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For web applications that only allow users to view data, or for those that include only a single user who can modify data, there's no threat of two concurrent users accidentally overwriting one another's changes.
For web applications that allow multiple users to update or delete data, however, there's the potential for one user's modifications to clash with another concurrent user's.
Since we used ad-hoc SQL queries in our original DAL, use this option here as well.
Figure 4: Specify the Data to Retrieve Using an Ad-Hoc SQL Statement (Click to view full-size image) On the following screen, enter the SQL query to use to retrieve the product information. Discontinued = discontinued End Sub _ Public Function Update Product( By Val product Name As String, By Val supplier ID As Nullable(Of Integer), _ By Val category ID As Nullable(Of Integer), By Val quantity Per Unit As String, _ By Val unit Price As Nullable(Of Decimal), By Val units In Stock As Nullable(Of Short), _ By Val units On Order As Nullable(Of Short), By Val reorder Level As Nullable(Of Short), _ By Val discontinued As Boolean, By Val product ID As Integer, _ _ By Val original_product Name As String, _ By Val original_supplier ID As Nullable(Of Integer), _ By Val original_category ID As Nullable(Of Integer), _ By Val original_quantity Per Unit As String, _ By Val original_unit Price As Nullable(Of Decimal), _ By Val original_units In Stock As Nullable(Of Short), _ By Val original_units On Order As Nullable(Of Short), _ By Val original_reorder Level As Nullable(Of Short), _ By Val original_discontinued As Boolean, _ By Val original_product ID As Integer) _ As Boolean ' STEP 1: Read in the current database product information Dim products As _ Northwind Optimistic Concurrency.
This results in an to the corresponding Beverages category ID, and so on.
The , that DB direct methods were those that accepts a list of scalar values as input parameters (rather than a strongly-typed Data Row or Data Table instance).Therefore, in situations where pessimistic concurrency is used, there's typically a timeout that, if reached, cancels the lock.Ticket sales websites, which lock a particular seating location for short period while the user completes the order process, is an example of pessimistic concurrency control.Figure 6: Enable Optimistic Concurrency Control by Checking the "Use optimistic concurrency" Check Box (Click to view full-size image) Lastly, indicate that the Table Adapter should use the data access patterns that both fill a Data Table and return a Data Table; also indicate that the DB direct methods should be created. Count = 0 Then ' no matching record found, return false Return False End If Dim product As _ Northwind Optimistic Concurrency.Change the method name for the Return a Data Table pattern from Get Data to Get Products, so as to mirror the naming conventions we used in our original DAL. Products Optimistic Concurrency Row = products(0) ' STEP 2: Assign the original values to the product instance Assign All Product Values( _ product, original_product Name, original_supplier ID, _ original_category ID, original_quantity Per Unit, original_unit Price, _ original_units In Stock, original_units On Order, original_reorder Level, _ original_discontinued) ' STEP 3: Accept the changes product.