Search Group Data in Cache with SQL Query

NCache provides object queries through which you use criteria given in a query to search result sets. To retrieve the data according to your specified criteria, NCache provides you with an extension of SQL. A special keyword $Group$ is used to specify that the condition under consideration uses group. A 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.

Prerequisites to Search Group 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.

Warning

If the searched group is not in the cache, the query will be returned as a Null value.

Search for Data in Groups using SQL Query

You can also search for the cache items present in groups through SQL. The following program searches for Customer IDs present in a group through SQL query.

// A user wants to see all the West Coast Customers using the SQL query.

// Preconditions: Cache is already connected
// Items with groups exist in the cache
// Custom class is query indexed through the NCache Management Center or config.ncconf
// Create an SQL Query with the specified criteria
// Make sure to use the Fully Qualified Name (FQN)
string query = "SELECT CustomerID,ContactName FROM Alachisoft.NCache.Samples.Data.Customer WHERE $Group$ = ? ";

// Use QueryCommand for query execution
var queryCommand = new QueryCommand(query);

// Providing parameters for query
queryCommand.Parameters.Add("$Group$", "West Coast Customers");

// Executing the 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 customerName = reader.GetValue<string>("ContactName");

        Console.WriteLine($"Customer '{customerName}' having ID '{customerID}' belongs to West Coast.");
    }
}
else
{
    Console.WriteLine($"No customers from West Coast found");
}

// A user wants to see all the West Coast Customers using the SQL query.

// Preconditions: Cache is already connected
// Items with groups exist in the cache
// Custom class is query indexed through the NCache Management Center or config.ncconf
// Create an SQL Query with the specified criteria
// Make sure to use the Fully Qualified Name (FQN)
String query = "SELECT customerID,contactName FROM com.alachisoft.ncache.samples.Customer WHERE $Group$ = ?";

// Use QueryCommand for query execution
QueryCommand queryCommand = new QueryCommand(query);

// Providing parameters for query
queryCommand.getParameters().put("$Group$", "West Coast Customers");

// Executing the 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 = null;
        customerID = reader.getValue("customerID", String.class);

        String customerName = null;
        customerName = reader.getValue("contactName", String.class);

        System.out.println("Customer '" + customerName + "' having ID '" + customerID + "' belongs to West Coast.");
    }
}
else {
    System.out.println("No customers from West Coast found");
}

# Preconditions: Cache is already connected
# Items with groups exist in cache
# Custom class is query indexed through the the NCache Management Center or config.ncconf
# Search for items with group
# Provide Fully Qualified Name(FQN) of your custom class
query = "SELECT $Group$ FROM FQN.Customer WHERE customer_name = ?"

# Use QueryCommand for query execution
query_command = ncache.QueryCommand(query)

# Providing parameters for query
parameters = {"$Group": "Important Customers"}
query_command.set_parameters(parameters)

# Executing QueryCommand

search_service = cache.get_search_service()
cache_reader = search_service.execute_reader(query_command)

# Check if the result set is not empty
if cache_reader.get_field_count() > 0:
    while cache_reader.read():
        # Perform operations
        group_name = cache_reader.get_value(str, 1)
else:
    # None query result set retrieved
    print("Query result is None")

// This is an async method
// Preconditions: Cache is already connected
// Items with groups exist in cache
// Custom class is query indexed through the NCache Management Center or config.ncconf
// Search for items with group
// Provide Fully Qualified Name (FQN) of your custom class
var query = "SELECT $Group$ FROM FQN.Customer WHERE CustomerName = ?";

// Use QueryCommand for query execution
var queryCommand = new ncache.QueryCommand(query);

// Providing parameters for query
var parameters = this.map.set("$Group","Important Customers");
queryCommand.setParameters(parameters);

// Executing QueryCommand
var searchService = await this.cache.getSearchService();
var cacheReader = await searchService.executeReader(queryCommand);

// Check if the result set is not empty
if (cacheReader.getFieldCount() > 0)
{
    while (cacheReader.read())
    {
        // Perform operations
        var groupName = cacheReader.getValue(1);
    }
}
else
{
    // Null query result set retrieved
}

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 Groups on GitHub.