DATACMNS-875 - Add support for exists projection in repository query derivation.

We now support exists projections in derived queries by parsing the exists keyword and expose it via PartTree.isExistsProjection().

Original pull request: #171.

src/main/java/org/springframework/data/repository/query/parser/PartTree.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2008-2015 the original author or authors.
+ * Copyright 2008-2016 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.
@@ -36,6 +36,7 @@ import org.springframework.util.StringUtils;
  * @author Oliver Gierke
  * @author Thomas Darimont
  * @author Christoph Strobl
+ * @author Mark Paluch
  */
 public class PartTree implements Iterable<OrPart> {
 
@@ -52,9 +53,10 @@ public class PartTree implements Iterable<OrPart> {
 	private static final String KEYWORD_TEMPLATE = "(%s)(?=(\\p{Lu}|\\P{InBASIC_LATIN}))";
 	private static final String QUERY_PATTERN = "find|read|get|query|stream";
 	private static final String COUNT_PATTERN = "count";
+	private static final String EXISTS_PATTERN = "exists";
 	private static final String DELETE_PATTERN = "delete|remove";
 	private static final Pattern PREFIX_TEMPLATE = Pattern.compile( //
-			"^(" + QUERY_PATTERN + "|" + COUNT_PATTERN + "|" + DELETE_PATTERN + ")((\\p{Lu}.*?))??By");
+			"^(" + QUERY_PATTERN + "|" + COUNT_PATTERN + "|" + EXISTS_PATTERN + "|" + DELETE_PATTERN + ")((\\p{Lu}.*?))??By");
 
 	/**
 	 * The subject, for example "findDistinctUserByNameOrderByAge" would have the subject "DistinctUser".
@@ -125,6 +127,16 @@ public class PartTree implements Iterable<OrPart> {
 		return subject.isCountProjection();
 	}
 
+	/**
+	 * Returns whether an exists projection shall be applied.
+	 *
+	 * @return
+	 * @since 1.13
+	 */
+	public Boolean isExistsProjection() {
+		return subject.isExistsProjection();
+	}
+
 	/**
 	 * return true if the created {@link PartTree} is meant to be used for delete operation.
 	 * 
@@ -262,6 +274,7 @@ public class PartTree implements Iterable<OrPart> {
 
 		private static final String DISTINCT = "Distinct";
 		private static final Pattern COUNT_BY_TEMPLATE = Pattern.compile("^count(\\p{Lu}.*?)??By");
+		private static final Pattern EXISTS_BY_TEMPLATE = Pattern.compile("^(" + EXISTS_PATTERN + ")(\\p{Lu}.*?)??By");
 		private static final Pattern DELETE_BY_TEMPLATE = Pattern.compile("^(" + DELETE_PATTERN + ")(\\p{Lu}.*?)??By");
 		private static final String LIMITING_QUERY_PATTERN = "(First|Top)(\\d*)?";
 		private static final Pattern LIMITED_QUERY_TEMPLATE = Pattern.compile("^(" + QUERY_PATTERN + ")(" + DISTINCT + ")?"
@@ -269,6 +282,7 @@ public class PartTree implements Iterable<OrPart> {
 
 		private final boolean distinct;
 		private final boolean count;
+		private final boolean exists;
 		private final boolean delete;
 		private final Integer maxResults;
 
@@ -276,6 +290,7 @@ public class PartTree implements Iterable<OrPart> {
 
 			this.distinct = subject == null ? false : subject.contains(DISTINCT);
 			this.count = matches(subject, COUNT_BY_TEMPLATE);
+			this.exists = matches(subject, EXISTS_BY_TEMPLATE);
 			this.delete = matches(subject, DELETE_BY_TEMPLATE);
 			this.maxResults = returnMaxResultsIfFirstKSubjectOrNull(subject);
 		}
@@ -314,6 +329,16 @@ public class PartTree implements Iterable<OrPart> {
 			return count;
 		}
 
+		/**
+		 * Returns {@literal true} if {@link Subject} matches {@link #EXISTS_BY_TEMPLATE}.
+		 *
+		 * @return
+		 * @since 1.13
+		 */
+		public boolean isExistsProjection() {
+			return exists;
+		}
+
 		public boolean isDistinct() {
 			return distinct;
 		}

src/test/java/org/springframework/data/repository/query/parser/PartTreeUnitTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2008-2015 the original author or authors.
+ * Copyright 2008-2016 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. You may obtain a copy of
@@ -44,10 +44,11 @@ import org.springframework.data.repository.query.parser.PartTree.OrPart;
  * @author Thomas Darimont
  * @author Martin Baumgartner
  * @author Christoph Strobl
+ * @author Mark Paluch
  */
 public class PartTreeUnitTests {
 
-	private String[] PREFIXES = { "find", "read", "get", "query", "stream", "count", "delete", "remove" };
+	private String[] PREFIXES = { "find", "read", "get", "query", "stream", "count", "delete", "remove", "exists" };
 
 	@Test(expected = IllegalArgumentException.class)
 	public void rejectsNullSource() throws Exception {
@@ -436,6 +437,16 @@ public class PartTreeUnitTests {
 		assertThat(tree.isCountProjection(), is(true));
 	}
 
+	/**
+	 * @see DATACMNS-875
+	 */
+	@Test
+	public void identifiesSimpleExistsByCorrectly() {
+
+		PartTree tree = new PartTree("existsByLastname", User.class);
+		assertThat(tree.isExistsProjection(), is(true));
+	}
+
 	/**
 	 * @see DATACMNS-399
 	 */
@@ -652,6 +663,16 @@ public class PartTreeUnitTests {
 		assertLimiting("countTop10DistinctUsersByLastname", User.class, false, null, true);
 	}
 
+	/**
+	 * @see DATACMNS-875
+	 */
+	@Test
+	public void shouldNotSupportLimitingExistQueries() {
+
+		assertLimiting("existsFirst10DistinctUsersByLastname", User.class, false, null, true);
+		assertLimiting("existsTop10DistinctUsersByLastname", User.class, false, null, true);
+	}
+
 	/**
 	 * @see DATACMNS-581
 	 */