Compute totals of invoice server side when invoice/invoiceLine changed - entity-framework

Question

I use Breeze with Durandal (still 1.2) and I am facing a problem which I haven't found an easy solution for. I have 2 entities: Invoice & InvoiceLine like described below:
public class Invoice
{
[Key]
public int Id { get; set; }
public string InvoiceNumber { get; set; }
public string Comment { get; set; }
public double? TotalExclVAT { get; set; }
public double? TotalInclVAT { get; set; }
public double? TotalVAT { get; set; }
public bool? WithoutVAT { get; set; }
public virtual List<InvoiceLine> Lines { get; set; }
}
public class InvoiceLine
{
[Key]
public int Id { get; set; }
public string Description { get; set; }
public double VatPercent { get; set; }
public double Amount { get; set; }
public int InvoiceId { get; set; }
public virtual Invoice Invoice { get; set; }
}
I need to compute the totals of the invoice (TotalExclVAT, TotalInclVAT, TotalVAT) in 2 cases:
Whenever someone adds/modifies an invoice line.
Whenever someone changes the flag WithoutVAT on the invoice.
I don't think this is a good idea to perform this compute client side. Performing this server side is better for security reasons mainly.
My first thought was to do the job in the BeforeSaveEntity of Invoice & InvoiceLine.
Here is what i did:
public bool BeforeSaveEntity(EntityState entityState, EntityInfo entityInfo)
{
var invoice = entityInfo.Entity as Invoice;
...
ComputeTotal(entityInfo, invoice);
}
private void ComputeTotal(EntityInfo entityInfo, Invoice invoice)
{
var query = Context.InvoiceLines.Where(x => x.invoiceId == invoice.Id).AsEnumerable();
double totalExclVAT = 0;
double totalVAT = 0;
int percent = 0;
foreach (var line in query.ToList())
{
totalExclVAT = ...
totalVAT = ...
}
entityInfo.OriginalValuesMap.Add("TotalExclVAT", invoice.TotalExclVAT);
entityInfo.OriginalValuesMap.Add("TotalInclVAT", invoice.TotalInclVAT);
entityInfo.OriginalValuesMap.Add("TotalVAT", invoice.TotalVAT);
accounting.TotalExclVAT = totalExclVAT;
accounting.TotalInclVAT = totalExclVAT + totalVAT;
accounting.TotalVAT = totalVAT;
}
The same kind of thing is done for the invoice line. As you can see in the ComputeTotal function, I perform a query to get invoice lines from DB then computing totals and saving results in the invoice.
It doesn't work quite well: in case of adding a new line on my invoice, performing a query on my DB doesn't get this added line! Because it is not already stored in DB.
It would have been easier to proceed client side but I don't think this is a good idea... is it?
So I am sure there is another way of doing but I don't find it myself.
Any help is greathly appreciated.
UPDATE
Below is my first shot with this problem.
public Dictionary<Type, List<EntityInfo>> BeforeSaveEntities(Dictionary<Type, List<EntityInfo>> saveMap)
{
List<EntityInfo> invoices;
List<EntityInfo> invoiceLines;
EntityInfo ei;
if (!saveMap.TryGetValue(typeof(InvoiceLine), out invoiceLines))
{
// if we fall here it means no invoice lines exists in the saveMap
}
if (!saveMap.TryGetValue(typeof(Invoice), out invoices))
{
// if we fall here it means no invoices exists in the saveMap
// >> getting the invoice from DB and add it to the map
using (var dc = new BreezeContext())
{
int invoiceId = ((InvoiceLine)invoiceLines[0].Entity).InvoiceId;
EFContextProvider<BreezeContext> cp = new EFContextProvider<BreezeContext>();
var acc = dc.Invoices.Where(x => x.Id == invoiceId).FirstOrDefault();
ei = cp.CreateEntityInfo(acc, Breeze.WebApi.EntityState.Modified);
