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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. As expected, the Grid View lists each product with an Edit and Delete button in the leftmost column.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. Figure 14: The Products are Listed in a Grid View (Click to view full-size image) If you click the Delete button for any product, a method.The Data Access Layer must issue a SQL statement that will only update the record if the original values that the user started editing are identical to the values still in the database. Figure 2: For the Update or Delete to Succeed, the Original Values Must Be Equal to the Current Database Values (Click to view full-size image) There are various approaches to implementing optimistic concurrency (see Peter A. After completing the wizard, the Object Data Source's declarative markup should look like the following: property at this point, since this property indicates that the BLL method expects the old (or original) values to be passed in as well as the new values.Bromberg's Optmistic Concurrency Updating Logic for a brief look at a number of options). NET Typed Data Set provides one implementation that can be configured with just the tick of a checkbox. Update, true)] public bool Update Product( // new parameter values string product Name, int? Furthermore, this property value indicates the input parameter names for the original values.Therefore, in situations where pessimistic concurrency is used, there's typically a timeout that, if reached, cancels the lock. NET page that can utilize the optimistic concurrency logic built in to the system.
Figure 3: Connect to the Same Northwind Database (Click to view full-size image) Next, we are prompted as to how to query the data: through an ad-hoc SQL statement, a new stored procedure, or an existing stored procedure. For deleting, there are no new values, so only the original values need be passed in. Once the original values have been assigned to the protected void Assign All Product Values (Northwind Optimistic Concurrency. However, there are a few subtleties that will creep up and cause us problems.
Once this groundwork has been laid, we'll be ready to create the ASP. To create a new Typed Data Set, right-click on the . Delete, true)] public bool Delete Product (int original_product ID, string original_product Name, int? original_category ID, string original_quantity Per Unit, decimal? This is possible because the Data Table keeps track of the original and modified values for its Data Row(s). This will add a Command Field whose Bound Fields will render as Text Boxes, requiring the user to enter the appropriate category and supplier as ID numbers.
As we saw in the first tutorial, doing so will add a new Table Adapter to the Typed Data Set, automatically launching the Table Adapter Configuration Wizard. Html Controls; using Northwind Optimistic Concurrency Table Adapters; [System. Data Object] public class Products Optimistic Concurrency BLL instance for each product record in the database. When the DAL issues its populated in Step 1 is populated directly from the database, meaning that the original values used by the Data Row are those that currently exist in the database, and not those that were bound to the Grid View at the start of the editing process. There will be no formatting for the numeric fields and no validation controls to ensure that the product's name has been supplied and that the unit price, units in stock, units on order, and reorder level values are both proper numeric values and are greater than or equal to zero.
Optimistic concurrency control works by ensuring that the record being updated or deleted has the same values as it did when the updating or deleting process started. Start by opening the methods from drop-down lists in the wizard.
For example, when clicking the Edit button in an editable Grid View, the record's values are read from the database and displayed in Text Boxes and other Web controls. Later, after the user makes her changes and clicks the Update button, the original values plus the new values are sent to the Business Logic Layer, and then down to the Data Access Layer. For the Update Product method, use the overload that accepts all of the product's data fields.
Pessimistic concurrency is rarely used because such locks, if not properly relinquished, can prevent other users from updating data.