Search Tag Data in Cache with SQL Query

NCache provides object queries through which you can search and delete result sets based on the criteria given to the query. To retrieve data according to your specified criteria, NCache provides you with an extension of SQL queries. It lets you search the data in your cache based on the criteria of the requirement. A special keyword $Tag$ is used to specify that the condition under consideration uses tags. The SQL query with the searching criteria is executed using ExecuteReader. The ExecuteReader processes the query on the server-side and then sends the result in chunks (as a dictionary containing keys and values) to the client in the tabular form to the ICacheReader type of instance.

You can query an item having a specific tag as explained below.

Prerequisites to Search Tag Data in Cache Using SQL Query

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, ExecuteReader, SearchService.

Search Data in Cache with One Tag

Using object queries, a single tag can be used to retrieve all the items associated with that tag.

Syntax

The following example retrieves all the items associated with the tag VIP Customers using the SQL query.

Note

Use the fully-qualified name (FQN) of the class Customer, e.g., Data.Customer.

// Precondition: Cache is already connected
// Create a query for search
// Use the Fully Qualified Name (FQN) of your own custom class
string query = "Select CustomerID,ContactName FROM Alachisoft.NCache.Samples.Data.Customer WHERE $Tag$ = ?";

// Use QueryCommand for query execution
var queryCommand = new QueryCommand(query);
queryCommand.Parameters.Add("$Tag$", "VIP Customers");

// Executing Query
ICacheReader reader = cache.SearchService.ExecuteReader(queryCommand);

// Read results if result set is not empty
if (reader.FieldCount > 0)
{
    while (reader.Read())
    {
        // Get the value of the result set
        string customerID = reader.GetValue<string>("CustomerID");
        string contactName = reader.GetValue<string>("ContactName");

        Console.WriteLine($"Customer '{contactName}' having ID '{customerID}' is a VIP Customer.");
    }
}
else
{
    Console.WriteLine($"No VIP Customers found");
}

// Pre-condition: Cache is already connected
// Create a query for search
// Use the Fully Qualified Name (FQN) of your custom class
String query = "Select customerID,contactName FROM com.alachisoft.ncache.sample.Customer WHERE $Tag$ = ?";

// Use QueryCommand for query execution
QueryCommand queryCommand = new QueryCommand(query);
queryCommand.getParameters().put("$Tag$", "VIP Customers");

// Executing Query
CacheReader reader = cache.getSearchService().executeReader(queryCommand);

// Read results if result set is not empty
if (reader.getFieldCount() > 0) {
    while (reader.read()) {
        // Get the value of the result set
        String customerID = reader.getValue("customerID", String.class);
        String contactName = reader.getValue("contactName", String.class);

        System.out.println("Customer '" + contactName + "' having ID '" + customerID + "' is a VIP Customer.");
    }
} else {
    System.out.println("No VIP Customers found");
}

# Preconditions: Cache is already connected
# Items are already present in the cache with tags
# Custom class is query indexed through NCache Management Center or config.ncconf

# Search for items with tags
# Use the Fully Qualified Name(FQN) of your own custom class
query = "Select $Value$ FROM FQN.Customer WHERE $Tag$ = ?"

# Use QueryCommand for query execution
query_command = ncache.QueryCommand(query)
query_command.set_parameters({"$Tag$": "Important Customers"})

# Executing query
search_service = cache.get_search_service()
reader = search_service.execute_reader(query_command)

# Check if result set is not empty

if reader.get_field_count() > 0:
    while reader.read():
        # Get the value of the result set
        result = reader.get_value(Customer, 1)
else:
    # None query result set retrieved
    print("Result set is None")

// Preconditions: Cache is already connected
// This is an async method

// Items are already present in the cache with tags
// Custom class is query indexed through NCache Management Center or config.ncconf

// Search for items with tags
// Use the Fully Qualified Name (FQN) of your own custom class
var query = "Select $Value$ FROM FQN.Customer WHERE $Tag$ = ?";

// Use QueryCommand for query execution
var queryCommand = new ncache.QueryCommand(query);
queryCommand.getParameters().set("$Tag$", "Important Customers");

// Executing query
var searchService = await this.cache.getSearchService();
var reader = await searchService.executeReader(queryCommand);

// Check if result set is not empty

if (reader.getFieldCount() > 0)
{
    while (reader.read())
    {
        // Get the value of the result set
        var result = reader.getValue(1);
    }
}
else
{
    // Null query result set retrieved
}

Warning

Providing a Null tag value for the query will throw an ArgumentNullException or NullPointerException.

In order to get more detail on NCache queries, please refer to the SQL Reference for NCache section.

Note

To ensure the operation is fail-safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.

Additional Resources

NCache provides sample application for Tags on GitHub.

Search Tag Data in Cache with SQL Query

Prerequisites to Search Tag Data in Cache Using SQL Query

Search Data in Cache with One Tag

Syntax

Note

Warning

Note

Additional Resources

See Also

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