Business Rules/Logic

Database engines include built-in mechanisms for transaction management. The application can begin a transaction and have it committed or rolled back. The database engine will ensure that uncommitted data will not be visible to other users.

Web applications cannot take advantage of transaction managers built into database engines. To ensure scalability, web applications maintain a pool of database connections shared by multiple users simultaneously. Transaction managers require that all modifications of data are performed in the context of a single open database connection. A typical web application may handle requests to modify data from a single user by utilizing multiple pooled connections.

Client-Side Caching

Developers can implement client-side caching of requests to update data. The application user modifies several data items on the client and requests to submit changes at once. The entire batch of modifications is sent to the web application server for processing. The server code will parse the batch and perform individual updates using a database transaction.

Users will have to stay on the same web page until the data is submitted. There is a potential for data loss if a browser window is accidentally closed. The data entry sessions must be short.

The application developer has to rely heavily on JavaScript when manipulating data. Every data entry screen becomes a specialty project.

Server-side Data Staging

A substantially more flexible solution is to “stage” data on the server. Data records are submitted straight to the database tables, and marked as “Draft” using various techniques. When the draft data is ready to be included in the main dataset, the status of the data rows is changed to “Committed”.

Users can submit draft data from multiple pages. The data is safely stored in the database instead of volatile browser cache. The drafted data may be perfected over any period of time from multiple devices.

Application developers can take full advantage of SQL when manipulating draft data. Code On Time web applications include mechanisms that make data staging implementation trivial.

Data Staging Strategies

Suppose that you have created an Order Form web application from the Northwind sample database. Each order is stored in two tables: dbo.Orders and dbo.[Order Details]. When a user wants to create a new order, they must first create the order record, and then add a few order details.

The user should have the opportunity to add or change details, or drop the order altogether before committing it to the primary data set.

However, these “draft” orders will be included in all data sets, such as Order Subtotals. It is necessary to segregate the draft order data from the primary data set.

Consider the following methods of draft data staging when implementing web transactions.

1. “Status” Field
   
   This method involves adding a “Status” field to the Orders table that will indicate whether the order is a draft or has been committed. The status of new orders will have the default value of “Draft”. A custom action will be added to the order form to submit the order and change the status to “Commited”.
   
2. Log Table
   
   This method creates a table that holds a log of all draft orders. When a new order is created, a reference will be created in the draft order log table. When the data is submitted, the reference will be deleted from the log table.
   
3. Data Staging Tables
   
   This method requires creation of duplicate “staging” tables that will hold the draft data. When the order is ready to be submitted, it is copied to the original tables and deleted from the staging tables.

The first two methods will use dynamic access control rules in order to prevent committed data from being displayed on the order form, and draft data from being displayed on all other pages.

The most robust method to ensure separation between “draft” and “committed” data is physical segregation of draft data in dedicated staging tables. When data is ready to be committed, it is moved from draft tables to the primary database tables. For example, orders in the Northwind sample database are stored in Orders and OrderDetails – the primary tables. DraftOrders and DraftOrderDetails tables will be created in order to store draft orders.

A custom action in DraftOrders controller will copy the draft order and order details to the primary tables, and delete the draft data rows.

Adding the DraftOrders and DraftOrderDetails Tables

Start SQL Server Management Studio. In the Object Explorer window, right-click on Databases / Northwind node, and press New Query.

Paste the following script into the query window:

create table dbo.DraftOrders(
    OrderID int IDENTITY(1,1) not null,
    CustomerID nchar(5) null,
    EmployeeID int null,
    OrderDate datetime null,
    RequiredDate datetime null,
    ShippedDate datetime null,
    ShipVia int null,
    Freight money null,
    ShipName nvarchar(40) null,
    ShipAddress nvarchar(60) null,
    ShipCity nvarchar(15) null,
    ShipRegion nvarchar(15) null,
    ShipPostalCode nvarchar(10) null,
    ShipCountry nvarchar(15) null,
    PRIMARY KEY (OrderID)
)
go

alter table dbo.DraftOrders add foreign key(CustomerID)
references dbo.Customers (CustomerID)
go

alter table dbo.DraftOrders  add foreign key(EmployeeID)
references dbo.Employees (EmployeeID)
go

alter table dbo.DraftOrders  add foreign key(ShipVia)
references dbo.Shippers (ShipperID)
go

create table dbo.DraftOrderDetails(
    OrderID int,
    ProductID int,
    UnitPrice money default (0),
    Quantity smallint default (1),
    Discount real default (0),
    primary key (OrderID, ProductID)
)
go

alter table dbo.DraftOrderDetails add foreign key (OrderID)
references dbo.DraftOrders (OrderID)
go

alter table dbo.DraftOrderDetails add foreign key (ProductID)
references dbo.Products (ProductID)
go

This script will create DraftOrders and DraftOrderDetails tables with the same columns as the primary Orders and OrderDetails tables. It also recreates the relationships with lookup tables – Customers, Employees, Shippers, and Products.

Run the script by pressing Execute on the toolbar.

Creating Draft Order Form

Follow the Order Form Sample tutorial to create a draft order form. Make sure to use DraftOrders and DraftOrderDetails instead of Orders and OrderDetails when implementing the form.

Creating “Submit Order” Action

The next step is to create an action that will move the draft order and draft order details into the original Orders and OrderDetails tables.

In the Project Designer, switch to the Controllers tab. Right-click on DraftOrders / Actions / ag2 (Form) node, and press New Action.

Assign the following values:

Press OK to save. Drop a100 – Custom, SubmitOrder | Submit Order node to the left side of the first action in ag2 to place it first in the group.

Handling the Action

Right-click on DraftOrders / Business Rules node, and press New Business Rule.

Assign these values:

In the Script property, enter the following:

begin transaction;

begin try
    -- move submitted order from DraftOrders to Orders
    insert into Orders (CustomerID, EmployeeID, OrderDate, 
                        RequiredDate, ShippedDate, ShipVia, 
                        Freight, ShipName, ShipAddress, 
                        ShipCity, ShipRegion, ShipPostalCode, 
                        ShipCountry)
    select CustomerID, EmployeeID, OrderDate, RequiredDate, 
            ShippedDate, ShipVia, Freight, ShipName, 
            ShipAddress, ShipCity, ShipRegion, ShipPostalCode, 
            ShipCountry
    from DraftOrders 
    where OrderID = @OrderID;

    -- find ID of committed order
    declare @NewOrderID int;
    select @NewOrderID = @@IDENTITY;

    -- move submitted order details from DraftOrderDetails to "Order Details"
    insert into "Order Details" (OrderID, ProductID, UnitPrice,
                                Quantity, Discount)
    select @NewOrderID, ProductID, UnitPrice,
            Quantity, Discount
    from DraftOrderDetails
    where OrderID = @OrderID;

    -- delete draft order and order details
    delete from DraftOrderDetails
    where OrderID = @OrderID;

    delete from DraftOrders
    where OrderID = @OrderID;

    commit transaction;

    -- refresh the page
    set @Result_NavigateUrl = 'OrderForm.aspx'
end try
begin catch
    rollback transaction;
    -- display error message
    declare @Error as nvarchar(500);
    select @Error = error_message();
    set @Result_ShowMessage = 'Order has not been submitted. ' + @Error;
end catch

Press OK to save.

Try testing the action – it will properly move the draft order and details into the Orders and OrderDetails tables. If any errors occur, the transaction will be rolled back and an error message will be displayed to the end user at the top of the web page.