DATAMONGO-2049 - Add support for $ltrim, $rtrim, and $trim.

Original pull request: #594.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/StringOperators.java

@@ -350,8 +350,7 @@ public class StringOperators {
 		 * @return
 		 */
 		public StrLenBytes length() {
-			return usesFieldRef() ? StrLenBytes.stringLengthOf(fieldReference)
+			return usesFieldRef() ? StrLenBytes.stringLengthOf(fieldReference) : StrLenBytes.stringLengthOf(expression);
-					: StrLenBytes.stringLengthOf(expression);
 		}
 
 		/**
@@ -391,6 +390,132 @@ public class StringOperators {
 			return usesFieldRef() ? SubstrCP.valueOf(fieldReference) : SubstrCP.valueOf(expression);
 		}
 
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and trims whitespaces
+		 * from the beginning and end. <br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @return new instance of {@link Trim}.
+		 * @since 2.1
+		 */
+		public Trim trim() {
+			return createTrim();
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and trims the given
+		 * character sequence from the beginning and end. <br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @param chars must not be {@literal null}.
+		 * @return new instance of {@link Trim}.
+		 * @since 2.1
+		 */
+		public Trim trim(String chars) {
+			return trim().chars(chars);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and trims the character
+		 * sequence resulting from the given {@link AggregationExpression} from the beginning and end. <br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link Trim}.
+		 * @since 2.1
+		 */
+		public Trim trim(AggregationExpression expression) {
+			return trim().charsOf(expression);
+		}
+
+		private Trim createTrim() {
+			return usesFieldRef() ? Trim.valueOf(fieldReference) : Trim.valueOf(expression);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and trims whitespaces
+		 * from the beginning. <br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @return new instance of {@link LTrim}.
+		 * @since 2.1
+		 */
+		public LTrim ltrim() {
+			return createLTrim();
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and trims the given
+		 * character sequence from the beginning. <br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @param chars must not be {@literal null}.
+		 * @return new instance of {@link LTrim}.
+		 * @since 2.1
+		 */
+		public LTrim ltrim(String chars) {
+			return ltrim().chars(chars);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and trims the character
+		 * sequence resulting from the given {@link AggregationExpression} from the beginning. <br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link LTrim}.
+		 * @since 2.1
+		 */
+		public LTrim ltrim(AggregationExpression expression) {
+			return ltrim().charsOf(expression);
+		}
+
+		private LTrim createLTrim() {
+			return usesFieldRef() ? LTrim.valueOf(fieldReference) : LTrim.valueOf(expression);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and trims whitespaces
+		 * from the end. <br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @return new instance of {@link RTrim}.
+		 * @since 2.1
+		 */
+		public RTrim rtrim() {
+			return createRTrim();
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and trims the given
+		 * character sequence from the end. <br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @param chars must not be {@literal null}.
+		 * @return new instance of {@link RTrim}.
+		 * @since 2.1
+		 */
+		public RTrim rtrim(String chars) {
+			return rtrim().chars(chars);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and trims the character
+		 * sequence resulting from the given {@link AggregationExpression} from the end. <br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RTrim}.
+		 * @since 2.1
+		 */
+		public RTrim rtrim(AggregationExpression expression) {
+			return rtrim().charsOf(expression);
+		}
+
+		private RTrim createRTrim() {
+			return usesFieldRef() ? RTrim.valueOf(fieldReference) : RTrim.valueOf(expression);
+		}
+
 		private boolean usesFieldRef() {
 			return fieldReference != null;
 		}
@@ -1072,4 +1197,257 @@ public class StringOperators {
 			return new SubstrCP(append(Arrays.asList(start, nrOfChars)));
 		}
 	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $trim} which removes whitespace or the specified characters from the
+	 * beginning and end of a string. <br />
+	 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+	 *
+	 * @author Christoph Strobl
+	 * @since 2.1
+	 */
+	public static class Trim extends AbstractAggregationExpression {
+
+		private Trim(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Creates new {@link Trim} using the value of the provided {@link Field fieldReference} as {@literal input} value.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link LTrim}.
+		 */
+		public static Trim valueOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+			return new Trim(Collections.singletonMap("input", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Creates new {@link Trim} using the result of the provided {@link AggregationExpression} as {@literal input}
+		 * value.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link Trim}.
+		 */
+		public static Trim valueOf(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+			return new Trim(Collections.singletonMap("input", expression));
+		}
+
+		/**
+		 * Optional specify the character(s) to trim from the beginning.
+		 *
+		 * @param chars must not be {@literal null}.
+		 * @return new instance of {@link Trim}.
+		 */
+		public Trim chars(String chars) {
+
