Search Group Data in Cache with SQL

Note

This feature is only available in NCache Enterprise Edition.

NCache provides object queries through which you use a 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.

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 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

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.

try
{
    // Pre-conditions: Cache is already connected

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

    /*Items with groups exist in the cache
    Custom class is query indexed through the NCache Web Manager 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");
    }
}
catch (OperationFailedException ex)
{
    if (ex.ErrorCode == NCacheErrorCodes.INCORRECT_FORMAT)
    {
        // Make sure that the query format is correct
    }
    else
    {
        // Exception can occur due to:
        // Connection Failures 
        // Operation Timeout
        // Operation performed during state transfer    
    }
}
catch (Exception ex)
{
    // Any generic exception like ArgumentException, ArgumentNullException    
}

try
{
    // Pre-conditions: Cache is already connected
    // Items with groups exist in cache
    // Custom class is query indexed through NCache Web Manager or config.ncconf

    // Search for items with group
    // Provide Fully Qualified Name (FQN) of your custom class
    String query = "SELECT CustomerID FROM FQN.Customer WHERE $Group$ = ?";

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

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

    // Executing QueryCommand through cacheReader
    CacheReader reader = cache.getSearchService().executeReader(queryCommand);

    // Check if the result set is not empty
    if (reader.getFieldCount() > 0)
    {
        while (reader.read())
        {
            String CustomerID = reader.getValue(1 , String.class);
            // Perform operations
        }
    }
    else
    {
        // Null query result set retrieved
    }
}
catch (OperationFailedException ex)
{
    if (ex.getErrorCode() == NCacheErrorCodes.INCORRECT_FORMAT)
    {
        // Make sure that the query format is correct
    }
    else
    {
        // Exception can occur due to:
        // Connection Failures
        // Operation Timeout
        // Operation performed during state transfer
    }
}
catch (Exception ex)
{
    // Any generic exception like NullPointerException or IllegalArgumentException
}

try {
    // Pre-conditions: Cache is already connected

    // Items with groups exist in cache
    // Custom class is query indexed through NCache Web Manager or config.ncconf

    // Search for items with group
    // Provide Fully Qualified Name (FQN) of your custom class
    val query = "SELECT CustomerID FROM FQN.Customer WHERE $Group$ = ?"

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

    // Providing parameters for query
    queryCommand.setParameters(Map("$Group$" -> "Important Customers"))

    // Executing QueryCommand through cacheReader
    val reader = cache.getSearchService.executeReader(queryCommand)

    // Check if the result set is not empty
    if (reader.getFieldCount > 0) {
      while (reader.read) {
      val CustomerID = reader.getValue(1, classOf[String])
      // Perform operations
      }
    } else {
      // Null query result set retrieved
    }
}
catch {
    case exception: Exception => {
      // Handle any errors
    }
}

// This is an async method
try
{
    // Pre-conditions: Cache is already connected
    // Items with groups exist in cache
    // Custom class is query indexed through NCache Web Manager 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
    }
}
catch(error)
{
   // Handle errors
}

try:
    # Pre-conditions: Cache is already connected
    # Items with groups exist in cache
    # Custom class is query indexed through NCache Web Manager 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")
except Exception as exp:
    # Handle errors

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.

Search Group Data in Cache with SQL

Note

Prerequisites

Warning

Search for Data in Groups

Note

Additional Resources

See Also