From d1a06bbcc8d3d87a61ef8015c44bbadd20e3973e Mon Sep 17 00:00:00 2001
From: Oliver Drotbohm <odrotbohm@pivotal.io>
Date: Tue, 2 Jul 2019 20:05:07 +0200
Subject: [PATCH] #1014 - Added API to conditionally add links to
 RepresentationModel.

This allows more fluent usage of the API.
---
 .../hateoas/RepresentationModel.java          | 36 +++++++++++++++++++
 .../hateoas/RepresentationModelUnitTest.java  | 24 +++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/src/main/java/org/springframework/hateoas/RepresentationModel.java b/src/main/java/org/springframework/hateoas/RepresentationModel.java
index f8577b56..9939d5df 100755
--- a/src/main/java/org/springframework/hateoas/RepresentationModel.java
+++ b/src/main/java/org/springframework/hateoas/RepresentationModel.java
@@ -19,6 +19,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Optional;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
 import org.springframework.lang.Nullable;
@@ -102,6 +103,41 @@ public class RepresentationModel<T extends RepresentationModel<? extends T>> {
 		return (T) this;
 	}
 
+	/**
+	 * Adds the {@link Link} produced by the given Supplier if the guard is {@literal true}.
+	 *
+	 * @param guard whether to add the {@link Link} produced by the given {@link Supplier}.
+	 * @param link the {@link Link} to add in case the guard is {@literal true}.
+	 * @return
+	 */
+	@SuppressWarnings("unchecked")
+	public T addIf(boolean guard, Supplier<Link> link) {
+
+		if (guard) {
+			add(link.get());
+		}
+
+		return (T) this;
+	}
+
+	/**
+	 * Adds all {@link Link}s produced by the given Supplier if the guard is {@literal true}.
+	 *
+	 * @param guard whether to add the {@link Link}s produced by the given {@link Supplier}.
+	 * @param links the {@link Link}s to add in case the guard is {@literal true}.
+	 * @return
+	 * @see Links
+	 */
+	@SuppressWarnings("unchecked")
+	public T addAllIf(boolean guard, Supplier<? extends Iterable<Link>> links) {
+
+		if (guard) {
+			add(links.get());
+		}
+
+		return (T) this;
+	}
+
 	/**
 	 * Returns whether the resource contains {@link Link}s at all.
 	 *
diff --git a/src/test/java/org/springframework/hateoas/RepresentationModelUnitTest.java b/src/test/java/org/springframework/hateoas/RepresentationModelUnitTest.java
index cf0e62bb..b7badfcf 100755
--- a/src/test/java/org/springframework/hateoas/RepresentationModelUnitTest.java
+++ b/src/test/java/org/springframework/hateoas/RepresentationModelUnitTest.java
@@ -170,4 +170,28 @@ class RepresentationModelUnitTest {
 		assertThat(support.hasLink("self")).isTrue();
 		assertThat(support.hasLink("another")).isTrue();
 	}
+
+	@Test // #1014
+	void addsGuardedLink() {
+
+		RepresentationModel<?> model = new RepresentationModel<>();
+
+		model.addIf(true, () -> new Link("added", "foo"));
+		assertThat(model.hasLink("foo")).isTrue();
+
+		model.addIf(false, () -> new Link("not-added", "bar"));
+		assertThat(model.hasLink("bar")).isFalse();
+	}
+
+	@Test // #1014
+	void addsGuardedLinks() {
+
+		RepresentationModel<?> model = new RepresentationModel<>();
+
+		model.addAllIf(true, () -> Links.of(new Link("added", "foo")));
+		assertThat(model.hasLink("foo")).isTrue();
+
+		model.addAllIf(false, () -> Links.of(new Link("not-added", "bar")));
+		assertThat(model.hasLink("bar")).isFalse();
+	}
 }