Added Set extension method that supports setting properties with inaccessible setters

ModelBuilder.UnitTests/ExtensionsTests.cs

@@ -100,5 +100,186 @@ public void SetThrowsExceptionWithNullInstance()
 
             action.Should().Throw<ArgumentNullException>();
         }
+
+        [Fact]
+        public void SetExpressionThrowsExceptionWithNullAction()
+        {
+            var sut = new PropertySetters();
+
+            Action action = () => sut.Set(null!, true);
+
+            action.Should().Throw<ArgumentNullException>();
+        }
+
+        [Fact]
+        public void SetExpressionThrowsExceptionWithNullInstance()
+        {
+            var sut = new PropertySetters();
+
+            Action action = () => ((PropertySetters)null!).Set(x => x.AutoPublic, Guid.Empty);
+
+            action.Should().Throw<ArgumentNullException>();
+        }
+
+        [Fact]
+        public void SetExpressionAutoPublicSetter()
+        {
+            var sut = new PropertySetters();
+            var expected = Guid.NewGuid();
+
+            var actual = sut.Set(x => x.AutoPublic, expected);
+
+            actual.AutoPublic.Should().Be(expected);
+            sut.AutoPublic.Should().Be(expected);
+        }
+
+        [Fact]
+        public void SetExpressionAutoReadonlySetter()
+        {
+            var sut = new PropertySetters();
+
+            var actual = sut.Set(x => x.AutoReadonly, null);
+
+            actual.AutoReadonly.Should().BeNull();
+            sut.AutoReadonly.Should().BeNull();
+        }
+
+        [Fact]
+        public void SetExpressionAutoPrivateSetter()
+        {
+            var sut = new PropertySetters();
+            var expected = Model.Create<int>();
+
+            var actual = sut.Set(x => x.AutoPrivate, expected);
+
+            actual.AutoPrivate.Should().Be(expected);
+            sut.AutoPrivate.Should().Be(expected);
+        }
+
+        [Fact]
+        public void SetExpressionAutoProtectedSetter()
+        {
+            var sut = new PropertySetters();
+            var expected = Model.Create<decimal>();
+
+            var actual = sut.Set(x => x.AutoProtected, expected);
+
+            actual.AutoProtected.Should().Be(expected);
+            sut.AutoProtected.Should().Be(expected);
+        }
+
+        [Fact]
+        public void SetExpressionAutoProtectedInternalSetter()
+        {
+            var sut = new PropertySetters();
+            var expected = Model.Create<Uri>();
+
+            var actual = sut.Set(x => x.AutoProtectedInternal, expected);
+
+            actual.AutoProtectedInternal.Should().BeEquivalentTo(expected);
+            sut.AutoProtectedInternal.Should().BeEquivalentTo(expected);
+        }
+
+        [Fact]
+        public void SetExpressionAutoInternalSetter()
+        {
+            var sut = new PropertySetters();
+            var expected = Model.Create<DateTimeOffset>();
+
+            var actual = sut.Set(x => x.AutoInternal, expected);
+
+            actual.AutoInternal.Should().Be(expected);
+            sut.AutoInternal.Should().Be(expected);
+        }
+
+        [Fact]
+        public void SetExpressionAutoPrivateInternalSetter()
+        {
+            var sut = new PropertySetters();
+            var expected = Model.Create<PropertySetters>();
+
+            var actual = sut.Set(x => x.AutoPrivateInternal, expected);
+
+            actual.AutoPrivateInternal.Should().BeEquivalentTo(expected);
+            sut.AutoPrivateInternal.Should().BeEquivalentTo(expected);
+        }
+
+        [Fact]
+        public void SetExpressionAutoInitSetter()
+        {
+            var sut = new PropertySetters();
+            var expected = Model.Create<ConsoleColor>();
+
+            var actual = sut.Set(x => x.AutoInit, expected);
+
+            actual.AutoInit.Should().Be(expected);
+            sut.AutoInit.Should().Be(expected);
+        }
+
+        [Fact]
+        public void SetExpressionBackingField()
+        {
+            var sut = new PropertySetters();
+            var expected = Model.Create<float>();
+
+            var actual = sut.Set(x => x._backingField, expected);
+
+            actual._backingField.Should().Be(expected);
+            sut._backingField.Should().Be(expected);
+        }
+
+        [Fact]
+        public void SetExpressionPublicBackingFieldSetter()
+        {
+            var sut = new PropertySetters();
+            var expected = Model.Create<float>();
+
+            var actual = sut.Set(x => x.PublicBackingField, expected);
+
+            actual.PublicBackingField.Should().Be(expected);
+            sut.PublicBackingField.Should().Be(expected);
+        }
+
+        [Fact]
+        public void SetExpressionPrivateBackingFieldSetter()
+        {
+            var sut = new PropertySetters();
+            var expected = Model.Create<float>();
+
+            var actual = sut.Set(x => x.PrivateBackingField, expected);
+
+            actual.PrivateBackingField.Should().Be(expected);
+            sut.PrivateBackingField.Should().Be(expected);
+        }
+
+        [Fact]
+        public void SetExpressionReadonlySetterThrowsException()
+        {
+            var sut = new PropertySetters();
+
+            Action action = () => sut.Set(x => x.Readonly, null);
+
+            action.Should().Throw<NotSupportedException>();
+        }
+
+        [Fact]
+        public void SetExpressionMethodThrowsException()
+        {
+            var sut = new PropertySetters();
+
+            Action action = () => sut.Set(x => x.BackingFieldMethod(), default(float));
+
+            action.Should().Throw<NotSupportedException>();
+        }
+
+        [Fact]
+        public void SetExpressionComplexExpressionThrowsException()
+        {
+            var sut = new PropertySetters();
+
+            Action action = () => sut.Set(x => x.AutoPublic.ToString(), string.Empty);
+
+            action.Should().Throw<NotSupportedException>();
+        }
     }
 }

