Add area lookup service and area relations support

src/Hqub.MusicBrainz.Tests/AreaGetTests.cs

@@ -0,0 +1,61 @@
+namespace Hqub.MusicBrainz.Tests
+{
+    using Hqub.MusicBrainz.Entities;
+    using NUnit.Framework;
+    using System.Linq;
+    using System.Threading.Tasks;
+
+    // Resource: area-get.json
+    // URL: https://musicbrainz.org/ws/2/area/c9ac1239-e832-41bc-9930-e252a1fd1105?inc=area-rels&fmt=json
+
+    public class AreaGetTests
+    {
+        private Area area;
+
+        [OneTimeSetUp]
+        public async Task Init()
+        {
+            var client = new MusicBrainzClient()
+            {
+                Cache = EmbeddedResourceCache.Instance
+            };
+
+            string[] inc = ["area-rels"];
+
+            area = await client.Area.GetAsync("c9ac1239-e832-41bc-9930-e252a1fd1105", inc);
+        }
+
+        [Test]
+        public void TestAreaElements()
+        {
+            Assert.That(area.Id, Is.EqualTo("c9ac1239-e832-41bc-9930-e252a1fd1105"));
+            Assert.That(area.Type, Is.EqualTo("City"));
+            Assert.That(area.Name, Is.EqualTo("Berlin"));
+            Assert.That(area.Relations, Is.Not.Null);
+            Assert.That(area.Iso2Codes, Is.Not.Null);
+        }
+
+        [Test]
+        public void TestAreaForwardRelations()
+        {
+            var list = area.Relations.Where(r => r.TargetType == "area" && r.Direction == "forward");
+
+            Assert.That(list.Count(), Is.GreaterThanOrEqualTo(6));
+        }
+
+        [Test]
+        public void TestAreaBackwardRelations()
+        {
+            var list = area.Relations.Where(r => r.TargetType == "area" && r.Direction == "backward");
+
+            Assert.That(list.Count(), Is.EqualTo(1));
+
+            var relation = list.First();
+
+            Assert.That(relation.Area, Is.Not.Null);
+            Assert.That(relation.Area.Type, Is.EqualTo("Country"));
+            Assert.That(relation.Area.Name, Is.EqualTo("Germany"));
+
+        }
+    }
+}

src/Hqub.MusicBrainz/Entities/Area.cs

@@ -11,6 +11,8 @@ namespace Hqub.MusicBrainz.Entities
     [DataContract(Name = "area")]
     public class Area : IEntity
     {
+        #region Properties
+
         /// <summary>
         /// Gets or sets the MusicBrainz id.
         /// </summary>
@@ -52,5 +54,20 @@ public class Area : IEntity
         /// </summary>
         [DataMember(Name = "iso-3166-2-codes")]
         public List<string> Iso2Codes { get; set; }
+
+        #endregion
+
+        #region Sub-queries
+
+        /// <summary>
+        /// Gets or sets a list of relations associated to this area.
+        /// </summary>
+        /// <example>
+        /// var e = await client.Area.GetAsync(mbid, "area-rels");
+        /// </example>
+        [DataMember(Name = "relations")]
+        public List<Relation> Relations { get; set; }
+
+        #endregion
     }
 }

src/Hqub.MusicBrainz/Entities/Relation.cs

@@ -86,6 +86,12 @@ public class Relation
         [DataMember(Name = "work")]
         public Work Work { get; set; }
 
+        /// <summary>
+        /// Gets or sets the area relationship (include area-rels).
+        /// </summary>
+        [DataMember(Name = "area")]
+        public Area Area { get; set; }
+
         // Other relationships:
         //
         //   /// <summary>

src/Hqub.MusicBrainz/MusicBrainzClient.cs

@@ -56,14 +56,19 @@
         /// </summary>
         public ILookupService<Work> Work { get; }
 
+        /// <summary>
+        /// Gets the area entity lookup service.
+        /// </summary>
+        public ILookupService<Area> Area { get; }
+
         #endregion
 
         /// <summary>
         /// Gets or sets the <see cref="IRequestCache"/> implementation.
         /// </summary>
         public IRequestCache Cache { get; set; }
 
-        private HttpClient client;
+        private readonly HttpClient client;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="MusicBrainzClient"/> class.
@@ -116,6 +121,7 @@
             ReleaseGroups = new ReleaseGroupService(this, urlBuilder);
 
             Work = new LookupService<Work>(this, urlBuilder, "work");
+            Area = new LookupService<Area>(this, urlBuilder, "area");
 
             client = httpClient;
         }
@@ -133,7 +139,7 @@
         {
             /// <summary>The error message.</summary>
             [DataMember(Name = "error")]
             public string Message;
         }
 
         internal async Task<T> GetAsync<T>(string url, CancellationToken ct = default)