add additional parameter to relationshipattribute to allow for specifying the internal name instead of only inferring it from the dto variable name, as that may not match the entity relationship name

Author: roblankey

src/Examples/JsonApiDotNetCoreExample/Models/Person.cs

@@ -21,7 +21,7 @@ public class Person : Identifiable, IHasMeta
         [HasMany("todo-collections")]
         public virtual List<TodoItemCollection> TodoItemCollections { get; set; }
 
-        [HasOne("unincludeable-item", Link.All, canInclude: false)]
+        [HasOne("unincludeable-item", documentLinks: Link.All, canInclude: false)]
         public virtual TodoItem UnIncludeableItem { get; set; }
 
         public Dictionary<string, object> GetMeta(IJsonApiContext context)

src/JsonApiDotNetCore/Builders/ContextGraphBuilder.cs

@@ -125,7 +125,7 @@ protected virtual List<RelationshipAttribute> GetRelationships(Type entityType)
             {
                 var attribute = (RelationshipAttribute)prop.GetCustomAttribute(typeof(RelationshipAttribute));
                 if (attribute == null) continue;
-                attribute.InternalRelationshipName = prop.Name;
+                if (attribute.InternalRelationshipName == null) attribute.InternalRelationshipName = prop.Name;
                 attribute.Type = GetRelationshipType(attribute, prop);
                 attributes.Add(attribute);
             }

src/JsonApiDotNetCore/Models/HasManyAttribute.cs

@@ -7,6 +7,7 @@ public class HasManyAttribute : RelationshipAttribute
         /// </summary>
         /// 
         /// <param name="publicName">The relationship name as exposed by the API</param>
+        /// <param name="internalName">The relationship name as defined in the entity layer, if not provided defaults to the variable name</param>
         /// <param name="documentLinks">Which links are available. Defaults to <see cref="Link.All"/></param>
         /// <param name="canInclude">Whether or not this relationship can be included using the <c>?include=public-name</c> query string</param>
         /// 
@@ -21,8 +22,9 @@ public class HasManyAttribute : RelationshipAttribute
         /// </code>
         /// 
         /// </example>
-        public HasManyAttribute(string publicName, Link documentLinks = Link.All, bool canInclude = true)
-        : base(publicName, documentLinks, canInclude)
+        public HasManyAttribute(string publicName, string internalName = null, Link documentLinks = Link.All, 
+            bool canInclude = true)
+        : base(publicName, internalName, documentLinks, canInclude)
         { }
 
         /// <summary>

src/JsonApiDotNetCore/Models/HasOneAttribute.cs

@@ -7,6 +7,7 @@ public class HasOneAttribute : RelationshipAttribute
         /// </summary>
         /// 
         /// <param name="publicName">The relationship name as exposed by the API</param>
+        /// <param name="internalName">The relationship name as defined in the entity layer, if not provided defaults to the variable name</param>
         /// <param name="documentLinks">Which links are available. Defaults to <see cref="Link.All"/></param>
         /// <param name="canInclude">Whether or not this relationship can be included using the <c>?include=public-name</c> query string</param>
         /// <param name="withForiegnKey">The foreign key property name. Defaults to <c>"{RelationshipName}Id"</c></param>
@@ -24,8 +25,9 @@ public class HasOneAttribute : RelationshipAttribute
         /// </code>
         /// 
         /// </example>
-        public HasOneAttribute(string publicName, Link documentLinks = Link.All, bool canInclude = true, string withForiegnKey = null)
-        : base(publicName, documentLinks, canInclude)
+        public HasOneAttribute(string publicName, string internalName = null, Link documentLinks = Link.All, 
+            bool canInclude = true, string withForiegnKey = null)
+        : base(publicName, internalName, documentLinks, canInclude)
         {
             _explicitIdentifiablePropertyName = withForiegnKey;
         }

src/JsonApiDotNetCore/Models/RelationshipAttribute.cs

@@ -4,11 +4,12 @@ namespace JsonApiDotNetCore.Models
 {
     public abstract class RelationshipAttribute : Attribute
     {
-        protected RelationshipAttribute(string publicName, Link documentLinks, bool canInclude)
+        protected RelationshipAttribute(string publicName, string internalName, Link documentLinks, bool canInclude)
         {
             PublicRelationshipName = publicName;
             DocumentLinks = documentLinks;
             CanInclude = canInclude;
+            InternalRelationshipName = internalName;
         }
 
         public string PublicRelationshipName { get; }

test/UnitTests/Builders/DocumentBuilder_Tests.cs

@@ -233,7 +233,7 @@ private class Model : Identifiable
         {
             [Attr("StringProperty")] public string StringProperty { get; set; }
 
-            [HasOne("related-model", Link.None)]
+            [HasOne("related-model", documentLinks: Link.None)]
             public RelatedModel RelatedModel { get; set; }
             public int RelatedModelId { get; set; }
         }