ModelBuilder.UnitTests/IsExternalInit.cs

@@ -0,0 +1,9 @@
+// the following namespace/class is required to be able to use init setters with framework versions lower than 5.0:
+// https://www.mking.net/blog/error-cs0518-isexternalinit-not-defined
+namespace System.Runtime.CompilerServices
+{
+    using System.ComponentModel;
+
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    internal static class IsExternalInit { }
+}

ModelBuilder.UnitTests/ModelBuilder.UnitTests.csproj

@@ -34,6 +34,7 @@
     <Compile Update="BuildConfigurationExtensionsTests.*.cs">
       <DependentUpon>BuildConfigurationExtensionsTests.cs</DependentUpon>
     </Compile>
+    <Compile Remove="IsExternalInit.cs" Condition="'$(TargetFramework)' == 'net5.0'" />
   </ItemGroup>
 
   <ItemGroup>

ModelBuilder.UnitTests/Models/PropertySetters.cs

@@ -0,0 +1,33 @@
+namespace ModelBuilder.UnitTests.Models
+{
+    using System;
+
+    public class PropertySetters
+    {
+        public Guid AutoPublic { get; set; }
+
+        public string? AutoReadonly { get; } = string.Empty;
+
+        public int AutoPrivate { get; private set; }
+
+        public decimal AutoProtected { get; protected set; }
+
+        public Uri? AutoProtectedInternal { get; protected internal set; }
+
+        public DateTimeOffset AutoInternal { get; internal set; }
+
+        public PropertySetters? AutoPrivateInternal { get; private protected set; }
+
+        public ConsoleColor AutoInit { get; init; }
+
+        internal float _backingField;
+        public float BackingFieldMethod() => _backingField;
+
+        public float PublicBackingField { get => _backingField; set => _backingField = value; }
+        public float BackingField { get => _backingField; set => _backingField = value; }
+
+        public float PrivateBackingField { get => _backingField; private set => _backingField = value; }
+
+        public char? Readonly => default;
+    }
+}

ModelBuilder/CommonExtensions.cs

@@ -2,6 +2,9 @@
 {
     using System;
     using System.Collections.Generic;
+    using System.Linq.Expressions;
+    using System.Reflection;
+    using System.Runtime.CompilerServices;
 
     /// <summary>
     ///     The <see cref="CommonExtensions" />
@@ -72,5 +75,74 @@ public static T Set<T>(this T instance, Action<T> action)
 
             return instance;
         }
+
+        /// <summary>
+        /// Supports setting properties with inaccessible setters such as private or protected
+        /// Also limited support for setting of readonly auto-properties
+        /// </summary>
+        /// <typeparam name="T">The type of instance being changed.</typeparam>
+        /// <typeparam name="TVALUE">The value to set the expresison function to.</typeparam>
+        /// <param name="instance">The instance to update.</param>
+        /// <param name="expressionFunc">The expresion function to set against the instance.</param>
+        /// <param name="value"></param>
+        /// <returns>The updated instance.</returns>
+        /// <exception cref="ArgumentNullException">The <paramref name="instance" /> parameter is <c>null</c>.</exception>
+        /// <exception cref="ArgumentNullException">The <paramref name="expressionFunc" /> parameter is <c>null</c>.</exception>
+        /// <exception cref="NotSupportedException">The <paramref name="expressionFunc" /> parameter is not supported - readonly and complex properties are not supported.</exception>
+        public static T Set<T, TVALUE>(this T instance, Expression<Func<T, TVALUE>> expressionFunc, TVALUE value)
+        {
+            instance = instance ?? throw new ArgumentNullException(nameof(instance));
+            expressionFunc = expressionFunc ?? throw new ArgumentNullException(nameof(expressionFunc));
+
+            var memberExpression = expressionFunc.Body as MemberExpression;
+            if (memberExpression == null)
+            {
+                throw new NotSupportedException("Only properties and fields are supported");
+            }
+
+            var member = memberExpression.Member;
+
+            var methodInfo = member as MethodInfo;
+            if (methodInfo != null)
+            {
+                throw new NotSupportedException("Methods are not supported");
+            }
+
+            var propertyInfo = member as PropertyInfo;
+            if (propertyInfo != null)
+            {
+                if (propertyInfo.GetSetMethod(true) != null)
+                {
+                    propertyInfo.SetValue(instance, value);
+                    return instance;
+                }
+
+                var declaringType = propertyInfo.DeclaringType;
+                if (declaringType == null)
+                {
+                    throw new NotSupportedException("Could not find declaring type");
+                }
+
+                var backingField = declaringType.GetField($"<{propertyInfo.Name}>k__BackingField", BindingFlags.NonPublic | BindingFlags.Instance);
+                if (backingField != null && backingField.GetCustomAttribute<CompilerGeneratedAttribute>() != null)
+                {
+                    member = backingField;
+                }
+                else
+                {
+                    throw new NotSupportedException("Could not find a backing field - readonly properties are not supported");
+                }
+            }
+
+            var fieldInfo = member as FieldInfo;
+            if (fieldInfo == null)
+            {
+                throw new NotSupportedException("The member is not supported");
+            }
+
+            fieldInfo.SetValue(instance, value);
+
+            return instance;
+        }
     }
 }