invoices = new List<EntityInfo>();
saveMap.Add(typeof(Invoice), invoices);
invoices.Add(ei);
}
}
// There is only 1 invoice at a time in the saveMap
Invoice invoice = (Invoice)invoices[0].Entity;
ei = invoices[0];
Dictionary<int, InvoiceLine> hashset = new Dictionary<int, InvoiceLine>();
// Retrieving values of invoice lines from database (server side)
using (var dc = new BreezeContext())
{
var linesServerSide = dc.InvoiceLines.Where(x => x.InvoiceId == invoice.Id).AsEnumerable();
foreach (var elm in linesServerSide)
{
hashset.Add(elm.Id, elm);
}
}
// Retrieving values of invoice lines from modified lines (client side)
foreach (var entityInfo in invoiceLines)
{
InvoiceLine entity = (InvoiceLine)entityInfo.Entity;
switch (entityInfo.EntityState)
{
case Breeze.WebApi.EntityState.Added:
hashset.Add(entity.Id, entity);
break;
case Breeze.WebApi.EntityState.Deleted:
hashset.Remove(entity.Id);
break;
case Breeze.WebApi.EntityState.Modified:
hashset.Remove(entity.Id);
hashset.Add(entity.Id, entity);
break;
}
}
// Computing totals based on my hashset
double totalExclVAT = 0;
double totalInclVAT = 0;
double totalVAT = 0;
foreach (var elm in hashset)
{
InvoiceLine line = elm.Value;
totalExclVAT += line.Amount;
totalVAT += line.Amount * (int)line.VatPercent.Value / 100;
}
totalInclVAT = totalExclVAT + totalVAT;
// Adding keys if necessary
if (!ei.OriginalValuesMap.ContainsKey("TotalExclVAT"))
ei.OriginalValuesMap.Add("TotalExclVAT", invoice.TotalExclVAT);
if (!ei.OriginalValuesMap.ContainsKey("TotalInclVAT"))
ei.OriginalValuesMap.Add("TotalInclVAT", invoice.TotalInclVAT);
if (!ei.OriginalValuesMap.ContainsKey("TotalVAT"))
ei.OriginalValuesMap.Add("TotalVAT", invoice.TotalVAT);
// Modifying total values
invoice.TotalExclVAT = totalExclVAT;
invoice.TotalInclVAT = totalInclVAT;
invoice.TotalVAT = totalVAT;
return saveMap;
}
The solution above works well whenever the invoice & the invoiceLines are modified client side. I have a problem when no invoice is modified client side (only lines modified). In this case I need to add the related invoice to the saveMap by getting it from DB. That's what I do in my code as you can see. But I need to add keys to the OriginalValuesMap for properties I manually modified here and I cannot in this case because my dictionary object is null. Then when I do...
ei.OriginalValuesMap.Add("TotalExclVAT", invoice.TotalExclVAT);
... on a null object (OriginalValuesMap) it doesn't work.
So my new problem is now the next: how to add an entity to the saveMap which already exists on DB. So I don't want to mark this entity as ei = cp.CreateEntityInfo(acc, Breeze.WebApi.EntityState.Add); but rather ei = cp.CreateEntityInfo(acc, Breeze.WebApi.EntityState.Modified);. In this case my OriginalValuesMap is null and it seems to be a problem.
Hope you understand what I try to explain here.

Answer 1

Is there any reason not to use a triggered stored procedure for this? This would certainly be the simplest approach...
But... if there is, then the other approach would be to use 'BeforeSaveEntities' instead of 'BeforeSaveEntity' because this will give you access to the entire 'SaveMap'.
Then create a hashset of all of the invoiceLines for each modified invoice and construct this as the combination of your server side query of invoice lines per invoice overlayed with client side invoiceLines associated with this invoice (from the SaveMap). Next just total each hashSet and use this update your 'Totalxxx' properties.
A little terse but hopefully this makes sense.