C#, EF: The 'hard' way to get JOIN...

EfHardJoin.cs

static class Sample
{
    /// <summary>
    /// Queries the requisitions.
    /// </summary>
    public static IQueryable<Requisition> QueryRequisitions()
    {
        var ctx = GetContext();
    
        var statusIdsQuery = ctx.OrderStatuses
            .Select(i => i.OrderStatusId);
    
        var orderIdsQuery = ctx.OrderDetails
            .Where(i => i.BusinessType == "R")
            .Select(i => i.OrderID);
    
        var rentalChildrenQuery = XavierContext.QueryRentalChildren()
            .Select(i => i.OrderId);
    
        var query = ctx.OrderHeaders
            .Include("OrderDetails")
            .Where(i => i.OrderId != null)
            .Where(i => i.RequisitionType == "R")
            .Where(i => statusIdsQuery.Contains(i.OrderStatusID))
            .Where(i => !orderIdsQuery.Contains(i.OrderId))
            .Where(i => i.IsRentalParent == false)
            .Where(i => !rentalChildrenQuery.Contains(i.OrderId))
            .Join(ctx.Departments,
                oh => oh.DepartmentID,
                dept => dept.DepartmentID,
                (oh, dept) => new {oh, dept})
            .Join(ctx.OrderStatuses,
                join => join.oh.OrderStatusID,
                status => status.OrderStatusId,
                (join, status) => new { join, status })
            .Join(ctx.OrderDetails,
                join => join.join.oh.OrderId,
                detail => detail.OrderID,
                (join, detail) => new { join, detail })
            .OrderByDescending(i => i.join.join.oh.OrderId)
            .Select(i => new Requisition
            {
                OrderId = i.join.join.oh.OrderId,
                OrderNumber = i.join.join.oh.OrderNumber,
                PONumber = i.join.join.oh.PONumber,
                DepartmentName = i.join.join.dept.DepartmentName,
                CustomerName = i.join.join.oh.CustomerName,
                CreatedDt = i.join.join.oh.CreatedDt,
                PriorityFl = i.join.join.oh.PriorityFl,
                OrderStatusDescription = i.join.status.StatusDescription,
                CreatedBy = i.join.join.oh.CreatedBy,
                OrderTotal = i.join.join.oh.OrderDetails.Sum(j => j.TotalAmount)
            });
    
        return query;
    }
}