When the style property on an OpenApiParameter is 'form' then the default value for the explode property should be true. For all other styles the default value is false. Cover this in a unit test.

Author: simon-pearson-lmk

src/Microsoft.OpenApi/Models/OpenApiParameter.cs

@@ -14,6 +14,8 @@ namespace Microsoft.OpenApi.Models
     /// </summary>
     public class OpenApiParameter : IOpenApiSerializable, IOpenApiReferenceable, IOpenApiExtensible
     {
+        private bool? _explode;
+
         /// <summary>
         /// Indicates if object is populated with data or is just a reference to the data
         /// </summary>
@@ -79,7 +81,11 @@ public class OpenApiParameter : IOpenApiSerializable, IOpenApiReferenceable, IOp
         /// When style is form, the default value is true.
         /// For all other styles, the default value is false.
         /// </summary>
-        public bool Explode { get; set; }
+        public bool Explode
+        {
+            get => _explode ?? Style == ParameterStyle.Form;
+            set => _explode = value;
+        }
 
         /// <summary>
         /// Determines whether the parameter value SHOULD allow reserved characters,

test/Microsoft.OpenApi.Tests/Models/OpenApiParameterTests.cs

@@ -163,6 +163,24 @@ public OpenApiParameterTests(ITestOutputHelper output)
             _output = output;
         }
 
+        [Theory]
+        [InlineData(ParameterStyle.Form, true)]
+        [InlineData(ParameterStyle.SpaceDelimited, false)]
+        [InlineData(null, false)]
+        public void WhenStyleIsFormTheDefaultValueOfExplodeShouldBeTrueOtherwiseFalse(ParameterStyle? style, bool expectedExplode)
+        {
+            // Arrange
+            var parameter = new OpenApiParameter
+            {
+                Name = "name1",
+                In = ParameterLocation.Query,
+                Style = style
+            };
+
+            // Act & Assert
+            parameter.Explode.Should().Be(expectedExplode);
+        }
+
         [Fact]
         public void SerializeBasicParameterAsV3JsonWorks()
         {