Lidarr/src/NzbDrone.Core/Datastore/Extensions/RelationshipExtensions.cs

using System;
using System.Linq;
using System.Linq.Expressions;
using Marr.Data;
using Marr.Data.Mapping;

namespace NzbDrone.Core.Datastore.Extensions
{
    public static class RelationshipExtensions
    {
        public static RelationshipBuilder<TParent> HasOne<TParent, TChild>(this RelationshipBuilder<TParent> relationshipBuilder, Expression<Func<TParent, LazyLoaded<TChild>>> portalExpression, Func<TParent, int> childIdSelector)
            where TParent : ModelBase
            where TChild : ModelBase
        {
            return relationshipBuilder.For(portalExpression.GetMemberName())
                                .LazyLoad(
                                            condition: parent => childIdSelector(parent) > 0,
                                            query: (db, parent) => 
                                            { 
                                                var id = childIdSelector(parent);
                                                return db.Query<TChild>().Where(c => c.Id == id).SingleOrDefault();
                                            }
                                         );
        }

        public static RelationshipBuilder<TParent> Relationship<TParent>(this ColumnMapBuilder<TParent> mapBuilder)
        {
            return mapBuilder.Relationships.MapProperties<TParent>();
        }

        private static string GetMemberName<T, TMember>(this Expression<Func<T, TMember>> member)
        {
            var expression = member.Body as MemberExpression;

            if (expression == null)
            {
                expression = (MemberExpression)((UnaryExpression)member.Body).Operand;
            }

            return expression.Member.Name;
        }
    }
}