+			Assert.notNull(chars, "Chars must not be null!");
+			return new Trim(append("chars", chars));
+		}
+
+		/**
+		 * Optional specify the reference to the {@link Field field} holding the character values to trim from the
+		 * beginning.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link Trim}.
+		 */
+		public Trim charsOf(String fieldReference) {
+			return new Trim(append("chars", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Optional specify the {@link AggregationExpression} evaluating to the character sequence to trim from the
+		 * beginning.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link Trim}.
+		 */
+		public Trim charsOf(AggregationExpression expression) {
+			return new Trim(append("chars", expression));
+		}
+
+		/**
+		 * Remove whitespace or the specified characters from the beginning of a string.<br />
+		 *
+		 * @return new instance of {@link LTrim}.
+		 */
+		public LTrim left() {
+			return new LTrim(argumentMap());
+		}
+
+		/**
+		 * Remove whitespace or the specified characters from the end of a string.<br />
+		 *
+		 * @return new instance of {@link RTrim}.
+		 */
+		public RTrim right() {
+			return new RTrim(argumentMap());
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$trim";
+		}
+	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $ltrim} which removes whitespace or the specified characters from the
+	 * beginning of a string. <br />
+	 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+	 *
+	 * @author Christoph Strobl
+	 * @since 2.1
+	 */
+	public static class LTrim extends AbstractAggregationExpression {
+
+		private LTrim(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Creates new {@link LTrim} using the value of the provided {@link Field fieldReference} as {@literal input} value.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link LTrim}.
+		 */
+		public static LTrim valueOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+			return new LTrim(Collections.singletonMap("input", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Creates new {@link LTrim} using the result of the provided {@link AggregationExpression} as {@literal input}
+		 * value.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link LTrim}.
+		 */
+		public static LTrim valueOf(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+			return new LTrim(Collections.singletonMap("input", expression));
+		}
+
+		/**
+		 * Optional specify the character(s) to trim from the beginning.
+		 *
+		 * @param chars must not be {@literal null}.
+		 * @return new instance of {@link LTrim}.
+		 */
+		public LTrim chars(String chars) {
+
+			Assert.notNull(chars, "Chars must not be null!");
+			return new LTrim(append("chars", chars));
+		}
+
+		/**
+		 * Optional specify the reference to the {@link Field field} holding the character values to trim from the
+		 * beginning.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link LTrim}.
+		 */
+		public LTrim charsOf(String fieldReference) {
+			return new LTrim(append("chars", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Optional specify the {@link AggregationExpression} evaluating to the character sequence to trim from the
+		 * beginning.
+		 * 
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link LTrim}.
+		 */
+		public LTrim charsOf(AggregationExpression expression) {
+			return new LTrim(append("chars", expression));
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$ltrim";
+		}
+	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $rtrim} which removes whitespace or the specified characters from the end
+	 * of a string. <br />
+	 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+	 *
+	 * @author Christoph Strobl
+	 * @since 2.1
+	 */
+	public static class RTrim extends AbstractAggregationExpression {
+
+		private RTrim(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Creates new {@link RTrim} using the value of the provided {@link Field fieldReference} as {@literal input} value.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link RTrim}.
+		 */
+		public static RTrim valueOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+			return new RTrim(Collections.singletonMap("input", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Creates new {@link RTrim} using the result of the provided {@link AggregationExpression} as {@literal input}
+		 * value.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RTrim}.
+		 */
+		public static RTrim valueOf(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+			return new RTrim(Collections.singletonMap("input", expression));
+		}
+
+		/**
+		 * Optional specify the character(s) to trim from the end.
+		 *
+		 * @param chars must not be {@literal null}.
+		 * @return new instance of {@link RTrim}.
+		 */
+		public RTrim chars(String chars) {
+
+			Assert.notNull(chars, "Chars must not be null!");
+			return new RTrim(append("chars", chars));
+		}
+
+		/**
+		 * Optional specify the reference to the {@link Field field} holding the character values to trim from the end.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link RTrim}.
+		 */
+		public RTrim charsOf(String fieldReference) {
+			return new RTrim(append("chars", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Optional specify the {@link AggregationExpression} evaluating to the character sequence to trim from the end.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RTrim}.
+		 */
+		public RTrim charsOf(AggregationExpression expression) {
+			return new RTrim(append("chars", expression));
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$rtrim";
+		}
+	}
 }

