Delete Tag Data from Cache with SQL
This feature is only available in NCache Enterprise.
Object queries can also be used to remove items from the cache with your query criteria being tags. Object queries let you search the data in your cache and then delete it.
The idea of a special keyword
$Tag$ also exists here.
ExecuteNonQuery is used in queries containing delete operations. It returns the number of affected rows after the query is executed.
You can remove the items present with a specific tag as explained below.
- To learn about the standard prerequisites required to work with all NCache client-side features please refer to the given page on Client Side API Prerequisites.
- Custom classes/searchable attributes must be indexed as explained in Configuring Query Indexes.
- For API details refer to: ICache, ICacheReader, QueryCommand, ExecuteNonQuery, SearchService.
SQL DELETE for One Tag
Using object queries, items can be deleted using a single tag. You can delete a single tag using the SQL query as explained in the example below.
The following example deletes all the items associated with the tag West Coast Customers using the SQL query.
// Precondition: Cache is already connected // Make sure to use the Fully Qualified Name (FQN) string query = "DELETE FROM Alachisoft.NCache.Samples.Data.Customer WHERE $Tag$ = ?"; // Create query command and add parameter var queryCommand = new QueryCommand(query); queryCommand.Parameters.Add("$Tag$", "West Coast Customers"); // Executing Query int rowsAffected = cache.SearchService.ExecuteNonQuery(queryCommand); if (rowsAffected == 0) Console.WriteLine($"No Customers from West Coast found");
Null tag value for the query will throw an ArgumentNullException or NullPointerException.
To ensure the operation is fail-safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.
To get more detail on object queries please refer to the SQL Reference for NCache section.
NCache provides a sample application for Tags on GitHub.