael Minella Date: Wed, 28 Feb 2018 22:36:56 -0600 Subject: [PATCH] BATCH-2465: add note about the importance to have a unique key constraint on the sortKey This PR is for BATCH-2465. It updates the reference documentation and the Javadoc to mention explicitly the importance to have a unique key constraint on the sortKey when using paging item readers. I deliberately used "It is important" and not "It is required" (or mandatory) because in the end this is not required but in that case there is no guarantee to not lose data between executions. Please let me know if the wording should be updated. --- .../item/database/JdbcPagingItemReader.java | 5 +++-- .../support/AbstractSqlPagingQueryProvider.java | 16 +++++++++------- src/site/docbook/reference/readersAndWriters.xml | 3 +++ 3 files changed, 15 insertions(+), 9 deletions(-) diff --git a/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/database/JdbcPagingItemReader.java b/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/database/JdbcPagingItemReader.java index 805e6af67..1aec29224 100644 --- a/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/database/JdbcPagingItemReader.java +++ b/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/database/JdbcPagingItemReader.java @@ -1,5 +1,5 @@ /* - * Copyright 2006-2013 the original author or authors. + * Copyright 2006-2018 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. @@ -51,7 +51,8 @@ import org.springframework.util.ClassUtils; * needed as {@link #read()} method is called, returning an object corresponding * to current position. On restart it uses the last sort key value to locate the * first page to read (so it doesn't matter if the successfully processed items - * have been removed or modified). + * have been removed or modified). It is important to have a unique key constraint on the + * sort key to guarantee that no data is lost between executions. *

* *

diff --git a/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/database/support/AbstractSqlPagingQueryProvider.java b/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/database/support/AbstractSqlPagingQueryProvider.java index d71d6e030..5dfd788ce 100644 --- a/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/database/support/AbstractSqlPagingQueryProvider.java +++ b/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/database/support/AbstractSqlPagingQueryProvider.java @@ -16,6 +16,12 @@ package org.springframework.batch.item.database.support; +import java.util.ArrayList; +import java.util.LinkedHashMap; +import java.util.List; +import java.util.Map; +import javax.sql.DataSource; + import org.springframework.batch.item.database.JdbcParameterUtils; import org.springframework.batch.item.database.Order; import org.springframework.batch.item.database.PagingQueryProvider; @@ -23,12 +29,6 @@ import org.springframework.dao.InvalidDataAccessApiUsageException; import org.springframework.util.Assert; import org.springframework.util.StringUtils; -import javax.sql.DataSource; -import java.util.ArrayList; -import java.util.LinkedHashMap; -import java.util.List; -import java.util.Map; - /** * Abstract SQL Paging Query Provider to serve as a base class for all provided * SQL paging query providers. @@ -42,7 +42,9 @@ import java.util.Map; * Provides properties and preparation for the mandatory "selectClause" and * "fromClause" as well as for the optional "whereClause". Also provides * property for the mandatory "sortKeys". Note: The columns that make up - * the sort key must be a true key and not just a column to order by. + * the sort key must be a true key and not just a column to order by. It is important + * to have a unique key constraint on the sort key to guarantee that no data is lost + * between executions. * * @author Thomas Risberg * @author Dave Syer diff --git a/src/site/docbook/reference/readersAndWriters.xml b/src/site/docbook/reference/readersAndWriters.xml index 1df2bd29c..436485040 100644 --- a/src/site/docbook/reference/readersAndWriters.xml +++ b/src/site/docbook/reference/readersAndWriters.xml @@ -2192,6 +2192,9 @@ itemReader.close(executionContext); also provide an optional where clause. These clauses will be used to build an SQL statement combined with the required sortKey. + It is important to have a unique key constraint on the `sortKey` to + guarantee that no data is lost between executions. + After the reader has been opened, it will pass back one item per call to read in the same basic fashion as any other ItemReader. The paging happens behind the