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/StringOperatorsUnitTests.java

@@ -0,0 +1,146 @@
+/*
+ * Copyright 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.
+ * 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.springframework.data.mongodb.core.aggregation;
+
+import org.assertj.core.api.Assertions;
+import org.bson.Document;
+import org.junit.Test;
+
+/**
+ * Unit test for {@link StringOperators}.
+ *
+ * @author Christoph Strobl
+ * @currentRead Royal Assassin - Robin Hobb
+ */
+public class StringOperatorsUnitTests {
+
+	static final String EXPRESSION_STRING = "{ \"$fitz\" : \"chivalry\" }";
+	static final Document EXPRESSION_DOC = Document.parse(EXPRESSION_STRING);
+	static final AggregationExpression EXPRESSION = context -> EXPRESSION_DOC;
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderTrim() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").trim().toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $trim: { \"input\" : \"$shrewd\" } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderTrimForExpression() {
+
+		Assertions.assertThat(StringOperators.valueOf(EXPRESSION).trim().toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $trim: { \"input\" : " + EXPRESSION_STRING + " } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderTrimWithChars() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").trim("sh").toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $trim: { \"input\" : \"$shrewd\", \"chars\" : \"sh\" } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderTrimWithCharsExpression() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").trim(EXPRESSION).toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $trim: { \"input\" : \"$shrewd\", \"chars\" : " + EXPRESSION_STRING + " } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderTrimLeft() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").trim().left().toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $ltrim: { \"input\" : \"$shrewd\" } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderTrimLeftWithChars() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").trim("sh").left().toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $ltrim: { \"input\" : \"$shrewd\", \"chars\" : \"sh\" } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderTrimRight() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").trim().right().toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $rtrim: { \"input\" : \"$shrewd\" } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderTrimRightWithChars() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").trim("sh").right().toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $rtrim: { \"input\" : \"$shrewd\", \"chars\" : \"sh\" } } "));
+	}
+	
+	@Test // DATAMONGO-2049
+	public void shouldRenderLTrim() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").ltrim().toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $ltrim: { \"input\" : \"$shrewd\" } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderLTrimForExpression() {
+
+		Assertions.assertThat(StringOperators.valueOf(EXPRESSION).ltrim().toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $ltrim: { \"input\" : " + EXPRESSION_STRING + " } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderLTrimWithChars() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").ltrim("sh").toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $ltrim: { \"input\" : \"$shrewd\", \"chars\" : \"sh\" } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderLTrimWithCharsExpression() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").ltrim(EXPRESSION).toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $ltrim: { \"input\" : \"$shrewd\", \"chars\" : " + EXPRESSION_STRING + " } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderRTrim() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").rtrim().toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $rtrim: { \"input\" : \"$shrewd\" } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderRTrimForExpression() {
+
+		Assertions.assertThat(StringOperators.valueOf(EXPRESSION).rtrim().toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $rtrim: { \"input\" : " + EXPRESSION_STRING + " } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderRTrimWithChars() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").rtrim("sh").toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $rtrim: { \"input\" : \"$shrewd\", \"chars\" : \"sh\" } } "));
+	}
+
+	@Test // DATAMONGO-2049
+	public void shouldRenderRTrimWithCharsExpression() {
+
+		Assertions.assertThat(StringOperators.valueOf("shrewd").rtrim(EXPRESSION).toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $rtrim: { \"input\" : \"$shrewd\", \"chars\" : " + EXPRESSION_STRING + " } } "));
+	}
+
+}

src/main/asciidoc/reference/mongodb.adoc

@@ -2119,7 +2119,7 @@ At the time of this writing, we provide support for the following Aggregation Op
 | `abs`, `add` (*via `plus`), `ceil`, `divide`, `exp`, `floor`, `ln`, `log`, `log10`, `mod`, `multiply`, `pow`, `sqrt`, `subtract` (*via `minus`), `trunc`
 
 | String Aggregation Operators
-| `concat`, `substr`, `toLower`, `toUpper`, `stcasecmp`, `indexOfBytes`, `indexOfCP`, `split`, `strLenBytes`, `strLenCP`, `substrCP`
+| `concat`, `substr`, `toLower`, `toUpper`, `stcasecmp`, `indexOfBytes`, `indexOfCP`, `split`, `strLenBytes`, `strLenCP`, `substrCP`, `trim`, `ltrim`, `rtim`
 
 | Comparison Aggregation Operators
 | `eq` (*via: `is`), `gt`, `gte`, `lt`, `lte`, `ne`