Exception thrown if relationship name doesn't match navigation property name

[jaredcnance]

Discovered in v2.4.0-beta3

JsonApiException: N2JsonApi.Models.Item does not contain a relationship named ...
JsonApiDotNetCore.Internal.ContextGraph in GetRelationship

JsonApiDotNetCore/src/JsonApiDotNetCore/Internal/ContextGraph.cs

Lines 51 to 63 in 271693a

	public object GetRelationship<TParent>(TParent entity, string relationshipName)
	{
	var parentEntityType = entity.GetType();
	var navigationProperty = parentEntityType
	.GetProperties()
	.SingleOrDefault(p => string.Equals(p.Name, relationshipName, StringComparison.OrdinalIgnoreCase));
	if (navigationProperty == null)
	throw new JsonApiException(400, $"{parentEntityType} does not contain a relationship named {relationshipName}");
	return navigationProperty.GetValue(entity);
	}

Update

Caused by: https://github.com/json-api-dotnet/JsonApiDotNetCore/pull/352/files#diff-967b2ba5f610a691c8d3f1b7ffbafe72L87

Need to improve API documentation so it is more clear what these methods do.

Also, need to add tests with compound (or just different) attribute names.